Electrical spin injection into GaAs based light emitting diodes using perpendicular magnetic tunnel junction-type spin injector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tao, B. S.; Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190; Barate, P.

Remanent electrical spin injection into an InGaAs/GaAs based quantum well light emitting diode is realized by using a perpendicularly magnetized MgO/CoFeB/Ta/CoFeB/MgO spin injector. We demonstrate that the Ta interlayer plays an important role to establish the perpendicular magnetic anisotropy and the thickness of Ta interlayer determines the type of exchange coupling between the two adjacent CoFeB layers. They are ferromagnetically or antiferromagnetically coupled for a Ta thickness of 0.5 nm or 0.75 nm, respectively. A circular polarized electroluminescence (P{sub c}) of about 10% is obtained at low temperature and at zero magnetic field. The direction of the electrically injected spins is determinedmore » only by the orientation of the magnetization of the bottom CoFeB layer which is adjacent to the MgO/GaAs interface. This work proves the critical role of the bottom CoFeB/MgO interface on the spin-injection and paves the way for the electrical control of spin injection via magnetic tunnel junction-type spin injector.« less

Giant thermal spin torque assisted magnetic tunnel junction switching

NASA Astrophysics Data System (ADS)

Pushp, Aakash

Spin-polarized charge-currents induce magnetic tunnel junction (MTJ) switching by virtue of spin-transfer-torque (STT). Recently, by taking advantage of the spin-dependent thermoelectric properties of magnetic materials, novel means of generating spin-currents from temperature gradients, and their associated thermal-spin-torques (TSTs) have been proposed, but so far these TSTs have not been large enough to influence MTJ switching. Here we demonstrate significant TSTs in MTJs by generating large temperature gradients across ultrathin MgO tunnel barriers that considerably affect the switching fields of the MTJ. We attribute the origin of the TST to an asymmetry of the tunneling conductance across the zero-bias voltage of the MTJ. Remarkably, we estimate through magneto-Seebeck voltage measurements that the charge-currents that would be generated due to the temperature gradient would give rise to STT that is a thousand times too small to account for the changes in switching fields that we observe. Reference: A. Pushp*, T. Phung*, C. Rettner, B. P. Hughes, S.-H. Yang, S. S. P. Parkin, 112, 6585-6590 (2015).

Bias Dependence of the Electrical Spin Injection into GaAs from Co -Fe -B /MgO Injectors with Different MgO Growth Processes

NASA Astrophysics Data System (ADS)

Barate, P.; Liang, S. H.; Zhang, T. T.; Frougier, J.; Xu, B.; Schieffer, P.; Vidal, M.; Jaffrès, H.; Lépine, B.; Tricot, S.; Cadiz, F.; Garandel, T.; George, J. M.; Amand, T.; Devaux, X.; Hehn, M.; Mangin, S.; Tao, B.; Han, X. F.; Wang, Z. G.; Marie, X.; Lu, Y.; Renucci, P.

2017-11-01

We investigate the influence of the MgO growth process on the bias dependence of the electrical spin injection from a Co -Fe -B /MgO spin injector into a GaAs-based light-emitting diode (spin LED). With this aim, textured MgO tunnel barriers are fabricated either by sputtering or molecular-beam-epitaxy (MBE) methods. For the given growth parameters used for the two techniques, we observe that the circular polarization of the electroluminescence emitted by spin LEDs is rather stable as a function of the injected current or applied bias for the samples with sputtered tunnel barriers, whereas the corresponding circular polarization decreases abruptly for tunnel barriers grown by MBE. We attribute these different behaviors to the different kinetic energies of the injected carriers linked to differing amplitudes of the parasitic hole current flowing from GaAs to Co-Fe-B in both cases.

Estimation of spin contamination error in dissociative adsorption of Au2 onto MgO(0 0 1) surface: First application of approximate spin projection (AP) method to plane wave basis

NASA Astrophysics Data System (ADS)

Tada, Kohei; Koga, Hiroaki; Okumura, Mitsutaka; Tanaka, Shingo

2018-06-01

Spin contamination error in the total energy of the Au2/MgO system was estimated using the density functional theory/plane-wave scheme and approximate spin projection methods. This is the first investigation in which the errors in chemical phenomena on a periodic surface are estimated. The spin contamination error of the system was 0.06 eV. This value is smaller than that of the dissociation of Au2 in the gas phase (0.10 eV). This is because of the destabilization of the singlet spin state due to the weakening of the Au-Au interaction caused by the Au-MgO interaction.

Generation and detection of dissipationless spin current in a MgO/Si bilayer

NASA Astrophysics Data System (ADS)

Lou, Paul C.; Kumar, Sandeep

2018-04-01

Spintronics is an analogue to electronics where the spin of the electron rather than its charge is functionally controlled for devices. The generation and detection of spin current without ferromagnetic or exotic/scarce materials are two of the biggest challenges for spintronics devices. In this study, we report a solution to the two problems of spin current generation and detection in Si. Using non-local measurement, we experimentally demonstrate the generation of helical dissipationless spin current using the spin-Hall effect. Contrary to the theoretical prediction, we observe the spin-Hall effect in both n-doped and p-doped Si. The helical spin current is attributed to the site-inversion asymmetry of the diamond cubic lattice of Si and structure inversion asymmetry in a MgO/Si bilayer. The spin to charge conversion in Si is insignificant due to weak spin-orbit coupling. For the efficient detection of spin current, we report spin to charge conversion at the MgO (1 nm)/Si (2 µm) (p-doped and n-doped) thin film interface due to Rashba spin-orbit coupling. We detected the spin current at a distance of  >100 µm, which is an order of magnitude larger than the longest spin diffusion length measured using spin injection techniques. The existence of spin current in Si is verified from the coercivity reduction in a Co/Pd multilayer due to spin-orbit torque generated by spin current from Si.

Composition dependence of spin transition in (Mg,Fe)SiO 3 bridgmanite

DOE PAGES

Dorfman, Susannah M.; Badro, James; Rueff, Jean -Pascal; ...

2015-10-01

Spin transitions in (Mg,Fe)SiO 3 bridgmanite have important implications for the chemistry and dynamics of Earth’s lower mantle, but have been complex to characterize in experiments. We examine the spin state of Fe in highly Fe-enriched bridgmanite synthesized from enstatites with measured compositions (Mg 0.61Fe 0.38Ca 0.01)SiO 3 and (Mg 0.25Fe 0.74Ca 0.01)SiO 3. Bridgmanite was synthesized at 78-88 GPa and 1800-2400 K and X-ray emission spectra were measured on decompression to 1 bar (both compositions) and compression to 126 GPa ((Mg 0.61Fe 0.38Ca 0.01)SiO 3 only) without additional laser heating. Observed spectra confirm that Fe in these bridgmanites ismore » dominantly high spin in the lower mantle. However, the total spin moment begins to decrease at ~50 GPa in the 74% FeSiO 3 composition. Lastly, these results support density functional theory predictions of a lower spin transition pressure in highly Fe-enriched bridgmanite and potentially explain the high solubility of FeSiO 3 in bridgmanite at pressures corresponding to Earth’s deep lower mantle.« less

Electrical spin injection from CoFe2O4 into p-Si semiconductor across MgO tunnel barrier for spin electronics

NASA Astrophysics Data System (ADS)

Panda, J.; Maji, Nilay; Nath, T. K.

2017-05-01

The room temperature spin injection and detection in non magnetic p-Si semiconductor have been studied in details in our CoFe2O4 (CFO)/MgO/p-Si heterojunction. The 3-terminal tunnel contacts have been made on the device for transport measurements. The electrical transport properties have been investigated at different isothermal conditions in the temperature range of 10-300 K. The spin accumulation in non magnetic p-Si semiconductor has been observed at different bias current under the applied magnetic field parallel to the film plane in the temperature range of 40-300 K. We have observed a giant spin accumulation in p-Si semiconductor using MgO/CFO tunnel contact. The Hanley effect is used to control the reduction of spin accumulation by applying magnetic field perpendicular to the carrier spin in the p-Si. The accumulated spin signal decays as a function of applied magnetic field for fixed bias current. These results will enable utilization of the spin degree of freedom in complementary Si devices and its further development.

Identification and properties of the non-cubic phases of Mg 2Pb

DOE PAGES

Li, Yuwei; Bian, Guang; Singh, David J.

2016-12-20

Mg 2Pb occurs in the cubic fluorite structure and is a semimetal with a band structure strongly affected by spin-orbit interaction on the Pb p states. Its properties are therefore of interest in the context of topological materials. In addition a different phase of Mg 2Pb was experimentally reported, but its crystal structure and properties remain unknown. Here we determine the structure of this phase using ab initio evolutionary methods and report its properties. The energy of one tetragonal phase, space group P4/ nmm, is 2 meV per atom higher than that of the ground state structure supporting the experimentalmore » observation. We find this tetragonal phase to be a compenstated anisotropic metal with strong spin orbit effects. As a result, many other metastable structures have also been identified, especially one orthorhombic structure, space group Pnma, of which energy is 17 meV per atom higher than that of ground state structure and which perhaps could be the phase that was reported based on similarity of lattice parameters.« less

Spin accumulation in Si channels using CoFe/MgO/Si and CoFe/AlO{sub x}/Si tunnel contacts with high quality tunnel barriers prepared by radical-oxygen annealing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akushichi, T., E-mail: taiju.aku7@isl.titech.ac.jp; Shuto, Y.; Sugahara, S., E-mail: sugahara@isl.titech.ac.jp

We investigate spin injection into Si channels using three-terminal spin-accumulation (3T-SA) devices with high-quality CoFe/MgO/n-Si and CoFe/AlO{sub x}/n-Si tunnel spin-injectors whose tunnel barriers are formed by radical oxidation of Mg and Al thin films deposited on Si(100) substrates and successive annealing under radical-oxygen exposure. When the MgO and AlO{sub x} barriers are not treated by the radical-oxygen annealing, the Hanle-effect signals obtained from the 3T-SA devices are closely fitted by a single Lorentz function representing a signal due to trap spins. On the other hand, when the tunnel barriers are annealed under radical-oxygen exposure, the Hanle-effect signals can be accuratelymore » fitted by the superposition of a Lorentz function and a non-Lorentz function representing a signal due to accumulated spins in the Si channel. These results suggest that the quality improvement of tunnel barriers treated by radical-oxygen annealing is highly effective for spin-injection into Si channels.« less

Ground-state phase diagram of an anisotropic spin-1/2 model on the triangular lattice

NASA Astrophysics Data System (ADS)

Luo, Qiang; Hu, Shijie; Xi, Bin; Zhao, Jize; Wang, Xiaoqun

2017-04-01

Motivated by a recent experiment on the rare-earth material YbMgGaO4 [Y. Li et al., Phys. Rev. Lett. 115, 167203 (2015), 10.1103/PhysRevLett.115.167203], which found that the ground state of YbMgGaO4 is a quantum spin liquid, we study the ground-state phase diagram of an anisotropic spin-1 /2 model that was proposed to describe YbMgGaO4. Using the density matrix renormalization-group method in combination with the exact-diagonalization method, we calculate a variety of physical quantities, including the ground-state energy, the fidelity, the entanglement entropy and spin-spin correlation functions. Our studies show that in the quantum phase diagram, there is a 120∘ phase and two distinct stripe phases. The transitions from the two stripe phases to the 120∘ phase are of the first order. However, the transition between the two stripe phases is not of the first order, which is different from its classical counterpart. Additionally, we find no evidence for a quantum spin liquid in this model. Our results suggest that additional terms may also be important to model the material YbMgGaO4. These findings will stimulate further experimental and theoretical works in understanding the quantum spin-liquid ground state in YbMgGaO4.

Structure-dependent magnetoresistance and spin-transfer torque in antiferromagnetic Fe |MgO |FeMn |Cu tunnel junctions

NASA Astrophysics Data System (ADS)

Jia, Xingtao; Tang, Huimin; Wang, Shizhuo; Qin, Minghui

2017-02-01

We predict large magnetoresistance (MR) and spin transfer torque (STT) in antiferromagnetic Fe |MgO |FeMn |Cu tunnel junctions based on first-principles scattering theory. MR as large as ˜100 % is found in one junction. Magnetic dynamic simulations show that STT acting on the antiferromagnetic order parameter dominates the spin dynamics, and an electronic bias of order 10-1mV and current density of order 105Acm-2 can switches a junction of three-layer MgO, they are about one order smaller than that in Fe |MgO |Fe junction with the same barrier thickness, respectively. The multiple scattering in the antiferromagnetic region is considered to be responsible for the enhanced spin torque and smaller switching current density.

Hf thickness dependence of spin-orbit torques in Hf/CoFeB/MgO heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramaswamy, Rajagopalan; Qiu, Xuepeng; Dutta, Tanmay

We have studied the spin-orbit torques in perpendicularly magnetized Hf/CoFeB/MgO system, by systematically varying the thickness of Hf underlayer. We have observed a sign change of effective fields between Hf thicknesses of 1.75 and 2 nm, indicating that competing mechanisms, such as the Rashba and spin Hall effects, contribute to spin-orbit torques in our system. For larger Hf thicknesses (>2 nm), both the components of spin-orbit torques arise predominantly from the bulk spin Hall effect. We have also confirmed these results using spin-orbit torque induced magnetization switching measurements. Our results could be helpful in designing Hf based SOT devices.

Spin transport and spin accumulation signals in Si studied in tunnel junctions with a Fe/Mg ferromagnetic multilayer and an amorphous SiOxNy tunnel barrier

NASA Astrophysics Data System (ADS)

Nakane, Ryosho; Hada, Takato; Sato, Shoichi; Tanaka, Masaaki

2018-04-01

We studied the spin accumulation signals in phosphorus-doped n+-Si (8 × 1019 cm-3) by measuring the spin transport in three-terminal vertical devices with Fe(3 nm)/Mg(0 and 1 nm)/SiOxNy(1 nm)/n+-Si(001) tunnel junctions, where the amorphous SiOxNy layer was formed by oxnitridation of the Si substrate with radio frequency plasma. Obvious spin accumulation signals were observed at 4-300 K in the spin extraction geometry when the thickness of the Mg insertion layer was 1 nm. We found that by inserting a thin (1 nm) Mg layer, intermixing of Fe and SiOxNy is suppressed, leading to the appearance of the spin accumulation signals, and this result is consistent with the dead layer model recently proposed by our group [S. Sato et al., Appl. Phys. Lett. 107, 032407 (2015)]. We obtained relatively high spin polarization (PS) of electrons tunneling through the junction and long spin lifetime (τS): PS = 16% and τS = 5.6 ns at 4 K and PS = 7.5% and τS = 2.7 ns at 300 K. Tunnel junctions with an amorphous SiOxNy tunnel barrier are very promising for Si-based spintronic devices, since they can be formed by the method compatible with the silicon complementary metal-oxide-semiconductor technology.

Inverse spin-valve effect in nanoscale Si-based spin-valve devices

NASA Astrophysics Data System (ADS)

Hiep, Duong Dinh; Tanaka, Masaaki; Hai, Pham Nam

2017-12-01

We investigated the spin-valve effect in nano-scale silicon (Si)-based spin-valve devices using a Fe/MgO/Ge spin injector/detector deposited on Si by molecular beam epitaxy. For a device with a 20 nm Si channel, we observed clear magnetoresistance up to 3% at low temperature when a magnetic field was applied in the film plane along the Si channel transport direction. A large spin-dependent output voltage of 20 mV was observed at a bias voltage of 0.9 V at 15 K, which is among the highest values in lateral spin-valve devices reported so far. Furthermore, we observed that the sign of the spin-valve effect is reversed at low temperatures, suggesting the possibility of a spin-blockade effect of defect states in the MgO/Ge tunneling barrier.

High Spin States in ^24Mg

NASA Astrophysics Data System (ADS)

Schwartz, J.; Lister, C. J.; Wuosmaa, A.; Betts, R. R.; Blumenthal, D.; Carpenter, M. P.; Davids, C. N.; Fischer, S. M.; Hackman, G.; Janssens, R. V. F.

1996-05-01

The ^12C(^16O,α)^24Mg reaction was used at 51.5MeV to populate high angular momentum states in ^24Mg. Gamma-rays de-exciting high spin states were detected in a 20 detector spectrometer (the AYE-ball) triggered by the ANL Fragment Mass Analyser (FMA). Channel selection, through detection of ^24Mg nuclei with the appropriate time of flight, was excellent. All the known decays from high spin states were seen in a few hours, with the exception of the 5.04 MeV γ-decay of the J^π=9^- state at 16.904 MeV footnote A.E.Smith et al., Phys. Lett. \\underlineB176, (1986)292. which could not be confirmed. The potential of the technique for studying the radiative decay of states with very high spin in light nuclei will be discussed.

Effect of NiO spin orientation on the magnetic anisotropy of the Fe film in epitaxially grown Fe/NiO/Ag(001) and Fe/NiO/MgO(001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, W.; Jin, E.; Wu, J.

Single crystalline Fe/NiO bilayers were epitaxially grown on Ag(001) and on MgO(001), and investigated by Low Energy Electron Diffraction (LEED), Magneto-Optic Kerr Effect (MOKE), and X-ray Magnetic Linear Dichroism (XMLD). We find that while the Fe film has an in-plane magnetization in both Fe/NiO/Ag(001) and Fe/NiO/MgO(001) systems, the NiO spin orientation changes from in-plane direction in Fe/NiO/Ag(001) to out-of-plane direction in Fe/NiO/MgO(001). These two different NiO spin orientations generate remarkable different effects that the NiO induced magnetic anisotropy in the Fe film is much greater in Fe/NiO/Ag(001) than in Fe/NiO/MgO(001). XMLD measurement shows that the much greater magnetic anisotropy inmore » Fe/NiO/Ag(001) is due to a 90{sup o}-coupling between the in-plane NiO spins and the in-plane Fe spins.« less

Demonstration of efficient spin injection and detection in various systems using Fe{sub 3}O{sub 4} based spin injectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhat, Shwetha G., E-mail: shwethabhat@physics.iisc.ernet.in; Anil Kumar, P. S.

2016-05-15

Half-metal based spin injector devices for spin injection and detection application have proven to be efficient owing to their enhanced injection and detection efficiency. In this study, we extend the all-electrical spin injection and detection studies into different systems like Si and GaAs using half-metal Fe{sub 3}O{sub 4} as a spin injector in the presence and absence of tunnel barrier MgO. Injection into GaAs is verified using conventional Fe/MgO/GaAs devices. Room temperature spin injection into both p-type and n-type Si is achieved and the spin injection could be observed down to 100 K. Obtained spin relaxation time for these n-typemore » and p-type Si at different temperatures agree well with the existing reports. Further, the temperature dependent spin injection and detection is also successfully achieved in Fe{sub 3}O{sub 4}/GaAs (n-type) Schottky devices, and a comparison study of the results with control experiment using Fe/MgO/GaAs (n-type) devices confirm the relaxation to be similar in the GaAs substrate, as expected. Hence, even Fe{sub 3}O{sub 4} material can be effectively used as an efficient spin injector as well as detector, making it an attractive candidate for the room temperature spintronics device applications.« less

Origin of fieldlike spin-orbit torques in heavy metal/ferromagnet/oxide thin film heterostructures

NASA Astrophysics Data System (ADS)

Ou, Yongxi; Pai, Chi-Feng; Shi, Shengjie; Ralph, D. C.; Buhrman, R. A.

2016-10-01

We report measurements of the thickness and temperature (T ) dependencies of current-induced spin-orbit torques, especially the fieldlike (FL) component, in various heavy metal (HM)/normal metal (NM) spacer/ferromagnet (FM)/oxide (MgO and Hf Ox/MgO ) heterostructures. The FL torque in these samples originates from spin current generated by the spin Hall effect in the HM. For a FM layer sufficiently thin that a substantial portion of this spin current can reach the FM/oxide interface, T-dependent spin scattering there can yield a strong FL torque that is, in some cases, opposite in sign to that exerted at the NM/FM interface.

Emergent order in the kagome Ising magnet Dy3Mg2Sb3O14

PubMed Central

Paddison, Joseph A. M.; Ong, Harapan S.; Hamp, James O.; Mukherjee, Paromita; Bai, Xiaojian; Tucker, Matthew G.; Butch, Nicholas P.; Castelnovo, Claudio; Mourigal, Martin; Dutton, S. E.

2016-01-01

The Ising model—in which degrees of freedom (spins) are binary valued (up/down)—is a cornerstone of statistical physics that shows rich behaviour when spins occupy a highly frustrated lattice such as kagome. Here we show that the layered Ising magnet Dy3Mg2Sb3O14 hosts an emergent order predicted theoretically for individual kagome layers of in-plane Ising spins. Neutron-scattering and bulk thermomagnetic measurements reveal a phase transition at ∼0.3 K from a disordered spin-ice-like regime to an emergent charge ordered state, in which emergent magnetic charge degrees of freedom exhibit three-dimensional order while spins remain partially disordered. Monte Carlo simulations show that an interplay of inter-layer interactions, spin canting and chemical disorder stabilizes this state. Our results establish Dy3Mg2Sb3O14 as a tuneable system to study interacting emergent charges arising from kagome Ising frustration. PMID:27996012

Shape coexistence in the N = 19 neutron-rich nucleus 31Mg explored by β-γ spectroscopy of spin-polarized 31Na

NASA Astrophysics Data System (ADS)

Nishibata, H.; Shimoda, T.; Odahara, A.; Morimoto, S.; Kanaya, S.; Yagi, A.; Kanaoka, H.; Pearson, M. R.; Levy, C. D. P.; Kimura, M.

2017-04-01

The structure of excited states in the neutron-rich nucleus 31Mg, which is in the region of the ;island of inversion; associated with the neutron magic number N = 20, is studied by β-γ spectroscopy of spin-polarized 31Na. Among the 31Mg levels below the one neutron separation energy of 2.3 MeV, the spin values of all five positive-parity levels are unambiguously determined by observing the anisotropic β decay. Two rotational bands with Kπ = 1 /2+ and 1 /2- are proposed based on the spins and energies of the levels. Comparison on a level-by-level basis is performed between the experimental results and theoretical calculations by the antisymmetrized molecular dynamics (AMD) plus generator coordinate method (GCM). It is found that various nuclear structures coexist in the low excitation energy region in 31Mg.

Re-examining the 26Mg(α ,α')26Mg reaction: Probing astrophysically important states in 26Mg

NASA Astrophysics Data System (ADS)

Adsley, P.; Brümmer, J. W.; Li, K. C. W.; Marín-Lámbarri, D. J.; Kheswa, N. Y.; Donaldson, L. M.; Neveling, R.; Papka, P.; Pellegri, L.; Pesudo, V.; Pool, L. C.; Smit, F. D.; van Zyl, J. J.

2017-11-01

Background: The 22Ne(α ,n )25Mg reaction is one of the neutron sources for the s process in massive stars. The properties of levels in 26Mg above the α -particle threshold control the strengths of the 22Ne(α ,n )25Mg and 22Ne(α ,γ )26Mg reactions. The strengths of these reactions as functions of temperature are one of the major uncertainties in the s process. Purpose: Information on the existence, spin, and parity of levels in 26Mg can assist in constraining the strengths of the 22Ne(α ,γ )26Mg and 22Ne(α ,n )25Mg reactions, and therefore in constraining s -process abundances. Methods: Inelastically scattered α particles from a 26Mg target were momentum-analyzed in the K600 magnetic spectrometer at iThemba LABS, South Africa. The differential cross sections of states were deduced from the focal-plane trajectory of the scattered α particles. Based on the differential cross sections, spin and parity assignments to states are made. Results: A newly assigned 0+ state was observed in addition to a number of other states, some of which can be associated with states observed in other experiments. Some of the deduced Jπ values of the states observed in the present study show discrepancies with those assigned in a similar experiment performed at RCNP Osaka. The reassignments and additions of the various states can strongly affect the reaction rate at low temperatures. Conclusion: The number, location, and assignment of levels in 26Mg that may contribute to the 22Ne+α reactions are not clear. Future experimental investigations of 26Mg must have an extremely good energy resolution to separate the contributions from different levels. Coincidence experiments of 26Mg provide a possible route for future investigations.

Compression of a multiphase mantle assemblage: Effects of undesirable stress and stress annealing on the iron spin state crossover in ferropericlase: Stresses and HS-LS Crossover in (Mg,Fe)O

DOE PAGES

Glazyrin, Konstantin; Miyajima, Nobuyoshi; Smith, Jesse S.; ...

2016-05-30

Using synchrotron-based X-ray diffraction, we explore characteristic signatures for nonhydrostaticstresses and their effect on the spin state crossover of ferrous iron in (Mg, Fe)O ferropericlase (Fp) uponcompression in a two-phase mixture which includes an Al- and Fe-bearing bridgmanite (Bm). Here, we observe aninfluence of nonhydrostatic stresses on the spin state crossover starting pressure and width. The undesirablestresses discussed here include uniaxial deviatoric stress evolving in the diamond anvil cell and effects ofintergrain interaction. And while the former leads to a pressure overestimation, the latter one lowers the pressure ofthe onset for the high-spin to low-spin electronic transition in Fe 2+more » in ferropericlase (Mg, Fe)O with respect tohydrostatic conditions.« less

First-principles study of intermediate-spin ferrous iron in the Earth's lower mantle

NASA Astrophysics Data System (ADS)

Hsu, Han; Wentzcovitch, Renata M.

2014-11-01

Spin crossover of iron is of central importance in solid Earth geophysics. It impacts all physical properties of minerals that altogether constitute ˜95 vol% of the Earth's lower mantle: ferropericlase [(Mg,Fe)O] and Fe-bearing magnesium silicate (MgSiO3) perovskite. Despite great strides made in the past decade, the existence of an intermediate-spin (IS) state in ferrous iron (Fe2 +) (with total electron spin S =1 ) and its possible role in the pressure-induced spin crossover in these lower-mantle minerals still remain controversial. Using density functional theory + self-consistent Hubbard U (DFT+Usc ) calculations, we investigate all possible types of IS states of Fe2 + in (Mg,Fe)O and (Mg,Fe)SiO3 perovskite. Among the possible IS states in these minerals, the most probable IS state has an electronic configuration that significantly reduces the electron overlap and the iron nuclear quadrupole splitting (QS). These most probable IS states, however, are still energetically disfavored, and their QSs are inconsistent with Mössbauer spectra. We therefore conclude that IS Fe2 + is highly unlikely in the Earth's lower mantle.

Giant Spin Hall Effect and Switching Induced by Spin-Transfer Torque in a W /Co40Fe40B20/MgO Structure with Perpendicular Magnetic Anisotropy

NASA Astrophysics Data System (ADS)

Hao, Qiang; Xiao, Gang

2015-03-01

We obtain robust perpendicular magnetic anisotropy in a β -W /Co40Fe40B20/MgO structure without the need of any insertion layer between W and Co40Fe40B20 . This is achieved within a broad range of W thicknesses (3.0-9.0 nm), using a simple fabrication technique. We determine the spin Hall angle (0.40) and spin-diffusion length for the bulk β form of tungsten with a large spin-orbit coupling. As a result of the giant spin Hall effect in β -W and careful magnetic annealing, we significantly reduce the critical current density for the spin-transfer-torque-induced magnetic switching in Co40Fe40B20 . The elemental β -W is a superior candidate for magnetic memory and spin-logic applications.

Negative tunneling magnetoresistance of Fe/MgO/NiO/Fe magnetic tunnel junction: Role of spin mixing and interface state

NASA Astrophysics Data System (ADS)

Zhang, Y.; Yan, X. H.; Guo, Y. D.; Xiao, Y.

2017-08-01

Motivated by a recent tunneling magnetoresistance (TMR) measurement in which the negative TMR is observed in MgO/NiO-based magnetic tunnel junctions (MTJs), we have performed systematic calculations of transmission, current, and TMR of Fe/MgO/NiO/Fe MTJ with different thicknesses of NiO and MgO layers based on noncollinear density functional theory and non-equilibrium Green's function theory. The calculations show that, as the thickness of NiO and MgO layers is small, the negative TMR can be obtained which is attributed to the spin mixing effect and interface state. However, in the thick MTJ, the spin-flipping scattering becomes weaker, and thus, the MTJs recover positive TMR. Based on our theoretical results, we believe that the interface state at Fe/NiO interface and the spin mixing effect induced by noncollinear interfacial magnetization will play important role in determining transmission and current of Fe/MgO/NiO/Fe MTJ. The results reported here will be important in understanding the electron tunneling in MTJ with the barrier made by transition metal oxide.

Electronic structure and O vacancy formation/migration in La0.825(Mg/Ca/Ba)0.125CoO3

NASA Astrophysics Data System (ADS)

Omotayo Akande, Salawu; Gan, Li-Yong; Schwingenschlögl, Udo

2016-04-01

The effect of A-site hole doping (Mg2+, Ca2+ or Ba2+) on the electronic and magnetic properties as well as the O vacancy formation and migration in perovskite LaCoO3 is studied using first-principles calculations. All three dopants are found to facilitate O vacancy formation. Substitution of La3+ with Ba2+/Mg2+ yields the lowest O vacancy formation energy for low/intermediate spin Co, implying that not only the structure but also the spin state of Co is a key parameter. Only for low spin Co the ionic radius is correlated with the O migration barrier. Enhanced migration for intermediate spin Co is ascribed to the availability of additional space at the transition state.

Anomalous spin-dependent tunneling statistics in Fe/MgO/Fe junctions induced by disorder at the interface

NASA Astrophysics Data System (ADS)

Yan, Jiawei; Wang, Shizhuo; Xia, Ke; Ke, Youqi

2018-01-01

We present first-principles analysis of interfacial disorder effects on spin-dependent tunneling statistics in thin Fe/MgO/Fe magnetic tunnel junctions. We find that interfacial disorder scattering can significantly modulate the tunneling statistics in the minority spin of the parallel configuration (PC) while all other spin channels remain dominated by the Poissonian process. For the minority-spin channel of PC, interfacial disorder scattering favors the formation of resonant tunneling channels by lifting the limitation of symmetry conservation at low concentration, presenting an important sub-Poissonian process in PC, but is destructive to the open channels at high concentration. We find that the important modulation of tunneling statistics is independent of the type of interfacial disorder. A bimodal distribution function of transmission with disorder dependence is introduced and fits very well our first-principles results. The increase of MgO thickness can quickly change the tunneling from a sub-Poissonian to Poissonian dominated process in the minority spin of PC with disorder. Our results provide a sensitive detection method of an ultralow concentration of interfacial defects.

Magnetotransport properties of spin-valve structures with Mg spacer layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martinez-Boubeta, C., E-mail: cboubeta@gmail.com; Ferrante, Y.; Graduate School of Excellence, Materials Science in Mainz, 55128 Mainz

2015-01-19

A theoretical prediction by Wang et al. [Phys. Rev. B 82, 054405 (2010)] suggests the preferential transmission of majority-spin states with Δ{sub 1} symmetry across a magnesium interlayer in Fe/Mg/MgO/Fe based magnetic tunnel junctions. Here, we report experiments to probe this question in CoFe/Mg/CoFe structures. We find that the strength of the interlayer coupling decays exponentially with increasing the spacer thickness, however, a non-monotonic variation of the magnetoresistance as a function of the Mg layer is observed. These data may help revisit the role of the insertion of a Mg interface layer in MgO-based devices.

Structural and magnetic properties of two branches of the tripod-kagome-lattice family A2R3Sb3O14 (A = Mg, Zn; R = Pr, Nd, Gd, Tb, Dy, Ho, Er, Yb)

NASA Astrophysics Data System (ADS)

Dun, Z. L.; Trinh, J.; Lee, M.; Choi, E. S.; Li, K.; Hu, Y. F.; Wang, Y. X.; Blanc, N.; Ramirez, A. P.; Zhou, H. D.

2017-03-01

We present a systematic study of the structural and magnetic properties of two branches of the rare-earth tripod-kagome-lattice (TKL) family A2R3Sb3O14 (A = Mg, Zn; R = Pr, Nd, Gd, Tb, Dy, Ho, Er, Yb; here, we use abbreviation A-R, as in MgPr for Mg2Pr3Sb3O14 ), which complements our previously reported work on MgDy, MgGd, and MgEr [Z. L. Dun et al., Phys. Rev. Lett. 116, 157201 (2016), 10.1103/PhysRevLett.116.157201]. The present susceptibility (χdc, χac) and specific-heat measurements reveal various magnetic ground states, including the nonmagnetic singlet state for MgPr, ZnPr; long-range orderings (LROs) for MgGd, ZnGd, MgNd, ZnNd, and MgYb; a long-range magnetic charge ordered state for MgDy, ZnDy, and potentially for MgHo; possible spin-glass states for ZnEr, ZnHo; the absence of spin ordering down to 80 mK for MgEr, MgTb, ZnTb, and ZnYb compounds. The ground states observed here bear both similarities as well as striking differences from the states found in the parent pyrochlore systems. In particular, while the TKLs display a greater tendency towards LRO, the lack of LRO in MgHo, MgTb, and ZnTb can be viewed from the standpoint of a balance among spin-spin interactions, anisotropies, and non-Kramers nature of single-ion state. While substituting Zn for Mg changes the chemical pressure, and subtly modifies the interaction energies for compounds with larger R ions, this substitution introduces structural disorder and modifies the ground states for compounds with smaller R ions (Ho, Er, Yb).

Natural abundance (25)Mg solid-state NMR of mg oxyanion systems: a combined experimental and computational study.

PubMed

Cahill, Lindsay S; Hanna, John V; Wong, Alan; Freitas, Jair C C; Yates, Jonathan R; Harris, Robin K; Smith, Mark E

2009-09-28

Solid-state (25)Mg magic angle spinning nuclear magnetic resonance (MAS NMR) data are reported from a range of organic and inorganic magnesium-oxyanion compounds at natural abundance. To constrain the determination of the NMR interaction parameters (delta(iso), chi(Q), eta(Q)) data have been collected at three external magnetic fields (11.7, 14.1 and 18.8 T). Corresponding NMR parameters have also been calculated by using density functional theory (DFT) methods using the GIPAW approach, with good correlations being established between experimental and calculated values of both chi(Q) and delta(iso). These correlations demonstrate that the (25)Mg NMR parameters are very sensitive to the structure, with small changes in the local Mg(2+) environment and the overall hydration state profoundly affecting the observed spectra. The observations suggest that (25)Mg NMR spectroscopy is a potentially potent probe for addressing some key problems in inorganic materials and of metal centres in biologically relevant molecules.

Highly Efficient Room Temperature Spin Injection Using Spin Filtering in MgO

NASA Astrophysics Data System (ADS)

Jiang, Xin

2007-03-01

Efficient electrical spin injection into GaAs/AlGaAs quantum well structures was demonstrated using CoFe/MgO tunnel spin injectors at room temperature. The spin polarization of the injected electron current was inferred from the circular polarization of electroluminescence from the quantum well. Polarization values as high as 57% at 100 K and 47% at 290 K were obtained in a perpendicular magnetic field of 5 Tesla. The interface between the tunnel spin injector and the GaAs interface remained stable even after thermal annealing at 400 ^oC. The temperature dependence of the electron-hole recombination time and the electron spin relaxation time in the quantum well was measured using time-resolved optical techniques. By taking into account of these properties of the quantum well, the intrinsic spin injection efficiency can be deduced. We conclude that the efficiency of spin injection from a CoFe/MgO spin injector is nearly independent of temperature and, moreover, is highly efficient with an efficiency of ˜ 70% for the temperature range studied (10 K to room temperature). Tunnel spin injectors are thus highly promising components of future semiconductor spintronic devices. Collaborators: Roger Wang^1, 3, Gian Salis^2, Robert Shelby^1, Roger Macfarlane^1, Seth Bank^3, Glenn Solomon^3, James Harris^3, Stuart S. P. Parkin^1 ^1 IBM Almaden Research Center, San Jose, CA 95120 ^2 IBM Zurich Research Laboratory, S"aumerstrasse 4, 8803 R"uschlikon, Switzerland ^3 Solid States and Photonics Laboratory, Stanford University, Stanford, CA 94305

Elasticity of ferropericlase across the spin crossover in the Earth’s lower mantle

DOE PAGES

Yang, Jing; Tong, Xinyue; Lin, Jung-Fu; ...

2015-12-01

Knowing the elasticity of ferropericlase across the spin transition can help explain seismic and mineralogical models of the lower-mantle including the origin of seismic heterogeneities in the middle to lowermost parts of the lower mantle1–4. However, the effects of spin transition on full elastic constants of ferropericlase remain experimentally controversial due to technical challenges in directly measuring sound velocities under lower-mantle conditions1–5. Here we have reliably measured both V P and V S of a single-crystal ferropericlase ((Mg 0.92,Fe 0.08)O) using complementary Brillouin Light Scattering and Impulsive Stimulated Light Scattering coupled with a diamond anvil cell up to 96 GPa.more » The derived elastic constants show drastically softened C 11 and C 12 within the spin transition at 40–60 GPa while C 44 is not affected. The spin transition is associated with a significant reduction of the aggregate V P/V S via the aggregate V P softening because V S softening does not visibly occur within the transition. Based on thermoelastic modelling along an expected geotherm, the spin crossover in ferropericlase can contribute to 2% reduction in V P/V S in a pyrolite mineralogical model in mid lower-mantle. Our results indicate that the middle to lowermost parts of the lower-mantle would exhibit enhanced seismic heterogeneities due to the occurrence of the mixed-spin and low-spin ferropericlase.« less

Electric measurement and magnetic control of spin transport in InSb-based lateral spin devices

NASA Astrophysics Data System (ADS)

Viglin, N. A.; Ustinov, V. V.; Demokritov, S. O.; Shorikov, A. O.; Bebenin, N. G.; Tsvelikhovskaya, V. M.; Pavlov, T. N.; Patrakov, E. I.

2017-12-01

Electric injection and detection of spin-polarized electrons in InSb semiconductors have been realized in nonlocal experimental geometry using an InSb-based "lateral spin valve." The valve of the InSb /MgO /C o0.9F e0.1 composition has semiconductor/insulator/ferromagnet nanoheterojunctions in which the thickness of the InSb layer considerably exceeded the spin diffusion length of conduction electrons. The spin direction in spin diffusion current has been manipulated by a magnetic field under the Hanle effect conditions. The spin polarization of the electron gas has been registered using ferromagnetic C o0.9F e0.1 probes by measuring electrical potentials arising in the probes in accordance with the Johnson-Silsbee concept of the spin-charge coupling. The developed theory is valid at any degree of degeneracy of electron gas in a semiconductor. The spin relaxation time and spin diffusion length of conduction electrons in InSb have been determined, and the electron-spin polarization in InSb has been evaluated for electrons injected from C o0.9F e0.1 through an MgO tunnel barrier.

Density-Pressure Profiles of Fe-Bearing MgSiO3 Liquid: Effects of Valence and Spin States, and Implications for the Chemical Evolution of the Lower Mantle

NASA Astrophysics Data System (ADS)

Karki, Bijaya B.; Ghosh, Dipta B.; Maharjan, Charitra; Karato, Shun-ichiro; Park, Jeffrey

2018-05-01

Density is a key property controlling the chemical state of Earth's interior. Our knowledge about the density of relevant melt compositions is currently poor at deep-mantle conditions. Here we report results from first-principles molecular-dynamics simulations of Fe-bearing MgSiO3 liquids considering different valence and spin states of iron over the whole mantle pressure conditions. Our simulations predict the high-spin to low-spin transition in both ferrous and ferric iron in the silicate liquid to occur gradually at pressures around 100 GPa. The calculated iron-induced changes in the melt density (about 8% increase for 25% iron content) are primarily due to the difference in atomic mass between Mg and Fe, with smaller contributions (<2%) from the valence and spin states. A comparison of the predicted density of mixtures of (Mg,Fe)(Si,Fe)O3 and (Mg,Fe)O liquids with the mantle density indicates that the density contrast between the melt and residual-solid depends strongly on pressure (depth): in the shallow lower mantle (depths < 1,000 km), the melt is lighter than the solids, whereas in the deep lower mantle (e.g., the D″ layer), the melt density exceeds the mantle density when iron content is relatively high and/or melt is enriched with Fe-rich ferropericlase.

Pressure Induced Iron Spin Crossover in MgGeO3 Perovskite and Post-perovskite

NASA Astrophysics Data System (ADS)

Wentzcovitch, R. M.; Shukla, G.; Topsakal, M.

2014-12-01

MgGeO3-perovskite is known to be a low-pressure analog of MgSiO3-perovskite in many respects, but especially in regard to the post-perovskite transition. As such, investigation of spin state changes in Fe-bearing MgGeO3 might help to clarify some aspects of this type of state change in Fe-bearing MgSiO3. Using DFT+U calculations, we have investigated pressure induced state changes in Fe-bearing MgGeO3 perovskite and post-perovskite. Owing to the relatively larger atomic size of germanium compared to silicon, germanate phases have larger unit cell volume and interatomic distances than equivalent silicate phases at same pressures. As a result, all pressure induced state changes in iron occur at higher pressures in germanate phases than in the silicate ones, be it a spin state change or position change of (ferrous) iron in the perovskite cage. The effect of iron in the post-perovskite transition is also investigated.

Tuning the properties of an MgO layer for spin-polarized electron transport

NASA Astrophysics Data System (ADS)

Zhao, Chong-Jun; Ding, Lei; Zhao, Zhi-Duo; Zhang, Peng; Cao, Xing-Zhong; Wang, Bao-Yi; Zhang, Jing-Yan; Yu, Guang-Hua

2014-08-01

The influence of substrate temperature and annealing on quality/microstructural evolution of MgO, as well as the resultant magnetoresistance (MR) ratio, has been investigated. It has been found that the crystallinity of MgO in the MgO/NiFe/MgO heterostructures gradually improves with increasing substrate temperature. This behavior facilitates the transport of spin-polarized electrons, resulting in a high MR value. After annealing, the formation of vacancy clusters in MgO layers observed through positron annihilation spectroscopy leads to an increase in MR at different levels because of the crystallinity improvement of MgO. However, these vacancy clusters as another important defect can limit further improvement in MR.

Spin-orbit torques in high-resistivity-W/CoFeB/MgO

NASA Astrophysics Data System (ADS)

Takeuchi, Yutaro; Zhang, Chaoliang; Okada, Atsushi; Sato, Hideo; Fukami, Shunsuke; Ohno, Hideo

2018-05-01

Magnetic heterostructures consisting of high-resistivity (238 ± 5 µΩ cm)-W/CoFeB/MgO are prepared by sputtering and their spin-orbit torques are evaluated as a function of W thickness through an extended harmonic measurement. W thickness dependence of the spin-orbit torque with the Slonczewski-like symmetry is well described by the drift-diffusion model with an efficiency parameter, the so-called effective spin Hall angle, of -0.62 ± 0.03. In contrast, the field-like spin-orbit torque is one order of magnitude smaller than the Slonczewski-like torque and shows no appreciable dependence on the W thickness, suggesting a different origin from the Slonczewski-like torque. The results indicate that high-resistivity W is promising for low-current and reliable spin-orbit torque-controlled devices.

Electron Density Distribution Changes of Magnesiowüstite With Pressure

NASA Astrophysics Data System (ADS)

Diamond, M. R.; Popov, D.; Shen, G.; Jeanloz, R.

2017-12-01

Magnesiowüstite is one of the dominant minerals in the earth's lower mantle; its density and elasticity, substantially altered by its spin crossover, have direct consequence to interpreting deep-earth geophysical data. High-resolution single-crystal x-ray diffraction data can portray the 3-dimensional distribution of electron density through the Fourier transform of measured form factors. Here we present experimentally measured changes in electron density distribution of single-crystal (Mg.85,Fe.15)O as it goes through its iron(II) high-spin to low-spin electronic transition between about 40 and 60 GPa [Lin and Tsuchiya, 2008], in a diamond-anvil cell. As (Mg,Fe)O undergoes a pressure induced spin crossover (from high spin at low pressure to low spin at high pressure) due to overlap of its eg orbitals, the t2g orbitals become more pronounced to due a higher population of electrons, while the eg orbitals diminish. The spin splitting energy becomes increasingly unfavorable compared to the spin orbital pairing energy. By looking at the population of electrons at different directions in real space, we directly observe these changes in orbital occupation leading up to and during the spin crossover. Since high-Mg magnesiowüstite has a high symmetry structure at these pressure conditions, detecting relative changes in electron density distribution (comparing subsequent pressure steps) is feasible by collecting high resolution data offered by high-energy X rays and wide opening-angle diamond-anvil cells.

Dependency of anti-ferro-magnetic coupling strength on Ru spacer thickness of [Co/Pd]{sub n}-synthetic-anti-ferro-magnetic layer in perpendicular magnetic-tunnel-junctions fabricated on 12-inch TiN electrode wafer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chae, Kyo-Suk; Samsung Electronics Co., Ltd., San #16 Banwol-dong, Hwasung-City, Gyeonggi-Do 445-701; Shim, Tae-Hun

We investigated the Ru spacer-thickness effect on the anti-ferro-magnetic coupling strength (J{sub ex}) of a [Co/Pd]{sub n}-synthetic-anti-ferro-magnetic layer fabricated with Co{sub 2}Fe{sub 6}B{sub 2}/MgO based perpendicular-magnetic-tunneling-junction spin-valves on 12-in. TiN electrode wafers. J{sub ex} peaked at a certain Ru spacer-thickness: specifically, a J{sub ex} of 0.78 erg/cm{sup 2} at 0.6 nm, satisfying the J{sub ex} criteria for realizing the mass production of terra-bit-level perpendicular-spin-transfer-torque magnetic-random-access-memory. Otherwise, J{sub ex} rapidly degraded when the Ru spacer-thickness was less than or higher than 0.6 nm. As a result, the allowable Ru thickness variation should be controlled less than 0.12 nm to satisfy the J{sub ex} criteria. However,more » the Ru spacer-thickness did not influence the tunneling-magneto-resistance (TMR) and resistance-area (RA) of the perpendicular-magnetic-tunneling-junction (p-MTJ) spin-valves since the Ru spacer in the synthetic-anti-ferro-magnetic layer mainly affects the anti-ferro-magnetic coupling efficiency rather than the crystalline linearity of the Co{sub 2}Fe{sub 6}B{sub 2} free layer/MgO tunneling barrier/Co{sub 2}Fe{sub 6}B{sub 2} pinned layer, although Co{sub 2}Fe{sub 6}B{sub 2}/MgO based p-MTJ spin-valves ex-situ annealed at 275 °C achieved a TMR of ∼70% at a RA of ∼20 Ω μm{sup 2}.« less

Evidence for a spinon Fermi surface in a triangular-lattice quantum-spin-liquid candidate

DOE PAGES

Shen, Yao; Li, Yao-Dong; Wo, Hongliang; ...

2016-12-05

A quantum spin liquid is an exotic quantum state of matter in which spins are highly entangled and remain disordered down to zero temperature. Such a state of matter is potentially relevant to high-temperature superconductivity and quantum-information applications, and experimental identification of a quantum spin liquid state is of fundamental importance for our understanding of quantum matter. Theoretical studies have proposed various quantum-spin-liquid ground states, most of which are characterized by exotic spin excitations with fractional quantum numbers (termed ‘spinons’). In this paper, we report neutron scattering measurements of the triangular-lattice antiferromagnet YbMgGaO 4 that reveal broad spin excitations coveringmore » a wide region of the Brillouin zone. The observed diffusive spin excitation persists at the lowest measured energy and shows a clear upper excitation edge, consistent with the particle–hole excitation of a spinon Fermi surface. Finally, our results therefore point to the existence of a quantum spin liquid state with a spinon Fermi surface in YbMgGaO 4, which has a perfect spin-1/2 triangular lattice as in the original proposal of quantum spin liquids.« less

Spin-wave thermal population as temperature probe in magnetic tunnel junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Le Goff, A., E-mail: adrien.le-goff@u-psud.fr; Devolder, T.; Nikitin, V.

We study whether a direct measurement of the absolute temperature of a Magnetic Tunnel Junction (MTJ) can be performed using the high frequency electrical noise that it delivers under a finite voltage bias. Our method includes quasi-static hysteresis loop measurements of the MTJ, together with the field-dependence of its spin wave noise spectra. We rely on an analytical modeling of the spectra by assuming independent fluctuations of the different sub-systems of the tunnel junction that are described as macrospin fluctuators. We illustrate our method on perpendicularly magnetized MgO-based MTJs patterned in 50 × 100 nm{sup 2} nanopillars. We apply hard axismore » (in-plane) fields to let the magnetic thermal fluctuations yield finite conductance fluctuations of the MTJ. Instead of the free layer fluctuations that are observed to be affected by both spin-torque and temperature, we use the magnetization fluctuations of the sole reference layers. Their much stronger anisotropy and their much heavier damping render them essentially immune to spin-torque. We illustrate our method by determining current-induced heating of the perpendicularly magnetized tunnel junction at voltages similar to those used in spin-torque memory applications. The absolute temperature can be deduced with a precision of ±60 K, and we can exclude any substantial heating at the spin-torque switching voltage.« less

Magnetic behavior of Si-Ge bond in SixGe4-x nano-clusters

NASA Astrophysics Data System (ADS)

Nahali, Masoud; Mehri, Ali

2018-06-01

The structure of SixGe4-x nano-clusters were optimized by MPW1B95 level of theory using MG3S and SDB-aug-cc-PVTZ basis set. The agreement of the calculated ionization and dissociation energies with experimental values validates the reported structures of nano-clusters and justifies the use of hybrid meta density functional method. Since the Si-Si bond is stronger than Si-Ge and Ge-Ge bonds, the Si-Si, Si-Ge, and Ge-Ge diagonal bonds determine the precedence of the stability in these nano-clusters. The hybrid meta density functional calculations were carried out to investigate the adsorption of CO on all possible SixGe4-x nano-clusters. It was found that the silicon atom generally makes a stronger bond with CO than germanium and thereby preferentially affects the shape of structures having higher multiplicity. In Si-Ge structures with higher spin more than 95% of spins accumulate on positions with less bonds to other atoms of the cluster. Through CO adsorption on these clusters bridge structures are made that behave as spin bridge which conduct the spin from the nano-cluster surface to the adsorbate atoms. A better understanding of bridged structures was achieved upon introducing the 'spin bridge' concept. Based on exhaustive spin density analysis, it was found that the reason for the extra negative charge on oxygen in the bridged structures is the relocation of spin from the surface through the bridge.

Probing the electronic and spintronic properties of buried interfaces by extremely low energy photoemission spectroscopy

PubMed Central

Fetzer, Roman; Stadtmüller, Benjamin; Ohdaira, Yusuke; Naganuma, Hiroshi; Oogane, Mikihiko; Ando, Yasuo; Taira, Tomoyuki; Uemura, Tetsuya; Yamamoto, Masafumi; Aeschlimann, Martin; Cinchetti, Mirko

2015-01-01

Ultraviolet photoemission spectroscopy (UPS) is a powerful tool to study the electronic spin and symmetry features at both surfaces and interfaces to ultrathin top layers. However, the very low mean free path of the photoelectrons usually prevents a direct access to the properties of buried interfaces. The latter are of particular interest since they crucially influence the performance of spintronic devices like magnetic tunnel junctions (MTJs). Here, we introduce spin-resolved extremely low energy photoemission spectroscopy (ELEPS) to provide a powerful way for overcoming this limitation. We apply ELEPS to the interface formed between the half-metallic Heusler compound Co2MnSi and the insulator MgO, prepared as in state-of-the-art Co2MnSi/MgO-based MTJs. The high accordance between the spintronic fingerprint of the free Co2MnSi surface and the Co2MnSi/MgO interface buried below up to 4 nm MgO provides clear evidence for the high interface sensitivity of ELEPS to buried interfaces. Although the absolute values of the interface spin polarization are well below 100%, the now accessible spin- and symmetry-resolved wave functions are in line with the predicted existence of non-collinear spin moments at the Co2MnSi/MgO interface, one of the mechanisms evoked to explain the controversially discussed performance loss of Heusler-based MTJs at room temperature. PMID:25702631

Continuous excitations of the triangular-lattice quantum spin liquid YbMgGaO 4

DOE PAGES

Paddison, Joseph A. M.; Daum, Marcus; Dun, Zhiling; ...

2016-12-05

A quantum spin liquid (QSL) is an exotic state of matter in which electrons’ spins are quantum entangled over long distances, but do not show magnetic order in the zero-temperature limit. The observation of QSL states is a central aim of experimental physics, because they host collective excitations that transcend our knowledge of quantum matter; however, examples in real materials are scarce. We report neutron-scattering experiments on YbMgGaO 4, a QSL candidate in which Yb 3+ ions with effective spin-1/2 occupy a triangular lattice. Furthermore, our measurements reveal a continuum of magnetic excitations—the essential experimental hallmark of a QSL7—at verymore » low temperature (0.06 K). The origin of this peculiar excitation spectrum is a crucial question, because isotropic nearest-neighbour interactions do not yield a QSL ground state on the triangular lattice. In using measurements the field-polarized state, we identify antiferromagnetic next-nearest-neighbour interactions spin-space anisotropies and chemical disorder between the magnetic layers as key ingredients in YbMgGaO 4.« less

Multiscale modeling of current-induced switching in magnetic tunnel junctions using ab initio spin-transfer torques

NASA Astrophysics Data System (ADS)

Ellis, Matthew O. A.; Stamenova, Maria; Sanvito, Stefano

2017-12-01

There exists a significant challenge in developing efficient magnetic tunnel junctions with low write currents for nonvolatile memory devices. With the aim of analyzing potential materials for efficient current-operated magnetic junctions, we have developed a multi-scale methodology combining ab initio calculations of spin-transfer torque with large-scale time-dependent simulations using atomistic spin dynamics. In this work we introduce our multiscale approach, including a discussion on a number of possible schemes for mapping the ab initio spin torques into the spin dynamics. We demonstrate this methodology on a prototype Co/MgO/Co/Cu tunnel junction showing that the spin torques are primarily acting at the interface between the Co free layer and MgO. Using spin dynamics we then calculate the reversal switching times for the free layer and the critical voltages and currents required for such switching. Our work provides an efficient, accurate, and versatile framework for designing novel current-operated magnetic devices, where all the materials details are taken into account.

Ultrafast Study of Dynamic Exchange Coupling in Ferromagnet/Oxide/Semiconductor Heterostructures

NASA Astrophysics Data System (ADS)

Ou, Yu-Sheng

Spintronics is the area of research that aims at utilizing the quantum mechanical spin degree of freedom of electrons in solid-state materials for information processing and data storage application. Since the discovery of the giant magnetoresistance, the field of spintronics has attracted lots of attention for its numerous potential advantages over contemporary electronics, such as less power consumption, high integration density and non-volatility. The realization of a spin battery, defined by the ability to create spin current without associated charge current, has been a long-standing goal in the field of spintronics. The demonstration of pure spin current in ferromagnet/nonmagnetic material hybrid structures by ferromagnetic resonance spin pumping has defined a thrilling direction for this field. As such, this dissertation targets at exploring the spin and magnetization dynamics in ferromagnet/oxide/semiconductor heterostructures (Fe/MgO/GaAs) using time-resolved optical pump-probe spectroscopy with the long-range goal of understanding the fundamentals of FMR-driven spin pumping. Fe/GaAs heterostructures are complex systems that contain multiple spin species, including paramagnetic spins (GaAs electrons), nuclear spins (Ga and As nuclei) and ferromagnetic spins (Fe). Optical pump-probe studies on their interplay have revealed a number of novel phenomena that has not been explored before. As such they will be the major focus of this dissertation. First, I will discuss the effect of interfacial exchange coupling on the GaAs free-carrier spin relaxation. Temperature- and field-dependent spin-resolved pump-probe studies reveal a strong correlation of the electron spin relaxation with carrier freeze-out, in quantitative agreement with a theoretical interpretation that at low temperatures the free-carrier spin lifetime is dominated by inhomogeneity in the local hyperfine field due to carrier localization. Second, we investigate the impact of tunnel barrier thickness on GaAs electron spin dynamics in Fe/MgO/GaAs heterostructures. Comparison of the Larmor frequency between samples with thick and thin MgO barriers reveals a four-fold variation in exchange coupling strength, and investigation of the spin lifetimes argues that inhomogeneity in the local hyperfine field dominates free-carrier spin relaxation across the entire range of barrier thickness. These results provide additional evidence to support the theory of hyperfine-dominated spin relaxation in GaAs. Third, we investigated the origin and dynamics of an emergent spin population by pump power and magnetic field dependent spin-resolved pump-probe studies. Power dependent study confirms its origin to be filling of electronic states in GaAs, and further field dependent studies reveal the impact of contact hyperfine coupling on the dynamics of electron spins occupying distinct electronic states. Beyond above works, we also pursue optical detection of dynamic spin pumping in Fe/MgO/GaAs heterostructures in parallel. I will discuss the development and progress that we have made toward this goal. This project can be simply divided into two phases. In the first phase, we focused on microwave excitation and optical detection of spin pumping. In the second phase, we focused on all-optical excitation and detection of spin pumping. A number of measurement strategies have been developed and executed in both stages to hunt for a spin pumping signal. I will discuss the preliminary data based upon them.

Characterization of MgO Based Tunnel Barriers in Graphene Based Spin Valve Devices

NASA Astrophysics Data System (ADS)

Avsar, Ahmet; Balakrishnan, Jayakumar; Koon, Gavin; Ho, Yuda; Patra, Ajit; Bae, Sukang; Hong, Byung-Hee; Özyilmaz, Barbaros

2012-02-01

The low spin orbit coupling and hyperfine interaction in graphene allows a high spin relaxation length even at room temperature [1]. The demonstration of comparable spin transport properties in CVD synthesized single layer and bilayer graphene with its exfoliated counterparts raised hopes for the realization of possible room temperature spintronic applications [2]. To improve the spin transport properties of CVD Graphene based spin valves further, contact induced spin relaxation should be reduced by creating pin-hole free tunneling barriers. In this presentation, we will compare MgO barriers deposited under different conditions towards establishing pin-hole free barriers. We will discuss the effect of the substrate smoothness on the formation of high quality tunnel barriers by studying growth on different substrates. [4pt] [1] N. Tombros, C. Jozsa, M. Popinciuc, H. T. Jonkman, and B. J. van Wees, Nature 448, 571-574 (2007) [0pt] [2] A. Avsar, T. Yang, S. Bae, J. Balakrishnan, F. Volmer, M. Jaiswal, Z. Yi, S. R. Ali, G. Guntherodt, B. H. Hong, B. Beschoten, B. Ozyilmaz, Nano Lett. 10.10.1021/nl200714q (2011)

Room temperature electrical spin injection into GaAs by an oxide spin injector

PubMed Central

Bhat, Shwetha G.; Kumar, P. S. Anil

2014-01-01

Spin injection, manipulation and detection are the integral parts of spintronics devices and have attracted tremendous attention in the last decade. It is necessary to judiciously choose the right combination of materials to have compatibility with the existing semiconductor technology. Conventional metallic magnets were the first choice for injecting spins into semiconductors in the past. So far there is no success in using a magnetic oxide material for spin injection, which is very important for the development of oxide based spintronics devices. Here we demonstrate the electrical spin injection from an oxide magnetic material Fe3O4, into GaAs with the help of tunnel barrier MgO at room temperature using 3-terminal Hanle measurement technique. A spin relaxation time τ ~ 0.9 ns for n-GaAs at 300 K is observed along with expected temperature dependence of τ. Spin injection using Fe3O4/MgO system is further established by injecting spins into p-GaAs and a τ of ~0.32 ns is obtained at 300 K. Enhancement of spin injection efficiency is seen with barrier thickness. In the field of spin injection and detection, our work using an oxide magnetic material establishes a good platform for the development of room temperature oxide based spintronics devices. PMID:24998440

Low-current-density spin-transfer switching in Gd{sub 22}Fe{sub 78}-MgO magnetic tunnel junction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kinjo, Hidekazu, E-mail: kinjou.h-lk@nhk.or.jp; Machida, Kenji; Aoshima, Ken-ichi

2014-05-28

Magnetization switching of a relatively thick (9 nm) Gd-Fe free layer was achieved with a low spin injection current density of 1.0 × 10{sup 6} A/cm{sup 2} using MgO based magnetic tunnel junction devices, fabricated for light modulators. At about 560 × 560 nm{sup 2} in size, the devices exhibited a tunneling magnetoresistance ratio of 7%. This low-current switching is mainly attributed to thermally assisted spin-transfer switching in consequence of its thermal magnetic behavior arising from Joule heating.

The Role of Affect Spin in the Relationships between Proactive Personality, Career Indecision, and Career Maturity

PubMed Central

Park, In-Jo

2015-01-01

This study attempted to investigate the influence of proactive personality on career indecision and career maturity, and to examine the moderating effects of affect spin. The author administered proactive personality, career indecision, and career maturity scales to 70 college students. Affect spin was calculated using the day reconstruction method, wherein participants evaluated their affective experiences by using 20 affective terms at the same time each day for 21 consecutive days. Hierarchical regression analyses showed that proactive personality significantly predicted career indecision and career maturity, even after controlling for valence and activation variability, neuroticism, age, and gender. Furthermore, affect spin moderated the associations of proactive personality with career indecision and maturity. The theoretical and practical implications of the moderating effects of affect spin are discussed. PMID:26635665

Equation of state and spin crossover of (Mg,Fe)O at high pressure, with implications for explaining topographic relief at the core-mantle boundary

DOE PAGES

Solomatova, Natalia V.; Jackson, Jennifer M.; Sturhahn, Wolfgang; ...

2016-05-01

Iron-bearing periclase is thought to represent a significant fraction of Earth’s lower mantle. However, the concentration of iron in (Mg,Fe)O is not well constrained at all mantle depths. Therefore, understanding the effect of iron on the density and elastic properties of this phase plays a major role in interpreting seismically observed complexity in the deep Earth. Here in this paper, we examine the high-pressure behavior of polycrystalline (Mg,Fe)O containing 48 mol% FeO, loaded hydrostatically with neon as a pressure medium. Using X-ray diffraction and synchrotron Mössbauer spectroscopy, we measure the equation of state to about 83 GPa and hyperfine parametersmore » to 107 GPa at 300 K. A gradual volume drop corresponding to a high-spin (HS) to low-spin (LS) crossover is observed between ~45 and 83 GPa with a volume drop of 1.85% at 68.8(2.7) GPa, the calculated spin transition pressure. Using a newly formulated spin crossover equation of state, the resulting zero-pressure isothermal bulk modulus K 0T,HS for the HS state is 160(2) GPa with a K' 0T,HS of 4.12(14) and a V 0,HS of 77.29(0) Å 3. For the LS state, the K 0T,LS is 173(13) GPa with a K' 0T,LS fixed to 4 and a V 0,LS of 73.64(94) Å 3. To confirm that the observed volume drop is due to a spin crossover, the quadrupole splitting (QS) and isomer shift (IS) are determined as a function of pressure. At low pressures, the Mössbauer spectra are well explained with two Fe 2+-like sites. At pressure between 44 and 84, two additional Fe 2+-like sites with a QS of 0 are required, indicative of low-spin iron. Above 84 GPa, two low-spin Fe 2+-like sites with increasing weight fraction explain the data well, signifying the completion of the spin crossover. To systematically compare the effect of iron on the equation of state parameters for (Mg,Fe)O, a spin crossover equation of state was fitted to the pressure-volume data of previous measurements. Our results show that K 0,HS is insensitive to iron concentration between 10 to 60 mol% FeO, while the spin transition pressure and width generally increases from about 50–80 and 2–25 GPa, respectively. A key implication is that iron-rich (Mg,Fe)O at the core-mantle boundary would likely contain a significant fraction of high-spin (less dense) iron, contributing a positive buoyancy to promote observable topographic relief in tomographic images of the lowermost mantle.« less

Tunneling-Magnetoresistance Ratio Comparison of MgO-Based Perpendicular-Magnetic-Tunneling-Junction Spin Valve Between Top and Bottom Co2Fe6B2 Free Layer Structure.

PubMed

Lee, Du-Yeong; Lee, Seung-Eun; Shim, Tae-Hun; Park, Jea-Gun

2016-12-01

For the perpendicular-magnetic-tunneling-junction (p-MTJ) spin valve with a nanoscale-thick bottom Co2Fe6B2 free layer ex situ annealed at 400 °C, which has been used as a common p-MTJ structure, the Pt atoms of the Pt buffer layer diffused into the MgO tunneling barrier. This transformed the MgO tunneling barrier from a body-centered cubic (b.c.c) crystallized layer into a mixture of b.c.c, face-centered cubic, and amorphous layers and rapidly decreased the tunneling-magnetoresistance (TMR) ratio. The p-MTJ spin valve with a nanoscale-thick top Co2Fe6B2 free layer could prevent the Pt atoms diffusing into the MgO tunneling barrier during ex situ annealing at 400 °C because of non-necessity of a Pt buffer layer, demonstrating the TMR ratio of ~143 %.

Ultrafast demagnetization enhancement in CoFeB/MgO/CoFeB magnetic tunneling junction driven by spin tunneling current.

PubMed

He, Wei; Zhu, Tao; Zhang, Xiang-Qun; Yang, Hai-Tao; Cheng, Zhao-Hua

2013-10-07

The laser-induced ultrafast demagnetization of CoFeB/MgO/CoFeB magnetic tunneling junction is exploited by time-resolved magneto-optical Kerr effect (TRMOKE) for both the parallel state (P state) and the antiparallel state (AP state) of the magnetizations between two magnetic layers. It was observed that the demagnetization time is shorter and the magnitude of demagnetization is larger in the AP state than those in the P state. These behaviors are attributed to the ultrafast spin transfer between two CoFeB layers via the tunneling of hot electrons through the MgO barrier. Our observation indicates that ultrafast demagnetization can be engineered by the hot electrons tunneling current. It opens the door to manipulate the ultrafast spin current in magnetic tunneling junctions.

Investigating and engineering spin-orbit torques in heavy metal/Co{sub 2}FeAl{sub 0.5}Si{sub 0.5}/MgO thin film structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Loong, Li Ming; Deorani, Praveen; Qiu, Xuepeng

2015-07-13

Current-induced spin-orbit torques (SOTs) have the potential to revolutionize magnetization switching technology. Here, we investigate SOT in a heavy metal (HM)/Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} (CFAS)/MgO thin film structure with perpendicular magnetic anisotropy (PMA), where the HM is either Pt or Ta. Our results suggest that both the spin Hall effect and the Rashba effect contribute significantly to the effective fields in the Pt underlayer samples. Moreover, after taking the PMA energies into account, current-induced SOT-based switching studies of both the Pt and Ta underlayer samples suggest that the two HM underlayers yield comparable switching efficiency in the HM/CFAS/MgO material system.

A novel reduced symmetry oxide (Mg3B2O6) for magnetic tunnel junctions based on FeCo or Fe leads

NASA Astrophysics Data System (ADS)

Stewart, Derek

2010-03-01

Magnetic tunnel junctions with high TMR values, such as FeMgOFe, capitalize on spin filtering in the oxide due to the band symmetry of incident electrons. However, these structures rely on magnetic leads and oxide regions of the same cubic symmetry class. This raises the question of whether reducing the oxide symmetry can enhance spin filtering. A new magnetic tunnel junction (FeCoMg3B2O6FeCo) is presented that uses a reduced symmetry oxide region (orthorhombic) to filter spins between two cubic magnetic leads. Symmetry analysis of coupling between states in the cubic leads and the orthorhombic oxide indicates that majority carrier tunneling through the oxide should be favored over minority carriers. Complex band structure analysis of Mg3B2O6 shows that the relevant evanescent states in the band gap are due to boron p states and that there is sufficient difference in the decay rates of the imaginary bands for spin filtering to occur. Electronic transport calculations through a FeMg3B2O6Fe magnetic tunnel junction are also performed to address the possible influence of interface states. Some recent experimental studies of FeCoBMgOFeCoB junctions, with B diffusion into the MgO region, indicate that this new type of junction may have already been fabricated. The prospect of developing a general class of magnetic tunnel junctions based on reduced symmetry oxides is also examined.

Comment on ?Spin crossover in (Mg,Fe)O: A M?ssbauer effect study with an alternative interpretation of x-ray emission spectroscopy data?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, J; Struzhkin, V V; Garriliuk, A

2006-05-23

Electronic spin-pairing transition of iron in magnesiow{umlt u}stite-(Mg,Fe)O has been recently studied with X-ray emission and M{umlt o}ssbauer spectroscopies under high pressures. While these studies reported a high-spin to low-spin transition of iron to occur at pressures above approximately 50 GPa, the width of the observed transition varies significantly. In particular, Kantor et al. reported that the transition in (Mg0.8,Fe0.2)O occurs over a pressure range of approximately 50 GPa in high-pressure M{umlt o}ssbauer measurements. To account for the discrepancy in the transition pressure, Kantor et al. reanalyzed the X-ray emission spectra by Lin et al. using a simple spectral decompositionmore » method and claimed that X-ray emission measurements are also consistent with a spin crossover of iron at high pressures. Here we show that the proposed fitting method is inadequate to describe the X-ray emission spectrum of the low-spin FeS2 and would give an erroneous satellite peak (K{sub beta}') intensity, leading to an artificial high-spin component and, consequently, to invalid conclusions regarding the width of the pressure-induced transition in magnesiow{umlt u}stite. Furthermore, we compare Kantor's M{umlt o}ssbauer data with other recent high-pressure M{umlt o}ssbauer studies and show that the width of the transition can be simply explained by different experimental conditions (sample thickness, diameter, and hydrostaticity).« less

Spin Polarization of Alternate Monatomic Epitaxial [Fe/Co]n Superlattice

NASA Astrophysics Data System (ADS)

Chu, In Chang; Doi, Masaaki; Sahashi, Masashi; Rajanikanth, Ammanabrolu; Takahashi, Yukiko; Hono, Kazuhiro

2012-09-01

The spin polarization (P) of alternate monatomic layered (AML) epitaxial [Fe/Co]n superlattices grown on MgO(001) substrates by electron beam (EB) evaporation has been measured by the point contact Andreev reflection (PCAR) method. The intrinsic transport P of 0.60 was obtained for the AML epitaxial [Fe/Co]n superlattice grown at 75 °C, which is comparable to that of half-metallic Heusler alloys measured by PCAR. The AML epitaxial [Fe/Co]n superlattices on MgO(001), which are expected to possess the B2 ordered structure, show the highest spin polarization of metallic Fe-Co alloy films.

Spin Polarization of Mg-23 in Mg-24 + Au, Cu and Al Collisions at 91 A MeV

NASA Technical Reports Server (NTRS)

Matsuta, K.; Fukuda, S.; Izumikawa, T.; Tanigaki, M.; Fukuda, M.; Nakazato, M.; Mihara, M.; Onishi, T.; Yamaguchi, T.; Miyake, T.

1994-01-01

Spin polarization of beta-emitting fragment Mg-23(I(sup pi) = 3/2(sup +), T(sub 1/2 = l1.3 s) produced through the projectile fragmentation process in Mg-24 + Au, Cu and Al collisions has been observed at 91 AMeV. General trend in the observed momentum dependence of polarization is reproduced well qualitatively by a simple fragmentation model based on the participant-spectator picture, for heavy and light targets. However the polarization behavior differs from this model in tern of zero crossing momentum, which become prominent in the case of Cu target, where the polarization is not monotone function of the fragment momentum.

High-spin Fe2+ and Fe3+ in single-crystal aluminous bridgmanite in the lower mantle

NASA Astrophysics Data System (ADS)

Lin, Jung-Fu; Mao, Zhu; Yang, Jing; Liu, Jin; Xiao, Yuming; Chow, Paul; Okuchi, Takuo

2016-07-01

Spin and valence states of iron in single-crystal bridgmanite (Mg0.89Fe0.12Al0.11Si0.89O3) are investigated using X-ray emission and Mössbauer spectroscopies with laser annealing up to 115 GPa. The results show that Fe predominantly substitutes for Mg2+ in the pseudo-dodecahedral A site, in which 80% of the iron is Fe3+ that enters the lattice via the charge-coupled substitution with Al3+ in the octahedral B site. The total spin momentum and hyperfine parameters indicate that these ions remain in the high-spin state with Fe2+ having extremely high quadrupole splitting due to lattice distortion. (Al,Fe)-bearing bridgmanite is expected to contain mostly high-spin, A-site Fe3+, together with a smaller amount of A-site Fe2+, that remains stable throughout the region. Even though the spin transition of B-site Fe3+ in bridgmanite was reported to cause changes in its elasticity at high pressures, (Fe,Al)-bearing bridgmanite with predominantly A-site Fe will not exhibit elastic anomalies associated with the spin transition.

Spin reorientation transition and hard magnetic properties of MnBi intermetallic compound

NASA Astrophysics Data System (ADS)

Suzuki, K.; Wu, X.; Ly, V.; Shoji, T.; Kato, A.; Manabe, A.

2012-04-01

The effects of mechanical grinding (MG) on the crystallite size, the spin reorientation transition temperature (TSR) and the hard magnetic properties in melt-spun low temperature phase (LTP) MnBi have been investigated in order to understand the origin of magnetic hardening induced by MG. The room-temperature coercive field (μ0Hcj) is enhanced dramatically from 0.08 T before MG to 1.5 T after MG for 43.2 ks while TSR is concurrently suppressed from 110 to 38 K. The coercive force exhibits positive temperature dependence approximately 50-60 K above TSR and the lowered TSR after MG could result in magnetic hardening at room temperature. The room-temperature coercive force of LTP-MnBi is highly dependent on the crystallite size (D) and is found to be described phenomenologically by the following relationship: μ0Hcj = μ0Ha(δ/D)n, where μ0Ha is ˜ 4 T, the Bloch wall width δ is 7 nm, and the exponent n is approximately 0.7. Our results suggest that the grain refinement is the primary origin of the hardening effect induced by MG with a possible minor hardening effect due to the suppression of the spin reorientation transition temperature.

Controlling spin-dependent tunneling by bandgap tuning in epitaxial rocksalt MgZnO films

DOE PAGES

Li, D. L.; Ma, Q. L.; Wang, S. G.; ...

2014-12-02

Widespread application of magnetic tunnel junctions (MTJs) for information storage has so far been limited by the complicated interplay between tunnel magnetoresistance (TMR) ratio and the product of resistance and junction area (RA). An intricate connection exists between TMR ratio, RA value and the bandgap and crystal structure of the barrier, a connection that must be unravelled to optimise device performance and enable further applications to be developed. In this paper, we demonstrate a novel method to tailor the bandgap of an ultrathin, epitaxial Zn-doped MgO tunnel barrier with rocksalt structure. This structure is attractive due to its good Δmore » 1 spin filtering effect, and we show that MTJs based on tunable MgZnO barriers allow effective balancing of TMR ratio and RA value. Finally, in this way spin-dependent transport properties can be controlled, a key challenge for the development of spintronic devices.« less

Controlling spin-dependent tunneling by bandgap tuning in epitaxial rocksalt MgZnO films

PubMed Central

Li, D. L.; Ma, Q. L.; Wang, S. G.; Ward, R. C. C.; Hesjedal, T.; Zhang, X.-G.; Kohn, A.; Amsellem, E.; Yang, G.; Liu, J. L.; Jiang, J.; Wei, H. X.; Han, X. F.

2014-01-01

Widespread application of magnetic tunnel junctions (MTJs) for information storage has so far been limited by the complicated interplay between tunnel magnetoresistance (TMR) ratio and the product of resistance and junction area (RA). An intricate connection exists between TMR ratio, RA value and the bandgap and crystal structure of the barrier, a connection that must be unravelled to optimise device performance and enable further applications to be developed. Here, we demonstrate a novel method to tailor the bandgap of an ultrathin, epitaxial Zn-doped MgO tunnel barrier with rocksalt structure. This structure is attractive due to its good Δ1 spin filtering effect, and we show that MTJs based on tunable MgZnO barriers allow effective balancing of TMR ratio and RA value. In this way spin-dependent transport properties can be controlled, a key challenge for the development of spintronic devices. PMID:25451163

Remote microwave monitoring of magnetization switching in CoFeB/Ta/CoFeB spin logic device

NASA Astrophysics Data System (ADS)

Morgunov, R.; L'vova, G.; Talantsev, A.; Koplak, O.; Petit-Watelot, S.; Devaux, X.; Migot, S.; Lu, Y.; Mangin, S.

2017-05-01

Stable magnetic states of the MgO/CoFeB/Ta/CoFeB/MgO/Ta spin valve as well as transitions between the states were detected by microwave magnetoresistance (MMR) measured in the cavity of an electron spin resonance spectrometer. Advantages of this experimental technique are the possibility to study the orientation dependence of the MMR, the absence of the additional contact/sample interfaces, the wireless control of the spin valves, and the compatibility of the MMR measurements with ferromagnetic resonance experiments. The magnetic field dependence of the first derivation of the microwave absorption allows one to judge about the negative magnetoresistance of the layers and positive interlayer giant magnetoresistance. The obtained experimental results could be used for engineering of the microwave high sensitive sensors available for remote identification of the stable magnetic and logic states of the spin valves needful in medical spintronics to detect biological objects labeled with nanoparticles.

Investigations of mechanical, electronic, and magnetic properties of non-magnetic MgTe and ferro-magnetic Mg0.75 TM 0.25Te (TM = Fe, Co, Ni): An ab-initio calculation

NASA Astrophysics Data System (ADS)

Q, Mahmood; S, M. Alay-e.-Abbas; I, Mahmood; Mahmood, Asif; N, A. Noor

2016-04-01

The mechanical, electronic and magnetic properties of non-magnetic MgTe and ferro-magnetic (FM) Mg0.75 TM 0.25Te (TM = Fe, Co, Ni) in the zinc-blende phase are studied by ab-initio calculations for the first time. We use the generalized gradient approximation functional for computing the structural stability, and mechanical properties, while the modified Becke and Johnson local (spin) density approximation (mBJLDA) is utilized for determining the electronic and magnetic properties. By comparing the energies of non-magnetic and FM calculations, we find that the compounds are stable in the FM phase, which is confirmed by their structural stabilities in terms of enthalpy of formation. Detailed descriptions of elastic properties of Mg0.75 TM 0.25Te alloys in the FM phase are also presented. For electronic properties, the spin-polarized electronic band structures and density of states are computed, showing that these compounds are direct bandgap materials with strong hybridizations of TM 3d states and Te p states. Further, the ferromagnetism is discussed in terms of the Zener free electron model, RKKY model and double exchange model. The charge density contours in the (110) plane are calculated to study bonding properties. The spin exchange splitting and crystal field splitting energies are also calculated. The distribution of electron spin density is employed in computing the magnetic moments appearing at the magnetic sites (Fe, Co, Ni), as well as at the non-magnetic sites (Mg, Te). It is found that the p-d hybridization causes not only magnetic moments on the magnetic sites but also induces negligibly small magnetic moments at the non-magnetic sites.

Experimental insights into spin state and hyperfine parameters of Fe3+ in bridgmanite and silicate glass up to 91 GPa

NASA Astrophysics Data System (ADS)

Lv, M.; Dorfman, S.; Liu, J.; Farmer, A. B.; Potapkin, V.; Chumakov, A. I.; McCammon, C. A.; Greenberg, E.; Prakapenka, V. B.; Popov, D.

2017-12-01

The spin and valence state of Fe in (Mg,Fe,Al)(Si,Fe,Al)O3 bridgmanite and silicate melts is important to understanding the composition, structure, and dynamics of the Earth's lower mantle. Previous experimental and theoretical studies conclude that Fe3+ in B-site of bridgmanite undergoes a high spin (HS) to low spin (LS) transition, but conflicting measurements of spin transition pressures (18-70 GPa) and significant disagreement on hyperfine parameters of LS Fe3+ need to be resolved. We performed energy-domain synchrotron Mössbauer spectroscopy (E-SMS) and X-ray diffraction (XRD) experiments up to 91 GPa (corresponding to 2000 km depth in the mid lower mantle) to explore the electronic behavior of Fe in both silicate glass and bridgmanite with measured composition (Mg0.97Fe0.20Si0.90O3). Fe3+ and Fe2+ were identified on the basis of center shift (CS) at 1 bar of 0.4 and 1 mm/s, respectively. The Mössbauer spectra of glass exhibit a continuous spin transition of Fe3+ between 11 to 40 GPa, while Fe2+ adopts the HS state up to 91 GPa. Bridgmanite Mössbauer spectra indicate two HS Fe2+ doublets corresponding to local distortion of the A-site, and that the bulk of the Fe3+ exhibits quadrupole splitting (QS) ranging from 0.8-1.3 mm/s over the entire pressure range studied. Because stoichiometry suggests most Fe3+ occupies the B-site, if the spin transition occurs it must have a small effect on Mössbauer parameters, as observed in recent studies of (Mg0.5Fe1.0Si0.5O3) and (Mg0.97Fe0.06Si0.97O3) bridgmanite. No discontinuity or softening is observed in the equation of state (EOS) of the bridgmanite between 38-103 GPa and 300 K. The bulk modulus and unit cell volume at ambient conditions obtained by fitting the unit cell volume data to the second-order Birch-Murnaghan EOS are 264(3) GPa and 163.6(3) Å3, respectively, consistent with previous studies of (Mg0.90Fe0.20Si0.90O3) bridgmanite. The spin transition in Fe3+ may have too small an effect on elastic properties of bridgmanite in the mantle to be detectable via seismic observations.

Increase in Spin Injection Efficiency of a CoFe/MgO (100) Tunnel Spin Injector with Thermal Annealing

DTIC Science & Technology

2005-01-24

geometry, the optical selection rules provide a direct correlation between the EL polarization and the spin polarization of the electrons just prior...Holland, Amsterdam, 1984d. 18M. Gurioli, A. Vinattieri, M. Colocci, C. Deparis, J. Massies, G. Neu, A. Bosacchi, and S. Franchi , Phys. Rev. B 44, 3115

Asymmetric angular dependence of spin-transfer torques in CoFe/Mg-B-O/CoFe magnetic tunnel junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Ling, E-mail: lingtang@zjut.edu.cn; Xu, Zhi-Jun, E-mail: xzj@zjut.edu.cn; Zuo, Xian-Jun

Using a first-principles noncollinear wave-function-matching method, we studied the spin-transfer torques (STTs) in CoFe/Mg-B-O/CoFe(001) magnetic tunnel junctions (MTJs), where three different types of B-doped MgO in the spacer are considered, including B atoms replacing Mg atoms (Mg{sub 3}BO{sub 4}), B atoms replacing O atoms (Mg{sub 4}BO{sub 3}), and B atoms occupying interstitial positions (Mg{sub 4}BO{sub 4}) in MgO. A strong asymmetric angular dependence of STT can be obtained both in ballistic CoFe/Mg{sub 3}BO{sub 4} and CoFe/Mg{sub 4}BO{sub 4} based MTJs, whereas a nearly symmetric STT curve is observed in the junctions based on CoFe/Mg{sub 4}BO{sub 3}. Furthermore, the asymmetry ofmore » the angular dependence of STT can be suppressed significantly by the disorder of B distribution. Such skewness of STTs in the CoFe/Mg-B-O/CoFe MTJs could be attributed to the interfacial resonance states induced by the B diffusion into MgO spacer.« less

Synthesis and magnetic properties of LiFePO4 substitution magnesium

NASA Astrophysics Data System (ADS)

Choi, Hyunkyung; Kim, Min Ji; Hahn, Eun Joo; Kim, Sam Jin; Kim, Chul Sung

2017-06-01

LiFe0.9Mg0.1PO4 sample was prepared by using a solid-state reaction method, and the temperature-dependent magnetic properties of the sample were studied. The X-ray diffraction (XRD) pattern showed an olivine-type orthorhombic structure with space group Pnma based on Rietveld refinement method. The effect of Mg substitution in antiferromagnetic LiFe0.9Mg0.1PO4 was investigated using a vibrating sample magnetometer (VSM) and Mössbauer spectroscopy. The temperature-dependence of the magnetization curves of LiFe0.9Mg0.1PO4 shows abnormal antiferromagnetic behavior with ordering temperature. Sudden changes in both the magnetic hyperfine field (Hhf) and its slope below 15 K suggest that magnetic phase transition associated to the abrupt occurrence of spin-reorientation. The Néel temperature (TN) and spin-reorientation temperature (TS) of LiFe0.9Mg0.1PO4 are lower than those of pure LiFePO4 (TN = 51 K, TS = 23 K). This is due to the Fe-O-Fe superexchange interaction being larger than that of the Fe-O-Mg link. Also, we have confirmed a change in the electric quadrupole splitting (ΔEQ) by the spin-orbit coupling effect and the shape of Mössbauer spectrum has provided the evidence for TS and a strong crystalline field. We have found that Mg ions in LiFe0.9Mg0.1PO4 induce an asymmetric charge density due to the presence of Mg2+ ions at the FeO6 octahedral sites.

Influence of MgO barrier quality on spin-transfer torque in magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Tiwari, Dhananjay; Sharma, Raghav; Heinonen, O. G.; Åkerman, Johan; Muduli, P. K.

2018-01-01

We studied the bias dependence of spin transfer torque in the MgO-based magnetic tunnel junction using a field-modulated spin torque ferromagnetic resonance measurement technique for three devices with tunneling magnetoresistances (MRs) of 60%, 67%, and 73%, respectively. The devices with a lower MR ratio showed the presence of multiple modes, while the device with higher MR (73%) showed a single resonance mode. We found a lower out-of-plane torkance in our devices compared to the in-plane torkance. The out-of-plane torque is linear with applied bias, while the bias dependence of in-plane torque shows a strong dependence on the MR ratio and hence the barrier quality.

Tunnel based spin injection devices for semiconductor spintronics

NASA Astrophysics Data System (ADS)

Jiang, Xin

This dissertation summarizes the work on spin-dependent electron transport and spin injection in tunnel based spintronic devices. In particular, it focuses on a novel three terminal hot electron device combining ferromagnetic metals and semiconductors---the magnetic tunnel transistor (MTT). The MTT has extremely high magnetic field sensitivity and is a useful tool to explore spin-dependent electron transport in metals, semiconductors, and at their interfaces over a wide energy range. In Chap. 1, the basic concept and fabrication of the MTT are discussed. Two types of MTTs, with ferromagnetic single and spin-valve base layers, respectively, are introduced and compared. In the following chapters, the transport properties of the MTT are discussed in detail, including the spin-dependent hot electron attenuation lengths in CoFe and NiFe thin films on GaAs (Chap. 2), the bias voltage dependence of the magneto-current (Chap. 3), the giant magneto-current effect in MTTs with a spin-valve base (Chap. 4), and the influence of non-magnetic seed layers on magneto-electronic properties of MTTs with a Si collector (Chap. 5). Chap. 6 concentrates on electrical injection of spin-polarized electrons into semiconductors, which is an essential ingredient in semiconductor spintronics. Two types of spin injectors are discussed: an MTT injector and a CoFe/MgO tunnel injector. The spin polarization of the injected electron current is detected optically by measuring the circular polarization of electroluminescence from a quantum well light emitting diode. Using an MTT injector a spin polarization of ˜10% is found for injection electron energy of ˜2 eV at 1.4K. This moderate spin polarization is most likely limited by significant electron spin relaxation at high energy. Much higher spin injection efficiency is obtained by using a CoFe/MgO tunnel injector with spin polarization values of ˜50% at 100K. The temperature and bias dependence of the electroluminescence polarization provides insight into spin relaxation mechanisms within the semiconductor heterostructure.

Spin-orbit torque in Cr/CoFeAl/MgO and Ru/CoFeAl/MgO epitaxial magnetic heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wen, Zhenchao; Kim, Junyeon; Sukegawa, Hiroaki

2016-05-15

We study the spin-orbit torque (SOT) effective fields in Cr/CoFeAl/MgO and Ru/CoFeAl/MgO magnetic heterostructures using the adiabatic harmonic Hall measurement. High-quality perpendicular-magnetic-anisotropy CoFeAl layers were grown on Cr and Ru layers. The magnitudes of the SOT effective fields were found to significantly depend on the underlayer material (Cr or Ru) as well as their thicknesses. The damping-like longitudinal effective field (ΔH{sub L}) increases with increasing underlayer thickness for all heterostructures. In contrast, the field-like transverse effective field (ΔH{sub T}) increases with increasing Ru thickness while it is almost constant or slightly decreases with increasing Cr thickness. The sign of ΔH{submore » L} observed in the Cr-underlayer devices is opposite from that in the Ru-underlayer devices while ΔH{sub T} shows the same sign with a small magnitude. The opposite directions of ΔH{sub L} indicate that the signs of spin Hall angle in Cr and Ru are opposite, which are in good agreement with theoretical predictions. These results show sizable contribution from SOT even for elements with small spin orbit coupling such as 3d Cr and 4d Ru.« less

Low-cost growth of magnesium doped gallium nitride thin films by sol-gel spin coating method

NASA Astrophysics Data System (ADS)

Amin, N. Mohd; Ng, S. S.

2018-01-01

Low-cost sol-gel spin coating growth of magnesium (Mg) doped gallium nitride (GaN) thin films with different concentrations of Mg was reported. The effects of the Mg concentration on the structural, surface morphology, elemental compositions, lattice vibrational, and electrical properties of the deposited films were investigated. X-ray diffraction results show that the Mg-doped samples have wurtzite structure with preferred orientation of GaN(002). The crystallite size decreases and the surface of the films with pits/pores were formed, while the crystalline quality of the films degraded as the Mg concentration increases from 2% to 6. %. All the Raman active phonon modes of the wurtzite GaN were observed while a broad peak attributed to the Mg-related lattice vibrational mode was detected at 669 cm-1. Hall effect results show that the resistivity of the thin films decreases while the hole concentration and hall mobility of thin films increases as the concentration of the Mg increases.

Spin-orbit torque in a bulk perpendicular magnetic anisotropy Pd/FePd/MgO system

PubMed Central

Lee, Hwang-Rae; Lee, Kyujoon; Cho, Jaehun; Choi, Young-Ha; You, Chun-Yeol; Jung, Myung-Hwa; Bonell, Frédéric; Shiota, Yoichi; Miwa, Shinji; Suzuki, Yoshishige

2014-01-01

Spin-orbit torques, including the Rashba and spin Hall effects, have been widely observed and investigated in various systems. Since interesting spin-orbit torque (SOT) arises at the interface between heavy nonmagnetic metals and ferromagnetic metals, most studies have focused on the ultra-thin ferromagnetic layer with interface perpendicular magnetic anisotropy. Here, we measured the effective longitudinal and transverse fields of bulk perpendicular magnetic anisotropy Pd/FePd (1.54 to 2.43 nm)/MgO systems using harmonic methods with careful correction procedures. We found that in our range of thicknesses, the effective longitudinal and transverse fields are five to ten times larger than those reported in interface perpendicular magnetic anisotropy systems. The observed magnitude and thickness dependence of the effective fields suggest that the SOT do not have a purely interfacial origin in our samples. PMID:25293693

A fundamental study on the [(μ-Cl) 3 Mg 2 (THF) 6 ] + dimer electrolytes for rechargeable Mg batteries

DOE PAGES

Liu, Tianbiao; Cox, Jonathan T.; Hu, Dehong; ...

2015-01-05

We present a fundamental study on [(μ-Cl) 3 Mg 2 (THF) 6 ] + dimer electrolytes using various physical methods including Subambient Pressure Ionization with Nanoelectrospray Mass spectrometry (SPIN-MS), Raman spectroscopy, 25Mg{ 1H} NMR, 27Al{ 1H} NMR and electrochemical analysis. For the first time, long time sought THF solvated [MgCl] + species was experimentally characterized by SPIN mass spectrometry in the solution of the Mgdimer containing electrolyte, confirming the mono-Cl- abstraction reaction between MgCl 2 and an Al Lewis acid. Solvated MgCl 2 in the electrolyte was confirmed by Raman spectroscopy. The experimental results establish the previously proposed dimerization equilibriummore » of solvated [MgCl] + and MgCl2 with [(μ-Cl) 3Mg 2(THF)6] +. 25Mg{ 1H} NMR, 27Al{ 1H} NMR and electrochemical analysis on chloration reaction of [(μ-Cl) 3Mg 2(THF) 6]AlPh 3Cl with external Cl- led to further insights on the coordination chemistry of the dimer electrolyte. Finally, a comprehensive mechanism is proposed for the reversible electrochemical Mg deposition and stripping and Mg 2+ and Cl- ion transports of the Mg dimer electrolytes in rechargeable Mg batteries.« less

Electronic spin state of Fe,Al-containing MgSiO3 perovskite at lower mantle conditions

NASA Astrophysics Data System (ADS)

Kupenko, I.; McCammon, C.; Sinmyo, R.; Prescher, C.; Chumakov, A. I.; Kantor, A.; Rüffer, R.; Dubrovinsky, L.

2014-02-01

We have investigated silicate perovskite with composition Mg0.83Fe0.21Al0.06Si0.91O3 relevant for the lower mantle at pressures up to 81 GPa and temperatures up to 2000 K using conventional Mössbauer spectroscopy and synchrotron Nuclear Forward Scattering (NFS) combined with double-sided laser heating in a diamond anvil cell. Room temperature Mössbauer and NFS spectra at low pressure are dominated by high-spin Fe2 +, with minor amounts of Fe3 + and a component assigned to a metastable position of high-spin Fe2 + in the A-site predicted by computational studies. NFS data show a sharp transition (< 20 GPa) from high-spin Fe2 + to a new component with extremely high quadrupole splitting, similar to previous studies. Mössbauer data show the same transition, but over a broader pressure range likely due to the higher pressure gradient. The new Fe2 + component is assigned to intermediate-spin Fe2 +, consistent with previous X-ray emission studies. NFS data at high temperatures and high pressures comparable to those in the lower mantle are consistent with the presence of Fe2 + only in the intermediate-spin state and Fe3 + only in the high-spin state. Our results are therefore consistent with the occurrence of spin crossover only in Fe2 + in Fe-, Al-containing perovskite within the lower mantle.

High-pressure orthorhombic ferromagnesite as a potential deep-mantle carbon carrier

DOE PAGES

Liu, Jin; Lin, Jung -Fu; Prakapenka, Vitali B.

2015-01-06

In this study, knowledge of the physical and chemical properties of candidate deep-carbon carriers such as ferromagnesite [(Mg,Fe)CO 3] at high pressure and temperature of the deep mantle is necessary for our understanding of deep-carbon storage as well as the global carbon cycle of the planet. Previous studies have reported very different scenarios for the (Mg,Fe)CO 3 system at deep-mantle conditions including the chemical dissociation to (Mg,Fe)O+CO 2, the occurrence of the tetrahedrally-coordinated carbonates based on CO 4 structural units, and various high-pressure phase transitions. Here we have studied the phase stability and compressional behavior of (Mg,Fe)CO 3 carbonates upmore » to relevant lower-mantle conditions of approximately 120 GPa and 2400 K. Our experimental results show that the rhombohedral siderite (Phase I) transforms to an orthorhombic phase (Phase II with Pmm2 space group) at approximately 50 GPa and 1400 K. The structural transition is likely driven by the spin transition of iron accompanied by a volume collapse in the Fe-rich (Mg,Fe)CO 3 phases; the spin transition stabilizes the high-pressure phase II at much lower pressure conditions than its Mg-rich counterpart. It is conceivable that the low-spin ferromagnesite phase II becomes a major deep-carbon carrier at the deeper parts of the lower mantle below 1900 km in depth.« less

Crystal structures of (Mg1-x,Fe(x))SiO3 postperovskite at high pressures.

PubMed

Yamanaka, Takamitsu; Hirose, Kei; Mao, Wendy L; Meng, Yue; Ganesh, P; Shulenburger, Luke; Shen, Guoyin; Hemley, Russell J

2012-01-24

X-ray diffraction experiments on postperovskite (ppv) with compositions (Mg(0.9)Fe(0.1))SiO(3) and (Mg(0.6)Fe(0.4))SiO(3) at Earth core-mantle boundary pressures reveal different crystal structures. The former adopts the CaIrO(3)-type structure with space group Cmcm, whereas the latter crystallizes in a structure with the Pmcm (Pmma) space group. The latter has a significantly higher density (ρ = 6.119(1) g/cm(3)) than the former (ρ = 5.694(8) g/cm(3)) due to both the larger amount of iron and the smaller ionic radius of Fe(2+) as a result of an electronic spin transition observed by X-ray emission spectroscopy (XES). The smaller ionic radius for low-spin compared to high-spin Fe(2+) also leads to an ordered cation distribution in the M1 and M2 crystallographic sites of the higher density ppv structure. Rietveld structure refinement indicates that approximately 70% of the total Fe(2+) in that phase occupies the M2 site. XES results indicate a loss of 70% of the unpaired electronic spins consistent with a low spin M2 site and high spin M1 site. First-principles calculations of the magnetic ordering confirm that Pmcm with a two-site model is energetically more favorable at high pressure, and predict that the ordered structure is anisotropic in its electrical and elastic properties. These results suggest that interpretations of seismic structure in the deep mantle need to treat a broader range of mineral structures than previously considered.

The role of the non-magnetic material in spin pumping and magnetization dynamics in NiFe and CoFeB multilayer systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruiz-Calaforra, A., E-mail: ruiz@physik.uni-kl.de; Brächer, T.; Lauer, V.

2015-04-28

We present a study of the effective magnetization M{sub eff} and the effective damping parameter α{sub eff} by means of ferromagnetic resonance spectroscopy on the ferromagnetic (FM) materials Ni{sub 81}Fe{sub 19} (NiFe) and Co{sub 40}Fe{sub 40}B{sub 20} (CoFeB) in FM/Pt, FM/NM, and FM/NM/Pt systems with the non-magnetic (NM) materials Ru, Cr, Al, and MgO. Moreover, for NiFe layer systems, the influence of interface effects is studied by way of thickness dependent measurements of M{sub eff} and α{sub eff}. Additionally, spin pumping in NiFe/NM/Pt is investigated by means of inverse spin Hall effect (ISHE) measurements. We observe a large dependence ofmore » M{sub eff} and α{sub eff} of the NiFe films on the adjacent NM layer. While Cr and Al do not induce a large change in the magnetic properties, Ru, Pt, and MgO affect M{sub eff} and α{sub eff} in different degrees. In particular, NiFe/Ru and NiFe/Ru/Pt systems show a large perpendicular surface anisotropy and a significant enhancement of the damping. In contrast, the magnetic properties of CoFeB films do not have a large influence of the NM adjacent material and only CoFeB/Pt systems present an enhancement of α{sub eff}. However, this enhancement is much more pronounced in NiFe/Pt. By the introduction of the NM spacer material, this enhancement is reduced. Furthermore, a difference in symmetry between NiFe/NM/Pt and NiFe/NM systems in the output voltage signal from the ISHE measurements reveals the presence of spin pumping into the Pt layer in all-metallic NiFe/NM/Pt and NiFe/Pt systems.« less

Positive holes in magnesium oxide - Correlation between magnetic, electric, and dielectric anomalies

NASA Technical Reports Server (NTRS)

Batllo, F.; Leroy, R. C.; Parvin, K.; Freund, F.; Freund, M. M.

1991-01-01

The present magnetic susceptibility investigation of high purity MgO single crystals notes an anomally at 800 K which is associated with increasing electrical conductivity, a rise in static dielectric constant from 9 to 150, and the appearance of a pronounced positive surface charge. These phenomena can be accounted for in terms of peroxy defects which represent self-trapped, spin-paired positive holes at Mg(2+) vacancy sites. The holes begin to decouple their spins above 600 K.

The millimeter and submillimeter rotational spectrum of the MgCN radical (X (sup 2) Sigma(+))

NASA Technical Reports Server (NTRS)

Anderson, M. A.; Steimle, T. C.; Ziurys, L. M.

1994-01-01

The pure rotational spectrum of the MgCN radical has been recorded in the laboratory using millimeter/submillimeter direct absorption spectroscopy. Twenty-seven rotational transitions of the species were observed in the range 101-376 GHz and indicate that the molecule is linear with a (sup 2)Sigma(+) ground electronic state, as predicted by theory. Spin rotation interactions were resolved in the spectra, but no hyperfine splittings were observed, which would originate with the nitrogen nuclear spin. The rotational and fine-structure constants were determined for this radical from a nonlinear least-squares fit to the data using a (sup 2)Sigma Hamiltonian. MgCN is of astrophysical interest because it is the metastable isomer of MgNC, which recently has been detected toward IRC +10216

Critical Slowing Down in Zn-Mg-Ho Quasicrystal

NASA Astrophysics Data System (ADS)

Sugiyama, Jun; Nozaki, Hiroshi; Ansaldo, Eduardo J.; Morris, Gerald D.; Brewer, Jess H.; Sato, Taku J.

By means of longitudinal field muon-spin spectroscopy, we have found a clear critical slowing down caused by spin fluctuation of Ho moments in the icosahedral quasicrystal (QC), i-ZnMgHo, with freezing temperature (Tf =1.95 K), for which the susceptibility showed an anomaly at5K. The difference is attributed to crystalline elec-tric field (CEF) effects. The muons experience a broad, fluctuating, field distribution, of width Δ ∼6.3Taround Tf . The effect of the CEF is also apparent in zero field and weak applied transverse field measurements, with an onset around 60 K. For the Cd-based QCs (CdMgHo and CdMgGd), which exhibited two freezing temperatures in the susceptibility, the change in fluctuation rate, i.e. freezing, occurs at the lower Tf .

Influence of MgO Barrier Quality on Spin-Transfer Torque in Magnetic Tunnel Junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tiwari, Dhananjay; Sharma, Raghav; Heinonen, O. G.

Here, we studied the bias dependence of spin transfer torque in the MgO-based magnetic tunnel junction using a field-modulated spin torque ferromagnetic resonance measurement technique for three devices with tunneling magnetoresistances (MRs) of 60%, 67%, and 73%, respectively. The devices with a lower MR ratio showed the presence of multiple modes, while the device with higher MR (73%) showed a single resonance mode. We found a lower out-of-plane torkance in our devices compared to the in-plane torkance. The out-of-plane torque is linear with applied bias, while the bias dependence of in-plane torque shows a strong dependence on the MR ratiomore » and hence the barrier quality.« less

Influence of MgO Barrier Quality on Spin-Transfer Torque in Magnetic Tunnel Junctions

DOE PAGES

Tiwari, Dhananjay; Sharma, Raghav; Heinonen, O. G.; ...

2018-01-08

Here, we studied the bias dependence of spin transfer torque in the MgO-based magnetic tunnel junction using a field-modulated spin torque ferromagnetic resonance measurement technique for three devices with tunneling magnetoresistances (MRs) of 60%, 67%, and 73%, respectively. The devices with a lower MR ratio showed the presence of multiple modes, while the device with higher MR (73%) showed a single resonance mode. We found a lower out-of-plane torkance in our devices compared to the in-plane torkance. The out-of-plane torque is linear with applied bias, while the bias dependence of in-plane torque shows a strong dependence on the MR ratiomore » and hence the barrier quality.« less

Abnormal Elasticity of Single-Crystal Magnesiosiderite across the Spin Transition in Earth's Lower Mantle

NASA Astrophysics Data System (ADS)

Fu, S.; Yang, J.; Lin, J. F.

2016-12-01

Carbon can be transported into deep Earth's interior via subduction of carbonated oceanic crust, hosted as Mg-Fe bearing carbonates. The existence of stable carbonate can significantly affect our understanding on geochemical and geophysical properties of the planet. Early studies have shown that iron spin-pairing transition could occur in the iron-enriched carbonates, generally called magnesiosiderite, under lower mantle conditions. The pressure-induced spin state change is accompanied by a sudden volume collaps. However, the effects of the spin-pairing transition on single-crystal elasticity of magnesiosiderite under high pressure conditions are still unclear. Understanding the elasticity of single-crystal magnesiosiderite at relevant lower mantle conditions plays an important role in better understanding the seismic signatures in the carbon-enriched region, and to constrain carbon storage and recycling in the mantle. In order to solve all individual elastic constants (C11, C22, C33, C44, C55, C66, C12, C23, and C13) of magnesiosiderite at high pressures via Christoffel's equations, we employed Brillouin Light Scattering (BLS) to measure shear wave (Vs) and compressional wave velocities (Vp) as a function of the azimuthal angle under lower mantle pressures, accompanied by Impulsive Stimulate Light Scattering (ISS) to measure the Vp when pressures are too high to measure it by BLS. A general thermoelastic modelling was developed to fit the elastic softening within the spin transition. We will further discuss the effects of pressures, as well as iron spin states, on the single-crystal elasticity and seismic parameters (Vp and Vs anisotropy AVp, AVs, etc) at lower mantle conditions. These results could provide clues in explaining regional seismic heterogeneities in deep mantle.

Effect of spinning workouts on affect.

PubMed

Szabo, Attila; Gáspár, Zoltán; Kiss, Nikolett; Radványi, Alexandra

2015-06-01

Numerous physical exercises trigger positive changes in affect after relatively short workouts. Spinning, also known as indoor-cycling, is a very popular form of exercise, especially among women, but its impact on affect have not been examined to date. The purpose of the current work was to investigate the possible benefits of spinning on affect in self-controlled and in instructor-led exercise sessions. Using baseline measures and pre- to post-exercise design with a psychometrically validated questionnaire, the net effects of spinning (without music) on positive- and negative-affect were measured in two exercise conditions: (1) self-controlled workout (i.e. without an instructor) and (2) instructor-led workout. After both conditions, 18 women rated the extent which they enjoyed the exercise session on a 10-point Likert scale. The findings revealed that positive affect increased while negative affect decreased after both workouts. Exerted effort, measured through the heart rate, did not differ between the two conditions. However, participants enjoyed more the instructor-led exercise session than the self-regulated workout (effect size, Cohen's d = 0.93). This research reveals that spinning improves post-exercise affect, even without music and regardless of instructor's presence. Therefore, it demonstrates the net benefits of this popular exercise on affect.

The complex-scaled multiconfigurational spin-tensor electron propagator method for low-lying shape resonances in Be-, Mg- and Ca-

NASA Astrophysics Data System (ADS)

Tsogbayar, Tsednee; Yeager, Danny L.

2017-01-01

We further apply the complex scaled multiconfigurational spin-tensor electron propagator method (CMCSTEP) for the theoretical determination of resonance parameters with electron-atom systems including open-shell and highly correlated (non-dynamical correlation) atoms and molecules. The multiconfigurational spin-tensor electron propagator method (MCSTEP) developed and implemented by Yeager and his coworkers for real space gives very accurate and reliable ionization potentials and electron affinities. CMCSTEP uses a complex scaled multiconfigurational self-consistent field (CMCSCF) state as an initial state along with a dilated Hamiltonian where all of the electronic coordinates are scaled by a complex factor. CMCSTEP is designed for determining resonances. We apply CMCSTEP to get the lowest 2P (Be-, Mg-) and 2D (Mg-, Ca-) shape resonances using several different basis sets each with several complete active spaces. Many of these basis sets we employ have been used by others with different methods. Hence, we can directly compare results with different methods but using the same basis sets.

Weak-field precession of nano-pillar spin-torque oscillators using MgO-based perpendicular magnetic tunnel junction

NASA Astrophysics Data System (ADS)

Zhang, Changxin; Fang, Bin; Wang, Bochong; Zeng, Zhongming

2018-04-01

This paper presents a steady auto-oscillation in a spin-torque oscillator using MgO-based magnetic tunnel junction (MTJ) with a perpendicular polarizer and a perpendicular free layer. As the injected d.c. current varied from 1.5 to 3.0 mA under a weak magnetic field of 290 Oe, the oscillation frequency decreased from 1.85 to 1.3 GHz, and the integrated power increased from 0.1 to 74 pW. A narrow linewidth down to 7 MHz corresponding to a high Q factor of 220 was achieved at 2.7 mA, which was ascribed to the spatial coherent procession of the free layer magnetization. Moreover, the oscillation frequency was quite sensitive to the applied field, about 3.07 MHz/Oe, indicating the potential applications as a weak magnetic field detector. These results suggested that the MgO-based MTJ with perpendicular magnetic easy axis could be helpful for developing spin-torque oscillators with narrow-linewidth and high sensitive.

Crystal structures of (Mg1-x,Fex)SiO3postperovskite at high pressures

PubMed Central

Yamanaka, Takamitsu; Hirose, Kei; Mao, Wendy L.; Meng, Yue; Ganesh, P.; Shulenburger, Luke; Shen, Guoyin; Hemley, Russell J.

2012-01-01

X-ray diffraction experiments on postperovskite (ppv) with compositions (Mg0.9Fe0.1)SiO3 and (Mg0.6Fe0.4)SiO3 at Earth core-mantle boundary pressures reveal different crystal structures. The former adopts the CaIrO3-type structure with space group Cmcm, whereas the latter crystallizes in a structure with the Pmcm (Pmma) space group. The latter has a significantly higher density (ρ = 6.119(1) g/cm3) than the former (ρ = 5.694(8) g/cm3) due to both the larger amount of iron and the smaller ionic radius of Fe2+ as a result of an electronic spin transition observed by X-ray emission spectroscopy (XES). The smaller ionic radius for low-spin compared to high-spin Fe2+ also leads to an ordered cation distribution in the M1 and M2 crystallographic sites of the higher density ppv structure. Rietveld structure refinement indicates that approximately 70% of the total Fe2+ in that phase occupies the M2 site. XES results indicate a loss of 70% of the unpaired electronic spins consistent with a low spin M2 site and high spin M1 site. First-principles calculations of the magnetic ordering confirm that Pmcm with a two-site model is energetically more favorable at high pressure, and predict that the ordered structure is anisotropic in its electrical and elastic properties. These results suggest that interpretations of seismic structure in the deep mantle need to treat a broader range of mineral structures than previously considered. PMID:22223656

Use of EPR Spin-Trapping Techniques to Detect Radicals from Rat Lung Lavage Fluid Following Sulfur Mustard Vapor Exposure

DTIC Science & Technology

1993-05-13

lung injury. Anesthetized rats were intratracheally intubated and exposed to 0.35 mg HD vapor over 50 min, Immediately, 1 hr or 24 hr after exposure...lungs were lavaged with the spin trap, alpha-phenyl-t-butyl nitrone (PBN; 0.35 mg/ml). Recovered lavage fluid was assayed by EPR spectroscopy for...in EtOH (100 Ml), or EtOH alone (control), was placed in a water Jacketed (37° C) vapor generator and the rats .ere exposed for 50 min. by which time

Antiferromagnetic spin Seebeck effect.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Stephen M.; Zhang, Wei; KC, Amit

2016-03-03

We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2. A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF2(110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2–80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in themore » spin Seebeck signal when large magnetic fields (>9T) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.« less

Antiferromagnetic Spin Seebeck Effect

NASA Astrophysics Data System (ADS)

Wu, Stephen M.; Zhang, Wei; KC, Amit; Borisov, Pavel; Pearson, John E.; Jiang, J. Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand

2016-03-01

We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2 . A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30 nm )/Pt (4 nm) grown by molecular beam epitaxy on a MgF2 (110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2-80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9 T ) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.

Abnormal bias dependence of magnetoresistance in CoFeB/MgO/Si spin-injection tunnel contacts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, June-Young; Park, Byong-Guk, E-mail: bgpark@kaist.ac.kr; Baek, Seung-heon Chris

We report a strong bias voltage dependence of magnetoresistance (MR) in CoFeB/MgO/Si spin-injection tunnel contacts using the three-terminal Hanle geometry. When a bias voltage is relatively large, the MR is composed of two characteristic signals: a conventional Hanle signal observed at a low magnetic field, which is due to the precession of injected spins, and another signal originating from the rotation of the magnetization at a larger magnetic field. In contrast, for a small bias voltage, additional signals appear at a wide range of magnetic fields, which occasionally overwhelms the conventional Hanle signals. Because the additional signals are pronounced atmore » a low bias and are significantly reduced by annealing at moderate temperatures, they can be attributed to multi-step tunneling via defect states at the interfaces or tunnel barrier. Our results demonstrate that the spin injection signal caused by the defect states can be evaluated by its bias voltage dependence.« less

Spin accumulation in permalloy-ZnO heterostructures from both electrical injection and spin pumping

NASA Astrophysics Data System (ADS)

Wang, Xiaowei; Yang, Yumeng; Wang, Ying; Luo, Ziyan; Xie, Hang; Wu, Yihong

2017-11-01

We report the results of room temperature spin injection and detection studies in ZnO using both electrical injection and spin pumping. At ferromagnetic resonance, an interfacial voltage with a constant polarity upon magnetization reversal is observed in permalloy-ZnO heterostructures, which is attributed to spin accumulation after ruling out other origins. Simultaneous electrical injection during spin pumping is achieved in samples with large interface resistance or insertion of a thin MgO layer at the interface of permalloy and ZnO. From the pumping frequency dependence of detected voltage, a spin lifetime of 32 ps is extracted for ZnO at room temperature, despite the fact that there was no Hanle effect observed in the same device using the conventional three-terminal DC measurement.

Strain-enhanced tunneling magnetoresistance in MgO magnetic tunnel junctions

PubMed Central

Loong, Li Ming; Qiu, Xuepeng; Neo, Zhi Peng; Deorani, Praveen; Wu, Yang; Bhatia, Charanjit S.; Saeys, Mark; Yang, Hyunsoo

2014-01-01

While the effects of lattice mismatch-induced strain, mechanical strain, as well as the intrinsic strain of thin films are sometimes detrimental, resulting in mechanical deformation and failure, strain can also be usefully harnessed for applications such as data storage, transistors, solar cells, and strain gauges, among other things. Here, we demonstrate that quantum transport across magnetic tunnel junctions (MTJs) can be significantly affected by the introduction of controllable mechanical strain, achieving an enhancement factor of ~2 in the experimental tunneling magnetoresistance (TMR) ratio. We further correlate this strain-enhanced TMR with coherent spin tunneling through the MgO barrier. Moreover, the strain-enhanced TMR is analyzed using non-equilibrium Green's function (NEGF) quantum transport calculations. Our results help elucidate the TMR mechanism at the atomic level and can provide a new way to enhance, as well as tune, the quantum properties in nanoscale materials and devices. PMID:25266219

Giant spin splitting in optically active ZnMnTe/ZnMgTe core/shell nanowires.

PubMed

Wojnar, Piotr; Janik, Elżbieta; Baczewski, Lech T; Kret, Sławomir; Dynowska, Elżbieta; Wojciechowski, Tomasz; Suffczyński, Jan; Papierska, Joanna; Kossacki, Piotr; Karczewski, Grzegorz; Kossut, Jacek; Wojtowicz, Tomasz

2012-07-11

An enhancement of the Zeeman splitting as a result of the incorporation of paramagnetic Mn ions in ZnMnTe/ZnMgTe core/shell nanowires is reported. The studied structures are grown by gold-catalyst assisted molecular beam epitaxy. The near band edge emission of these structures, conspicuously absent in the case of uncoated ZnMnTe nanowires, is activated by the presence of ZnMgTe coating. Giant Zeeman splitting of this emission is studied in ensembles of nanowires with various average Mn concentrations of the order of a few percent, as well as in individual nanowires. Thus, we show convincingly that a strong spin sp-d coupling is indeed present in these structures.

Effect of quantum tunneling on spin Hall magnetoresistance

NASA Astrophysics Data System (ADS)

Ok, Seulgi; Chen, Wei; Sigrist, Manfred; Manske, Dirk

2017-02-01

We present a formalism that simultaneously incorporates the effect of quantum tunneling and spin diffusion on the spin Hall magnetoresistance observed in normal metal/ferromagnetic insulator bilayers (such as Pt/Y3Fe5O12) and normal metal/ferromagnetic metal bilayers (such as Pt/Co), in which the angle of magnetization influences the magnetoresistance of the normal metal. In the normal metal side the spin diffusion is known to affect the landscape of the spin accumulation caused by spin Hall effect and subsequently the magnetoresistance, while on the ferromagnet side the quantum tunneling effect is detrimental to the interface spin current which also affects the spin accumulation. The influence of generic material properties such as spin diffusion length, layer thickness, interface coupling, and insulating gap can be quantified in a unified manner, and experiments that reveal the quantum feature of the magnetoresistance are suggested.

Al embedded MgO barrier MTJ: A first principle study for application in fast and compact STT-MRAMs

NASA Astrophysics Data System (ADS)

Yadav, Manoj Kumar; Gupta, Santosh Kumar; Rai, Sanjeev; Pandey, Avinash C.

2017-03-01

The first principle comparative study of a novel single Al sheet embedded MgO and pure MgO barrier having Fe electrodes magnetic tunnel junction has been presented. Al embedded MgO is reported to provide enhanced spin polarised tunnelling current due to increase of spin-polarized density of states at Fermi energy in the barrier region. This novel MTJ provides a current density and resistance area (RA) product of 94.497 ×107 A / cm2 and 0.105  Ω - μm2 respectively. With such a low RA product; it allows higher deriving current due to which switching time of magnetization reversal reduces without inducing barrier related breakdowns in non-volatile magnetic random access memories. The low RA product and high current density of the proposed MTJ may have possible applications in integration with existing MOS circuits.

Multiphoton Coherent Manipulation in Large-Spin Qubits

NASA Astrophysics Data System (ADS)

Bertaina, S.; Chen, L.; Groll, N.; van Tol, J.; Dalal, N. S.; Chiorescu, I.

2009-02-01

Large-spin Mn2+ ions (S=5/2) diluted in a nonmagnetic MgO matrix of high crystalline symmetry are used to realize a six-level system that can be operated by means of multiphoton coherent Rabi oscillations. This spin system has a very small anisotropy which can be tuned in situ to reversibly transform the system between harmonic and nonharmonic level configurations. Decoherence effects are strongly suppressed as a result of the quasi-isotropic electron interaction with the crystal field and with the Mn55 nuclear spins. These results suggest new ways of manipulating, reading, and resetting spin quantum states which can be applied to encode a qubit across several quantum levels.

Spin-Glass Ground State in a Triangular-Lattice Compound YbZnGaO4

NASA Astrophysics Data System (ADS)

Ma, Zhen; Wang, Jinghui; Dong, Zhao-Yang; Zhang, Jun; Li, Shichao; Zheng, Shu-Han; Yu, Yunjie; Wang, Wei; Che, Liqiang; Ran, Kejing; Bao, Song; Cai, Zhengwei; Čermák, P.; Schneidewind, A.; Yano, S.; Gardner, J. S.; Lu, Xin; Yu, Shun-Li; Liu, Jun-Ming; Li, Shiyan; Li, Jian-Xin; Wen, Jinsheng

2018-02-01

We report on comprehensive results identifying the ground state of a triangular-lattice structured YbZnGaO4 as a spin glass, including no long-range magnetic order, prominent broad excitation continua, and the absence of magnetic thermal conductivity. More crucially, from the ultralow-temperature ac susceptibility measurements, we unambiguously observe frequency-dependent peaks around 0.1 K, indicating the spin-glass ground state. We suggest this conclusion holds also for its sister compound YbMgGaO4 , which is confirmed by the observation of spin freezing at low temperatures. We consider disorder and frustration to be the main driving force for the spin-glass phase.

Defect and adsorbate induced ferromagnetic spin-order in magnesium oxide nanocrystallites

NASA Astrophysics Data System (ADS)

Kumar, Ashok; Kumar, Jitendra; Priya, Shashank

2012-05-01

We report the correlation between d0 ferromagnetism, photoluminescence (PL), and adsorbed hydrogen (H-) species in magnesium oxide (MgO) nanocrystallites. Our study suggests that the oxygen vacancies, namely singly ionized anionic vacancies (F+) and dimers (F22+) induce characteristic photoluminescence and the room-temperature ferromagnetic spin-order. Nanocrystallites with low population of oxygen vacancies have revealed diamagnetic behavior. Intriguingly, on adsorption of hydrogen (H-) species in the MgO nanocrystallites, ferromagnetic behavior was either enhanced (in the case of highly oxygen deficient nanocrystallites) or begun to percolate (in the case of nanocrystallite with low population density of oxygen vacancies).

Effect of post annealing on spin accumulation and transport signals in Co{sub 2}FeSi/MgO/n{sup +}-Si on insulator devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tiwari, Ajay, E-mail: ajay1.tiwari@toshiba.co.jp; Inokuchi, Tomoaki; Ishikawa, Mizue

The post annealing temperature dependence of spin accumulation and transport signals in Co{sub 2}FeSi/MgO/n{sup +}-Si on insulator were investigated. The spin signals were detected using 3- and 4-terminal Hanle, 2-terminal local and 4-terminal nonlocal magnetoresistance measurements. The post annealing temperature (T{sub A}) dependence of the magnitude in 3-terminal narrow Hanle signals is nearly constant up to T{sub A} < 400°C, however a slight decrease above T{sub A} ≥ 400°C is observed. This behavior is consistent with the T{sub A} dependence of the magnitude of 4-terminal nonlocal magnetoresistance (MR) signals. The spin polarization estimated from the 3-terminal narrow Hanle signals andmore » the magnitude of 2-terminal local MR signals show a slight improvement with increasing post annealing temperature with a peak at around 325°C and then start reducing slowly. The slight increase in the spin signal would be due to high spin polarization of Co{sub 2}FeSi as a result of structural ordering. The 2-terminal local MR signals do not vary significantly by annealing between as-deposited and T{sub A} = 400°C, indicating the robustness of our device. This result would be useful for future Si spintronics devices.« less

In-plane current-driven spin-orbit torque switching in perpendicularly magnetized films with enhanced thermal tolerance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Di; Department of Optical Science and Engineering, Key Laboratory of Micro and Nano Photonic Structures; Yu, Guoqiang, E-mail: guoqiangyu@ucla.edu

2016-05-23

We study spin-orbit-torque (SOT)-driven magnetization switching in perpendicularly magnetized Ta/Mo/Co{sub 40}Fe{sub 40}B{sub 20} (CoFeB)/MgO films. The thermal tolerance of the perpendicular magnetic anisotropy (PMA) is enhanced, and the films sustain the PMA at annealing temperatures of up to 430 °C, due to the ultra-thin Mo layer inserted between the Ta and CoFeB layers. More importantly, the Mo insertion layer also allows for the transmission of the spin current generated in the Ta layer due to spin Hall effect, which generates a damping-like SOT and is able to switch the perpendicular magnetization. When the Ta layer is replaced by a Pt layer,more » i.e., in a Pt/Mo/CoFeB/MgO multilayer, the direction of the SOT-induced damping-like effective field becomes opposite because of the opposite sign of spin Hall angle in Pt, which indicates that the SOT-driven switching is dominated by the spin current generated in the Ta or Pt layer rather than the Mo layer. Quantitative characterization through harmonic measurements reveals that the large SOT effective field is preserved for high annealing temperatures. This work provides a route to applying SOT in devices requiring high temperature processing steps during the back-end-of-line processes.« less

Theoretical studies of the local structures and spin Hamiltonian parameters for Cu2+ in alkaline earth alumino borate glasses

NASA Astrophysics Data System (ADS)

Guo, Jia-Xing; Wu, Shao-Yi; Kuang, Min-Quan; Peng, Li; Wu, Li-Na

2018-01-01

The local structures and spin Hamiltonian parameters are theoretically studied for Cu2+ in alkaline earth alumino borate (XAB, X = Mg, Ca and Sr) glasses by using the perturbation calculations for tetragonally elongated octahedral 3d9 groups. The [CuO6]10- groups are subject to the large relative tetragonal elongation ratios of 15.4%, 13.4% and 13.0% for MgAB, CaAB and SrAB glasses, respectively, arising from the Jahn-Teller effect. The decreasing cubic field parameter Dq, orbital reduction factor k and relative elongation ratio with the increase of the radius of alkaline earth ion X from Mg to Ca or Sr are analyzed for the studied systems in a uniform way.

Proposed formation mechanism and active species of hydrogen molecules generated from a novel magnesium-citric acid-hydroxypropyl cellulose coating (MgCC) material

NASA Astrophysics Data System (ADS)

Kobayashi, Shigeki; Chikuma, Toshiyuki; Chiba, Kazuyoshi; Tsuchiya, Daisuke; Hirai, Tomomitsu

2016-02-01

The presence of acids is known to accelerate the reaction (Mg + 2H2O = Mg(OH)2 + H2). We developed a novel Mg-citric acid coating (MgCC) material produced by milling Mg powder coated with hydroxypropyl cellulose (HPC); because of its H2 generation, this material could be used in antioxidant therapy and antiaging applications. After milling in the presence of citric acid, this material produced H2-rich water upon addition to cooled water. Although the reaction was considered to involve a two-electron transfer from Mg to 2H2O, the role of the acid in H2 generation remains incompletely understood. To clarify the reaction mechanism, we performed studies on the deuterium kinetic isotope effects (KIE) and electron spin resonance (ESR). We observed differences in the concentration ratios, such as H2/D2 > 1 and H2/(H2 + D2 + HD) > 1, involved in H2, D2, and (H2 + D2 + HD) production, and found that adducts with hydrogen atoms (Hrad) were not obtained from the spin-trapping reaction between 5-(2, 2-Dimethyl-1,3-propoxy cyclophosphoryl)-5-methyl-1-pyrroline N-oxide (CYPMPO) and the MgCC material. The H2, D2, and HD produced from MgCC were identified by using a gas chromatograph connected to a mass spectrometer. The spin-trapping techniques showed that the Hrad adducts formed by the reaction of NaBH4 with CYPMPO could not be observed from reaction of MGCC with CYPMPO in H2O. The data suggest that the rate-controlling step and proposed transition state (TS) exist in the reaction pathway of the O-H bond cleavage and H-H bond formation. A TS of a structure such as [Mg(OH2)2]∗ could be expected in the reaction pathway between Mg and 2H2O by density functional theory calculations. Also, these results show that H2 generation is accelerated in the presence of acids because the activation energy of the TS is significantly smaller than that of H2O.

Enhancement of Spin-transfer torque switching via resonant tunneling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chatterji, Niladri; Tulapurkar, Ashwin A.; Muralidharan, Bhaskaran

We propose the use of resonant tunneling as a route to enhance the spin-transfer torque switching characteristics of magnetic tunnel junctions. The proposed device structure is a resonant tunneling magnetic tunnel junction based on a MgO-semiconductor heterostructure sandwiched between a fixed magnet and a free magnet. Using the non-equilibrium Green's function formalism coupled self consistently with the Landau-Lifshitz-Gilbert-Slonczewski equation, we demonstrate enhanced tunnel magneto-resistance characteristics as well as lower switching voltages in comparison with traditional trilayer devices. Two device designs based on MgO based heterostructures are presented, where the physics of resonant tunneling leads to an enhanced spin transfer torquemore » thereby reducing the critical switching voltage by up to 44%. It is envisioned that the proof-of-concept presented here may lead to practical device designs via rigorous materials and interface studies.« less

Modulation of spin dynamics via voltage control of spin-lattice coupling in multiferroics

DOE PAGES

Zhu, Mingmin; Zhou, Ziyao; Peng, Bin; ...

2017-02-03

Our work aims at magnonics manipulation by the magnetoelectric coupling effect and is motivated by the most recent progresses in both magnonics (spin dynamics) and multiferroics fields. Here, voltage control of magnonics, particularly the surface spin waves, is achieved in La 0.7Sr 0.3MnO 3/0.7Pb(Mg 1/3Nb 2/3)O 3-0.3PbTiO 3 multiferroic heterostructures. With the electron spin resonance method, a large 135 Oe shift of surface spin wave resonance (≈7 times greater than conventional voltage-induced ferromagnetic resonance shift of 20 Oe) is determined. A model of the spin-lattice coupling effect, i.e., varying exchange stiffness due to voltage-induced anisotropic lattice changes, has been establishedmore » to explain experiment results with good agreement. In addition, an “on” and “off” spin wave state switch near the critical angle upon applying a voltage is created. The modulation of spin dynamics by spin-lattice coupling effect provides a platform for realizing energy-efficient, tunable magnonics devices.« less

Detection of Short-Waved Spin Waves in Individual Microscopic Spin-Wave Waveguides Using the Inverse Spin Hall Effect.

PubMed

Brächer, T; Fabre, M; Meyer, T; Fischer, T; Auffret, S; Boulle, O; Ebels, U; Pirro, P; Gaudin, G

2017-12-13

The miniaturization of complementary metal-oxide-semiconductor (CMOS) devices becomes increasingly difficult due to fundamental limitations and the increase of leakage currents. Large research efforts are devoted to find alternative concepts that allow for a larger data-density and lower power consumption than conventional semiconductor approaches. Spin waves have been identified as a potential technology that can complement and outperform CMOS in complex logic applications, profiting from the fact that these waves enable wave computing on the nanoscale. The practical application of spin waves, however, requires the demonstration of scalable, CMOS compatible spin-wave detection schemes in material systems compatible with standard spintronics as well as semiconductor circuitry. Here, we report on the wave-vector independent detection of short-waved spin waves with wavelengths down to 150 nm by the inverse spin Hall effect in spin-wave waveguides made from ultrathin Ta/Co 8 Fe 72 B 20 /MgO. These findings open up the path for miniaturized scalable interconnects between spin waves and CMOS and the use of ultrathin films made from standard spintronic materials in magnonics.

Electrical spin injection and detection in molybdenum disulfide multilayer channel

PubMed Central

Liang, Shiheng; Yang, Huaiwen; Renucci, Pierre; Tao, Bingshan; Laczkowski, Piotr; Mc-Murtry, Stefan; Wang, Gang; Marie, Xavier; George, Jean-Marie; Petit-Watelot, Sébastien; Djeffal, Abdelhak; Mangin, Stéphane; Jaffrès, Henri; Lu, Yuan

2017-01-01

Molybdenum disulfide has recently emerged as a promising two-dimensional semiconducting material for nano-electronic, opto-electronic and spintronic applications. However, the demonstration of an electron spin transport through a semiconducting MoS2 channel remains challenging. Here we show the evidence of the electrical spin injection and detection in the conduction band of a multilayer MoS2 semiconducting channel using a two-terminal spin-valve configuration geometry. A magnetoresistance around 1% has been observed through a 450 nm long, 6 monolayer thick MoS2 channel with a Co/MgO tunnelling spin injector and detector. It is found that keeping a good balance between the interface resistance and channel resistance is mandatory for the observation of the two-terminal magnetoresistance. Moreover, the electron spin-relaxation is found to be greatly suppressed in the multilayer MoS2 channel with an in-plane spin polarization. The long spin diffusion length (approximately ∼235 nm) could open a new avenue for spintronic applications using multilayer transition metal dichalcogenides. PMID:28387252

Spin-orbit coupling control of anisotropy, ground state and frustration in 5d 2Sr 2MgOsO 6

DOE PAGES

Morrow, Ryan; Taylor, Alice E.; Singh, D. J.; ...

2016-08-30

The influence of spin-orbit coupling (SOC) on the physical properties of the 5d 2 system Sr 2MgOsO 6 is probed via a combination of magnetometry, specific heat measurements, elastic and inelastic neutron scattering, and density functional theory calculations. Although a significant degree of frustration is expected, we find that Sr 2MgOsO 6 orders in a type I antiferromagnetic structure at the remarkably high temperature of 108 K. The measurements presented allow for the first accurate quantification of the size of the magnetic moment in a 5d 2 system of 0.60(2) μ B a significantly reduced moment from the expected valuemore » for such a system. Furthermore, significant anisotropy is identified via a spin excitation gap, and we confirm by first principles calculations that SOC not only provides the magnetocrystalline anisotropy, but also plays a crucial role in determining both the ground state magnetic order and the moment size in this compound. In conclusion, through comparison to Sr 2ScOsO 6, it is demonstrated that SOC-induced anisotropy has the ability to relieve frustration in 5d 2 systems relative to their 5d 3 counterparts, providing an explanation of the high TN found in Sr 2MgOsO 6.« less

Spin-orbit coupling control of anisotropy, ground state and frustration in 5d2 Sr2MgOsO6

PubMed Central

Morrow, Ryan; Taylor, Alice E.; Singh, D. J.; Xiong, Jie; Rodan, Steven; Wolter, A. U. B.; Wurmehl, Sabine; Büchner, Bernd; Stone, M. B.; Kolesnikov, A. I.; Aczel, Adam A.; Christianson, A. D.; Woodward, Patrick M.

2016-01-01

The influence of spin-orbit coupling (SOC) on the physical properties of the 5d2 system Sr2MgOsO6 is probed via a combination of magnetometry, specific heat measurements, elastic and inelastic neutron scattering, and density functional theory calculations. Although a significant degree of frustration is expected, we find that Sr2MgOsO6 orders in a type I antiferromagnetic structure at the remarkably high temperature of 108 K. The measurements presented allow for the first accurate quantification of the size of the magnetic moment in a 5d2 system of 0.60(2) μB –a significantly reduced moment from the expected value for such a system. Furthermore, significant anisotropy is identified via a spin excitation gap, and we confirm by first principles calculations that SOC not only provides the magnetocrystalline anisotropy, but also plays a crucial role in determining both the ground state magnetic order and the size of the local moment in this compound. Through comparison to Sr2ScOsO6, it is demonstrated that SOC-induced anisotropy has the ability to relieve frustration in 5d2 systems relative to their 5d3 counterparts, providing an explanation of the high TN found in Sr2MgOsO6. PMID:27571715

Spin-orbit coupling control of anisotropy, ground state and frustration in 5d(2) Sr2MgOsO6.

PubMed

Morrow, Ryan; Taylor, Alice E; Singh, D J; Xiong, Jie; Rodan, Steven; Wolter, A U B; Wurmehl, Sabine; Büchner, Bernd; Stone, M B; Kolesnikov, A I; Aczel, Adam A; Christianson, A D; Woodward, Patrick M

2016-08-30

The influence of spin-orbit coupling (SOC) on the physical properties of the 5d(2) system Sr2MgOsO6 is probed via a combination of magnetometry, specific heat measurements, elastic and inelastic neutron scattering, and density functional theory calculations. Although a significant degree of frustration is expected, we find that Sr2MgOsO6 orders in a type I antiferromagnetic structure at the remarkably high temperature of 108 K. The measurements presented allow for the first accurate quantification of the size of the magnetic moment in a 5d(2) system of 0.60(2) μB -a significantly reduced moment from the expected value for such a system. Furthermore, significant anisotropy is identified via a spin excitation gap, and we confirm by first principles calculations that SOC not only provides the magnetocrystalline anisotropy, but also plays a crucial role in determining both the ground state magnetic order and the size of the local moment in this compound. Through comparison to Sr2ScOsO6, it is demonstrated that SOC-induced anisotropy has the ability to relieve frustration in 5d(2) systems relative to their 5d(3) counterparts, providing an explanation of the high TN found in Sr2MgOsO6.

Spin-Driven Emergent Antiferromagnetism and Metal-Insulator Transition in Nanoscale p-Si

NASA Astrophysics Data System (ADS)

Lou, Paul C.; Kumar, Sandeep

2018-04-01

The entanglement of the charge, spin and orbital degrees of freedom can give rise to emergent behavior especially in thin films, surfaces and interfaces. Often, materials that exhibit those properties require large spin orbit coupling. We hypothesize that the emergent behavior can also occur due to spin, electron and phonon interactions in widely studied simple materials such as Si. That is, large intrinsic spin-orbit coupling is not an essential requirement for emergent behavior. The central hypothesis is that when one of the specimen dimensions is of the same order (or smaller) as the spin diffusion length, then non-equilibrium spin accumulation due to spin injection or spin-Hall effect (SHE) will lead to emergent phase transformations in the non-ferromagnetic semiconductors. In this experimental work, we report spin mediated emergent antiferromagnetism and metal insulator transition in a Pd (1 nm)/Ni81Fe19 (25 nm)/MgO (1 nm)/p-Si (~400 nm) thin film specimen. The spin-Hall effect in p-Si, observed through Rashba spin-orbit coupling mediated spin-Hall magnetoresistance behavior, is proposed to cause the spin accumulation and resulting emergent behavior. The phase transition is discovered from the diverging behavior in longitudinal third harmonic voltage, which is related to the thermal conductivity and heat capacity.

Divalent metal ions modulated strong frustrated M(II)-Fe(III)3O (M = Fe, Mn, Mg) chains with metamagnetism only in a mixed valence iron complex.

PubMed

Wu, Qi-Long; Han, Song-De; Wang, Qing-Lun; Zhao, Jiong-Peng; Ma, Feng; Jiang, Xue; Liu, Fu-Chen; Bu, Xian-He

2015-10-25

Linking magnetically frustrated triangular FeO units by divalent metal ions (M(II) = Fe(II) for 1, Mn(II) for 2) gives isostructural 1D spin chains. Strong antiferromagnetic interactions were found in these complexes with significant frustrations but very interesting ferrimagnetic like transition and metamagnetism were found in mixed valence 1. By comparing the magnetic behaviours with isostructural complex 3 (with M(II) = Mg(II)), it is proposed that the spins of Fe(II) ions and Mn(II) ions have ferromagnetic and antiferromagnetic contributions respectively.

High-frequency electron-spin-resonance measurements on Mn x Mg1-x O (x = 1.0×10-4) and DPPH at very low temperatures

NASA Astrophysics Data System (ADS)

Ishikawa, Y.; Ohya, K.; Miura, S.; Fujii, Y.; Mitsudo, S.; Mizusaki, T.; Fukuda, A.; Matsubara, A.; Kikuchi, H.; Asano, T.; Yamamori, H.; Lee, S.; Vasiliev, S.

2018-03-01

We have developed a millimeter-wave electron-spin-resonance (ESR) system for very low temperatures (T < 1 K) that can be employed for nuclear-magnetic-resonance measurements by using dynamic nuclear polarization. The system uses a Fabry-Pérot resonator that works in the frequency range of 125 – 130 GHz and covers the temperature range of 0.09 – 6.5 K. We have performed ESR measurements in the frequency around 128 GHz by using Mn x Mg1-x O (x = 1.0 × 10-4) and free-radical samples of 1, 1-diphenyl-2-picrylhydrazyl (DPPH), because these samples have been proposed as field and sensitivity markers. Temperature dependence of the ESR signal intensity for Mn x Mg1-x O shows anomalies originating from magnetic order are found around 3.5 – 4 K. We estimate the sensitivity of the system for ESR detections to be 6 × 1013 spins/G at 5.8 K. Because DPPH shows no observable shift in the magnetic field, we propose it as a useful standard marker for ESR measurements at very low temperatures.

Effect of electron trap states on spin-dependent transport characteristics in CoFe/MgO/n{sup +}-Si junctions investigated by Hanle effect measurements and inelastic electron tunneling spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Inokuchi, Tomoaki, E-mail: tomoaki.inokuchi@toshiba.co.jp; Ishikawa, Mizue; Sugiyama, Hideyuki

2014-12-08

Spin-dependent transport properties in CoFe/MgO/n{sup +}-Si junctions were investigated by Hanle effect measurements and inelastic electron tunneling (IET) spectroscopy. The CoFe/MgO/n{sup +}-Si junctions examined in this study exhibited two different Hanle curves. In the low bias region, broad Hanle signals were mainly observed; in the high bias region, narrow Hanle signals were mainly observed. The d{sup 2}I/dV{sup 2}-V curves (which correspond to IET spectra) contain several peaks originating from phonon modes and other peaks originating from electron trap states. At the bias voltage where electron trap states are observed, Δd{sup 2}I/dV{sup 2} depends on the magnetic field and the fullmore » width at half-maximum of the Δd{sup 2}I/dV{sup 2}–H curves corresponds to that of the broad Hanle signals. These results indicate that electron trap states are located in the low energy region and cause a decrease in spin lifetime.« less

Development of a polarized 31Mg+ beam as a spin-1/2 probe for BNMR

NASA Astrophysics Data System (ADS)

Levy, C. D. P.; Pearson, M. R.; Dehn, M. H.; Karner, V. L.; Kiefl, R. F.; Lassen, J.; Li, R.; MacFarlane, W. A.; McFadden, R. M. L.; Morris, G. D.; Stachura, M.; Teigelhöfer, A.; Voss, A.

2016-12-01

A 28 keV beam of 31Mg+ ions was extracted from a uranium carbide, proton-beam-irradiated target coupled to a laser ion source. The ion beam was nuclear-spin polarized by collinear optical pumping on the 2it {S}_{1/2}-2it {P}_{1/2} transition at 280 nm. The polarization was preserved by an extended 1 mT guide field as the beam was transported via electrostatic bends into a 2.5 T longitudinal magnetic field. There the beam was implanted into a single crystal MgO target and the beta decay asymmetry was measured. Both hyperfine ground states were optically pumped with a single frequency light source, using segmentation of the beam energy, which boosted the polarization by approximately 50 % compared to pumping a single ground state. The total decay asymmetry of 0.06 and beam intensity were sufficient to provide a useful spin-1/2 beam for future BNMR experiments. A variant of the method was used previously to optically pump the full Doppler-broadened absorption profile of a beam of 11Be+ with a single-frequency light source.

Effect of interfacial structures on spin dependent tunneling in epitaxial L1 0-FePt/MgO/FePt perpendicular magnetic tunnel junctions

DOE PAGES

Yang, G.; Li, D. L.; Wang, S. G.; ...

2015-02-24

In this study, epitaxial FePt(001)/MgO/FePt magnetic tunnel junctions with L1 0-FePt electrodes showing perpendicular magnetic anisotropy were fabricated by molecular beam epitaxial growth. Tunnel magnetoresistance ratios of 21% and 53% were obtained at 300 K and 10 K, respectively. Our previous work, based on transmission electron microscopy, confirmed a semi-coherent interfacial structure with atomic steps (Kohn et al., APL 102, 062403 (2013)). Here, we show by x-ray photoemission spectroscopy and first-principles calculation that the bottom FePt/MgO interface is either Pt-terminated for regular growth or when an Fe layer is inserted at the interface, it is chemically bonded to O. Finally,more » both these structures have a dominant role in spin dependent tunneling across the MgO barrier resulting in a decrease of the tunneling magnetoresistance ratio compared with previous predictions.« less

Effect of interfacial structures on spin dependent tunneling in epitaxial L1{sub 0}-FePt/MgO/FePt perpendicular magnetic tunnel junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, G.; Li, D. L.; Wang, S. G., E-mail: Sgwang@iphy.ac.cn

2015-02-28

Epitaxial FePt(001)/MgO/FePt magnetic tunnel junctions with L1{sub 0}-FePt electrodes showing perpendicular magnetic anisotropy were fabricated by molecular beam epitaxial growth. Tunnel magnetoresistance ratios of 21% and 53% were obtained at 300 K and 10 K, respectively. Our previous work, based on transmission electron microscopy, confirmed a semi-coherent interfacial structure with atomic steps (Kohn et al., APL 102, 062403 (2013)). Here, we show by x-ray photoemission spectroscopy and first-principles calculation that the bottom FePt/MgO interface is either Pt-terminated for regular growth or when an Fe layer is inserted at the interface, it is chemically bonded to O. Both these structures have a dominantmore » role in spin dependent tunneling across the MgO barrier resulting in a decrease of the tunneling magnetoresistance ratio compared with previous predictions.« less

Spin dependent transport properties of Mn-Ga/MgO/Mn-Ga magnetic tunnel junctions with metal(Mg, Co, Cr) insertion layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, S. H.; Tao, L. L.; Liu, D. P., E-mail: dpliu@iphy.ac.cn

We report a first principles theoretical investigation of spin polarized quantum transport in Mn{sub 2}Ga/MgO/Mn{sub 2}Ga and Mn{sub 3}Ga/MgO/Mn{sub 3}Ga magnetic tunneling junctions (MTJs) with the consideration of metal(Mg, Co, Cr) insertion layer effect. By changing the concentration of Mn, our calculation shows a considerable disparity in transport properties: A tunneling magnetoresistance (TMR) ratio of 852% was obtained for Mn{sub 2}Ga-based MTJs, however, only a 5% TMR ratio for Mn{sub 3}Ga-based MTJs. In addition, the influence of insertion layer has been considered in our calculation. We found the Co insertion layer can increase the TMR of Mn{sub 2}Ga-based MTJ tomore » 904%; however, the Cr insertion layer can decrease the TMR by 668%; A negative TMR ratio can be obtained with Mg insertion layer. Our work gives a comprehensive understanding of the influence of different insertion layer in Mn-Ga based MTJs. It is proved that, due to the transmission can be modulated by the interfacial electronic structure of insertion, the magnetoresistance ratio of Mn{sub 2}Ga/MgO/Mn{sub 2}Ga MTJ can be improved by inserting Co layer.« less

Room-Temperature Spin Polariton Diode Laser

NASA Astrophysics Data System (ADS)

Bhattacharya, Aniruddha; Baten, Md Zunaid; Iorsh, Ivan; Frost, Thomas; Kavokin, Alexey; Bhattacharya, Pallab

2017-08-01

A spin-polarized laser offers inherent control of the output circular polarization. We have investigated the output polarization characteristics of a bulk GaN-based microcavity polariton diode laser at room temperature with electrical injection of spin-polarized electrons via a FeCo /MgO spin injector. Polariton laser operation with a spin-polarized current is characterized by a threshold of ˜69 A / cm2 in the light-current characteristics, a significant reduction of the electroluminescence linewidth and blueshift of the emission peak. A degree of output circular polarization of ˜25 % is recorded under remanent magnetization. A second threshold, due to conventional photon lasing, is observed at an injection of ˜7.2 kA /cm2 . The variation of output circular and linear polarization with spin-polarized injection current has been analyzed with the carrier and exciton rate equations and the Gross-Pitaevskii equations for the condensate and there is good agreement between measured and calculated data.

Intuitive approach to the unified theory of spin relaxation

NASA Astrophysics Data System (ADS)

Szolnoki, Lénárd; Dóra, Balázs; Kiss, Annamária; Fabian, Jaroslav; Simon, Ferenc

2017-12-01

Spin relaxation is conventionally discussed using two different approaches for materials with and without inversion symmetry. The former is known as the Elliott-Yafet (EY) theory and for the latter the D'yakonov-Perel' (DP) theory applies. We discuss herein a simple and intuitive approach to demonstrate that the two seemingly disparate mechanisms are closely related. A compelling analogy between the respective Hamiltonians is presented, and that the usual derivation of spin-relaxation times, in the respective frameworks of the two theories, can be performed. The result also allows us to obtain less canonical spin-relaxation regimes, i.e. the generalization of the EY when the material has a large quasiparticle broadening, and the DP mechanism in ultrapure semiconductors. The method also allows a practical and intuitive numerical implementation of the spin-relaxation calculation, which is demonstrated for MgB2, which has anomalous spin-relaxation properties.

Mn concentration and quantum size effects on spin-polarized transport through CdMnTe based magnetic resonant tunneling diode.

PubMed

Mnasri, S; Abdi-Ben Nasrallahl, S; Sfina, N; Lazzari, J L; Saïd, M

2012-11-01

Theoretical studies on spin-dependent transport in magnetic tunneling diodes with giant Zeeman splitting of the valence band are carried out. The studied structure consists of two nonmagnetic layers CdMgTe separated by a diluted magnetic semiconductor barrier CdMnTe, the hole is surrounded by two p-doped CdTe layers. Based on the parabolic valence band effective mass approximation and the transfer matrix method, the magnetization and the current densities for holes with spin-up and spin-down are studied in terms of the Mn concentration, the well and barrier thicknesses as well as the voltage. It is found that, the current densities depend strongly on these parameters and by choosing suitable values; this structure can be a good spin filter. Such behaviors are originated from the enhancement and suppression in the spin-dependent resonant states.

On the search for new anticancer drugs 14: the plasma pharmacokinetics and tissue distribution of spin-labeled thio-TEPA (SL-O-TT).

PubMed

Gutierrez, P L; Cohen, B E; Sosnovsky, G; Davis, T A; Egorin, M J

1985-01-01

We defined the plasma and tissue concentrations and pharmacokinetics of SL-O-TT, a spin-labeled analog of thio-TEPA, in 35-44-g male Swiss Webster mice that had received spin-labeled thio-TEPA at a dosage of 10 mg/kg. Concentrations of spin-labeled thio-TEPA in ethyl acetate extracts of tissue and plasma were determined by gas-liquid chromatography and electron spin resonance spectroscopy. Plasma concentrations of spin-labeled thio-TEPA declined in a biexponential fashion that was well described by the equation: Ct = 21.5e-0.276t + 2.30e-0.026t indicating a half-life alpha of 2.5 min and a half-life beta of 26.6 min. After 2 h there was still spin-labeled thio-TE-PA in plasma, but not in tissues. In tissues, no spin-labeled thio-TEPA was detected with gas-liquid chromatography 15 min after injection, but with electron-spin resonance label was found in lung and skeletal muscle. The main metabolite of spin-labeled thio-TEPA is spin-labeled TEPA, where oxidative desulfurization is invoked as the main metabolic mechanism. Reduction of the spin label to the hydroxylamine was also observed with time.

Detection of current induced spin polarization in epitaxial Bi2Te3 thin film

NASA Astrophysics Data System (ADS)

Dey, Rik; Roy, Anupam; Pramanik, Tanmoy; Rai, Amritesh; Heon Shin, Seung; Majumder, Sarmita; Register, Leonard F.; Banerjee, Sanjay K.

2017-03-01

We electrically detect charge current induced spin polarization on the surface of a molecular beam epitaxy grown Bi2Te3 thin film in a two-terminal device with a ferromagnetic MgO/Fe contact and a nonmagnetic Ti/Au contact. The two-point resistance, measured in an applied magnetic field, shows a hysteresis tracking the magnetization of Fe. A theoretical estimate is obtained for the change in resistance on reversing the magnetization direction of Fe from coupled spin-charge transport equations based on the quantum kinetic theory. The order of magnitude and the sign of the hysteresis are consistent with the spin-polarized surface state of Bi2Te3.

Functional conservation and structural diversification of silk sericins in two moth species.

PubMed

Zurovec, Michal; Kludkiewicz, Barbara; Fedic, Robert; Sulitkova, Jitka; Mach, Vaclav; Kucerova, Lucie; Sehnal, Frantisek

2013-06-10

Sericins are hydrophilic structural proteins produced by caterpillars in the middle section of silk glands and layered over fibroin proteins secreted in the posterior section. In the process of spinning, fibroins form strong solid filaments, while sericins seal the pair of filaments into a single fiber and glue the fiber into a cocoon. Galleria mellonella and the previously examined Bombyx mori harbor three sericin genes that encode proteins containing long repetitive regions. Galleria sericin genes are similar to each other and the protein repeats are built from short and extremely serine-rich motifs, while Bombyx sericin genes are diversified and encode proteins with long and complex repeats. Developmental changes in sericin properties are controlled at the level of gene expression and splicing. In Galleria , MG-1 sericin is produced throughout larval life until the wandering stage, while the production of MG-2 and MG-3 reaches a peak during cocoon spinning.

Finite-temperature behavior of a classical spin-orbit-coupled model for YbMgGaO4 with and without bond disorder

NASA Astrophysics Data System (ADS)

Parker, Edward; Balents, Leon

2018-05-01

We present the results of finite-temperature classical Monte Carlo simulations of a strongly spin-orbit-coupled nearest-neighbor triangular-lattice model for the candidate U (1 ) quantum spin liquid YbMgGaO4 at large system sizes. We find a single continuous finite-temperature stripe-ordering transition with slowly diverging heat capacity that completely breaks the sixfold ground-state degeneracy, despite the absence of a known conformal field theory describing such a transition. We also simulate the effect of random-bond disorder in the model, and find that even weak bond disorder destroys the transition by fragmenting the system into very large domains—possibly explaining the lack of observed ordering in the real material. The Imry-Ma argument only partially explains this fragility to disorder, and we extend the argument with a physical explanation for the preservation of our system's time-reversal symmetry even under a disorder model that preserves the same symmetry.

In the search for new anticancer drugs XII. Synthesis and biological evaluation of spin labeled nitrosoureas.

PubMed

Sosnovsky, G; Li, S W

1985-04-15

The spin labeled nitrosourea 1-(2-chloroethyl)-3-(1-oxyl-2,2,6,6- tetramethyl-piperidinyl)-1-nitrosourea (SLCNU, 4) and its analogues 5-7 were synthesized either by a regio-selective method or by a conventional route via the nitrosation of the spin labeled intermediates (11a-e). Nitrosation of the ureas 11a-e with dinitrogen tetraoxide resulted in better yields than those obtained with sodium nitrite. The nitrosoureas 4-8 were tested for their anticancer activity against the lymphocytic leukemia P388 in mice. Thus, either at the equal molar dose or at the dose of equal toxicity level, the SLCNU (4) was found to be more active than the clinically used CCNU (1). Unlike CCNU (1) whose LD50 is 56 mg/kg, the SLCNU (4) possesses a low toxicity (LD50 123 mg/kg). Therefore, SLCNU (4) is a promising new entry into the nitrosourea class of anticancer drugs.

How do external companions affect spin-orbit misalignment of hot Jupiters?

NASA Astrophysics Data System (ADS)

Lai, Dong; Anderson, Kassandra R.; Pu, Bonan

2018-04-01

Consider a planet with its orbital angular momentum axis aligned with the spin axis of its host star. To what extent does an inclined distant companion (giant planet or binary star) affect this alignment? We provide an analytic, quantitative answer and apply it to hot Jupiter systems, for which misalignments between the orbital axis and the stellar spin axis have been detected. We also show how similar consideration can be applied to multiplanet systems with distant companions (such as Kepler-56). The result of this paper provides a simple method to assess the dynamical role played by external companions on spin-orbit misalignments in exoplanetary systems.

Deformations of the spin currents by topological screw dislocation and cosmic dispiration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jianhua; Ma, Kai, E-mail: makainca@gmail.com; Li, Kang

2015-11-15

We study the spin currents induced by topological screw dislocation and cosmic dispiration. By using the extended Drude model, we find that the spin dependent forces are modified by the nontrivial geometry. For the topological screw dislocation, only the direction of spin current is bent by deforming the spin polarization vector. In contrast, the force induced by cosmic dispiration could affect both the direction and magnitude of the spin current. As a consequence, the spin-Hall conductivity does not receive corrections from screw dislocation.

Lowering of the firing voltage and reducing of the discharge delay time in alternating current plasma display panels by a discontinuous spin-coated LaB{sub 6} film on the MgO protective layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, Jiang, E-mail: dj78291@163.com; Zeng, Baoqing; Zhongshan Institute, University of Electronic Science and Technology of China, 528402 zhongshan

2014-03-15

A spin coated LaB{sub 6} discontinuous film is covered on MgO protective layer to improve the discharge performance of alternating current plasma display panels. Under the premise of high transmittance of more than 90%, a very small amount of polycrystal LaB{sub 6} powders added in an organic solvent are chosen as the coating solution. The discharge characteristics results show that with 250 torr 5% Xe-Ne pressure, the firing voltage and discharge delay time of the test panel with LaB{sub 6}/MgO double protective layer are decreased by 13.4% and 36.5%, respectively, compared with that of conventional MgO protective layer, likely owingmore » to the low work function of LaB{sub 6.} Furthermore, the aging time of the proposed structure is comparable to that of pure MgO protective layer. Therefore, it will not increase the production costs and is highly suitable to be applied for alternating current plasma display panels with low electrical power consumption.« less

Theoretical Modeling for the X-ray Spectroscopy of Iron-bearing MgSiO3 under High Pressure

NASA Astrophysics Data System (ADS)

Wang, X.; Tsuchiya, T.

2012-12-01

The behaviors of iron (Fe) in MgSiO3 perovskite, including valence state, spin state, and chemical environments, at high pressures are of fundamental importance for more detailed understanding the properties of the Earth's lower mantle. The pressure induced spin transition of Fe-bearing MgO and MgSiO3 are detected often by using high-resolution K-edge X-ray emission spectroscopy (XES) [1,2,3] and confirmed by theoretical simulations. [4,5] Since the Fe K-edge XES is associated to the 3p orbital, which is far from the valence orbitals (3d and 4s), it provides no information about its coordination environments. However, the Fe L-edge XES and X-ray absorption spectroscopy (XAS) can directly present the distribution and intensity of Fe-3d character. To identify both the spin states and the coordination environments of iron-bearing MgSiO3, we systematically investigate the L-edge XAS, XES and X-ray photoelectron (XPS) spectroscopy of Fe2+- and Fe3+-bearing MgSiO3 under high pressure by using the first-principles density functional method combined with the slater-transition method. Our results show that Fe2+ and Fe3+ can be distinguished easily by taking the XPS spectra. The spin transition of Fe2+ and Fe3+ can also be clearly certified by XAS and XES. Interestingly, the broadness of L-edge XES of Fe changes depending on the iron position, meaning that its coordination environment might also be distinguishable by using high-resolution XES measurements. Research supported by the Ehime University G-COE program and KAKENHI. [1] James Badro, Guillaume Fiquet, FranÇois Guyot, Jean-Pascal Rueff, Viktor V. Struzhkin, György VankÓ, and Giulio Monaco. Science 300, 789 (2003), [2] James Badro, Jean-Pascal Rueff, György VankÓ, Giulio Monaco, Guillaume Fiquet, and FranÇois Guyot, Science 305, 383 (2004), [3] Jung-Fu Lin, Viktor V. Struzhkin, Steven D. Jacobsen, Michael Y. Hu, Paul Chow, Jennifer Kung, Haozhe Liu, Ho-kwang Mao, and Gussell J. Hemley, Nature 436, 377 (2005). [4] Taku Tsuchiya, Renata M. Wentzcovitch, Cesar R.S. da Silva, and Stefano de Gironcoli, Phys. Rev. Lett. 96, 198501 (2006). [4] Han Hsu, Peter Blaha, Matteo Cococcioni, and Renata M. Wentzcovitch, Phys. Rev. Lett. 106, 118501 (2011).

Spin-Hall effect and emergent antiferromagnetic phase transition in n-Si

NASA Astrophysics Data System (ADS)

Lou, Paul C.; Kumar, Sandeep

2018-04-01

Spin current experiences minimal dephasing and scattering in Si due to small spin-orbit coupling and spin-lattice interactions is the primary source of spin relaxation. We hypothesize that if the specimen dimension is of the same order as the spin diffusion length then spin polarization will lead to non-equilibrium spin accumulation and emergent phase transition. In n-Si, spin diffusion length has been reported up to 6 μm. The spin accumulation in Si will modify the thermal transport behavior of Si, which can be detected with thermal characterization. In this study, we report observation of spin-Hall effect and emergent antiferromagnetic phase transition behavior using magneto-electro-thermal transport characterization. The freestanding Pd (1 nm)/Ni80Fe20 (75 nm)/MgO (1 nm)/n-Si (2 μm) thin film specimen exhibits a magnetic field dependent thermal transport and spin-Hall magnetoresistance behavior attributed to Rashba effect. An emergent phase transition is discovered using self-heating 3ω method, which shows a diverging behavior at 270 K as a function of temperature similar to a second order phase transition. We propose that spin-Hall effect leads to the spin accumulation and resulting emergent antiferromagnetic phase transition. We propose that the length scale for Rashba effect can be equal to the spin diffusion length and two-dimensional electron gas is not essential for it. The emergent antiferromagnetic phase transition is attributed to the site inversion asymmetry in diamond cubic Si lattice.

Giant tunneling magnetoresistance and tunneling spin polarization in magnetic tunnel junctions with MgO (100) tunnel barriers

NASA Astrophysics Data System (ADS)

Parkin, Stuart

2006-03-01

Recent advances in generating, manipulating and detecting spin-polarized electrons and electrical current make possible new classes of spin based sensor, memory and logic devices [1]. One key component of many such devices is the magnetic tunneling junction (MTJ) - a sandwich of thin layers of metallic ferromagnetic electrodes separated by a tunneling barrier, typically an oxide material only a few atoms thick. The magnitude of the tunneling current passing through the barrier can be adjusted by varying the relative magnetic orientation of the adjacent ferromagnetic layers. As a result, MTJs can be used to sense the magnitude of magnetic fields or to store information. The electronic structure of the ferromagnet together with that of the insulator determines the spin polarization of the current through an MTJ -- the ratio of 'up' to 'down' spin electrons. Using conventional amorphous alumina tunnel barriers tunneling spin polarization (TSP) values of up to ˜55% are found for conventional 3d ferromagnets, such as CoFe, but using highly textured crystalline MgO tunnel barriers TSP values of more than 90% can be achieved for otherwise the same ferromagnet [2]. Such TSP values rival those previously observed only with half-metallic ferromagnets. Corresponding giant values of tunneling magnetoresistance (TMR) are found, exceeding 350% at room temperature and nearly 600% at 3K. Perhaps surprisingly the MgO tunnel barrier can be quite rough: its thickness depends on the local crystalline texture of the barrier, which itself is influenced by structural defects in the underlayer. We show that the magnitude and the sign of the TMR is strongly influenced by defects in the tunnel barrier and by the detailed structure of the barrier/ferromagnet interfaces. The observation of Kondo-assisted tunneling phenomena will be discussed as well as the detailed dependence of TMR on chemical bonding at the interfaces [3]. [1] .S.S.P. Parkin, X. Jiang, C. Kaiser, et al., Proc. IEEE 91, 661 (2003). [2] S. S. P. Parkin, C. Kaiser, A. Panchula, et al., Nature Mater. 3, 862 (2004). [3] C. Kaiser, S. van Dijken, S.-H. Yang, H. Yang and S.S.P. Parkin, Phys. Rev. Lett. 94, 247203 (2005).

Local magnetizations in impure two-dimensional antiferromagnets

NASA Astrophysics Data System (ADS)

van Luijk, J. A.; Arts, A. F. M.; de Wijn, H. W.

1980-03-01

The local magnetizations near dilute substitutional impurities in the quadratic-layer antiferromagnet K2MnF4 are studied both experimentally and theoretically. The impurities considered are the nonmagnetic Zn and Mg, as well as Ni. The magnetizations are probed through the positions of the impurity-associated satellites in the nuclear magnetic resonance of the out-of-layer and in-layer 19F nuclei adjacent to the magnetic ions. It is discussed in which way the effects of lattice deformations can be eliminated in order to obtain the variations of the local magnetizations with temperature. The theoretical treatment is based on Green's-function techniques. The decoupling employed is within the local spin-deviation operators and accounts for correlation between nearest neighbors. It reduces the renormalized spin-wave Hamiltonian to an effective quadratic form, rendering decoupling of Green's functions unnecessary. The spectral distributions of the excitations are calculated including local modes. The theory is subsequently applied to the 13-site cluster consisting of the impurity and the first three shells of Mn around it. Good agreement is found. The magnetization is significantly modified in the first shell. The further shells are only weakly affected, however somewhat stronger than in comparable three-dimensional systems. For nonmagnetic impurities the thermal spin deviation in the first shell is about 13 larger than that of the host; in the Ni-doped system the additional deviations are within 1%. The zero-point deviation of the Ni is 0.11 units of spin, as compared to 0.17 in the host. A further experimental result is a uniform shift, increasing with concentration, of the sublattice magnetization at large distance from the impurity. It must be related to the finite density of states near the zone center in two-dimensional systems. Finally, some data are presented on the local susceptibilities.

Effect of solution concentration on MEH-PPV thin films

NASA Astrophysics Data System (ADS)

Affendi, I. H. H.; Sarah, M. S. P.; Alrokayan, Salman A. H.; Khan, Haseeb A.; Rusop, M.

2018-05-01

MEH-PPV thin films were prepared with a mixture of THF (tetrahydrofuran) solution deposited by spin coating method. The surface topology of MEH-PPV thin film were characterize by atomic force microscopy (AFM) and optical properties of absorption spectra were characterized by using Ultraviolet-visible-near-infrared (UV-Vis-NIR). The MEH-PPV concentration variation affects the surface and optical properties of the thin film where 0.5 mg/ml MEH-PPV concentration have a good surface topology provided the same film also gives the highest absorption coefficient were then deposited to a TiO2 thin film forming composite layer. The composite layer then shows low current flow of short circuit current of Isc = -5.313E-7 A.

Spin transfer and spin pumping in disordered normal metal-antiferromagnetic insulator systems

NASA Astrophysics Data System (ADS)

Gulbrandsen, Sverre A.; Brataas, Arne

2018-02-01

We consider an antiferromagnetic insulator that is in contact with a metal. Spin accumulation in the metal can induce spin-transfer torques on the staggered field and on the magnetization in the antiferromagnet. These torques relate to spin pumping: the emission of spin currents into the metal by a precessing antiferromagnet. We investigate how the various components of the spin-transfer torque are affected by spin-independent disorder and spin-flip scattering in the metal. Spin-conserving disorder reduces the coupling between the spins in the antiferromagnet and the itinerant spins in the metal in a manner similar to Ohm's law. Spin-flip scattering leads to spin-memory loss with a reduced spin-transfer torque. We discuss the concept of a staggered spin current and argue that it is not a conserved quantity. Away from the interface, the staggered spin current varies around a 0 mean in an irregular manner. A network model explains the rapid decay of the staggered spin current.

A systematic experimental investigation of significant parameters affecting model tire hydroplaning

NASA Technical Reports Server (NTRS)

Wray, G. A.; Ehrlich, I. R.

1973-01-01

The results of a comprehensive parametric study of model and small pneumatic tires operating on a wet surface are presented. Hydroplaning inception (spin down) and rolling restoration (spin up) are discussed. Conclusions indicate that hydroplaning inception occurs at a speed significantly higher than the rolling restoration speed. Hydroplaning speed increases considerably with tread depth, surface roughness and tire inflation pressure of footprint pressure, and only moderately with increased load. Water film thickness affects spin down speed only slightly. Spin down speed varies inversely as approximately the one-sixth power of film thickness. Empirical equations relating tire inflation pressure, normal load, tire diameter and water film thickness have been generated for various tire tread and surface configurations.

Radiation reaction for spinning bodies in effective field theory. II. Spin-spin effects

NASA Astrophysics Data System (ADS)

Maia, Natália T.; Galley, Chad R.; Leibovich, Adam K.; Porto, Rafael A.

2017-10-01

We compute the leading post-Newtonian (PN) contributions at quadratic order in the spins to the radiation-reaction acceleration and spin evolution for binary systems, entering at four-and-a-half PN order. Our calculation includes the backreaction from finite-size spin effects, which is presented for the first time. The computation is carried out, from first principles, using the effective field theory framework for spinning extended objects. At this order, nonconservative effects in the spin-spin sector are independent of the spin supplementary conditions. A nontrivial consistency check is performed by showing that the energy loss induced by the resulting radiation-reaction force is equivalent to the total emitted power in the far zone. We find that, in contrast to the spin-orbit contributions (reported in a companion paper), the radiation reaction affects the evolution of the spin vectors once spin-spin effects are incorporated.

Magnetic states of Mn and Co atoms at Co2MnGe/MgO interfaces seen via soft x-ray magnetic circular dichroism

NASA Astrophysics Data System (ADS)

Asakura, D.; Koide, T.; Yamamoto, S.; Tsuchiya, K.; Shioya, T.; Amemiya, K.; Singh, V. R.; Kataoka, T.; Yamazaki, Y.; Sakamoto, Y.; Fujimori, A.; Taira, T.; Yamamoto, M.

2010-11-01

The magnetic states of Mn and Co atoms in Co-rich Co2MnGe Heusler alloy thin films facing an MgO barrier were studied by means of soft x-ray magnetic circular dichroism (XMCD). In particular, the Co2MnGe film-thickness dependence of the Mn and Co magnetic moments was investigated. With a decrease in the Co2MnGe film thickness to 1-2 monolayers (MLs), the spin magnetic moment of Mn decreased and the MnL2,3 -edge x-ray absorption spectra (XAS) showed a Mn2+ -like multiplet structure in MnO, in contrast to samples thicker than 4 ML, indicating that the Mn atoms of the 1 and 2 ML samples were oxidized. The Co spin magnetic moment increased slightly with decreasing thickness. A Co2+ -like multiplet structure in CoO was not observed in all the CoL2,3 -edge XAS and XMCD, indicating that, even in the ultrathin samples, the Co atoms were not oxidized, and were more strongly spin polarized than those in the thicker samples. Co spin magnetic moments of 1.40-1.77μB larger than the theoretical value for ideal stoichiometric Co2MnGe (˜1μB) and the Co-rich film composition imply the presence of Co antisites that would lower the spin polarization.

Ferromagnetic Peierls insulator state in A Mg4Mn6O15(A =K ,Rb ,Cs )

NASA Astrophysics Data System (ADS)

Yamaguchi, T.; Sugimoto, K.; Ohta, Y.; Tanaka, Y.; Sato, H.

2018-04-01

Using the density-functional-theory-based electronic structure calculations, we study the electronic state of recently discovered mixed-valent manganese oxides A Mg4Mn6O15(A =K ,Rb ,Cs ) , which are fully spin-polarized ferromagnetic insulators with a cubic crystal structure. We show that the system may be described as a three-dimensional arrangement of the one-dimensional chains of a 2 p orbital of O and a 3 d orbital of Mn running along the three axes of the cubic lattice. We thereby argue that in the ground state the chains are fully spin polarized due to the double-exchange mechanism and are distorted by the Peierls mechanism to make the system insulating.

Long spin lifetime and large barrier polarisation in single electron transport through a CoFe nanoparticle

PubMed Central

Temple, R. C.; McLaren, M.; Brydson, R. M. D.; Hickey, B. J.; Marrows, C. H.

2016-01-01

We have investigated single electron spin transport in individual single crystal bcc Co30Fe70 nanoparticles using scanning tunnelling microscopy with a standard tungsten tip. Particles were deposited using a gas-aggregation nanoparticle source and individually addressed as asymmetric double tunnel junctions with both a vacuum and a MgO tunnel barrier. Spectroscopy measurements on the particles show a Coulomb staircase that is correlated with the measured particle size. Field emission tunnelling effects are incorporated into standard single electron theory to model the data. This formalism allows spin-dependent parameters to be determined even though the tip is not spin-polarised. The barrier spin polarisation is very high, in excess of 84%. By variation of the resistance, several orders of magnitude of the system timescale are probed, enabling us to determine the spin relaxation time on the island. It is found to be close to 10 μs, a value much longer than previously reported. PMID:27329575

Gigantic terahertz magnetochromism via electromagnons in the hexaferrite magnet Ba2Mg2Fe12O22

NASA Astrophysics Data System (ADS)

Kida, N.; Kumakura, S.; Ishiwata, S.; Taguchi, Y.; Tokura, Y.

2011-02-01

Effects of temperature (6-225 K) and magnetic field (0-7 T) on the low-energy (1.2-5 meV) electrodynamics of the electromagnon, the magnetic resonance driven by the light electric field, have been investigated for a hexaferrite magnet Ba2Mg2Fe12O22 by using terahertz time-domain spectroscopy. We find the gigantic terahertz magnetochromism via electromagnons; the magnetochromic change, as defined by the difference of the absorption intensity with and without magnetic field, exceeds 500% even at 0.6 T. The results arise from the fact that the spectral intensity of the electromagnon critically depends on the magnetic structure. With changing the conical spin structures in terms of the conical angle θ from the proper screw (θ=0°) to the ferrimagnetic (θ=90°) through the conical spin-ordered phases (0°<θ<90°) by external magnetic fields, we identify the maximal magnetochromism around θ≈45°. On the contrary, there is no remarkable signature of the electromagnon in the proper screw and spin-collinear (ferrimagnetic) phases, clearly indicating the important role of the conical spin order to produce the magnetically controllable electromagnons. The possible origin of this electromagnon is argued in terms of the exchange-striction mechanism.

Enhanced spin accumulation in Fe3O4 based spin injection devices below the Verwey transition

NASA Astrophysics Data System (ADS)

Bhat, Shwetha G.; Kumar, P. S. Anil

2016-12-01

Spin injection into GaAs and Si (both n and p-type) semiconductors using Fe3O4 is achieved with and without a tunnel barrier (MgO) via three-terminal electrical Hanle measurement. Interestingly, the magnitude of spin accumulation voltage (ΔV) in semiconductor is found to be associated with a drastic increment in ΔV in Fe3O4 based devices for temperature <120 K (T V, the Verwey transition). Such an enhancement of ΔV is absent in the devices with Fe as spin source. Further, the overall device resistance has no drastic difference at T V. This renders a direct proof that the observed ΔV is not influenced by the so-called metal-to-insulator transition of Fe3O4 at T V. Observations from our elaborate investigations show that spin polarization of Fe3O4 has an explicit influence on the enhanced spin injection. It is argued that the theoretical prediction of half-metallicity of Fe3O4 above and below T V has to be reinvestigated.

Oscillation characteristics of zero-field spin transfer oscillators with field-like torque

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Yuan-Yuan; Xue, Hai-Bin, E-mail: xuehaibin@tyut.edu.cn; Department of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024

2015-05-15

We theoretically investigate the influence of the field-like spin torque term on the oscillation characteristics of spin transfer oscillators, which are based on MgO magnetic tunnel junctions (MTJs) consisting of a perpendicular magnetized free layer and an in-plane magnetized pinned layer. It is demonstrated that the field-like torque has a strong impact on the steady-state precession current region and the oscillation frequency. In particular, the steady-state precession can occur at zero applied magnetic field when the ratio between the field-like torque and the spin transfer torque takes up a negative value. In addition, the dependence of the oscillation properties onmore » the junction sizes has also been analyzed. The results indicate that this compact structure of spin transfer oscillator without the applied magnetic field is practicable under certain conditions, and it may be a promising configuration for the new generation of on-chip oscillators.« less

Magnetization and anisotropy of cobalt ferrite thin films

NASA Astrophysics Data System (ADS)

Eskandari, F.; Porter, S. B.; Venkatesan, M.; Kameli, P.; Rode, K.; Coey, J. M. D.

2017-12-01

The magnetization of thin films of cobalt ferrite frequently falls far below the bulk value of 455 kA m-1 , which corresponds to an inverse cation distribution in the spinel structure with a significant orbital moment of about 0.6 μB that is associated with the octahedrally coordinated Co2+ ions. The orbital moment is responsible for the magnetostriction and magnetocrystalline anisotropy and its sensitivity to imposed strain. We have systematically investigated the structure and magnetism of films produced by pulsed-laser deposition on different substrates (Ti O2 , MgO, MgA l2O4 , SrTi O3 , LSAT, LaAl O3 ) and as a function of temperature (500 -700 °C) and oxygen pressure (10-4-10 Pa ) . Magnetization at room-temperature ranges from 60 to 440 kA m-1 , and uniaxial substrate-induced anisotropy ranges from +220 kJ m-3 for films on deposited on MgO (100) to -2100 kJ m-3 for films deposited on MgA l2O4 (100), where the room-temperature anisotropy field reaches 14 T. No rearrangement of high-spin Fe3+ and Co2+ cations on tetrahedral and octahedral sites can reduce the magnetization below the bulk value, but a switch from Fe3+ and Co2+ to Fe2+ and low-spin Co3+ on octahedral sites will reduce the low-temperature magnetization to 120 kA m-1 , and a consequent reduction of Curie temperature can bring the room-temperature value to near zero. Possible reasons for the appearance of low-spin cobalt in the thin films are discussed.

Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities

NASA Astrophysics Data System (ADS)

Luengo-Kovac, M.; Huang, S.; Del Gaudio, D.; Occena, J.; Goldman, R. S.; Raimondi, R.; Sih, V.

2017-11-01

The current-induced spin polarization and momentum-dependent spin-orbit field were measured in InxGa1 -xAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin-polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbit coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spin-orbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the current-induced spin polarization.

Spin torque efficiency of Ta, W, and Pt in metallic bilayers evaluated by harmonic Hall and spin Hall magnetoresistance measurements

NASA Astrophysics Data System (ADS)

Lau, Yong-Chang; Hayashi, Masamitsu

2017-08-01

We investigate the efficiency of current-induced torque, i.e., the spin torque efficiency, in in-plane magnetized heavy metal/CoFeB/MgO heterostructures (heavy metals = Pt, W, and Ta) using the harmonic Hall technique and the spin Hall magnetoresistance. We find that the amplitude of the external magnetic field has a strong influence on the spin torque efficiency evaluation by the harmonic Hall measurements. This can be corrected by measuring the corresponding Hall resistance susceptibility. The sign and magnitude of the resulting Slonczewski-like spin torque efficiencies are in agreement with previous reports and the measurements utilizing the spin Hall magnetoresistance, except for the Pt underlayer films. The origin of the discrepancy for the Pt underlayer films is unclear. The field like torque efficiencies, upon subtracting the Oersted field contribution, are quite low or negligible. This is in significant contrast to what has been found for the field like torque in heterostructures with perpendicular magnetization. These results suggest that a more advanced model is required in order to describe accurately spin transport and momentum transfer at metallic interfaces.

Research on the optical and EPR spectral data and the local structure for the trigonal Mn4+ centers in MgTiO3 crystal

NASA Astrophysics Data System (ADS)

Liao, Bi-Tao; Mei, Yang; Chen, Bo-Wei; Zheng, Wen-Chen

2017-07-01

The optical bands and EPR (or spin-Hamiltonian) parameters (g factors g//, g⊥ and zero-field splitting D) for Mn4+ ions at the trigonal octahedral Ti4+ site of MgTiO3 crystal are uniformly computed by virtue of the complete diagonalization (of energy matrix) method based on the two-spin-orbit-parameter model, where besides the effects of spin-orbit parameter of central dn ion on the spectral data (in the classical crystal field theory), those of ligands are also contained. The computed eight optical and EPR spectral data with four suitable adjustable parameters (note: differing from those in the previous work within cubic symmetry approximation where the used Racah parameters violate the nephelauxetic effect, the present Racah parameters obey the effect and hence are suitable) are rationally coincident with the experimental values. In particular, the calculated ground state splitting 2D, the first excited splitting ΔE(2E) and g-anisotropy Δg (=g//-g⊥) (they depend strongly on the angular distortion of d3 centers) are in excellent agreement with the observed values, suggesting that the angular distortions caused by the impurity-induced local lattice relaxation obtained from the above calculation for the trigonal Mn4+ impurity center in MgTiO3: Mn4+ crystal seem to be acceptable.

Layer thickness dependence of the current-induced effective field vector in Ta|CoFeB|MgO.

PubMed

Kim, Junyeon; Sinha, Jaivardhan; Hayashi, Masamitsu; Yamanouchi, Michihiko; Fukami, Shunsuke; Suzuki, Tetsuhiro; Mitani, Seiji; Ohno, Hideo

2013-03-01

Current-induced effective magnetic fields can provide efficient ways of electrically manipulating the magnetization of ultrathin magnetic heterostructures. Two effects, known as the Rashba spin orbit field and the spin Hall spin torque, have been reported to be responsible for the generation of the effective field. However, a quantitative understanding of the effective field, including its direction with respect to the current flow, is lacking. Here we describe vector measurements of the current-induced effective field in Ta|CoFeB|MgO heterostructrures. The effective field exhibits a significant dependence on the Ta and CoFeB layer thicknesses. In particular, a 1 nm thickness variation of the Ta layer can change the magnitude of the effective field by nearly two orders of magnitude. Moreover, its sign changes when the Ta layer thickness is reduced, indicating that there are two competing effects contributing to it. Our results illustrate that the presence of atomically thin metals can profoundly change the landscape for controlling magnetic moments in magnetic heterostructures electrically.

Towards sub-nanometer real-space observation of spin and orbital magnetism at the Fe/MgO interface

PubMed Central

Thersleff, Thomas; Muto, Shunsuke; Werwiński, Mirosław; Spiegelberg, Jakob; Kvashnin, Yaroslav; Hjӧrvarsson, Björgvin; Eriksson, Olle; Rusz, Ján; Leifer, Klaus

2017-01-01

While the performance of magnetic tunnel junctions based on metal/oxide interfaces is determined by hybridization, charge transfer, and magnetic properties at the interface, there are currently only limited experimental techniques with sufficient spatial resolution to directly observe these effects simultaneously in real-space. In this letter, we demonstrate an experimental method based on Electron Magnetic Circular Dichroism (EMCD) that will allow researchers to simultaneously map magnetic transitions and valency in real-space over interfacial cross-sections with sub-nanometer spatial resolution. We apply this method to an Fe/MgO bilayer system, observing a significant enhancement in the orbital to spin moment ratio that is strongly localized to the interfacial region. Through the use of first-principles calculations, multivariate statistical analysis, and Electron Energy-Loss Spectroscopy (EELS), we explore the extent to which this enhancement can be attributed to emergent magnetism due to structural confinement at the interface. We conclude that this method has the potential to directly visualize spin and orbital moments at buried interfaces in magnetic systems with unprecedented spatial resolution. PMID:28338011

Towards sub-nanometer real-space observation of spin and orbital magnetism at the Fe/MgO interface

NASA Astrophysics Data System (ADS)

Thersleff, Thomas; Muto, Shunsuke; Werwiński, Mirosław; Spiegelberg, Jakob; Kvashnin, Yaroslav; Hjӧrvarsson, Björgvin; Eriksson, Olle; Rusz, Ján; Leifer, Klaus

2017-03-01

While the performance of magnetic tunnel junctions based on metal/oxide interfaces is determined by hybridization, charge transfer, and magnetic properties at the interface, there are currently only limited experimental techniques with sufficient spatial resolution to directly observe these effects simultaneously in real-space. In this letter, we demonstrate an experimental method based on Electron Magnetic Circular Dichroism (EMCD) that will allow researchers to simultaneously map magnetic transitions and valency in real-space over interfacial cross-sections with sub-nanometer spatial resolution. We apply this method to an Fe/MgO bilayer system, observing a significant enhancement in the orbital to spin moment ratio that is strongly localized to the interfacial region. Through the use of first-principles calculations, multivariate statistical analysis, and Electron Energy-Loss Spectroscopy (EELS), we explore the extent to which this enhancement can be attributed to emergent magnetism due to structural confinement at the interface. We conclude that this method has the potential to directly visualize spin and orbital moments at buried interfaces in magnetic systems with unprecedented spatial resolution.

Temperature dependence of spin-torque driven ferromagnetic resonance in MgO-based magnetic tunnel junction with a perpendicularly free layer

NASA Astrophysics Data System (ADS)

Wang, Xiao; Feng, Jiafeng; Guo, Peng; Wei, H. X.; Han, X. F.; Fang, B.; Zeng, Z. M.

2017-12-01

We report the temperature dependence of the spin-torque (ST) driven ferromagnetic resonance in MgO-based magnetic tunnel junction (MTJ) nanopillars with a perpendicularly free layer and an in-plane reference layer. From the evolution of the resonance frequency with magnetic field, we clearly identify the free-layer resonance mode and reference-layer mode. For the reference layer, we demonstrate a monotonic increase in resonance frequency and the effective damping with decreasing temperature, which suggests the saturated magnetization of the reference layer is dominant. However, for the free layer, the frequency and damping exhibit almost no change with temperature, indicating that the perpendicular magnetic anisotropy plays an important role in magnetization dynamics of the free layer.

Transport and spin transfer torques in Fe/MgO/Fe tunnel barriers.

NASA Astrophysics Data System (ADS)

Heiliger, Christian

2008-03-01

The prediction of very high tunneling magnetoresistance (TMR) ratios in crystalline Fe/MgO/Fe [1,2] tunnel junctions has been verified by a number of experiments [3,4]. The high TMR can be understood in terms of the electronic structure of the system. In MgO the δ1 states at the Brillouin zone center decay the most slowly and dominate the tunnelling current. For coherent interfaces, which are achievable due to the small lattice mismatch between Fe and MgO, these δ1 states at the Brillouin zone center are half-metallic in the Fe layers. The dominance of the δ1 states and their half-metallicity cause the high tunnelling magnetoresistance measured in Fe/MgO/Fe tunnel junctions [5]. For the spin transfer torque, we calculate the linear response for small currents and voltages. Our calculations show that the half metallicity of the Fe δ1 states leads to a strong localization of the spin transfer torque to the interface. As a result, the linear current dependence of the torque in the plane of the two magnetizations is independent of the free layer thickness for more than three monolayers of Fe. For perfect samples we also find a linear current dependence of the out-of-plane component. However, this linear piece oscillates rapidly with thickness and averages to zero in the presence of structural imperfections like thickness fluctuation, in agreement with experiment [6]. In this talk I discuss the bias dependence of the TMR and spin transfer torque effects mentioned above and the influence on them of the following factors: the interface structure Fe/MgO, the barrier thickness, and the structure of the leads [7]. This work has been supported in part by the NIST-CNST/UMD-NanoCenter Cooperative Agreement. [1] W. Butler, X.-G. Zhang, T. Schulthess, J. MacLaren, Phys. Rev. B 63 (2001) 054416. [2] J. Mathon, A. Umerski, Phys. Rev. B 63 (2001) 220403. [3] S. Yuasa, T. Nagahama, A. Fukushima, Y. Suzuki, K. Ando, Nature Materials 3 (2004) 868. [4] S.S.P. Parkin, C. Kaiser, A. Panchula, P.M. Rice, B. Hughes, M. Samant, S.-H. Yang Nature Materials 3 (2004) 862. [5] C. Heiliger, P. Zahn, I. Mertig, Materials Today 9 (2006) 46. [6] J. C. Sankey, P. M. Braganca, A. G. F. Garcia, I. N. Krivorotov, R. A. Buhrman, and D. C. Ralph, Phys. Rev. Lett. 96 (2006) 227601. [7] C. Heiliger, M.Gradhand, P. Zahn, I. Mertig, Phys. Rev. Lett. 99 (2007) 066804.

Detection of erythrocyte membrane structural abnormalities in lecithin: cholesterol acyltransferase deficiency using a spin label approach.

PubMed

Maraviglia, B; Herring, F G; Weeks, G; Godin, D V

1979-01-01

The membrane fluidity of erythrocytes from patients with Lecithin: cholesterol acyltransferase (LCAT) deficiency was studied by means of electron spin resonance. The temperature dependence of the separation of the outer extrema of the spectra of 2-(3-carboxy-propyl)-4,4-dimethyl, 2-tridecyl-3-oxazolidinyloxyl spin probe was monitored for normal, presumed carrier and clinically affected subjects. The temperature profile of controls was significantly different from that of the presumed carriers and the clinically affected individuals. The results show that the compositional abnormalities previously noted in erythrocyte membranes from patients with LCAT deficiency are associated with alterations in the physiocochemical state of the membrane. An investigation of the spectral lineshapes below 10 degrees C allowed a distinction to be made at the membrane level between clinically affected subjects and clinically normal heterozygous carriers. Alterations in the temperature dependence of elec-ron spin resonance parameters may provide a sensitive index of red cell membrane alterations in pathological states of generalized membrane involvement.

Applications of the First-principles LDA+Usc Method to Spin-crossover Minerals: the NAL Phase and (Mg,Fe)CO3 ferromagnesite

NASA Astrophysics Data System (ADS)

Hsu, H.

2016-12-01

Spin crossover (SCO) in iron-bearing minerals has attracted tremendous attention in recent years, as SCO usually leads to anomalous changes of the elastic, conducting, and thermodynamic properties of these minerals. Possible geophysical effects of SCO have been anticipated as well. With the development of the local density approximation + self-consistent Hubbard U (LDA+Usc) method, first-principles calculations have elucidated SCO in many lower-mantle minerals. The success of LDA+Usc lies in its capability to correctly identify the ground state in a wide pressure range and to accurately determine the mechanism of SCO, including the transition pressure PT. In this talk, two recent LDA+Usc studies of SCO minerals are presented: the "new aluminous (NAL) phase" [1] and (Mg,Fe)CO3 ferromagnesite [2]. The former is considered as a main host of aluminum in the subducted basalt and may be related to the seismic heterogeneities, and the latter is believed to be the major carbon carrier in the Earth's lower mantle and play a key role in the deep carbon cycle. For both minerals, the abrupt change of iron quadrupole splitting and the volume/elastic anomalies accompanying the SCO obtained in our calculations are in great agreement with experiments. Our calculations also suggest that the spin transition pressure PT in the NAL phase is not very sensitive to temperature, due to its nearly degenerate low-spin (LS) states, in contrast with (Mg,Fe)O ferropericlase and (Mg,Fe)CO3 systems, in which PT significantly increases with temperature. By examining the overall performance of the LDA+Usc method in the NAL phase and ferromagnesite, along with our previous calculations for ferropericlase and Fe-bearing MgSiO3 bridgmanite [3-5], we have established LDA+Usc a highly reliable method to study iron-bearing minerals and related materials under high pressure. [1] H. Hsu, in preparation. [2] S.-C. Huang and H. Hsu, Phys. Rev. B (Rapid Comm.), in press. [3] H. Hsu and R. M. Wentzcovitch, Phys. Rev. B 90, 195205 (2014). [4] H. Hsu et al., Earth Planet. Sci. Lett. 359-360, 34 (2012). [5] H. Hsu et al., Phys. Rev. Lett. 106, 118501 (2011).

Tunable spin splitting and spin lifetime in polar WSTe monolayer

NASA Astrophysics Data System (ADS)

Adhib Ulil Absor, Moh.; Kotaka, Hiroki; Ishii, Fumiyuki; Saito, Mineo

2018-04-01

The established spin splitting with out-of-plane Zeeman spin polarizations in the monolayer (ML) of transition metal dichalcogenides (TMDs) is dictated by inversion symmetry breaking together with mirror symmetry in the surface plane. Here, by density functional theory calculations, we find that mirror symmetry breaking in the polar WSTe ML leads to large spin splitting exhibiting in-plane Rashba spin polarizations. We also find that the interplay between the out-of-plane Zeeman- and in-plane Rashba spin-polarized states sensitively affects the spin lifetime, which can be effectively controlled by in-plane strain. In addition, the tunability of spin splitting using an external electric field is also demonstrated. Our study clarifies that the use of in-plane strain and an external electric field is effective for tuning the spin splitting and spin lifetime of the polar WSTe ML; thus, it is useful for designing spintronic devices.

Doped indium nitride thin film by sol-gel spin coating method

NASA Astrophysics Data System (ADS)

Lee, Hui San; Ng, Sha Shiong; Yam, Fong Kwong

2017-12-01

In this study, magnesium doped indium nitride (InN:Mg) thin films grown on silicon (100) substrate were prepared via sol-gel spin coating method followed by nitridation process. A custom-made tube furnace was used to perform the nitridation process. Through this method, the low dissociation temperature issue of InN:Mg thin films can be solved. The deposited InN:Mg thin films were investigated using various techniques. The X-rays diffraction results revealed that two intense diffraction peaks correspond to wurtzite structure InN (100), and InN (101) were observed at 29° and 33.1° respectively. Field emission scanning electron microscopy images showed that the surface of the films exhibits densely packed grains. The elemental composition of the deposited thin films was analyzed using energy dispersive X-rays spectroscopy. The detected atomic percentages for In, N, and Mg were 43.22 %, 3.28 %, and 0.61 % respectively. The Raman spectra showed two Raman- and infrared-active modes of E2 (High) and A1 (LO) of the wurtzite InN. The band gap obtained from the Tauc plot showed around 1.74 eV. Lastly, the average surface roughness measured by AFM was around 0.133 µm.

Thermoelasticity of (Mg,Fe)SiO3 perovskite

NASA Astrophysics Data System (ADS)

Shukla, Gaurav; Wu, Zhongqing; Hsu, Han; Cococcioni, Matteo; Wentzcovitch, Renata

2015-03-01

We present LDA+U calculations of high temperature elastic properties of (Mg(1 - x)Fex2+)SiO3 bridgemanite (0 <= x <= 0 . 125), the most abundant constituent of Earth's lower mantle. Calculations of aggregate elastic moduli and acoustic velocities for the Mg-end member (x=0) are in excellent agreement with the latest high pressure and high temperature experimental measurements. In the iron bearing system, we particularly focus on the change in thermoelastic parameters across the state change that occurs in ferrous iron above ~30 GPa, often attributed to a high-spin (HS) to intermediate spin (IS) crossover but explained by calculations as a lateral displacement of substitutional iron in the perovskite cage. We show that the measured effect on the equation of state of this change in the state of iron can be explained by the lateral displacement of substitutional iron, not by the HS to IS crossover. Calculated elastic properties of (Mg0.875 Fe0.125 2 +)SiO3 along an adiabatic mantle geotherm, somewhat overestimate longitudinal velocities but produce densities and shear velocities consistent with Preliminary Reference Earth Model data throughout most of the lower mantle. Research supported by NSF/EAR and NSF/CAREER.

Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities

DOE PAGES

Luengo-Kovac, Marta; Huang, Simon; Del Gaudio, Davide; ...

2017-11-16

Here, the current-induced spin polarization and momentum-dependent spin-orbit field were measured in In xGa 1-xAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin-polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbitmore » coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spin-orbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the current-induced spin polarization.« less

Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luengo-Kovac, Marta; Huang, Simon; Del Gaudio, Davide

Here, the current-induced spin polarization and momentum-dependent spin-orbit field were measured in In xGa 1-xAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin-polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbitmore » coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spin-orbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the current-induced spin polarization.« less

Spin Dependence in Tidal Disruption Events

NASA Astrophysics Data System (ADS)

Kesden, Michael; Stone, Nicholas; van Velzen, Sjoert

2018-01-01

A supermassive black hole (SBH) can tidally disrupt stars when its tidal field overwhelms the stars’ self-gravity. The stellar debris produced in such tidal disruption events (TDEs) evolves into tidal streams that can self-intersect. These inelastic stream collisions dissipate orbital energy, both circularizing the tidal stream and contributing to the emission observed during the TDE. Once circularized into a disk, the stellar debris can be viscously accreted by the SBH powering additional luminous emission. We explore how SBH spin can affect the tidal disruption process. Tidal forces are spin dependent, as is the minimum orbital angular momentum below which stars are directly captured by the SBH. This implies that the TDE rate will be spin dependent, particularly for more massive SBHs for which relativistic effects are more significant. SBH spin also affects TDE light curves through the initial debris orbits, the nature of the stream collisions, the viscous evolution of the accretion disk, and the possibility of launching jets. We explore the spin dependence of these phenomena to identify promising signatures for upcoming surveys expected to discover hundreds of TDE candidates in the next decade.

Voltage Control of Two-Magnon Scattering and Induced Anomalous Magnetoelectric Coupling in Ni-Zn Ferrite.

PubMed

Xue, Xu; Dong, Guohua; Zhou, Ziyao; Xian, Dan; Hu, Zhongqiang; Ren, Wei; Ye, Zuo-Guang; Chen, Wei; Jiang, Zhuang-De; Liu, Ming

2017-12-13

Controlling spin dynamics through modulation of spin interactions in a fast, compact, and energy-efficient way is compelling for its abundant physical phenomena and great application potential in next-generation voltage controllable spintronic devices. In this work, we report electric field manipulation of spin dynamics-the two-magnon scattering (TMS) effect in Ni 0.5 Zn 0.5 Fe 2 O 4 (NZFO)/Pb(Mg 2/3 Nb 1/3 )-PbTiO 3 (PMN-PT) multiferroic heterostructures, which breaks the bottleneck of magnetostatic interaction-based magnetoelectric (ME) coupling in multiferroics. An alternative approach allowing spin-wave damping to be controlled by external electric field accompanied by a significant enhancement of the ME effect has been demonstrated. A two-way modulation of the TMS effect with a large magnetic anisotropy change up to 688 Oe has been obtained, referring to a 24 times ME effect enhancement at the TMS critical angle at room temperature. Furthermore, the anisotropic spin-freezing behaviors of NZFO were first determined via identifying the spatial magnetic anisotropy fluctuations. A large spin-freezing temperature change of 160 K induced by the external electric field was precisely determined by electron spin resonance.

Voltage Control of Two-Magnon Scattering and Induced Anomalous Magnetoelectric Coupling in Ni–Zn Ferrite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xue, Xu; Dong, Guohua; Zhou, Ziyao

2017-12-01

Controlling spin dynamics through modulation of spin interactions in a fast, compact, and energy-efficient way is compelling for its abundant physical phenomena and great application potential in next-generation voltage controllable spintronic devices. In this work, we report electric field manipulation of spin dynamics-the two-magnon scattering (TMS) effect in Ni0.5Zn0.5Fe2O4 (NZFO)/Pb(Mg2/3Nb1/3)-PbTiO3 (PMN-PT) multiferroic heterostructures, which breaks the bottleneck of magnetostatic interaction-based magnetoelectric (ME) coupling in multiferroics. An alternative approach allowing spin-wave damping to be controlled by external electric field accompanied by a significant enhancement of the ME effect has been demonstrated. A two-way modulation of the TMS effect with a largemore » magnetic anisotropy change up to 688 Oe has been obtained, referring to a 24 times ME effect enhancement at the TMS critical angle at room temperature. Furthermore, the anisotropic spin-freezing behaviors of NZFO were first determined via identifying the spatial magnetic anisotropy fluctuations. A large spin-freezing temperature change of 160 K induced by the external electric field was precisely determined by electron spin resonance.« less

The high-pressure electronic structure of magnesiowustite (Mg, Fe)O: applications to the physics and chemistry of the lower mantle

USGS Publications Warehouse

Sherman, David M.

1991-01-01

The electronic structure of magnesiowustite is investigated using self-consistent field X?? scattered wave (SCF-X??-SW) molecular orbital calculations on (FeO6)10- and (FeMg12O14)2- clusters. Calculated one-electron transition energies are used to interpret the optical spectrum of (Mg, Fe)O. The results are applied to the electrical and thermal conductivity of the lower mantle. This is especially true if Fe2+ adopts the low-spin configuration. The geophysically significant properties of (Fe, Mg)O probably result from defect Fe3+. -from Author

An asymmetric pair of vortices adjacent to a spinning cylinder

NASA Astrophysics Data System (ADS)

Iosilevskii, G.; Seginer, A.

The two-dimensional flow field over a spinning circular cylinder is analyzed using an extension of the Foeppl method. Equilibrium equations for two asymmetric point vortices in the wake of the cylinder are solved for a case when both vortices are equidistant from the cylinder. The two Foeppl solutions for the cylinder are presented. It is observed that the spin does not affect the angle between the two vortices; however, it displaces the vortex pair in the spin direction and the sinus of the displacement angle is proportional to the spin rate.

Giant Tunnel Magnetoresistance with a Single Magnetic Phase-Transition Electrode

NASA Astrophysics Data System (ADS)

Zhang, Jia; Chen, X. Z.; Song, C.; Feng, J. F.; Wei, H. X.; Lü, Jing-Tao

2018-04-01

The magnetic phase-transition tunnel-magnetoresistance (MPT-TMR) effect with a single magnetic electrode is investigated by first-principles calculations. The calculations show that the MPT-TMR of an α'-FeRh /MgO /Cu tunnel junction can be as high as hundreds of percent when the magnetic structure of α'-FeRh changes from G -type antiferromagnetic (G -AFM ) to ferromagnetic order. This type of MPT-TMR may be superior to the tunnel anisotropic magnetoresistance because of its huge magnetoresistance effect and similar structural simplicity. The main mechanism for the giant MPT-TMR can be attributed to the formation of interface resonant states at the G -AFM FeRh /MgO interface. A direct FeRh /MgO interface is found to be necessary for achieving a high MPT-TMR experimentally. Moreover, we find the α'-FeRh /MgO interface with FeRh in the ferromagnetic phase has nearly full spin polarization due to the negligible majority transmission and significantly different Fermi surface of two spin channels. Thus, it may act as a highly efficient and tunable spin injector. In addition, the electric-field-driven MPT of FeRh-based heteromagnetic nanostructures can be utilized to design various energy-efficient tunnel-junction structures and the corresponding lower-power-consumption devices. We also discuss the consequence of various junction defects on MPT-TMR. The interface oxygen layer is found to be detrimental to MPT-TMR. The sign of MPT-TMR is reversed with Rh termination due to the lack of contribution from the interface resonance states. However, the MPT-TMR may be robust against the oxygen vacancy inside of MgO and the shift of the Fermi energy. Our results will stimulate further experimental investigations of MPT-TMR and other fascinating phenomenon of FeRh-based tunnel junctions that may be promising in antiferromagnetic spintronics.

An ab initio MO study of heavy atom effects on the zero-field splitting tensors of high-spin nitrenes: how the spin-orbit contributions are affected.

PubMed

Sugisaki, Kenji; Toyota, Kazuo; Sato, Kazunobu; Shiomi, Daisuke; Kitagawa, Masahiro; Takui, Takeji

2014-05-21

The CASSCF and the hybrid CASSCF-MRMP2 methods are applied to the calculations of spin-spin and spin-orbit contributions to the zero-field splitting tensors (D tensors) of the halogen-substituted spin-septet 2,4,6-trinitrenopyridines, focusing on the heavy atom effects on the spin-orbit term of the D tensors (D(SO) tensors). The calculations reproduced experimentally determined |D| values within an error of 15%. Halogen substitutions at the 3,5-positions are less influential in the spin-spin dipolar (D(SS)) term of 2,4,6-trinitrenopyridines, although the D(SO) terms are strongly affected by the introduction of heavier halogens. The absolute sign of the D(SO) value (D = D(ZZ) - (D(XX) + D(YY))/2) of 3,5-dibromo derivative 3 is predicted to be negative, which contradicts the Pederson-Khanna (PK) DFT result previously reported. The large negative contributions to the D(SO) value of 3 arise from the excited spin-septet states ascribed mainly to the excitations of in-plane lone pair of bromine atoms → SOMO of π nature. The importance of the excited states involving electron transitions from the lone pair orbital of the halogen atom is also confirmed in the D(SO) tensors of halogen-substituted para-phenylnitrenes. A new scheme based on the orbital region partitioning is proposed for the analysis of the D(SO) tensors as calculated by means of the PK-DFT approach.

Estimating the spin diffusion length and the spin Hall angle from spin pumping induced inverse spin Hall voltages

NASA Astrophysics Data System (ADS)

Roy, Kuntal

2017-11-01

There exists considerable confusion in estimating the spin diffusion length of materials with high spin-orbit coupling from spin pumping experiments. For designing functional devices, it is important to determine the spin diffusion length with sufficient accuracy from experimental results. An inaccurate estimation of spin diffusion length also affects the estimation of other parameters (e.g., spin mixing conductance, spin Hall angle) concomitantly. The spin diffusion length for platinum (Pt) has been reported in the literature in a wide range of 0.5-14 nm, and in particular it is a constant value independent of Pt's thickness. Here, the key reasonings behind such a wide range of reported values of spin diffusion length have been identified comprehensively. In particular, it is shown here that a thickness-dependent conductivity and spin diffusion length is necessary to simultaneously match the experimental results of effective spin mixing conductance and inverse spin Hall voltage due to spin pumping. Such a thickness-dependent spin diffusion length is tantamount to the Elliott-Yafet spin relaxation mechanism, which bodes well for transitional metals. This conclusion is not altered even when there is significant interfacial spin memory loss. Furthermore, the variations in the estimated parameters are also studied, which is important for technological applications.

Nuclear magnetic relaxation by the dipolar EMOR mechanism: Three-spin systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Zhiwei; Halle, Bertil, E-mail: bertil.halle@bpc.lu.se

2016-07-21

In aqueous systems with immobilized macromolecules, including biological tissue, the longitudinal spin relaxation of water protons is primarily induced by exchange-mediated orientational randomization (EMOR) of intra- and intermolecular magnetic dipole-dipole couplings. Starting from the stochastic Liouville equation, we have developed a non-perturbative theory that can describe relaxation by the dipolar EMOR mechanism over the full range of exchange rates, dipole couplings, and Larmor frequencies. Here, we implement the general dipolar EMOR theory for a macromolecule-bound three-spin system, where one, two, or all three spins exchange with the bulk solution phase. In contrast to the previously studied two-spin system with amore » single dipole coupling, there are now three dipole couplings, so relaxation is affected by distinct correlations as well as by self-correlations. Moreover, relaxation can now couple the magnetizations with three-spin modes and, in the presence of a static dipole coupling, with two-spin modes. As a result of this complexity, three secondary dispersion steps with different physical origins can appear in the longitudinal relaxation dispersion profile, in addition to the primary dispersion step at the Larmor frequency matching the exchange rate. Furthermore, and in contrast to the two-spin system, longitudinal relaxation can be significantly affected by chemical shifts and by the odd-valued (“imaginary”) part of the spectral density function. We anticipate that the detailed studies of two-spin and three-spin systems that have now been completed will provide the foundation for developing an approximate multi-spin dipolar EMOR theory sufficiently accurate and computationally efficient to allow quantitative molecular-level interpretation of frequency-dependent water-proton longitudinal relaxation data from biophysical model systems and soft biological tissue.« less

The enhancement of anomalous Hall effect by inserting MgO layer in perpendicular anisotropic Pd/Co2MnSi/MgO/Pd films

NASA Astrophysics Data System (ADS)

Fu, H. R.; Ma, L.; Tian, N.; You, C. Y.; Wang, K.

2018-05-01

A systematic study of anomalous Hall effect (AHE) was performed in perpendicular magnetic anisotropic Pd/Co2MnSi(tCMS)/MgO/Pd films. The AHE was significantly intensified by inserting MgO layer, which can be ascribed to the enhancement of spin-orbit coupling and interfacial scattering contribution. Moreover, it was found that the Co and Mn ions were reduced at the interface of Co2MnSi/MgO with annealing process. The stable amount of Mn-O bonding was observed at the Co2MnSi/MgO interface after annealing, implying that the proper Mn-O bonding could be favorable for achieving large AHE.

The tunneling magnetoresistance current dependence on cross sectional area, angle and temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Z. H., E-mail: zhaohui@physics.umanitoba.ca; Bai, Lihui; Hu, C.-M.

2015-03-15

The magnetoresistance of a MgO-based magnetic tunnel junction (MTJ) was studied experimentally. The magnetoresistance as a function of current was measured systematically on MTJs for various MgO cross sectional areas and at various temperatures from 7.5 to 290.1 K. The resistance current dependence of the MTJ was also measured for different angles between the two ferromagnetic layers. By considering particle and angular momentum conservation of transport electrons, the current dependence of magnetoresistance can be explained by the changing of spin polarization in the free magnetic layer of the MTJ. The changing of spin polarization is related to the magnetoresistance, itsmore » angular dependence and the threshold current where TMR ratio equals zero. A phenomenological model is used which avoid the complicated barrier details and also describes the data.« less

Ground-State Properties of Mg Isotopes in and Beyond the Island of Inversion through Reaction Cross Sections

NASA Astrophysics Data System (ADS)

Watanabe, Shin; Minomo, Kosho; Shimada, Mitsuhiro; Tagami, Shingo; Kimura, Masaaki; Takechi, Maya; Fukuda, Mitsunori; Nishimura, Daiki; Suzuki, Takeshi; Matsumoto, Takuma; Shimizu, Yoshifumi R.; Yahiro, Masanobu

We analyze recently measured total reaction cross sections (σR) for 24-38Mg incident on 12C targets at 240 MeV/nucleon by using the microscopic framework based on the double folding model and antisymmetrized molecular dynamics (AMD). The framework reproduces not only the measured σR but also other existing measured ground-state properties of Mg Isotopes (spin parity, total binding energy, one-neutron separation energy, and 2+ and 4+ excitation energies) quite well. AMD predicts large deformation from 31Mg19 to a drip-line nucleus 40Mg28, indicating that both the N = 20 and 28 magicities disappear.

Selective coupling of individual electron and nuclear spins with integrated all-spin coherence protection

NASA Astrophysics Data System (ADS)

Terletska, Hanna; Dobrovitski, Viatcheslav

2015-03-01

The electron spin of the NV center in diamond is a promising platform for spin sensing. Applying the dynamical decoupling, the NV electron spin can be used to detect the individual weakly coupled carbon-13 nuclear spins in diamond and employ them for small-scale quantum information processing. However, the nuclear spins within this approach remain unprotected from decoherence, which ultimately limits the detection and restricts the fidelity of the quantum operation. Here we investigate possible schemes for combining the resonant decoupling on the NV spin with the decoherence protection of the nuclear spins. Considering several schemes based on pulse and continuous-wave decoupling, we study how the joint electron-nuclear spin dynamics is affected. We identify regimes where the all-spin coherence protection improves the detection and manipulation. We also discuss potential applications of the all-spin decoupling for detecting spins outside diamond, with the purpose of implementing the nanoscale NMR. This work was supported by the US Department of Energy Basic Energy Sciences (Contract No. DE-AC02-07CH11358).

Spin and valley filter across line defect in silicene

NASA Astrophysics Data System (ADS)

Wang, Sake; Ren, Chongdan; Li, Yunfang; Tian, Hongyu; Lu, Weitao; Sun, Minglei

2018-05-01

We propose a new scheme to achieve an effective spin/valley filter in silicene with extended line defect on the basis of spin–valley coupling due to the intrinsic spin-orbit coupling (SOC). The transmission coefficient of the spin/valley states is seriously affected by the SOC. When a perpendicular magnetic field is applied on one side of the line defect, one valley state will experience backscattering, but the other valley will not; this leads to high valley polarization in all transmission directions. Moreover, the spin/valley polarization can be enhanced to 96% with the aid of a perpendicular electric field.

Manifolds of magnetic ordered states and excitations in the almost Heisenberg pyrochlore antiferromagnet MgCr2O4

NASA Astrophysics Data System (ADS)

Gao, S.; Guratinder, K.; Stuhr, U.; White, J. S.; Mansson, M.; Roessli, B.; Fennell, T.; Tsurkan, V.; Loidl, A.; Ciomaga Hatnean, M.; Balakrishnan, G.; Raymond, S.; Chapon, L.; Garlea, V. O.; Savici, A. T.; Cervellino, A.; Bombardi, A.; Chernyshov, D.; Rüegg, Ch.; Haraldsen, J. T.; Zaharko, O.

2018-04-01

In spinels A Cr2O4(A =Mg, Zn), realization of the classical pyrochlore Heisenberg antiferromagnet model is complicated by a strong spin-lattice coupling: the extensive degeneracy of the ground state is lifted by a magneto-structural transition at TN=12.5 K. We study the resulting low-temperature low-symmetry crystal structure by synchrotron x-ray diffraction. The consistent features of x-ray low-temperature patterns are explained by the tetragonal model of Ehrenberg et al. [Pow. Diff. 17, 230 (2002), 10.1154/1.1479738], while other features depend on sample or cooling protocol. A complex, partially ordered magnetic state is studied by neutron diffraction and spherical neutron polarimetry. Multiple magnetic domains of configuration arms of the propagation vectors k1=(1/2 1/2 0 ) ,k2=(1 0 1/2 ) appear. The ordered moment reaches 1.94(3) μB/Cr3 + for k1 and 2.08(3) μB/Cr3 + for k2, if equal amount of the k1 and k2 phases is assumed. The magnetic arrangements have the dominant components along the [110] and [1 -10 ] diagonals and a smaller c component. We use inelastic neutron scattering to investigate the spin excitations, which comprise a mixture of dispersive spin waves propagating from the magnetic Bragg peaks and resonance modes centered at equal energy steps of 4.5 meV. We interpret these as acoustic and optical spin wave branches, but show that the neutron scattering cross sections of transitions within a unit of two corner-sharing tetrahedra match the observed intensity distribution of the resonances. The distinctive fingerprint of clusterlike excitations in the optical spin wave branches suggests that propagating excitations are localized by the complex crystal structure and magnetic orders.

High spin polarization in CoFeMnGe equiatomic quaternary Heusler alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bainsla, Lakhan; Magnetic Materials Unit, National Institute for Materials Science, Tsukuba 305-0047; Suresh, K. G., E-mail: suresh@phy.iitb.ac.in

2014-11-28

We report the structure, magnetic property, and spin polarization of CoFeMnGe equiatomic quaternary Heusler alloy. The alloy was found to crystallize in the cubic Heusler structure (prototype LiMgPdSn) with considerable amount of DO{sub 3} disorder. Thermal analysis result indicated the Curie temperature is about 750 K without any other phase transformation up to melting temperature. The magnetization value was close to that predicted by the Slater-Pauling curve. Current spin polarization of P = 0.70 ± 0.01 was deduced using point contact andreev reflection measurements. The temperature dependence of electrical resistivity has been fitted in the temperature range of 5–300 K in order to check for themore » half metallic behavior. Considering the high spin polarization and Curie temperature, this material appears to be promising for spintronic applications.« less

Ultralow-current-density and bias-field-free spin-transfer nano-oscillator

PubMed Central

Zeng, Zhongming; Finocchio, Giovanni; Zhang, Baoshun; Amiri, Pedram Khalili; Katine, Jordan A.; Krivorotov, Ilya N.; Huai, Yiming; Langer, Juergen; Azzerboni, Bruno; Wang, Kang L.; Jiang, Hongwen

2013-01-01

The spin-transfer nano-oscillator (STNO) offers the possibility of using the transfer of spin angular momentum via spin-polarized currents to generate microwave signals. However, at present STNO microwave emission mainly relies on both large drive currents and external magnetic fields. These issues hinder the implementation of STNOs for practical applications in terms of power dissipation and size. Here, we report microwave measurements on STNOs built with MgO-based magnetic tunnel junctions having a planar polarizer and a perpendicular free layer, where microwave emission with large output power, excited at ultralow current densities, and in the absence of any bias magnetic fields is observed. The measured critical current density is over one order of magnitude smaller than previously reported. These results suggest the possibility of improved integration of STNOs with complementary metal-oxide-semiconductor technology, and could represent a new route for the development of the next-generation of on-chip oscillators. PMID:23478390

Ultralow-current-density and bias-field-free spin-transfer nano-oscillator.

PubMed

Zeng, Zhongming; Finocchio, Giovanni; Zhang, Baoshun; Khalili Amiri, Pedram; Katine, Jordan A; Krivorotov, Ilya N; Huai, Yiming; Langer, Juergen; Azzerboni, Bruno; Wang, Kang L; Jiang, Hongwen

2013-01-01

The spin-transfer nano-oscillator (STNO) offers the possibility of using the transfer of spin angular momentum via spin-polarized currents to generate microwave signals. However, at present STNO microwave emission mainly relies on both large drive currents and external magnetic fields. These issues hinder the implementation of STNOs for practical applications in terms of power dissipation and size. Here, we report microwave measurements on STNOs built with MgO-based magnetic tunnel junctions having a planar polarizer and a perpendicular free layer, where microwave emission with large output power, excited at ultralow current densities, and in the absence of any bias magnetic fields is observed. The measured critical current density is over one order of magnitude smaller than previously reported. These results suggest the possibility of improved integration of STNOs with complementary metal-oxide-semiconductor technology, and could represent a new route for the development of the next-generation of on-chip oscillators.

Characterization of Magnetic Tunnel Junctions by IETS and STS

NASA Astrophysics Data System (ADS)

Yang, Hyunsoo; Yang, See-Hun

2005-03-01

Inelastic electron tunneling spectroscopy (IETS) and superconducting tunneling spectroscopy (STS) have been employed to investigate spin-dependent tunneling in magnetic tunnel junctions (MTJs). MTJs were studied in which the ferromagnetic electrodes were formed from the 3d transition metals, Fe, Co and Ni and their alloys, and the tunnel barriers were formed from various nitrides and oxides including MgO. MTJs with MgO barriers exhibit more than 220% tunneling magnetoresistance (TMR) at room temperature[1]. IETS was used to measure the contributions of defects and impurities, as well as phonons and magnons, to the tunneling current. These processes give rise to conductance peaks at characteristic voltages according to their excitation energies. STS was used to measure the spin polarization of the tunneling current as well as to explore the role of spin-flip scattering in the tunneling process. The goal of this research is a more complete understanding of the mechanisms which gives rise to the bias voltage dependence of the TMR as well as indirect tunneling through states in the barrier. [1] S. S. P. Parkin, C. Kaiser, A. Panchula, P. Rice, B. Hughes, M. Samant, and S.-H. Yang, Nature Materials, vol. Published online: 31 October 2004, 2004.

A transverse separate-spin-evolution streaming instability

NASA Astrophysics Data System (ADS)

Iqbal, Z.; Andreev, Pavel A.; Murtaza, G.

2018-05-01

By using the separate spin evolution quantum hydrodynamical model, the instability of transverse mode due to electron streaming in a partially spin polarized magnetized degenerate plasma is studied. The electron spin polarization gives birth to a new spin-dependent wave (i.e., separate spin evolution streaming driven ordinary wave) in the real wave spectrum. It is shown that the spin polarization and streaming speed significantly affect the frequency of this new mode. Analyzing growth rate, it is found that the electron spin effects reduce the growth rate and shift the threshold of instability as well as its termination point towards higher values. Additionally, how the other parameters like electron streaming and Fermi pressure influence the growth rate is also investigated. Current study can help towards better understanding of the existence of new waves and streaming instability in the astrophysical plasmas.

Influences of the coordinate dependent noncommutative space on charged and spin currents

NASA Astrophysics Data System (ADS)

Ren, Ya-Jie; Ma, Kai

2018-06-01

We study the charged and spin currents on a coordinate dependent noncommutative space. Starting from the noncommutative extended relativistic equation of motion, the nonrelativistic approximation is obtained by using the Foldy-Wouthuysen transformation, and then the charged and spin currents are derived by using the extended Drude model. We find that the charged current is twisted by modifying the off-diagonal elements of the Hall conductivity, however, the spin current is not affected up to leading order of the noncommutative parameter.

Nuclear reactivity control using laser induced polarization

DOEpatents

Bowman, Charles D.

1991-01-01

A control element for reactivity control of a fission source provides an atomic density of .sup.3 He in a control volume which is effective to control criticality as the .sup.3 He is spin-polarized. Spin-polarization of the .sup.3 He affects the cross section of the control volume for fission neutrons and hence, the reactivity. An irradiation source is directed within the .sup.3 He for spin-polarizing the .sup.3 He. An alkali-metal vapor may be included with the .sup.3 He where a laser spin-polarizes the alkali-metal atoms which in turn, spin-couple with .sup.3 He to spin-polarize the .sup.3 He atoms.

Nuclear reactivity control using laser induced polarization

DOEpatents

Bowman, Charles D.

1990-01-01

A control element for reactivity control of a fission source provides an atomic density of .sup.3 He in a control volume which is effective to control criticality as the .sup.3 He is spin-polarized. Spin-polarization of the .sup.3 He affects the cross section of the control volume for fission neturons and hence, the reactivity. An irradiation source is directed within the .sup.3 He for spin-polarizing the .sup.3 He. An alkali-metal vapor may be included with the .sup.3 He where a laser spin-polarizes the alkali-metal atoms which in turn, spin-couple with .sup.3 He to spin-polarize the .sup.3 He atoms.

Measuring one nucleon transfer reaction 24Mg( p, d)23Mg for astrophysical reaction rates

NASA Astrophysics Data System (ADS)

Lee, E. J.; Chae, K. Y.

2017-12-01

The level structure of a radionuclide 23Mg has been studied by using the 24Mg( p, d)23Mg one nucleon transfer reaction measurement for the astrophysical 19Ne(α, γ)23Mg reaction rate. A 41 MeV proton beam was produced and accelerated at the 25 MV tandem accelerator of the Holifield Radioactive Ion Beam Facility of the Oak Ridge National Laboratory in the United States. The beam particles impinged on an isotopically-enriched 24Mg solid target. Angular distributions of recoiling deuterons were extracted by using a large area silicon strip detector array. By comparing the experimentally-obtained angular distributions with zero range distorted wave Born approximation calculations, spins and parities of three energy levels of 23Mg could be constrained for the first time, which is very important information needed to understand the 19Ne(α, γ)23Mg reaction rate.

Metal spintronics: Tunneling spectroscopy in junctions with magnetic and superconducting electrodes

NASA Astrophysics Data System (ADS)

Yang, Hyunsoo

Recent advances in generating, manipulating and detecting spin-polarized electrons and their electrical current make possible entirely new classes of spin-based sensor, logic and storage devices. An important such device is the magnetic tunnel junction (MTJ) which has been under intensive study in recent years: important applications include nonvolatile memory cells for high performance magnetic random access memory (MRAMs), and magnetic field sensors for high density hard disk drive read heads. Many aspects of the tunneling magnetoresistance (TMR) phenomenon are poorly understood although it is clear that the fundamental origin of TMR is the spin-polarization of the tunneling current. Thus, the measurement of the magnitude and sign of the tunneling spin polarization (TSP) is very important to help the further understanding of TMR. Recently, an extremely high TMR value, of up to 350% at room temperature, has been reported in practical MTJ devices. These MTJs are fabricated with highly oriented crystalline MgO(100) tunnel barriers by straightforward magnetron sputter deposition at room temperature. In parallel with this observation, we report extremely high TSP values exceeding 90% from CoFe/MgO tunnel spin injectors. These TSP values rival the highest polarization values previously reported using exotic half-metallic oxide ferromagnets. The spin polarization of electrons extracted from ferromagnetic films can be probed by a variety of techniques. Amongst these techniques, STS is perhaps the most relevant with respect to TMR but until now all measurements have been made with Al superconducting films which have low superconducting transition temperatures (Tc) so that the measurements must be made at temperatures below 400mK. We demonstrate the use of superconducting electrodes formed from NbN which has a much higher Tc (˜16K) than Al. The use of NbN allows measurements of TSP at higher temperatures above 1K. We have observed the phenomenon of Kondo-assisted tunneling in planar magnetic tunnel junctions. We demonstrate not only an increased conductance at low bias but also show that the tunneling magnetoresistance is quenched in the Kondo regime. The Kondo effect may be a useful means of detecting and possibly manipulating the spins of individual electrons in nanodots.

The effect of black tea and caffeine on regional cerebral blood flow measured with arterial spin labeling

PubMed Central

Vidyasagar, Rishma; Greyling, Arno; Draijer, Richard; Corfield, Douglas R; Parkes, Laura M

2013-01-01

Black tea consumption has been shown to improve peripheral vascular function. Its effect on brain vasculature is unknown, though tea contains small amounts of caffeine, a psychoactive substance known to influence cerebral blood flow (CBF). We investigated the effects on CBF due to the intake of tea components in 20 healthy men in a double-blinded, randomized, placebo-controlled study. On separate days, subjects received a single dose of 184 mg caffeine (equivalent to one strong espresso coffee), 2,820 mg black tea solids containing 184 mg caffeine (equivalent to 6 cups of tea), 2,820 mg decaffeinated black tea solids, or placebo. The CBF and cerebrovascular reactivity (CVR) to hypercapnia were measured with arterial spin labeled magnetic resonance imaging (MRI) before and 2 hours after administration. We found a significant global reduction with caffeine (20%) and tea (21%) in gray matter CBF, with no effect of decaffeinated tea, suggesting that only caffeine influences CBF acutely. Voxelwise analysis revealed the effect of caffeine to be regionally specific. None of the interventions had an effect on CVR. Additional research is required to conclude on the physiologic relevance of these findings and the chronic effects of caffeine and tea intake on CBF. PMID:23486295

Comparison of structural and magnetic properties of Zn{sub x}Mg{sub 1.5-x}Mn{sub 0.5}FeO{sub 4} and MgAl{sub x}Cr{sub x}Fe{sub 2-2x}O{sub 4} spinel oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thummer, K. P., E-mail: kpthummer@yahoo.co.in; Tanna, A. R., E-mail: ashish.tanna@rku.ac.in; Joshi, H. H.

2016-05-23

The spinel oxides Zn{sub x}Mg{sub 1.5-x}Mn{sub 0.5}FeO{sub 4} (x = 0.0 to 0.6) and MgAl{sub x}Cr{sub x}Fe{sub 2-2x}O{sub 4} (x = 0.0 to 0.6) abbreviated as ZMMFO and MACFO respectively, were synthesized by standard ceramic processing. The compositional purity of all the specimens was checked by EDAX technique. The X-ray diffractometry was employed to determine the lattice constants and distribution of cations in the interstitial voids. The initial decrease of cell edge parameter (a) for ZMMFO up to x = 0.2 and thereafter expected rise in the ‘a’ and the initial slower rate of reduction in the lattice constant formore » MACFO are explained as basic of cation occupancy. The magnetic ordering in both systems is explained by invoking statistical canting models. The compositional variation of magneton number (n{sub B}) for ZMMFO could be very well explained by Localized canting of spin (LCS) model while Random canting of spin (RCS) model was used for MACFO system.« less

Manipulation of perpendicular magnetic anisotropy of single Fe atom adsorbed graphene via MgO(1 1 1) substrate

NASA Astrophysics Data System (ADS)

Fu, Mingming; Tang, Weiqing; Wu, Yaping; Ke, Congming; Guo, Fei; Zhang, Chunmiao; Yang, Weihuang; Wu, Zhiming; Kang, Junyong

2018-05-01

Perpendicular magnetic anisotropy is significantly important for realizing a long-term retention of information for spintronics devices. Inspired by 2D graphene with its high charge carrier mobility and long spin diffusion length, we report a first-principles design framework on perpendicular magnetic anisotropy engineering of a Fe atom adsorbed graphene by employing a O-terminated MgO (1 1 1) substrate. Determined by the adsorption sites of the Fe atom, a tunable magnetic anisotropy is realized in Fe/graphene/MgO (1 1 1) structure, with the magnetic anisotropy energy of  ‑0.48 meV and 0.23 meV, respectively, corresponding to the in-plane and out of plane easy magnetizations. Total density of states suggest a half-metallicity with a 100% spin polarization in the system. Decomposed densities of Fe-3d states reveal the orbital contributions to the magnetic anisotropy for different Fe adsorption sites. Bonding interaction and charge redistribution regulated by MgO substrate are found responsible for the novel perpendicular magnetic anisotropy engineering in the system. The effective manipulation of perpendicular magnetic anisotropy in present work offers some references for the design and construction of 2D spintronics devices.

Abnormal Elasticity of Single-Crystal Magnesiosiderite across the Spin Transition in Earth's Lower Mantle

NASA Astrophysics Data System (ADS)

Fu, Suyu; Yang, Jing; Lin, Jung-Fu

2017-01-01

Brillouin light scattering and impulsive stimulated light scattering have been used to determine the full elastic constants of magnesiosiderite [(Mg0.35Fe0.65)CO3 ] up to 70 GPa at room temperature in a diamond-anvil cell. Drastic softening in C11 , C33 , C12 , and C13 elastic moduli associated with the compressive stress component and stiffening in C44 and C14 moduli associated with the shear stress component are observed to occur within the spin transition between ˜42.4 and ˜46.5 GPa . Negative values of C12 and C13 are also observed within the spin transition region. The Born criteria constants for the crystal remain positive within the spin transition, indicating that the mixed-spin state remains mechanically stable. Significant auxeticity can be related to the electronic spin transition-induced elastic anomalies based on the analysis of Poisson's ratio. These elastic anomalies are explained using a thermoelastic model for the rhombohedral system. Finally, we conclude that mixed-spin state ferromagnesite, which is potentially a major deep-carbon carrier, is expected to exhibit abnormal elasticity, including a negative Poisson's ratio of -0.6 and drastically reduced VP by 10%, in Earth's midlower mantle.

Magnetic ground states in the three O s6 + (5 d2 ) double perovskites B a2M Os O6 (M =Mg ,Zn,and Cd) from Néel order to its suppression

NASA Astrophysics Data System (ADS)

Marjerrison, C. A.; Thompson, C. M.; Sharma, A. Z.; Hallas, A. M.; Wilson, M. N.; Munsie, T. J. S.; Flacau, R.; Wiebe, C. R.; Gaulin, B. D.; Luke, G. M.; Greedan, J. E.

2016-10-01

Three closely related double perovskites (DP) based on the 5 d2 ion, O s6 +,B a2M Os O6 , with M =Mg , Zn, and Cd have been prepared and characterized using x-ray (XRD) and neutron diffraction (ND), dc magnetization, heat capacity, and muon spin relaxation (μ SR ) techniques. All three are cubic, Fm-3 m , at ambient temperature from XRD with Δ d /d ˜5 ×10-4 resolution. For both M =Mg and Zn, ND data at 3.5 K and lower, Δ d /d =2 ×10-3 , resolution show no signs of a distortion. The results are compared with the known DP material, B a2CaOs O6 , which shows antiferromagnetic (AF) order below TN=49 K and a moderate frustration index, f ˜4 , (f =| θCW|/ TN ), where θCW is the Curie-Weiss temperature. B a2MgOs O6 with a unit cell constant a0=8.0757 (1 ) Å , 3% smaller than for B a2CaOs O6 , also shows Néel order below TN=51 K with f ˜2 . However, B a2ZnOs O6,a0=8.0975 (1 ) Å , 0.27% larger than B a2MgOs O6 , does not show Néel order from either heat capacity or μ SR data. A zero field cooled/field cooled (ZFC/FC) irreversibility occurs near 30 K and a broad heat capacity anomaly is detected at a similar temperature. The μ SR data are consistent with a weak spin ordering with an onset below 28 K but with a coexisting dynamic component. B a2CdOs O6 with a0=8.3190 (1 ) Å , 0.5% smaller than B a2CaOs O6 , shows no evidence for any type of order/spin freezing to 0.47 K from any of the measurement techniques applied. The results for M =Zn and Cd appear to lie outside of the mean field theory of Chen and Balents [Phys. Rev. B 84, 094420 (2011), 10.1103/PhysRevB.84.094420] for cubic d2 DP with strong spin orbit coupling, but B a2MgOs O6 , along with B a2CaOs O6 , is likely one of the three predicted AF phases. The remarkable contrast between the doppelgänger pairs M =Mg /Zn and M =Ca /Cd may be traceable to differences in electronic structure of the diamagnetic M ions. All of the super-super exchange pathways in these DP materials involve Os-O-M -O-Os linkages.

Spin Hall magnetoresistance in CoFe 2O 4/Pt films

DOE PAGES

Wu, Hao; Qintong, Zhang; Caihua, Wan; ...

2015-05-13

Pulse laser deposition and magnetron sputtering techniques have been employed to prepare MgO(001)//CoFe 2O 4/Pt samples. Cross section transmission electron microscope results prove that the CoFe 2O 4 film epitaxially grew along (001) direction. X-ray magnetic circular dichroism results show that magnetic proximity effect in this sample is negligible. Magnetoresistance (MR) properties confirm that spin Hall MR (SMR) dominates in this system. Spin Hall effect-induced anomalous Hall voltage was also observed in this sample. Lastly, these results not only demonstrate the universality of SMR effect but also demonstrate the utility in spintronics of CoFe 2O 4 as a new typemore » of magnetic insulator.« less

Room temperature ferromagnetism in Mg-doped ZnO nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Jaspal, E-mail: jaspal0314@gmail.com; Vashihth, A.; Gill, Pritampal Singh

Zn{sub 1-x}Mg{sub x}O (x = 0, 0,10) nanoparticles were successfully synthesized using sol-gel method. X-ray diffraction (XRD) confirms that the synthesized nanoparticles possess wurtzite phase having hexagonal structure. Morphological analysis was carried out using transmission electron microscopy (TEM) which depicts the spherical morphology of ZnO nanoparticles. Energy dispersive spectroscopy (EDS) showed the presence of Mg in ZnO nanoparticles. Electron spin resonance (ESR) signal was found to be decreasing with increasing of Mg-doping concentration. The room temperature ferromagnetism was observed in undoped and Mg-doped ZnO nanoparticles. The increase of Mg-doping concentration resulted in decrease of saturation magnetization value which could bemore » attributed to decrease of oxygen vacancies present in host nanoparticles.« less

Spin-orbit-coupled superconductivity

PubMed Central

Lo, Shun-Tsung; Lin, Shih-Wei; Wang, Yi-Ting; Lin, Sheng-Di; Liang, C.-T.

2014-01-01

Superconductivity and spin-orbit (SO) interaction have been two separate emerging fields until very recently that the correlation between them seemed to be observed. However, previous experiments concerning SO coupling are performed far beyond the superconducting state and thus a direct demonstration of how SO coupling affects superconductivity remains elusive. Here we investigate the SO coupling in the critical region of superconducting transition on Al nanofilms, in which the strength of disorder and spin relaxation by SO coupling are changed by varying the film thickness. At temperatures T sufficiently above the superconducting critical temperature Tc, clear signature of SO coupling reveals itself in showing a magneto-resistivity peak. When T < Tc, the resistivity peak can still be observed; however, its line-shape is now affected by the onset of the quasi two-dimensional superconductivity. By studying such magneto-resistivity peaks under different strength of spin relaxation, we highlight the important effects of SO interaction on superconductivity. PMID:24961726

Dynamical spin accumulation in large-spin magnetic molecules

NASA Astrophysics Data System (ADS)

Płomińska, Anna; Weymann, Ireneusz; Misiorny, Maciej

2018-01-01

The frequency-dependent transport through a nanodevice containing a large-spin magnetic molecule is studied theoretically in the Kondo regime. Specifically, the effect of magnetic anisotropy on dynamical spin accumulation is of primary interest. Such accumulation arises due to finite components of frequency-dependent conductance that are off diagonal in spin. Here, employing the Kubo formalism and the numerical renormalization group method, we demonstrate that the dynamical transport properties strongly depend on the relative orientation of spin moments in electrodes of the device, as well as on intrinsic parameters of the molecule. In particular, the effect of dynamical spin accumulation is found to be greatly affected by the type of magnetic anisotropy exhibited by the molecule, and it develops for frequencies corresponding to the Kondo temperature. For the parallel magnetic configuration of the device, the presence of dynamical spin accumulation is conditioned by the interplay of ferromagnetic-lead-induced exchange field and the Kondo correlations.

Polaron spin echo envelope modulations in an organic semiconducting polymer

DOE PAGES

Mkhitaryan, V. V.; Dobrovitski, V. V.

2017-06-01

Here, we present a theoretical analysis of the electron spin echo envelope modulation (ESEEM) spectra of polarons in semiconducting π -conjugated polymers. We show that the contact hyperfine coupling and the dipolar interaction between the polaron and the proton spins give rise to different features in the ESEEM spectra. Our theory enables direct selective probe of different groups of nuclear spins, which affect the polaron spin dynamics. Namely, we demonstrate how the signal from the distant protons (coupled to the polaron spin via dipolar interactions) can be distinguished from the signal coming from the protons residing on the polaron sitemore » (coupled to the polaron spin via contact hyperfine interaction). We propose a method for directly probing the contact hyperfine interaction, that would enable detailed study of the polaron orbital state and its immediate environment. Lastly, we also analyze the decay of the spin echo modulation, and its connection to the polaron transport.« less

Non-equilibrium tunneling in zigzag graphene nanoribbon break-junction results in spin filtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Liming; Department of Electrical and Electronic Engineering, The University of Melbourne, Parkville 3010; National ICT Australia, The University of Melbourne, Parkville 3010

Spintronic devices promise new faster and lower energy-consumption electronic systems. Graphene, a versatile material and candidate for next generation electronics, is known to possess interesting spintronic properties. In this paper, by utilizing density functional theory and non-equilibrium green function formalism, we show that Fano resonance can be generated by introducing a break junction in a zigzag graphene nanoribbon (ZGNR). Using this effect, we propose a new spin filtering device that can be used for spin injection. Our theoretical results indicate that the proposed device could achieve high spin filtering efficiency (over 90%) at practical fabrication geometries. Furthermore, our results indicatemore » that the ZGNR break junction lattice configuration can dramatically affect spin filtering efficiency and thus needs to be considered when fabricating real devices. Our device can be fabricated on top of spin transport channel and provides good integration between spin injection and spin transport.« less

Activities of the Solid State Physics Research Institute

NASA Technical Reports Server (NTRS)

1985-01-01

Topics addressed include: muon spin rotation; annealing problems in gallium arsenides; Hall effect in semiconductors; computerized simulation of radiation damage; single-nucleon removal from Mg-24; and He-3 reaction at 200 and 400 MeV.

Interface control of the magnetic chirality in CoFeB/MgO heterostructures with heavy-metal underlayers.

PubMed

Torrejon, Jacob; Kim, Junyeon; Sinha, Jaivardhan; Mitani, Seiji; Hayashi, Masamitsu; Yamanouchi, Michihiko; Ohno, Hideo

2014-08-18

Recent advances in the understanding of spin orbital effects in ultrathin magnetic heterostructures have opened new paradigms to control magnetic moments electrically. The Dzyaloshinskii-Moriya interaction (DMI) is said to play a key role in forming a Néel-type domain wall that can be driven by the spin Hall torque. Here we show that the strength and sign of the DMI can be changed by modifying the adjacent heavy-metal underlayer (X) in perpendicularly magnetized X/CoFeB/MgO heterostructures. The sense of rotation of a domain wall spiral is reversed when the underlayer is changed from Hf, Ta to W and the strength of DMI varies as the filling of 5d orbitals, or the electronegativity, of the heavy-metal layer changes. The DMI can even be tuned by adding nitrogen to the underlayer, thus allowing interface engineering of the magnetic texture in ultrathin magnetic heterostructures.

Perpendicular magnetic anisotropy in Mn2CoAl thin film

NASA Astrophysics Data System (ADS)

Sun, N. Y.; Zhang, Y. Q.; Fu, H. R.; Che, W. R.; You, C. Y.; Shan, R.

2016-01-01

Heusler compound Mn2CoAl (MCA) is attracting more attentions due to many novel properties, such as high resistance, semiconducting behavior and suggestion as a spin-gapless material with a low magnetic moment. In this work, Mn2CoAl epitaxial thin film was prepared on MgO(100) substrate by magnetron sputtering. The transport property of the film exhibits a semiconducting-like behavior. Moreover, our research reveals that perpendicular magnetic anisotropy (PMA) can be induced in very thin Mn2CoAl films resulting from Mn-O and Co-O bonding at Mn2CoAl/MgO interface, which coincides with a recent theoretical prediction. PMA and low saturation magnetic moment could lead to large spin-transfer torque with low current density in principle, and thus our work may bring some unanticipated Heusler compounds into spintronics topics such as the domain wall motion and the current-induced magnetization reversal.

Magnetically induced phonon splitting in A Cr 2 O 4 spinels from first principles

DOE PAGES

Wysocki, Aleksander L.; Birol, Turan

2016-04-22

We study the magnetically-induced phonon splitting in cubic ACr 2O 4 (A=Mg, Zn, Cd) spinels from first principles and demonstrate that the sign of the splitting, which is experimentally observed to be opposite in CdCr 2O 4 compared to ZnCr 2O 4 and MgCr 2O 4, is determined solely by the particular magnetic ordering pattern observed in these compounds. We further show that this interaction between magnetism and phonon frequencies can be fully described by the previously proposed spin-phonon coupling model [C. J. Fennie and K. M. Rabe, Phys. Rev. Lett. 96, 205505 (2006)] that includes only the nearest neighbormore » exchange. In conclusion, using this model with materials specific parameters calculated from first principles, we provide additional insights into the physics of spin-phonon coupling in this intriguing family of compounds.« less

Single-valley quantum Hall ferromagnet in a dilute Mg xZn 1-xO/ZnO strongly correlated two-dimensional electron system

DOE PAGES

Kozuka, Y.; Tsukazaki, A.; Maryenko, D.; ...

2012-02-03

We investigate the spin susceptibility (g*m*) of dilute two-dimensional (2D) electrons confined at the Mg xZn 1-xO/ZnO heterointerface. Magnetotransport measurements show a four-fold enhancement of g*m*, dominated by the increase in the Landé g-factor. The g-factor enhancement leads to a ferromagnetic instability of the electron gas as evidenced by sharp resistance spikes. At high magnetic field, the large g*m* leads to full spin polarization, where we found sudden increase in resistance around the filling factors of half-integer, accompanied by complete disappearance of fractional quantum Hall (QH) states. Along with its large effective mass and the high electron mobility, our resultmore » indicates that the ZnO 2D system is ideal for investigating the effect of electron correlations in the QH regime.« less

Fabrication of Metallic Glass Powder for Brazing Paste for High-Temperature Thermoelectric Modules

NASA Astrophysics Data System (ADS)

Seo, Seung-Ho; Kim, Suk Jun; Lee, Soonil; Seo, Won-Seon; Kim, Il-Ho; Choi, Soon-Mok

2018-06-01

Metallic glass (MG) offers the advantage of outstanding oxidation resistance, since it has disordered atomic-scale structure without grain boundaries. We fabricated Al-based MG ribbons (Al84.5Y10Ni5.5) by a melt spinning process. We evaluated the adhesion strength of interfaces between the Al-based MG and a Ni-coated Cu electrode formed under various conditions at high temperature. In addition, we attempted to optimize the process conditions for pulverizing MG ribbons to < 100 micrometers by combining high-energy ball milling and planetary milling. We confirmed that the electrical resistivity of the Al-based MG ribbon was substantially reduced after annealing at high temperature (over 300°C) due to crystallization.

Ultrafast spintronics roadmap: from femtosecond spin current pulses to terahertz non-uniform spin dynamics via nano-confined spin transfer torques (Conference Presentation)

NASA Astrophysics Data System (ADS)

Melnikov, Alexey; Razdolski, Ilya; Alekhin, Alexandr; Ilin, Nikita; Meyburg, Jan; Diesing, Detlef; Roddatis, Vladimir; Rungger, Ivan; Stamenova, Maria; Sanvito, Stefano; Bovensiepen, Uwe

2016-10-01

Further development of spintronics requires miniaturization and reduction of characteristic timescales of spin dynamics combining the nanometer spatial and femtosecond temporal ranges. These demands shift the focus of interest towards the fundamental open question of the interaction of femtosecond spin current (SC) pulses with a ferromagnet (FM). The spatio-temporal properties of the spin transfer torque (STT) exerted by ultrashort SC pulses on the FM open the time domain for studying STT fingerprint on spatially non-uniform magnetization dynamics. Using the sensitivity of magneto-induced second harmonic generation to SC, we develop technique for SC monitoring. With 20 fs resolution, we demonstrate the generation of 250 fs-long SC pulses in Fe/Au/Fe/MgO(001) structures. Their temporal profile indicates (i) nearly-ballistic hot electron transport in Au and (ii) that the pulse duration is primarily determined by the thermalization time of laser-excited hot carriers in Fe. Together with strongly spin-dependent Fe/Au interface transmission calculated for these carriers, this suggests the non-thermal spin-dependent Seebeck effect dominating the generation of ultrashort SC pulses. The analysis of SC transmission/reflection at the Au/Fe interface shows that hot electron spins orthogonal to the Fe magnetization rotate gaining huge parallel (anti-parallel) projection in transmitted (reflected) SC. This is accompanied by a STT-induced perturbation of the magnetization localized at the interface, which excites the inhomogeneous high-frequency spin dynamics in the FM. Time-resolved magneto-optical studies reveal the excitation of several standing spin wave modes in the Fe film with their spectrum extending up to 0.6 THz and indicating the STT spatial confinement to 2 nm.

Roles of NN-interaction components in shell-structure evolution

NASA Astrophysics Data System (ADS)

Umeya, Atsushi; Muto, Kazuo

2016-11-01

Since the importance of the monopole interaction was first emphasized in 1960s, roles of monopole strengths of two-body nucleon-nucleon interaction in shell structure have been discussed. Through the monopole strengths, we study the roles in shell-structure evolution, starting from explicit forms of the interaction. For the tensor component of the interaction, we show the derivation of the relation, (2j> + 1)Vjj> + (2j< + 1)Vjj< = 0, with a detailed manipulation. We show that one-body spin-orbit term appears in the multipole expansion of two-body spin-orbit interaction. Only the spin-orbit components can affect the spin-orbit energy splitting between spin-orbit partners, when the spin-orbit partner orbits are fully occupied.

The 18Ne(α,p)21Na breakout reaction in x-ray bursts: Experimental determination of spin-parities for α resonances in 22Mg via resonant elastic scattering of 21Na+p

NASA Astrophysics Data System (ADS)

He, J. J.; Zhang, L. Y.; Parikh, A.; Xu, S. W.; Yamaguchi, H.; Kahl, D.; Kubono, S.; Hu, J.; Ma, P.; Chen, S. Z.; Wakabayashi, Y.; Sun, B. H.; Wang, H. W.; Tian, W. D.; Chen, R. F.; Guo, B.; Hashimoto, T.; Togano, Y.; Hayakawa, S.; Teranishi, T.; Iwasa, N.; Yamada, T.; Komatsubara, T.

2013-07-01

The 18Ne(α,p)21Na reaction provides a pathway for breakout from the hot CNO cycles to the rp process in type-I x-ray bursts. To better determine this astrophysical reaction rate, the resonance parameters of the compound nucleus 22Mg have been investigated by measuring the resonant elastic scattering of 21Na+p. An 89 MeV 21Na radioactive ion beam was produced at the CNS Radioactive Ion Beam Separator and bombarded an 8.8 mg/cm2 thick polyethylene target. The recoiled protons were measured at scattering angles of θc.m.≈175∘ and 152∘ by three ΔE-E silicon telescopes. The excitation function was obtained with a thick-target method over energies Ex(22Mg) = 5.5-9.2 MeV. The resonance parameters have been determined through an R-matrix analysis. For the first time, the Jπ values for ten states above the α threshold in 22Mg have been experimentally determined in a single consistent measurement. We have made three new Jπ assignments and confirmed seven of the ten tentative assignments in the previous work. The 18Ne(α,p)21Na reaction rate has been recalculated, and the astrophysical impact of our new rate has been investigated through one-zone postprocessing x-ray burst calculations. We find that the 18Ne(α,p)21Na rate significantly affects the peak nuclear energy generation rate and the onset temperature of this breakout reaction in these phenomena.

Fabrication and characterization of nanostructured Mg-doped CdS/AAO nanoporous membrane for sensing applications

NASA Astrophysics Data System (ADS)

Shaban, Mohamed; Mustafa, Mona; Hamdy, Hany

2016-04-01

In this study, Mg-doped CdS nanostructure was deposited onto anodic aluminum oxide (AAO) membrane substrate using sol-gel spin coating method. The AAO membrane was prepared by a two-step anodization process combined with pore widening process. The morphology, chemical composition, and structure of the spin- coated CdS nanostructure have been studied. The morphology of the fabricated AAO membrane and the deposited Mg-doped CdS nanostructure was investigated using scanning electron microscopy (SEM). The SEM of AAO illustrates a typical hexagonal and smooth nanoporous alumina membrane with interpore distance of ~ 100 nm, the pore diameter of ~ 60 nm. SEM of Mgdoped CdS shows porous nanostructured film of CdS nanoparticles. This film well adherents and covers the AAO substrate. The energy dispersive X-ray (EDX) pattern exhibits the signals of Al, O from AAO membrane and Mg, Cd, and S from the deposited CdS. This indicates the high purity of the fabricated membrane and the deposited Mg-doped CdS nanostructure. Using X-ray diffraction (XRD) pattern, Scherrer equation was used to calculate the average crystallite size. Additionally, the texture coefficients and density of dislocations were calculated. The fabricated CdS/AAO was applied to detect glucose of different concentrations. The proposed method has some advantages such as simple technology, low cost of processing, and high throughput. All of these factors facilitate the use of the prepared films in sensing applications.

Equations of motion of test particles for solving the spin-dependent Boltzmann–Vlasov equation

DOE PAGES

Xia, Yin; Xu, Jun; Li, Bao-An; ...

2016-06-16

A consistent derivation of the equations of motion (EOMs) of test particles for solving the spin-dependent Boltzmann–Vlasov equation is presented. The resulting EOMs in phase space are similar to the canonical equations in Hamiltonian dynamics, and the EOM of spin is the same as that in the Heisenburg picture of quantum mechanics. Considering further the quantum nature of spin and choosing the direction of total angular momentum in heavy-ion reactions as a reference of measuring nucleon spin, the EOMs of spin-up and spin-down nucleons are given separately. The key elements affecting the spin dynamics in heavy-ion collisions are identified. Themore » resulting EOMs provide a solid foundation for using the test-particle approach in studying spin dynamics in heavy-ion collisions at intermediate energies. Future comparisons of model simulations with experimental data will help to constrain the poorly known in-medium nucleon spin–orbit coupling relevant for understanding properties of rare isotopes and their astrophysical impacts.« less

β decay of Na32

NASA Astrophysics Data System (ADS)

Mattoon, C. M.; Sarazin, F.; Hackman, G.; Cunningham, E. S.; Austin, R. A. E.; Ball, G. C.; Chakrawarthy, R. S.; Finlay, P.; Garrett, P. E.; Grinyer, G. F.; Hyland, B.; Koopmans, K. A.; Leslie, J. R.; Phillips, A. A.; Schumaker, M. A.; Scraggs, H. C.; Schwarzenberg, J.; Smith, M. B.; Svensson, C. E.; Waddington, J. C.; Walker, P. M.; Washbrook, B.; Zganjar, E.

2007-01-01

The β-decay of Na32 has been studied using β-γ coincidences. New transitions and levels are tentatively placed in the level scheme of Mg32 from an analysis of γ-γ and β-γ-γ coincidences. The observation of the indirect feeding of the 2321 keV state in Mg32 removes some restrictions previously placed on the spin assignment for this state. No evidence of a state at 2117 keV in Mg32 is found. Previously unobserved weak transitions up to 5.4 MeV were recorded but could not be placed in the decay scheme of Na32.

Correlated magnetic impurities in a superconductor: electron density profiles and robustness of superconductivity.

PubMed

Sacramento, P D; Dugaev, V K; Vieira, V R; Araújo, M A N

2010-01-20

The insertion of magnetic impurities in a conventional superconductor leads to various effects. In this work we show that the electron density is affected by the spins (considered as classical) both locally and globally. The charge accumulation is solved self-consistently. This affects the transport properties along magnetic domain walls. Also, we show that superconductivity is more robust if the spin locations are not random but correlated. © 2010 IOP Publishing Ltd

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bose, Arnab, E-mail: arnabbose@ee.iitb.ac.in; Jain, Sourabh; Asam, Nagarjuna

We report the thermally driven giant field-like spin-torque in magnetic tunnel junctions (MTJ) on application of heat current from top to bottom. The field-like term is detected by the shift of the magneto-resistance hysteresis loop applying temperature gradient. We observed that the field-like term depends on the magnetic symmetry of the MTJ. In asymmetric structures, with different ferromagnetic materials for free and fixed layers, the field-like term is greatly enhanced. Our results show that a pure spin current density of the order of 10{sup 9 }A/m{sup 2} can be produced by creating a 120 mK temperature difference across 0.9 nm thick MgOmore » tunnelling barrier. Our results will be useful for writing MTJ and domain wall-based memories using thermally driven spin torque.« less

Influence of tantalum underlayer on magnetization dynamics in Ni{sub 81}Fe{sub 19} films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwon, Jae Hyun; Deorani, Praveen; Yoon, Jungbum

2015-07-13

The effect of tantalum (Ta) underlayer is investigated in Ni{sub 81}Fe{sub 19} thin films for magnetization dynamics. The damping parameters extracted from spin wave measurements increase systematically with increasing Ta thickness, whereas the damping parameters from ferromagnetic resonance measurements are found to be weakly dependent on the Ta thickness. The difference is attributed to propagating properties of spin wave and short spin diffusion length in Ta. The group velocity of spin waves is found to be constant for different Ta thicknesses, and nonreciprocity of spin waves is not affected by the Ta thickness. The experimental observations are supported by micromagneticmore » simulations.« less

A review of the quantum Hall effects in MgZnO/ZnO heterostructures

NASA Astrophysics Data System (ADS)

Falson, Joseph; Kawasaki, Masashi

2018-05-01

This review visits recent experimental efforts on high mobility two-dimensional electron systems (2DES) hosted at the Mg x Zn1-x O/ZnO heterointerface. We begin with the growth of these samples, and highlight the key characteristics of ozone-assisted molecular beam epitaxy required for their production. The transport characteristics of these structures are found to rival that of traditional semiconductor material systems, as signified by the high electron mobility (μ > 1000 000 cm2 Vs‑1) and rich quantum Hall features. Owing to a large effective mass and small dielectric constant, interaction effects are an order of magnitude stronger in comparison with the well studied GaAs-based 2DES. The strong correlation physics results in robust Fermi-liquid renormalization of the effective mass and spin susceptibility of carriers, which in turn dictates the parameter space for the quantum Hall effect. Finally, we explore the quantum Hall effect with a particular emphasis on the spin degree of freedom of carriers, and how their large spin splitting allows control of the ground states encountered at ultra-low temperatures within the fractional quantum Hall regime. We discuss in detail the physics of even-denominator fractional quantum Hall states, whose observation and underlying character remain elusive and exotic.

Iron Partitioning in Ferropericlase and Consequences for the Magma Ocean.

NASA Astrophysics Data System (ADS)

Braithwaite, J. W. H.; Stixrude, L. P.; Holmstrom, E.; Pinilla, C.

2016-12-01

The relative buoyancy of crystals and liquid is likely to exert a strong influence on the thermal and chemical evolution of the magma ocean. Theory indicates that liquids approach, but do not exceed the density of iso-chemical crystals in the deep mantle. The partitioning of heavy elements, such as Fe, is therefore likely to control whether crystals sink or float. While some experimental results exist, our knowledge of silicate liquid-crystal element partitioning is still limited in the deep mantle. We have developed a method for computing the Mg-Fe partitioning of Fe in such systems. We have focused initially on ferropericlase, as a relatively simple system where the buoyancy effects of Fe partitioning are likely to be large. The method is based on molecular dynamics driven by density functional theory (spin polarized, PBEsol+U). We compute the free energy of Mg for Fe substitution in simulations of liquid and B1 crystalline phases via adiabatic switching. We investigate the dependence of partitioning on pressure, temperature, and iron concentration. We find that the liquid is denser than the coexisting crystalline phase at all conditions studies. We also find that the high-spin to low-spin transition in the crystal and the liquid, have an important influence on partitioning behavior.

Spin crossover in (Mg,Fe3+)(Si,Fe3+)O3 bridgmanite: effects of disorder, iron concentration, and temperature

NASA Astrophysics Data System (ADS)

Shukla, Gaurav; Wentzcovitch, Renata

The spin crossover of iron in Fe3+-bearing bridgmanite, the most abundant mineral of the Earth's lower mantle, is by now a well-established phenomenon, though several aspects of this crossover remain unclear. Here we investigate effects of disorder, iron concentration, and temperature on this crossover using ab initio LDA + USC calculations. Disorder and concentration effects are addressed using complete statistical samplings of coupled substituted configurations up to 80 atoms supercells, while the vibrational effects using the quasiharmonic approximation. Our calculated compression curves for iron-free and iron-bearing bridgmanite compare well with the latest experimental measurements. The comparison also suggests that in a closed system, Fe2+ present in the sample may transform into Fe3+ by introduction of Mg and O vacancies with increasing pressure. As in the spin crossover in ferropericlase, this crossover in bridgmanite is accompanied by a clear volume reduction and an anomalous softening of the bulk modulus throughout the crossover pressure range. Though the concentration of [Fe3+]Si in bridgmanite may be small, related elastic anomalies may impact the interpretation of radial and lateral velocity structures of the Earth's lower mantle. This research was supported primarily by NSF Grant EAR 1348066. Computations are performed at the Minnesota Supercomputing Institute (MSI).

Thermoelasticity of Fe2+-bearing bridgmanite

NASA Astrophysics Data System (ADS)

Shukla, Gaurav; Wu, Zhongqing; Hsu, Han; Floris, Andrea; Cococcioni, Matteo; Wentzcovitch, Renata M.

2015-03-01

We present local density approximation augmented by the Hubbard-type correction calculations of high-temperature elastic properties of bridgmanite with composition (Mg(1-x)Fex2+)SiO3 for 0≤×≤0.125. Results of elastic moduli and acoustic velocities for the Mg end-member (x=0) agree very well with the latest high-pressure and high-temperature experimental measurements. In the iron-bearing system, we focus particularly on the change in thermoelastic parameters across the state change that occurs in ferrous iron above ˜30 GPa, often attributed to a high-spin (HS) to intermediate-spin (IS) crossover but explained by first-principles calculations as a lateral displacement of substitutional iron in the perovskite cage. We show that the measured effect of this change on the equation of state of this system can be explained by the lateral displacement of substitutional iron and not by the HS to IS crossover. The calculated elastic properties of (Mg0.875Fe0.1252+)SiO3 along an adiabatic mantle geotherm somewhat overestimate longitudinal velocities but produce densities and shear velocities quite consistent with the Preliminary Reference Earth Model data throughout most of the lower mantle.

An experimental study of the effect of tail configuration on the spinning characteristics of general aviation aircraft. M.S. Thesis; [static wind tunnel force measurements

NASA Technical Reports Server (NTRS)

Ballin, M. G.

1982-01-01

The feasibility of using static wind tunnel tests to obtain information about spin damping characteristics of an isolated general aviation aircraft tail was investigated. A representative tail section was oriented to the tunnel free streamline at angles simulating an equilibrium spin. A full range of normally encountered spin conditions was employed. Results of parametric studies performed to determine the effect of spin damping on several tail design parameters show satisfactory agreement with NASA rotary balance tests. Wing and body interference effects are present in the NASA studies at steep spin attitudes, but agreement improves with increasing pitch angle and spin rate, suggesting that rotational flow effects are minimal. Vertical position of the horizontal stabilizer is found to be a primary parameter affecting yaw damping, and horizontal tail chordwise position induces a substantial effect on pitching moment.

Spin splitting generated in a Y-shaped semiconductor nanostructure with a quantum point contact

NASA Astrophysics Data System (ADS)

Wójcik, P.; Adamowski, J.; Wołoszyn, M.; Spisak, B. J.

2015-07-01

We have studied the spin splitting of the current in the Y-shaped semiconductor nanostructure with a quantum point contact (QPC) in a perpendicular magnetic field. Our calculations show that the appropriate tuning of the QPC potential and the external magnetic field leads to an almost perfect separation of the spin-polarized currents: electrons with opposite spins flow out through different output branches. The spin splitting results from the joint effect of the QPC, the spin Zeeman splitting, and the electron transport through the edge states formed in the nanowire at the sufficiently high magnetic field. The Y-shaped nanostructure can be used to split the unpolarized current into two spin currents with opposite spins as well as to detect the flow of the spin current. We have found that the separation of the spin currents is only slightly affected by the Rashba spin-orbit coupling. The spin-splitter device is an analogue of the optical device—the birefractive crystal that splits the unpolarized light into two beams with perpendicular polarizations. In the magnetic-field range, in which the current is carried through the edges states, the spin splitting is robust against the spin-independent scattering. This feature opens up a possibility of the application of the Y-shaped nanostructure as a non-ballistic spin-splitter device in spintronics.

Spin splitting generated in a Y-shaped semiconductor nanostructure with a quantum point contact

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wójcik, P., E-mail: pawel.wojcik@fis.agh.edu.pl; Adamowski, J., E-mail: janusz.adamowski@fis.agh.edu.pl; Wołoszyn, M.

2015-07-07

We have studied the spin splitting of the current in the Y-shaped semiconductor nanostructure with a quantum point contact (QPC) in a perpendicular magnetic field. Our calculations show that the appropriate tuning of the QPC potential and the external magnetic field leads to an almost perfect separation of the spin-polarized currents: electrons with opposite spins flow out through different output branches. The spin splitting results from the joint effect of the QPC, the spin Zeeman splitting, and the electron transport through the edge states formed in the nanowire at the sufficiently high magnetic field. The Y-shaped nanostructure can be usedmore » to split the unpolarized current into two spin currents with opposite spins as well as to detect the flow of the spin current. We have found that the separation of the spin currents is only slightly affected by the Rashba spin-orbit coupling. The spin-splitter device is an analogue of the optical device—the birefractive crystal that splits the unpolarized light into two beams with perpendicular polarizations. In the magnetic-field range, in which the current is carried through the edges states, the spin splitting is robust against the spin-independent scattering. This feature opens up a possibility of the application of the Y-shaped nanostructure as a non-ballistic spin-splitter device in spintronics.« less

Corrosion Screening of EV31A Magnesium and Other Magnesium Alloys using Laboratory-Based Accelerated Corrosion and Electro-Chemical Methods

DTIC Science & Technology

2014-07-01

corrosion studies (16). A schematic of the SWAP process and example of the powder produced is included in figure 4. This alloy contains amounts of Al ...advanced powder -based alloy and ZAXE1711 (both from Japan) were produced using a Spinning Water Atomization Process (SWAP) to yield powder particles with...and ZAXE1711 Mg alloy powders and (b) morphology of coarse Mg alloy powder prepared by SWAP

Anomalous Swelling in Wet-Spin Films of Divalent Calf-Thymus DNA

NASA Astrophysics Data System (ADS)

Marlowe, R. L.; Lee, S. A.; Rupprecht, A.

2004-03-01

The dimension of wet-spun oriented films of Ca- and MgDNA in the direction perpendicular to the helical axis has been measured using optical microscopy as a function of relative humidity (RH). Earlier work on monovalent DNA films found that the perpendicular dimension increases monotonically with RH. In contrast, both Ca - and MgDNA films display a 15% shrinkage in the perpendicular direction at about 93% RH and expand at higher values of RH.

Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures

NASA Astrophysics Data System (ADS)

Peng, Shouzhong; Wang, Mengxing; Yang, Hongxin; Zeng, Lang; Nan, Jiang; Zhou, Jiaqi; Zhang, Youguang; Hallal, Ali; Chshiev, Mairbek; Wang, Kang L.; Zhang, Qianfan; Zhao, Weisheng

2015-12-01

Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbit coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM.

Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures.

PubMed

Peng, Shouzhong; Wang, Mengxing; Yang, Hongxin; Zeng, Lang; Nan, Jiang; Zhou, Jiaqi; Zhang, Youguang; Hallal, Ali; Chshiev, Mairbek; Wang, Kang L; Zhang, Qianfan; Zhao, Weisheng

2015-12-11

Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbit coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM.

Excitons in strongly correlated oxide nanocrystals NicMg1-cO

NASA Astrophysics Data System (ADS)

Sokolov, V. I.; Churmanov, V. N.; Pustovarov, V. A.; Gruzdev, N. B.; Uimin, M. A.; Byzov, I. V.; Zatsepin, A. F.; Kuznetsova, J. A.

2018-05-01

This paper reports about excitons in strongly correlated oxide nanocrystals NicMg1-cO (c = 0.008 and c = 1). At 8 K two weak peaks were firstly observed in the optical density spectrum of NiO nanocrystals at the energies of 3.510 eV and 3.543 eV. The intensity of the peaks subsides with an increase of temperature and a decrease of nanoparticle sizes from 25 nm to 10 nm. The peaks were attributed to the formation of p-d charge transfer excitons {d9h}. A tunneling annihilation for {d9h} excitons diminishes their lifetime drastically, even at low temperatures. This fact is considered as an inherent feature in the p-d charge transfer excitons {d9h}, which makes them significantly different from the Wannier-Mott excitons for semiconductors with direct allowed transitions. We believe that energy shift between two peaks originates due to the spin-orbit splitting of the top of the valence band, equals 33 meV. In p-d charge transfer photoluminescence excitation spectrum of NicMg1-cO (c = 0.008), we have revealed two [d9h] exciton lines near the charge transfer band edge. Energy shift of these lines (equals 25 meV) is due to the spin-orbit splitting of MgO valence band top.

Access to long-term optical memories using photon echoes retrieved from electron spins in semiconductor quantum wells

NASA Astrophysics Data System (ADS)

Poltavtsev, S. V.; Langer, L.; Yugova, I. A.; Salewski, M.; Kapitonov, Y. V.; Yakovlev, D. R.; Karczewski, G.; Wojtowicz, T.; Akimov, I. A.; Bayer, M.

2016-10-01

We use spontaneous (two-pulse) and stimulated (three-pulse) photon echoes for studying the coherent evolution of optically excited ensemble of trions which are localized in semiconductor CdTe/CdMgTe quantum well. Application of transverse magnetic field leads to the Larmor precession of the resident electron spins, which shuffles optically induced polarization between optically accessible and inaccessible states. This results in several spectacular phenomena. First, magnetic field induces oscillations of spontaneous photon echo amplitude. Second, in three-pulse excitation scheme, the photon echo decay is extended by several orders of magnitude. In this study, short-lived optical excitation which is created by the first pulse is coherently transferred into a long-lived electron spin state using the second optical pulse. This coherent spin state of electron ensemble persists much longer than any optical excitation in the system, preserving information on initial optical field, which can be retrieved as a photon echo by means of third optical pulse.

Nonlinear and Nonequilibrium Spin Injection in Magnetic Tunneling Junctions

NASA Astrophysics Data System (ADS)

Guo, Hong

2007-03-01

Quantitative analysis of charge and spin quantum transport in spintronic devices requires an atomistic first principles approach that can handle nonlinear and nonequilibrium transport conditions. We have developed an approach for this purpose based on real space density functional theory (DFT) carried out within the Keldysh nonequilibrium Green's function formalism (NEGF). We report theoretical analysis of nonlinear and nonequilibrium spin injection and quantum transport in Fe/MgO/Fe trilayer structures as a function of external bias voltage. Devices with well relaxed atomic structures and with FeO oxidization layers are investigated as a function of external bias voltage. We also report calculations of nonequilibrium spin injection into molecular layers and graphene. Comparisons to experimental data will be presented. Work in collaborations with: Derek Waldron, Vladimir Timochevski (McGill University); Ke Xia (Institute of Physics, Chinese Academy of Science, Beijing, China); Eric Zhu, Jian Wang (University of Hong Kong); Paul Haney, and Allan MacDonald (University of Texas at Austin).

Evidence of spin phonon coupling in magnetoelectric NiFe{sub 2}O{sub 4}/PMN-PT composite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahlawat, Anju; Satapathy, S., E-mail: srinu73@rrcat.gov.in, E-mail: srinusatapathy@gmail.com; Gupta, P. K.

2013-12-16

The coupling of phonon with spin in strain coupled magnetoelectric NiFe{sub 2}O{sub 4} (NFO)/0.65Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3}–0.35PbTiO{sub 3} (PMN-PT) composite was investigated by temperature-dependent Raman spectroscopy and magnetic measurements in the range 30–350 °C. Pure NFO shows usual ferromagnetic behaviour in this temperature range while NFO/PMN-PT composite show dramatic change in magnetic moment across ferroelectric transition temperature (T{sub c} ∼ 180 °C) of PMN-PT. The temperature evolution of the Raman spectra for the composite shows significant phonon anomalies in T-site (Fe-O) and O-site (Ni/Fe-O) phonon modes at ferroelectric transition temperature is attributed to spin phonon coupling in NFO/PMN-PT composite. The strain mediated magnetoelectric couplingmore » mechanism in this composite is apparent from the observed spin phonon interaction.« less

Gap state charge induced spin-dependent negative differential resistance in tunnel junctions

NASA Astrophysics Data System (ADS)

Jiang, Jun; Zhang, X.-G.; Han, X. F.

2016-04-01

We propose and demonstrate through first-principles calculation a new spin-dependent negative differential resistance (NDR) mechanism in magnetic tunnel junctions (MTJ) with cubic cation disordered crystals (CCDC) AlO x or Mg1-x Al x O as barrier materials. The CCDC is a class of insulators whose band gap can be changed by cation doping. The gap becomes arched in an ultrathin layer due to the space charge formed from metal-induced gap states. With an appropriate combination of an arched gap and a bias voltage, NDR can be produced in either spin channel. This mechanism is applicable to 2D and 3D ultrathin junctions with a sufficiently small band gap that forms a large space charge. It provides a new way of controlling the spin-dependent transport in spintronic devices by an electric field. A generalized Simmons formula for tunneling current through junction with an arched gap is derived to show the general conditions under which ultrathin junctions may exhibit NDR.

Measuring absolute spin polarization in dissolution-DNP by Spin PolarimetrY Magnetic Resonance (SPY-MR)

NASA Astrophysics Data System (ADS)

Vuichoud, Basile; Milani, Jonas; Chappuis, Quentin; Bornet, Aurélien; Bodenhausen, Geoffrey; Jannin, Sami

2015-11-01

Dynamic nuclear polarization at 1.2 K and 6.7 T allows one to achieve spin temperatures on the order of a few millikelvin, so that the high-temperature approximation (Δ E < kT) is violated for the nuclear Zeeman interaction Δ E = γB0h/(2 π) of most isotopes. Provided that, after rapid dissolution and transfer to an NMR or MRI system, the hyperpolarized molecules contain at least two nuclear spins I and S with a scalar coupling JIS, the polarization of spin I (short for 'investigated') can be determined from the asymmetry AS of the multiplet of spin S (short for 'spy'), provided perturbations due to second-order (strong coupling) effects are properly taken into account. If spin S is suitably discreet and does not affect the relaxation of spin I, this provides an elegant way of measuring spin polarizations 'on the fly' in a broad range of molecules, thus obviating the need for laborious measurements of signal intensities at thermal equilibrium. The method, dubbed Spin PolarimetrY Magnetic Resonance (SPY-MR), is illustrated for various pairs of 13 C spins (I, S) in acetate and pyruvate.

Designing spin-channel geometries for entanglement distribution

NASA Astrophysics Data System (ADS)

Levi, E. K.; Kirton, P. G.; Lovett, B. W.

2016-09-01

We investigate different geometries of spin-1/2 nitrogen impurity channels for distributing entanglement between pairs of remote nitrogen vacancy centers (NVs) in diamond. To go beyond the system size limits imposed by directly solving the master equation, we implement a matrix product operator method to describe the open system dynamics. In so doing, we provide an early demonstration of how the time-evolving block decimation algorithm can be used for answering a problem related to a real physical system that could not be accessed by other methods. For a fixed NV separation there is an interplay between incoherent impurity spin decay and coherent entanglement transfer: Long-transfer-time, few-spin systems experience strong dephasing that can be overcome by increasing the number of spins in the channel. We examine how missing spins and disorder in the coupling strengths affect the dynamics, finding that in some regimes a spin ladder is a more effective conduit for information than a single-spin chain.

The effect of the MgO buffer layer thickness on magnetic anisotropy in MgO/Fe/Cr/MgO buffer/MgO(001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozioł-Rachwał, Anna, E-mail: a.koziolrachwal@aist.go.jp; AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Kraków; Nozaki, Takayuki

2016-08-28

The relationship between the magnetic properties and MgO buffer layer thickness d was studied in epitaxial MgO/Fe(t)/Cr/MgO(d) layers grown on MgO(001) substrate in which the Fe thickness t ranged from 0.4 nm to 1.1 nm. For 0.4 nm ≤ t ≤ 0.7 nm, a non-monotonic coercivity dependence on the MgO buffer thickness was shown by perpendicular magneto-optic Kerr effect magnetometry. For thicker Fe films, an increase in the buffer layer thickness resulted in a spin reorientation transition from perpendicular to the in-plane magnetization direction. Possible origins of these unusual behaviors were discussed in terms of the suppression of carbon contamination at the Fe surface and changes inmore » the magnetoelastic anisotropy in the system. These results illustrate a method to control magnetic anisotropy in MgO/Fe/Cr/MgO(d) via an appropriate choice of MgO buffer layer thickness d.« less

β decay of proton-rich nucleus Al23 and astrophysical consequences

NASA Astrophysics Data System (ADS)

Iacob, V. E.; Zhai, Y.; Al-Abdullah, T.; Fu, C.; Hardy, J. C.; Nica, N.; Park, H. I.; Tabacaru, G.; Trache, L.; Tribble, R. E.

2006-10-01

We present the first study of the β decay of Al23 undertaken with pure samples. The study was motivated by nuclear astrophysics questions. Pure samples of Al23 were obtained from the momentum achromat recoil separator (MARS) of Texas A&M University, collected on a fast tape-transport system, and moved to a shielded location where β and β-γ coincidence measurements were made. We deduced β branching ratios and log ft values for transitions to states in Mg23, and from them determined unambiguously the spin and parity of the Al23 ground state to be Jπ=5/2+. We discuss how this excludes the large increases in the radiative proton capture cross section for the reaction Mg22(p,γ)Al23 at astrophysical energies, which were implied by claims that the spin and parity is Jπ=1/2+. The log ft for the Fermi transition to its isobaric analog state (IAS) in Mg23 is also determined for the first time. This IAS and a state 16 keV below it are observed, well separated in the same experiment for the first time. We can now solve a number of inconsistencies in the literature, exclude strong isospin mixing claimed before, and obtain a new determination of the resonance strength. Both states are resonances in the Na22(p,γ)Mg23 reaction at energies important in novae. The reactions Mg22(p,γ)Al23 and Na22(p,γ)Mg23 have both been suggested as possible candidates for diverting some of the flux in oxygen-neon novae explosions from the A=22 into the A=23 mass chain.

Valley dependent g-factor anisotropy in Silicon quantum dots

NASA Astrophysics Data System (ADS)

Ferdous, Rifat; Kawakami, Erika; Scarlino, Pasquale; Nowak, Michal; Klimeck, Gerhard; Friesen, Mark; Coppersmith, Susan N.; Eriksson, Mark A.; Vandersypen, Lieven M. K.; Rahman, Rajib

Silicon (Si) quantum dots (QD) provide a promising platform for a spin based quantum computer, because of the exceptionally long spin coherence times in Si and the existing industrial infrastructure. Due to the presence of an interface and a vertical electric field, the two lowest energy states of a Si QD are primarily composed of two conduction band valleys. Confinement by the interface and the E-field not only affect the charge properties of these states, but also their spin properties through the spin-orbit interaction (SO), which differs significantly from the SO in bulk Si. Recent experiments have found that the g-factors of these states are different and dependent on the direction of the B-field. Using an atomistic tight-binding model, we investigate the electric and magnetic field dependence of the electron g-factor of the valley states in a Si QD. We find that the g-factors are valley dependent and show 180-degree periodicity as a function of an in-plane magnetic field orientation. However, atomic scale roughness can strongly affect the anisotropic g-factors. Our study helps to reconcile disparate experimental observations and to achieve better external control over electron spins in Si QD, by electric and magnetic fields.

Interface-induced phenomena in magnetism

DOE PAGES

Hellman, Frances; Hoffmann, Axel; Tserkovnyak, Yaroslav; ...

2017-06-05

Our article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important conceptsmore » include spin accumulation, spin currents, spin transfer torque, and spin pumping. We provide an overview for the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. Our article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes.« less

Interface-Induced Phenomena in Magnetism

PubMed Central

Hoffmann, Axel; Tserkovnyak, Yaroslav; Beach, Geoffrey S. D.; Fullerton, Eric E.; Leighton, Chris; MacDonald, Allan H.; Ralph, Daniel C.; Arena, Dario A.; Dürr, Hermann A.; Fischer, Peter; Grollier, Julie; Heremans, Joseph P.; Jungwirth, Tomas; Kimel, Alexey V.; Koopmans, Bert; Krivorotov, Ilya N.; May, Steven J.; Petford-Long, Amanda K.; Rondinelli, James M.; Samarth, Nitin; Schuller, Ivan K.; Slavin, Andrei N.; Stiles, Mark D.; Tchernyshyov, Oleg; Thiaville, André; Zink, Barry L.

2017-01-01

This article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important concepts include spin accumulation, spin currents, spin transfer torque, and spin pumping. An overview is provided to the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. The article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes. PMID:28890576

Crafting ferromagnetism in Mn-doped MgO surfaces with p-type defects

PubMed Central

Panigrahi, Puspamitra; Araujo, C Moyses; Hussen, Tanveer; Ahuja, Rajeev

2014-01-01

We have employed first-principles calculations based on density functional theory (DFT) to investigate the underlying physics of unusual magnetism in Mn-doped MgO surface. We have studied two distinct scenarios. In the first one, two Mn atoms are substitutionally added to the surface, occupying the Mg sites. Both are stabilized in the Mn valence state carrying a local moment of 4.3 having a high-spin configuration. The magnetic interaction between the local moments display a very short-ranged characteristic, decaying very quickly with distance, and having antiferromagnetic ordering lower in energy. The energetics analysis also indicates that the Mn ions prefer to stay close to each other with an oxygen atom bridging the local interaction. In the second scenario, we started exploring the effect of native defects on the magnetism by crafting both Mg and O vacancies, which are p- and n-type defects, respectively. It is found that the electrons and holes affect the magnetic interaction between Mn ions in a totally different manner. The n-type defect leads to very similar magnetism, with the AFM configuration being energetically preferred. However, in the presence of Mg vacancy, the situation is quite different. The Mn atoms are further oxidized, giving rise to mixed Mn(d) ionic states. As a consequence, the Mn atoms couple ferromagnetically, when placed in the close configuration, and the obtained electronic structure is coherent with the double-exchange type of magnetic interaction. To guarantee the robustness of our results, we have benchmarked our calculations with three distinct theory levels, namely DFT-GGA, DFT-GGA+U and DFT-hybrid functionals. On the surface, the Mg vacancy displays lower formation energy occurring at higher concentrations. Therefore, our model systems can be the basis to explain a number of controversial results regarding transition metal doped oxides. PMID:27877684

Geometric Magnetic Frustration in Li3Mg2OsO6 Studied with Muon Spin Relaxation

NASA Astrophysics Data System (ADS)

Carlo, J. P.; Derakhshan, S.; Greedan, J. E.

Geometric frustration manifests when the spatial arrangement of ions inhibits magnetic order. Typically associated with antiferromagnetically (AF)-correlated moments on triangular or tetrahedral lattices, frustration occurs in a variety of structures and systems, resulting in rich phase diagrams and exotic ground states. As a window to exotic physics revealed by the cancellation of normally dominant interactions, the research community has taken great interest in frustrated systems. One family of recent interest are the rock-salt ordered oxides A5BO6, in which the B sites are occupied by magnetic ions comprising a network of interlocked tetrahedra, and nonmagnetic ions on the A sites control the B oxidation state through charge neutrality. Here we will discuss studies of Li3Mg2OsO6 using muon spin relaxation (μSR), a highly sensitive local probe of magnetism. Previous studies of this family included Li5OsO6, which exhibits AF order below 50K with minimal evidence for frustration, and Li4MgReO6, which exhibits glassy magnetism. Li3Mg2RuO6, meanwhile, exhibits long-range AF, with the ordering temperature suppressed by frustration. But its isoelectronic twin, Li3Mg2OsO6 (5d3 vs. 4d3) exhibits very different behavior, revealed by μSR to be a glassy ground state below 12K. Understanding why such similar systems exhibit diverse ground-state behavior is key to understanding the nature of geometric magnetic frustration. Financial support from the Research Corporation for Science Advancement.

Process optimization electrospinning fibrous material based on polyhydroxybutyrate

NASA Astrophysics Data System (ADS)

Olkhov, A. A.; Tyubaeva, P. M.; Staroverova, O. V.; Mastalygina, E. E.; Popov, A. A.; Ischenko, A. A.; Iordanskii, A. L.

2016-05-01

The article analyzes the influence of the main technological parameters of electrostatic spinning on the morphology and properties of ultrathin fibers on the basis of polyhydroxybutyrate. It is found that the electric conductivity and viscosity of the spinning solution affects the process of forming fibers macrostructure. The fiber-based materials PHB lets control geometry and optimize the viscosity and conductivity of a spinning solution. The resulting fibers have found use in medicine, particularly in the construction elements musculoskeletal.

Improved Mg-based alloys for hydrogen storage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sapru, K.; Ming, L.; Stetson, N.T.

1998-08-01

The overall objective of this on-going work is to develop low temperature alloys capable of reversibly storing at least 3 wt.% hydrogen, allowing greater than for 2 wt.% at the system level which is required by most applications. Surface modification of Mg can be used to improve its H-sorption kinetics. The authors show here that the same Mg-transition metal-based multi-component alloy when prepared by melt-spinning results in a more homogeneous materials with a higher plateau pressure as compared to preparing the material by mechanical grinding. They have also shown that mechanically alloyed Mg{sub 50}Al{sub 45}Zn{sub 5} results in a samplemore » having a higher plateau pressure.« less

Spin-transfer torque switched magnetic tunnel junctions in magnetic random access memory

NASA Astrophysics Data System (ADS)

Sun, Jonathan Z.

2016-10-01

Spin-transfer torque (or spin-torque, or STT) based magnetic tunnel junction (MTJ) is at the heart of a new generation of magnetism-based solid-state memory, the so-called spin-transfer-torque magnetic random access memory, or STT-MRAM. Over the past decades, STT-based switchable magnetic tunnel junction has seen progress on many fronts, including the discovery of (001) MgO as the most favored tunnel barrier, which together with (bcc) Fe or FeCo alloy are yielding best demonstrated tunnel magneto-resistance (TMR); the development of perpendicularly magnetized ultrathin CoFeB-type of thin films sufficient to support high density memories with junction sizes demonstrated down to 11nm in diameter; and record-low spin-torque switching threshold current, giving best reported switching efficiency over 5 kBT/μA. Here we review the basic device properties focusing on the perpendicularly magnetized MTJs, both in terms of switching efficiency as measured by sub-threshold, quasi-static methods, and of switching speed at super-threshold, forced switching. We focus on device behaviors important for memory applications that are rooted in fundamental device physics, which highlights the trade-off of device parameters for best suitable system integration.

Transverse spin Seebeck effect versus anomalous and planar Nernst effects in Permalloy thin films.

PubMed

Schmid, M; Srichandan, S; Meier, D; Kuschel, T; Schmalhorst, J-M; Vogel, M; Reiss, G; Strunk, C; Back, C H

2013-11-01

Transverse magnetothermoelectric effects are studied in Permalloy thin films grown on MgO and GaAs substrates and compared to those grown on suspended SiN(x) membranes. The transverse voltage along platinum strips patterned on top of the Permalloy films is measured versus the external magnetic field as a function of the angle and temperature gradients. After the identification of the contribution of the planar and anomalous Nernst effects, we find an upper limit for the transverse spin Seebeck effect, which is several orders of magnitude smaller than previously reported.

Universal spin-momentum locked optical forces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalhor, Farid; Thundat, Thomas; Jacob, Zubin, E-mail: zjacob@purdue.edu

2016-02-08

Evanescent electromagnetic waves possess spin-momentum locking, where the direction of propagation (momentum) is locked to the inherent polarization of the wave (transverse spin). We study the optical forces arising from this universal phenomenon and show that the fundamental origin of recently reported non-trivial optical chiral forces is spin-momentum locking. For evanescent waves, we show that the direction of energy flow, the direction of decay, and the direction of spin follow a right hand rule for three different cases of total internal reflection, surface plasmon polaritons, and HE{sub 11} mode of an optical fiber. Furthermore, we explain how the recently reportedmore » phenomena of lateral optical force on chiral and achiral particles are caused by the transverse spin of the evanescent field and the spin-momentum locking phenomenon. Finally, we propose an experiment to identify the unique lateral forces arising from the transverse spin in the optical fiber and point to fundamental differences of the spin density from the well-known orbital angular momentum of light. Our work presents a unified view on spin-momentum locking and how it affects optical forces on chiral and achiral particles.« less

Numerical relativity simulations of precessing binary neutron star mergers

NASA Astrophysics Data System (ADS)

Dietrich, Tim; Bernuzzi, Sebastiano; Brügmann, Bernd; Ujevic, Maximiliano; Tichy, Wolfgang

2018-03-01

We present the first set of numerical relativity simulations of binary neutron mergers that include spin precession effects and are evolved with multiple resolutions. Our simulations employ consistent initial data in general relativity with different spin configurations and dimensionless spin magnitudes ˜0.1 . They start at a gravitational-wave frequency of ˜392 Hz and cover more than 1 precession period and about 15 orbits up to merger. We discuss the spin precession dynamics by analyzing coordinate trajectories, quasilocal spin measurements, and energetics, by comparing spin aligned, antialigned, and irrotational configurations. Gravitational waveforms from different spin configuration are compared by calculating the mismatch between pairs of waveforms in the late inspiral. We find that precession effects are not distinguishable from nonprecessing configurations with aligned spins for approximately face-on binaries, while the latter are distinguishable from nonspinning configurations. Spin precession effects are instead clearly visible for approximately edge-on binaries. For the parameters considered here, precession does not significantly affect the characteristic postmerger gravitational-wave frequencies nor the mass ejection. Our results pave the way for the modeling of spin precession effects in the gravitational waveform from binary neutron star events.

Activated Metal Oxide Surfaces as Highly Basic and Reducing Environments.

DTIC Science & Technology

1987-05-21

were formed, as illustrated by [Mg iO] and 93 12[Mg9AI301 2] . Unique reaction properties were described. 2. Spin Traps Organic nitroso and nitrone ...J. V. Ortiz, R. Basu and Y. Ohrn, Chem. Phys. Lett. 103, 29 (1983). 39. K. J. Klabunde and A. Whetten, J. Am. Chem. Soc., 108, 6529 (1986). 40 . G. H...editor, Elsevier, in press. 40 . F. Mousa and K. J. Klabunde, "Base Condensation of Carbonyl Compounds on Thermally Activated Magnesium Oxide

Spin-orbit torque magnetization switching of a three-terminal perpendicular magnetic tunnel junction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cubukcu, Murat; Boulle, Olivier; Drouard, Marc

2014-01-27

We report on the current-induced magnetization switching of a three-terminal perpendicular magnetic tunnel junction by spin-orbit torque and its read-out using the tunnelling magnetoresistance (TMR) effect. The device is composed of a perpendicular Ta/FeCoB/MgO/FeCoB stack on top of a Ta current line. The magnetization of the bottom FeCoB layer can be switched reproducibly by the injection of current pulses with density 5 × 10{sup 11} A/m{sup 2} in the Ta layer in the presence of an in-plane bias magnetic field, leading to the full-scale change of the TMR signal. Our work demonstrates the proof of concept of a perpendicular spin-orbit torque magnetic memorymore » cell.« less

Elastic anomalies and acoustic dissipation associated with spin state transitions in LnCoO3 (Ln=La, Nd, Gd) and Co3O4: analogue behaviour for spin state transitions in minerals

NASA Astrophysics Data System (ADS)

Zhang, Z.; Carpenter, M. A.; Koppensteiner, J.; Schranz, W.

2010-12-01

Iron ions in lower mantle minerals magnesiowüstitue (Mg,Fe)O, perovskite (Mg,Fe)(Si,Al)O3 and post-perovskite phases undergo electronic spin state transitions from high spin (HS) to low spin (LS) or intermediate spin (IS) at high pressures and high temperatures. These spin state transitions give rise to changes in bulk and shear moduli which have significant implications for the physical and chemical properties of the lower mantle. However, the possibility of increased attenuation does not appear to have been considered yet. Co3+ is isoelectronic with Fe2+ and shows analogous HS/LS behaviour at ambient pressure in a temperature range which is easily accessible for in-situ investigations. We have studied spin state transitions in cobalt perovskites LaCoO3, NdCoO3, GdCoO3 and in Co3O4 using resonant ultrasound spectroscopy (RUS) at high frequencies 0.1-1.5 MHz, and dynamic mechanical analysis (DMA) at low frequencies 0.1-50 Hz, in the temperature range 10-1200 K. The specific objectives were to characterize anomalies in the shear moduli and in acoustic attenuation accompanying changes in the spin state of Co3+. Anomalies in shear moduli have been observed at ~110 K and ~590 K for LaCoO3, ~325 K and ~695 K for NdCoO3, ~720 K for GdCoO3, and ~30 K for Co3O4. For LaCoO3, a spin order parameter qspin is expected to couple with volume strain ea as λeaqspin and with shear strain es as λes2qspin. As a consequence of linear/quadratic coupling with es, the shear modulus is expected to vary linearly with qspin. This appears to be approximately the case for LaCoO3. Changes in spin state do not appear to give rise to acoustic attenuation at either DMA frequencies (~1 Hz) or RUS frequencies (~1 MHz), consistent with the expectation that spin/lattice relaxation is rapid in comparison with the time scale of applied stress in each case. On the other hand, for LaCoO3 there is a peak in dissipation near 590 K at low frequencies, which is attributed to freezing of ferroelastic twin walls. At high frequencies, acoustic attenuation increases steeply below ~110 K, and this is attributed to movement of magnetic polarons under stress. Data for thermally activated relaxation processes in LaCoO3 based on different measurements from the literature and our own elasticity data have been combined to give a preliminary anelasticity map. At seismic frequencies, loss mechanisms are likely to be only due to twin wall and magnetic polaron mobility. NdCoO3 and GdCoO3 both have the Pnma structure at room temperature. They also show significant non-linear behaviour in shear modulus as a function of temperature but neither show evidence of significant attenuation which might be attributed to microstructure, spin/lattice coupling or polarons. On the other hand, Co3O4 shows evidence of increasing attenuation above ~800 K and below ~30 K at high frequencies. The origin of the latter is clearly associated with magnetic ordering in this system but the origin of the former is not yet understood, particularly as Co3O4 crystals are not expected to contain any transformation microstructure.

Perpendicular magnetic anisotropy in Mn{sub 2}CoAl thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, N. Y.; Zhang, Y. Q.; Che, W. R.

Heusler compound Mn{sub 2}CoAl (MCA) is attracting more attentions due to many novel properties, such as high resistance, semiconducting behavior and suggestion as a spin-gapless material with a low magnetic moment. In this work, Mn{sub 2}CoAl epitaxial thin film was prepared on MgO(100) substrate by magnetron sputtering. The transport property of the film exhibits a semiconducting-like behavior. Moreover, our research reveals that perpendicular magnetic anisotropy (PMA) can be induced in very thin Mn{sub 2}CoAl films resulting from Mn-O and Co-O bonding at Mn{sub 2}CoAl/MgO interface, which coincides with a recent theoretical prediction. PMA and low saturation magnetic moment could leadmore » to large spin-transfer torque with low current density in principle, and thus our work may bring some unanticipated Heusler compounds into spintronics topics such as the domain wall motion and the current-induced magnetization reversal.« less

Localized states in advanced dielectrics from the vantage of spin- and symmetry-polarized tunnelling across MgO.

PubMed

Schleicher, F; Halisdemir, U; Lacour, D; Gallart, M; Boukari, S; Schmerber, G; Davesne, V; Panissod, P; Halley, D; Majjad, H; Henry, Y; Leconte, B; Boulard, A; Spor, D; Beyer, N; Kieber, C; Sternitzky, E; Cregut, O; Ziegler, M; Montaigne, F; Beaurepaire, E; Gilliot, P; Hehn, M; Bowen, M

2014-08-04

Research on advanced materials such as multiferroic perovskites underscores promising applications, yet studies on these materials rarely address the impact of defects on the nominally expected materials property. Here, we revisit the comparatively simple oxide MgO as the model material system for spin-polarized solid-state tunnelling studies. We present a defect-mediated tunnelling potential landscape of localized states owing to explicitly identified defect species, against which we examine the bias and temperature dependence of magnetotransport. By mixing symmetry-resolved transport channels, a localized state may alter the effective barrier height for symmetry-resolved charge carriers, such that tunnelling magnetoresistance decreases most with increasing temperature when that state is addressed electrically. Thermal excitation promotes an occupancy switchover from the ground to the excited state of a defect, which impacts these magnetotransport characteristics. We thus resolve contradictions between experiment and theory in this otherwise canonical spintronics system, and propose a new perspective on defects in dielectrics.

Giant magnetoelectric effects achieved by tuning spin cone symmetry in Y-type hexaferrites

DOE PAGES

Zhai, Kun; Wu, Yan; Shen, Shipeng; ...

2017-09-12

Multiferroics materials, which exhibit coupled magnetic and ferroelectric properties, have attracted tremendous research interest because of their potential in constructing next-generation multifunctional devices. The application of single-phase multiferroics is currently limited by their usually small magnetoelectric effects. Here, we report the realization of giant magnetoelectric effects in a Y-type hexaferrite Ba 0.4Sr 1.6Mg 2Fe 12O 22 single crystal, which exhibits record-breaking direct and converse magnetoelectric coefficients and a large electric-field-reversed magnetization. We have uncovered the origin of the giant magnetoelectric effects by a systematic study in the Ba 2-x Sr x Mg 2Fe 12O 22 family with magnetization, ferroelectricity andmore » neutron diffraction measurements. With the transverse spin cone symmetry restricted to be two-fold, the one-step sharp magnetization reversal is realized and giant magnetoelectric coefficients are achieved. Our study reveals that tuning magnetic symmetry is an effective route to enhance the magnetoelectric effects also in multiferroic hexaferrites.« less

Giant magnetoelectric effects achieved by tuning spin cone symmetry in Y-type hexaferrites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhai, Kun; Wu, Yan; Shen, Shipeng

Multiferroics materials, which exhibit coupled magnetic and ferroelectric properties, have attracted tremendous research interest because of their potential in constructing next-generation multifunctional devices. The application of single-phase multiferroics is currently limited by their usually small magnetoelectric effects. Here, we report the realization of giant magnetoelectric effects in a Y-type hexaferrite Ba 0.4Sr 1.6Mg 2Fe 12O 22 single crystal, which exhibits record-breaking direct and converse magnetoelectric coefficients and a large electric-field-reversed magnetization. We have uncovered the origin of the giant magnetoelectric effects by a systematic study in the Ba 2-x Sr x Mg 2Fe 12O 22 family with magnetization, ferroelectricity andmore » neutron diffraction measurements. With the transverse spin cone symmetry restricted to be two-fold, the one-step sharp magnetization reversal is realized and giant magnetoelectric coefficients are achieved. Our study reveals that tuning magnetic symmetry is an effective route to enhance the magnetoelectric effects also in multiferroic hexaferrites.« less

Tunneling magnetoresistance from a symmetry filtering effect

PubMed Central

Butler, William H

2008-01-01

This paper provides a brief overview of the young, but rapidly growing field of spintronics. Its primary objective is to explain how as electrons tunnel through simple insulators such as MgO, wavefunctions of certain symmetries are preferentially transmitted. This symmetry filtering property can be converted into a spin-filtering property if the insulator is joined epitaxially to a ferromagnetic electrode with the same two-dimensional symmetry parallel to the interface. A second requirement of the ferromagnetic electrodes is that a wavefunction with the preferred symmetry exists in one of the two spin channels but not in the other. These requirements are satisfied for electrons traveling perpendicular to the interface for Fe–MgO–Fe tunnel barriers. This leads to a large change in the resistance when the magnetic moment of one of the electrodes is rotated relative to those of the other electrode. This large tunneling magnetoresistance effect is being used as the read sensor in hard drives and may form the basis for a new type of magnetic memory. PMID:27877932

Shape anisotropy and hybridization enhanced magnetization in nanowires of Fe/MgO/Fe encapsulated in carbon nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aryee, Dennis; Seifu, Dereje

Arrays of tunneling magnetoresistance (TMR) nanowires were synthesized for the first time by filling Fe/MgO/Fe inside vertically grown and substrate supported carbon nanotubes. The magnetic properties of nanowires and planar nanoscale thin films of Fe/MgO/Fe showed several similarities, such as two-fold magnetic symmetry and ratio of orbital moment to spin moment. Nanowires of Fe/MgO/Fe showed higher saturation magnetization by a factor of 2.7 compared to planar thin films of Fe/MgO/Fe at 1.5 kOe. The enhanced magnetic properties likely resulted from shape anisotropy of the nanowires and as well as the hybridization that occur between the π- electronic states of carbonmore » and 3d-bands of the Fe-surface.« less

Synthetic and natural chromium-bearing spinels: an optical spectroscopy study

NASA Astrophysics Data System (ADS)

Taran, M. N.; Parisi, F.; Lenaz, D.; Vishnevskyy, A. A.

2014-09-01

Four samples of synthetic chromium-bearing spinels of (Mg, Fe2+)(Cr, Fe3+)2O4 composition and four samples of natural spinels of predominantly (Mg, Fe2+)(Al, Cr)2O4 composition were studied at ambient conditions by means of optical absorption spectroscopy. Synthetic end-member MgCr2O4 spinel was also studied at pressures up to ca. 10 GPa. In both synthetic and natural samples, chromium is present predominantly as octahedral Cr3+ seen in the spectra as two broad intense absorption bands in the visible range caused by the electronic spin-allowed 4 A 2 g → 4 T 2 g and 4 A 2 g → 4 T 1 g transitions (U- and Y-band, respectively). A distinct doublet structure of the Y-band in both synthetic and natural spinels is related to trigonal distortion of the octahedral site in the spinel structure. A small, if any, splitting of the U-band can only be resolved at curve-fitting analysis. In all synthetic high-chromium spinels, a couple of relatively narrow and weak bands of the spin-allowed transitions 4 A 2 g → 2 E g and 4 A 2 g → 2 T 1 g of Cr3+, intensified by exchange-coupled interaction between Cr3+ and Fe3+ at neighboring octahedral sites of the structure, appear at ~14,400 and ~15,100 cm-1. A vague broad band in the range from ca. 15,000 to 12,000 cm-1 in synthetic spinels is tentatively attributed to IVCr2+ + VICr3+ → IVCr3+ + VICr2+ intervalence charge-transfer transition. Iron, mainly as octahedral Fe3+, causes intense high-energy absorption edge in near UV-range (ligand-metal charge-transfer O2- → Fe3+, Fe2+ transitions). As tetrahedral Fe2+, it appears as a strong infrared absorption band at around 4,850 cm-1 caused by electronic spin-allowed 5 E → 5 T 2 transitions of IVFe2+. From the composition shift of the U-band in natural and synthetic MgCr2O4 spinels, the coefficient of local structural relaxation around Cr3+ in spinel MgAl2O4-MgCr2O4 system was evaluated as ~0.56(4), one of the lowest among (Al, Cr)O6 polyhedra known so far. The octahedral modulus of Cr3+ in MgCr2O4, derived from pressure-induced shift of the U-band of Cr3+, is ~313 (50) GPa, which is nearly the same as in natural low-chromium Mg, Al-spinel reported by Langer et al. (1997). Calculated from the results of the curve-fitting analysis, the Racah parameter B of Cr3+ in natural and synthetic MgCr2O4 spinels indicates that Cr-O-bonding in octahedral sites of MgCr2O4 has more covalent character than in the diluted natural samples. Within the uncertainty of determination in synthetic MgAl2O4 spinel, B does not much depend on pressure.

Measuring absolute spin polarization in dissolution-DNP by Spin PolarimetrY Magnetic Resonance (SPY-MR).

PubMed

Vuichoud, Basile; Milani, Jonas; Chappuis, Quentin; Bornet, Aurélien; Bodenhausen, Geoffrey; Jannin, Sami

2015-11-01

Dynamic nuclear polarization at 1.2 K and 6.7 T allows one to achieve spin temperatures on the order of a few millikelvin, so that the high-temperature approximation (ΔE

Double perovskites with strong spin-orbit coupling

NASA Astrophysics Data System (ADS)

Cook, Ashley M.

We first present theoretical analysis of powder inelastic neutron scattering experiments in Ba2FeReO6 performed by our experimental collaborators. Ba2FeReO6, a member of the double perovskite family of materials, exhibits half-metallic behavior and high Curie temperatures Tc, making it of interest for spintronics applications. To interpret the experimental data, we develop a local moment model, which incorporates the interaction of Fe spins with spin-orbital locked magnetic moments on Re, and show that it captures the experimental observations. We then develop a tight-binding model of the double perovskite Ba 2FeReO6, a room temperature ferrimagnet with correlated and spin-orbit coupled Re t2g electrons moving in the background of Fe moments stabilized by Hund's coupling. We show that for such 3d/5d double perovskites, strong correlations on the 5d-element (Re) are essential in driving a half-metallic ground state. Incorporating both strong spin-orbit coupling and the Hubbard repulsion on Re leads to a band structure consistent with ab initio calculations. The uncovered interplay of strong correlations and spin-orbit coupling lends partial support to our previous work, which used a local moment description to capture the spin wave dispersion found in neutron scattering measurements. We then adapt this tight-binding model to study {111}-grown bilayers of half-metallic double perovskites such as Sr2FeMoO6. The combination of spin-orbit coupling, inter-orbital hybridization and symmetry-allowed trigonal distortion leads to a rich phase diagram with tunable ferromagnetic order, topological C= +/-1, +/-2 Chern bands, and a C = +/-2 quantum anomalous Hall insulator regime. We have also performed theoretical analysis of inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites La2ZnIrO 6 and La2MgIrO6. Models with dominant Kitaev exchange seem to most naturally account for the neutron data as well as the measured frustration parameters of these materials, while the uniaxial Ising anisotropy does not. Our findings highlight how even seemingly conventional magnetic orders in oxide materials containing heavy transition metal ions may be driven by highly-directional exchange interactions rooted in strong spin-orbit coupling. Motivated by experiments on the double perovskites La2ZnIrO 6 and La2MgIrO6, we lastly study the magnetism of spin-orbit coupled jeff =1/2 iridium moments on the three-dimensional, geometrically frustrated, facecentered cubic lattice. The symmetry-allowed nearest-neighbor interaction includes Heisenberg, Kitaev, and symmetric off-diagonal exchange. A Luttinger-Tisza analysis shows a rich variety of orders, including collinear AII type antiferromagnetism, stripe order with moments along the {111}-direction, and incommensurate non-coplanar spirals, and we use Monte Carlo simulations to determine their magnetic ordering temperatures.

Numerical calculation of ion polarization in the NICA collider

NASA Astrophysics Data System (ADS)

Kovalenko, A. D.; Butenko, A. V.; Kekelidze, V. D.; Mikhaylov, V. A.; Kondratenko, M. A.; Kondratenko, A. M.; Filatov, Yu N.

2016-02-01

The NICA Collider with two solenoid Siberian snakes is “transparent” to the spin. The collider transparent to the spin provides a unique capability to control any polarization direction of protons and deuterons using additional weak solenoids without affecting orbital parameters of the beam. The spin tune induced by the control solenoids must significantly exceed the strength of the zero-integer spin resonance, which contains a coherent part associated with errors in the collider's magnetic structure and an incoherent part associated with the beam emittances. We present calculations of the coherent part of the resonance strength in the NICA collider for proton and deuteron beams.

Antiferromagnetic resonance excited by oscillating electric currents

NASA Astrophysics Data System (ADS)

Sluka, Volker

2017-12-01

In antiferromagnetic materials the order parameter exhibits resonant modes at frequencies that can be in the terahertz range, making them interesting components for spintronic devices. Here, it is shown that antiferromagnetic resonance can be excited using the inverse spin-Hall effect in a system consisting of an antiferromagnetic insulator coupled to a normal-metal waveguide. The time-dependent interplay between spin torque, ac spin accumulation, and magnetic degrees of freedom is studied. It is found that the dynamics of the antiferromagnet affects the frequency-dependent conductivity of the normal metal. Further, a comparison is made between spin-current-induced and Oersted-field-induced excitation under the condition of constant power injection.

Spin dynamics in helical molecules with nonlinear interactions

NASA Astrophysics Data System (ADS)

Díaz, E.; Albares, P.; Estévez, P. G.; Cerveró, J. M.; Gaul, C.; Diez, E.; Domínguez-Adame, F.

2018-04-01

It is widely admitted that the helical conformation of certain chiral molecules may induce a sizable spin selectivity observed in experiments. Spin selectivity arises as a result of the interplay between a helicity-induced spin–orbit coupling (SOC) and electric dipole fields in the molecule. From the theoretical point of view, different phenomena might affect the spin dynamics in helical molecules, such as quantum dephasing, dissipation and the role of metallic contacts. With a few exceptions, previous studies usually neglect the local deformation of the molecule about the carrier, but this assumption seems unrealistic to describe charge transport in molecular systems. We introduce an effective model describing the electron spin dynamics in a deformable helical molecule with weak SOC. We find that the electron–lattice interaction allows the formation of stable solitons such as bright solitons with well defined spin projection onto the molecule axis. We present a thorough study of these bright solitons and analyze their possible impact on the spin dynamics in deformable helical molecules.

Electric-field-induced interferometric resonance of a one-dimensional spin-orbit-coupled electron

PubMed Central

Fan, Jingtao; Chen, Yuansen; Chen, Gang; Xiao, Liantuan; Jia, Suotang; Nori, Franco

2016-01-01

The efficient control of electron spins is of crucial importance for spintronics, quantum metrology, and quantum information processing. We theoretically formulate an electric mechanism to probe the electron spin dynamics, by focusing on a one-dimensional spin-orbit-coupled nanowire quantum dot. Owing to the existence of spin-orbit coupling and a pulsed electric field, different spin-orbit states are shown to interfere with each other, generating intriguing interference-resonant patterns. We also reveal that an in-plane magnetic field does not affect the interval of any neighboring resonant peaks, but contributes a weak shift of each peak, which is sensitive to the direction of the magnetic field. We find that this proposed external-field-controlled scheme should be regarded as a new type of quantum-dot-based interferometry. This interferometry has potential applications in precise measurements of relevant experimental parameters, such as the Rashba and Dresselhaus spin-orbit-coupling strengths, as well as the Landé factor. PMID:27966598

Near-Earth asteroid satellite spins under spin-orbit coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Naidu, Shantanu P.; Margot, Jean-Luc

We develop a fourth-order numerical integrator to simulate the coupled spin and orbital motions of two rigid bodies having arbitrary mass distributions under the influence of their mutual gravitational potential. We simulate the dynamics of components in well-characterized binary and triple near-Earth asteroid systems and use surface of section plots to map the possible spin configurations of the satellites. For asynchronous satellites, the analysis reveals large regions of phase space where the spin state of the satellite is chaotic. For synchronous satellites, we show that libration amplitudes can reach detectable values even for moderately elongated shapes. The presence of chaoticmore » regions in the phase space has important consequences for the evolution of binary asteroids. It may substantially increase spin synchronization timescales, explain the observed fraction of asychronous binaries, delay BYORP-type evolution, and extend the lifetime of binaries. The variations in spin rate due to large librations also affect the analysis and interpretation of light curve and radar observations.« less

Magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs 2CuBr 4

DOE PAGES

Zvyagin, S. A.; Ozerov, M.; Kamenskyi, D.; ...

2015-11-27

We present on high- field electron spin resonance (ESR) studies of magnetic excitations in the spin- 1/2 triangular-lattice antiferromagnet Cs 2CuBr 4. Frequency- field diagrams of ESR excitations are measured for different orientations of magnetic fields up to 25 T. We show that the substantial zero- field energy gap, Δ ≈ 9.5 K, observed in the low-temperature excitation spectrum of Cs 2CuBr 4 [Zvyagin et al:, Phys. Rev. Lett. 112, 077206 (2014)], is present well above T N. Noticeably, the transition into the long-range magnetically ordered phase does not significantly affect the size of the gap, suggesting that even belowmore » T N the high-energy spin dynamics in Cs 2CuBr 4 is determined by short-range-order spin correlations. The experimental data are compared with results of model spin-wave-theory calculations for spin-1/2 triangle-lattice antiferromagnet.« less

Spectrum, symmetries, and dynamics of Heisenberg spin-1/2 chains

NASA Astrophysics Data System (ADS)

Joel, Kira; Kollmar, Davida; Santos, Lea

2013-03-01

Quantum spin chains are prototype quantum many-body systems. They are employed in the description of various complex physical phenomena. Here we provide an introduction to the subject by focusing on the time evolution of Heisenberg spin-1/2 chains with couplings between nearest-neighbor sites only. We study how the anisotropy parameter and the symmetries of the model affect its time evolution. Our predictions are based on the analysis of the eigenvalues and eigenstates of the system and then confirmed with actual numerical results.

Spin Filtering in Storage Rings

NASA Astrophysics Data System (ADS)

Nikolaev, N. N.; Pavlov, F. F.

The spin filtering in storage rings is based on a multiple passage of a stored beam through a polarized internal gas target. Apart from the polarization by the spin-dependent transmission, a unique geometrical feature of interaction with the target in such a filtering process, pointed out by H.O. Meyer,1 is a scattering of stored particles within the beam. A rotation of the spin in the scattering process affects the polarization buildup. We derive here a quantum-mechanical evolution equation for the spin-density matrix of a stored beam which incorporates the scattering within the beam. We show how the interplay of the transmission and scattering within the beam changes from polarized electrons to polarized protons in the atomic target. After discussions of the FILTEX results on the filtering of stored protons,2 we comment on the strategy of spin filtering of antiprotons for the PAX experiment at GSI FAIR.3.

The influence of spin orbit coupling and a current dependent potential on the residual resistivity of disordered magnetic alloys

NASA Astrophysics Data System (ADS)

Ebert, H.; Vernes, A.; Banhart, J.

1999-11-01

It has been shown recently, for a number of various magnetic disordered alloy systems, that the spin-orbit coupling (SOC) may have an important influence on the isotropic residual resistivity and that it is the primary source of the galvano-magnetic properties spontaneous magnetoresistance anisotropy (SMA) and anomalous Hall resistivity (AHR). Here it is demonstrated that—in contrast to many other spin-orbit induced phenomena—all these findings stem from the part of the spin-orbit coupling that gives rise to a mixing of the two spin sub-systems. In line with this result it is shown that inclusion of a current dependent potential within a calculation of the underlying electronic structure hardly affects the transport properties if the corresponding magnetic vector potential does not lead to a mixing of the spin sub-systems.

Magnetic edge states in Aharonov-Bohm graphene quantum rings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farghadan, R., E-mail: rfarghadan@kashanu.ac.ir; Heidari Semiromi, E.; Saffarzadeh, A.

2013-12-07

The effect of electron-electron interaction on the electronic structure of Aharonov-Bohm (AB) graphene quantum rings (GQRs) is explored theoretically using the single-band tight-binding Hamiltonian and the mean-field Hubbard model. The electronic states and magnetic properties of hexagonal, triangular, and circular GQRs with different sizes and zigzag edge terminations are studied. The results show that, although the AB oscillations in the all types of nanoring are affected by the interaction, the spin splitting in the AB oscillations strongly depends on the geometry and the size of graphene nanorings. We found that the total spin of hexagonal and circular rings is zeromore » and therefore, no spin splitting can be observed in the AB oscillations. However, the non-zero magnetization of the triangular rings breaks the degeneracy between spin-up and spin-down electrons, which produces spin-polarized AB oscillations.« less

Effect of Freezing Conditions on Distances and Their Distributions Derived from Double Electron Electron Resonance (DEER): A Study of Doubly-Spin-Labeled T4 Lysozyme

PubMed Central

Georgieva, Elka R.; Roy, Aritro S.; Grigoryants, Vladimir M.; Borbat, Petr P.; Earle, Keith A.; Scholes, Charles P.; Freed, Jack H.

2012-01-01

Pulsed dipolar ESR spectroscopy, DEER and DQC, require frozen samples. An important issue in the biological application of this technique is how the freezing rate and concentration of cryoprotectant could possibly affect the conformation of biomacromolecule and/or spin-label. We studied in detail the effect of these experimental variables on the distance distributions obtained by DEER from a series of doubly spin-labeled T4 lysozyme mutants. We found that the rate of sample freezing affects mainly the ensemble of spin-label rotamers, but the distance maxima remain essentially unchanged. This suggests that proteins frozen in a regular manner in liquid nitrogen faithfully maintain the distance-dependent structural properties in solution. We compared the results from rapidly freeze-quenched (≤100 μs) samples to those from commonly shock-frozen (slow freeze, 1s or longer) samples. For all the mutants studied we obtained inter-spin distance distributions, which were broader for rapidly frozen samples than for slowly frozen ones. We infer that rapid freezing trapped a larger ensemble of spin label rotamers; whereas, on the time-scale of slower freezing the protein and spin-label achieve a population showing fewer low-energy conformers. We used glycerol as a cryoprotectant in concentrations of 10% and 30% by weight. With 10% glycerol and slow freezing, we observed an increased slope of background signals, which in DEER is related to increased local spin concentration, in this case due to insufficient solvent vitrification, and therefore protein aggregation. This effect was considerably suppressed in slowly frozen samples containing 30% glycerol and rapidly frozen samples containing 10% glycerol. The assignment of bimodal distributions to tether rotamers as opposed to protein conformations is aided by comparing results using MTSL and 4-Bromo MTSL spin-labels. The latter usually produce narrower distance distributions. PMID:22341208

Role of spin polarization in FM/Al/FM trilayer film at low temperature

NASA Astrophysics Data System (ADS)

Lu, Ning; Webb, Richard

2014-03-01

Measurements of electronic transport in diffusive FM/normal metal/FM trilayer film are performed at temperature ranging from 2K to 300K to determine the behavior of the spin polarized current in normal metal under the influence of quantum phase coherence and spin-orbital interaction. Ten samples of Hall bar with length of 200 micron and width of 20 micron are fabricated through e-beam lithography followed by e-gun evaporation of Ni0.8Fe0.2, aluminum and Ni0.8Fe0.2 with different thickness (5nm to 45nm) in vacuum. At low temperature of 4.2K, coherent backscattering, Rashba spin-orbital interaction and spin flip scattering of conduction electrons contribute to magnetoresistance at low field. Quantitative analysis of magnetoresistance shows transition between weak localization and weak anti-localization for samples with different thickness ratio, which indicates the spin polarization actually affects the phase coherence length and spin-orbital scattering length. However, at temperature between 50K and 300K, only the spin polarization dominates the magnetoresistance.

Direct penetration of spin-triplet superconductivity into a ferromagnet in Au/SrRuO3/Sr2RuO4 junctions

NASA Astrophysics Data System (ADS)

Anwar, M. S.; Lee, S. R.; Ishiguro, R.; Sugimoto, Y.; Tano, Y.; Kang, S. J.; Shin, Y. J.; Yonezawa, S.; Manske, D.; Takayanagi, H.; Noh, T. W.; Maeno, Y.

2016-10-01

Efforts have been ongoing to establish superconducting spintronics utilizing ferromagnet/superconductor heterostructures. Previously reported devices are based on spin-singlet superconductors (SSCs), where the spin degree of freedom is lost. Spin-polarized supercurrent induction in ferromagnetic metals (FMs) is achieved even with SSCs, but only with the aid of interfacial complex magnetic structures, which severely affect information imprinted to the electron spin. Use of spin-triplet superconductors (TSCs) with spin-polarizable Cooper pairs potentially overcomes this difficulty and further leads to novel functionalities. Here, we report spin-triplet superconductivity induction into a FM SrRuO3 from a leading TSC candidate Sr2RuO4, by fabricating microscopic devices using an epitaxial SrRuO3/Sr2RuO4 hybrid. The differential conductance, exhibiting Andreev-reflection features with multiple energy scales up to around half tesla, indicates the penetration of superconductivity over a considerable distance of 15 nm across the SrRuO3 layer without help of interfacial complex magnetism. This demonstrates potential utility of FM/TSC devices for superspintronics.

Direct penetration of spin-triplet superconductivity into a ferromagnet in Au/SrRuO3/Sr2RuO4 junctions

PubMed Central

Anwar, M. S.; Lee, S. R.; Ishiguro, R.; Sugimoto, Y.; Tano, Y.; Kang, S. J.; Shin, Y. J.; Yonezawa, S.; Manske, D.; Takayanagi, H.; Noh, T. W.; Maeno, Y.

2016-01-01

Efforts have been ongoing to establish superconducting spintronics utilizing ferromagnet/superconductor heterostructures. Previously reported devices are based on spin-singlet superconductors (SSCs), where the spin degree of freedom is lost. Spin-polarized supercurrent induction in ferromagnetic metals (FMs) is achieved even with SSCs, but only with the aid of interfacial complex magnetic structures, which severely affect information imprinted to the electron spin. Use of spin-triplet superconductors (TSCs) with spin-polarizable Cooper pairs potentially overcomes this difficulty and further leads to novel functionalities. Here, we report spin-triplet superconductivity induction into a FM SrRuO3 from a leading TSC candidate Sr2RuO4, by fabricating microscopic devices using an epitaxial SrRuO3/Sr2RuO4 hybrid. The differential conductance, exhibiting Andreev-reflection features with multiple energy scales up to around half tesla, indicates the penetration of superconductivity over a considerable distance of 15 nm across the SrRuO3 layer without help of interfacial complex magnetism. This demonstrates potential utility of FM/TSC devices for superspintronics. PMID:27782151

Iron Spin Crossover in the New Hexagonal Aluminous (NAL) Phase

NASA Astrophysics Data System (ADS)

Hsu, H.

2017-12-01

The new hexagonal aluminous (NAL) phase, chemical formula AB2C6O12 (A = Na+, K+, Ca2+; B = Mg2+, Fe2+, Fe3+; C = Al3+, Si4+, Fe3+), is considered a major component ( 20 vol%) of mid-ocean ridge basalt (MORB) at lower-mantle conditions. Given that MORB can be transported back into the Earth's lower mantle via subduction, a thorough knowledge of the NAL phase is essential to fully understand the fate of subducted MORB and its role in mantle dynamics and heterogeneity. In this presentation, the complicated spin crossover of the Fe-bearing NAL phase will be discussed based on a series of first-principles calculations [1], in which the local density approximation + self-consistent Hubbard U (LDA+Usc) method was adopted. As revealed by these calculations, only the ferric iron (Fe3+) substituting Al/Si in the octahedral (C) site undergoes a crossover from the high-spin (HS) to the low-spin (LS) state at 40 GPa, while iron substituting Mg in the trigonal-prismatic (B) site remains in the HS state, regardless of its oxidation state (Fe2+ or Fe3+). The volume/elastic anomalies, iron nuclear quadrupole splittings, and crystal field spltting determined by calculations are in great agreement with experiments [2,3]. The calculations further predict that the HS-LS transition pressure of the NAL phase barely increases with temperature due to the three nearly degenerate LS states of Fe3+, suggesting that the elastic anomalies of this mineral can occur at the top lower mantle. [1] H. Hsu, Phys. Rev. B 95, 020406(R) (2017). [2] Y. Wu et al. Earth Planet. Sci. Lett. 434, 91-100 (2016). [3] S. S. Lobanov et al., J. Geophys. Res. Solid Earth 122, 3565 (2017).

Tunneling spin polarization in planar tunnel junctions: measurements using NbN superconducting electrodes and evidence for Kondo-assisted tunneling

NASA Astrophysics Data System (ADS)

Yang, Hyunsoo

2006-03-01

The fundamental origin of tunneling magnetoresistance in magnetic tunnel junctions (MTJs) is the spin-polarized tunneling current, which can be measured directly using superconducting tunneling spectroscopy (STS). The STS technique was first developed by Meservey and Tedrow using aluminum superconducting electrodes. Al has been widely used because of its low spin orbit scattering. However, measurements must be made at low temperatures (<0.4 K) because of the low superconducting transition temperature of Al. Here, we demonstrate that superconducting electrodes formed from NbN can be used to measure tunneling spin polarization (TSP) at higher temperatures up to ˜1.2K. The tunneling magnetoresistance and polarization of the tunneling current in MTJs is highly sensitive to the detailed structure of the tunneling barrier. Using MgO tunnel barriers we find TSP values as high as 90% at 0.25K. The TMR is, however, depressed by insertion of ultra thin layers of both non-magnetic and magnetic metals in the middle of the MgO barrier. For ultra-thin, discontinuous magnetic layers of CoFe, we find evidence of Kondo assisted tunneling, from increased conductance at low temperatures (<50K) and bias voltage (<20 mV). Over the same temperature and bias voltage regimes the tunneling magnetoresistance is strongly depressed. We present other evidence of Kondo resonance including the logarithmic temperature dependence of the zero bias conductance peak. We infer the Kondo temperature from both the spectra width of this conductance peak as well as the temperature dependence of the TMR depression. The Kondo temperature is sensitive to the thickness of the inserted CoFe layer and decreases with increased CoFe thickness. * performed in collaboration with S-H. Yang, C. Kaiser, and S. Parkin.

Spin-sensitive interference due to Majorana state on the interface between normal and superconducting leads

NASA Astrophysics Data System (ADS)

Barański, J.; Kobiałka, A.; Domański, T.

2017-02-01

We investigate the subgap spectrum and transport properties of the quantum dot on the interface between the metallic and superconducting leads and additionally side-coupled to the edge of the topological superconducting (TS) chain, hosting the Majorana quasiparticle. Due to the chiral nature of the Majorana states only one spin component of the quantum dot electrons (say \\uparrow ) is directly affected, however the proximity induced on-dot pairing transmits its influence on the opposite spin as well. We investigate the unique interferometric patterns driven by the Majorana quasiparticle that are different for each spin component. We also address the spin-sensitive interplay with the Kondo effect manifested at the same zero-energy and we come to the conclusion that quantum interferometry can unambiguously identify the Majorana quasiparticle.

Observation of the spin-orbit components of the 3B 2g( 3A 2g) ground state in the system Ni 2+:MgF 2 by fluorescence line narrowing

NASA Astrophysics Data System (ADS)

Tonucci, R. J.; Jacobsen, S. M.; Yen, W. M.

1990-10-01

Using a tunable narrow-band infrared laser, we demonstrate for the first time infrared-fluorescnece line narrowing in the system Ni 2+:MgF 2. High-resolution emission spectra were obtained by pumping the lowest spin-orbit component B 3 ( 3T 2g) (orthorhombic notation with octahedral notation in parentheses) of the 3T 2g multiplet and observing the B 3( 3T 2g)→B 1, A, B 2( 3A 2g) luminescent transitions at low temperature. By tuning the narrow-band laser over the B 3( 3T 2g) band, resonant and non-resonant fluorescence were obtained which narrowed with respect to the inhomogeneously broadened profile, and additional lines were observed. The spectra can be understood in terms of a simultaneous excitation of two different subsets of Ni 2+ ions which have their B 2( 3A 2g)→B 3( 3T 2g) and A( 3A 2g)→B 3( 3T 2g) transitions in resonance with the laser. The A( 3A 2g) and B 1( 3A 2g) spin-orbit components of the ground-state multiplet lie 1.9 cm -1 and 6.5 cm -1 above the B 2( 3A 2g) ground state, respectively, at 2 K.

The magnetic Curie temperature and exchange coupling between cations in tetragonal spinel oxide Mn2.5M0.5O4 (M = Co, Ni, Mn, Cr, and Mg) films

NASA Astrophysics Data System (ADS)

Kuo, K.; Cheng, C. W.; Chern, G.

2012-04-01

Mn3O4 is a Jahn-Taller tetragonal ferrite that has a relatively low Curie temperature (Tc) of ˜43 K due to weak coupling between the canting spins. In this study, we fabricated a series of 100-nm-thick Mn2.5M0.5O4 (M = Co, Ni, Mn, Cr, and Mg) films via oxygen-plasma-assisted molecular beam epitaxy and measured the structural and magnetic properties of these films. These films show single phase quality, and the c-axis lattice parameter of pure Mn3O4 is 0.944 nm, with a c/a ratio ˜1.16, consistent with the bulk values. The replacement of Mn by M (M = Co, Ni, Cr, and Mg) changes the lattice parameters, and the c/a ratio varies between 1.16 and 1.06 depending upon the cation distribution of the films. The magnetic Curie temperatures of these films also vary in the range of 25-66 K in that Ni and Co enhance the Tc whereas Mg reduces the Tc (Cr shows no effect on the Tc). These changes to the Tc are related to both the element electronic state and the cation distributions in these compounds. As a non-collinear spin configuration can induce electrical polarization, the present study provides a systematic way to enhance the magnetic transition temperature in tetragonal spinel ferrites.

Investigation of the thermonuclear 18Ne(α,p)21Na reaction rate via resonant elastic scattering of 21Na + p

NASA Astrophysics Data System (ADS)

Zhang, L. Y.; He, J. J.; Parikh, A.; Xu, S. W.; Yamaguchi, H.; Kahl, D.; Kubono, S.; Mohr, P.; Hu, J.; Ma, P.; Chen, S. Z.; Wakabayashi, Y.; Wang, H. W.; Tian, W. D.; Chen, R. F.; Guo, B.; Hashimoto, T.; Togano, Y.; Hayakawa, S.; Teranishi, T.; Iwasa, N.; Yamada, T.; Komatsubara, T.; Zhang, Y. H.; Zhou, X. H.

2014-01-01

The 18Ne(α,p)21Na reaction is thought to be one of the key breakout reactions from the hot CNO cycles to the rp process in type I x-ray bursts. In this work, the resonant properties of the compound nucleus 22Mg have been investigated by measuring the resonant elastic scattering of 21Na + p. An 89-MeV 21Na radioactive beam delivered from the CNS Radioactive Ion Beam Separator bombarded an 8.8 mg/cm2 thick polyethylene (CH2)n target. The 21Na beam intensity was about 2×105 pps, with a purity of about 70% on target. The recoiled protons were measured at the center-of-mass scattering angles of θc.m.≈175.2∘, 152.2∘, and 150.5∘ by three sets of ΔE-E telescopes, respectively. The excitation function was obtained with the thick-target method over energies Ex(22Mg)=5.5-9.2 MeV. In total, 23 states above the proton-threshold in 22Mg were observed, and their resonant parameters were determined via an R-matrix analysis of the excitation functions. We have made several new Jπ assignments and confirmed some tentative assignments made in previous work. The thermonuclear 18Ne(α,p)21Na rate has been recalculated based on our recommended spin-parity assignments. The astrophysical impact of our new rate has been investigated through one-zone postprocessing x-ray burst calculations. We find that the 18Ne(α,p)21Na rate significantly affects the peak nuclear energy generation rate, reaction fluxes, and onset temperature of this breakout reaction in these astrophysical phenomena.

Optically controlled locking of the nuclear field via coherent dark-state spectroscopy.

PubMed

Xu, Xiaodong; Yao, Wang; Sun, Bo; Steel, Duncan G; Bracker, Allan S; Gammon, Daniel; Sham, L J

2009-06-25

A single electron or hole spin trapped inside a semiconductor quantum dot forms the foundation for many proposed quantum logic devices. In group III-V materials, the resonance and coherence between two ground states of the single spin are inevitably affected by the lattice nuclear spins through the hyperfine interaction, while the dynamics of the single spin also influence the nuclear environment. Recent efforts have been made to protect the coherence of spins in quantum dots by suppressing the nuclear spin fluctuations. However, coherent control of a single spin in a single dot with simultaneous suppression of the nuclear fluctuations has yet to be achieved. Here we report the suppression of nuclear field fluctuations in a singly charged quantum dot to well below the thermal value, as shown by an enhancement of the single electron spin dephasing time T(2)*, which we measure using coherent dark-state spectroscopy. The suppression of nuclear fluctuations is found to result from a hole-spin assisted dynamic nuclear spin polarization feedback process, where the stable value of the nuclear field is determined only by the laser frequencies at fixed laser powers. This nuclear field locking is further demonstrated in a three-laser measurement, indicating a possible enhancement of the electron spin T(2)* by a factor of several hundred. This is a simple and powerful method of enhancing the electron spin coherence time without use of 'spin echo'-type techniques. We expect that our results will enable the reproducible preparation of the nuclear spin environment for repetitive control and measurement of a single spin with minimal statistical broadening.

How does the spin-state of Co ions affect the insulator-metal transition in Bi2A2Co2O8 (A = Ca, Sr, Ba)?

PubMed Central

Huang, Xiaokun; Zhang, Weiyi

2016-01-01

The misfit layered Bi2A2Co2O8 (A = Ca, Sr, Ba) compounds experience an insulator to metal transition as A’s ionic radius increases. This feature is contradictory to the conventional wisdom that larger lattice constant favors insulating rather than metallic state, and is also difficult to be reconciled using the Anderson weak localization theory. In this paper, we show from the first-principles calculation that an insulator-metal transition takes place from a nonmagnetic low-spin state of Co3+ ions to a hexagonally arranged intermediate-spin low-spin mixed-state in CoO2 plane when ionic radius increases from Ca to Ba. The predicted low-spin state of Bi2Ca2Co2O8 and Bi2Sr2Co2O8 and intermediate-spin low-spin mixed-state of Bi2Ba2Co2O8 are consistent not only with their measured transport properties, but also with the magnetic-field suppressed specific-heat peak observed at the transition temperature. In agreement with experiments, strong electronic correlation is required to stabilize the low-spin insulator and intermediate-spin low-spin metal. PMID:27901119

A study of environmental effects on galaxy spin using MaNGA data

NASA Astrophysics Data System (ADS)

Lee, Jong Chul; Hwang, Ho Seong; Chung, Haeun

2018-06-01

We investigate environmental effects on galaxy spin using the recent public data of Mapping Nearby Galaxies at APO (MaNGA) integral field spectroscopic survey containing ˜2800 galaxies. We measure the spin parameter of 1830 galaxies through the analysis of two-dimensional stellar kinematic maps within the effective radii, and obtain their large-scale (background mass density from 20 nearby galaxies) and small-scale (distance to and morphology of the nearest neighbour galaxy) environmental parameters for 1529 and 1767 galaxies, respectively. We first examine the mass dependence of galaxy spin, and find that the spin parameter of early-type galaxies decreases with stellar mass at log (M*/M⊙) ≳ 10, consistent with the results from previous studies. We then divide the galaxies into three subsamples using their stellar masses to minimize the mass effects on galaxy spin. The spin parameters of galaxies in each subsample do not change with background mass density, but do change with distance to and morphology of the nearest neighbour. In particular, the spin parameter of late-type galaxies decreases as early-type neighbours approach within the virial radius. These results suggest that the large-scale environments hardly affect the galaxy spin, but the small-scale environments such as hydrodynamic galaxy-galaxy interactions can play a substantial role in determining galaxy spin.

How does the spin-state of Co ions affect the insulator-metal transition in Bi2A2Co2O8 (A = Ca, Sr, Ba)?

PubMed

Huang, Xiaokun; Zhang, Weiyi

2016-11-30

The misfit layered Bi 2 A 2 Co 2 O 8 (A = Ca, Sr, Ba) compounds experience an insulator to metal transition as A's ionic radius increases. This feature is contradictory to the conventional wisdom that larger lattice constant favors insulating rather than metallic state, and is also difficult to be reconciled using the Anderson weak localization theory. In this paper, we show from the first-principles calculation that an insulator-metal transition takes place from a nonmagnetic low-spin state of Co 3+ ions to a hexagonally arranged intermediate-spin low-spin mixed-state in CoO 2 plane when ionic radius increases from Ca to Ba. The predicted low-spin state of Bi 2 Ca 2 Co 2 O 8 and Bi 2 Sr 2 Co 2 O 8 and intermediate-spin low-spin mixed-state of Bi 2 Ba 2 Co 2 O 8 are consistent not only with their measured transport properties, but also with the magnetic-field suppressed specific-heat peak observed at the transition temperature. In agreement with experiments, strong electronic correlation is required to stabilize the low-spin insulator and intermediate-spin low-spin metal.

Proton threshold states in the Na22(p,γ)Mg23 reaction and astrophysical implications

NASA Astrophysics Data System (ADS)

Comisel, H.; Hategan, C.; Graw, G.; Wolter, H. H.

2007-04-01

Proton threshold states in Mg23 are important for the astrophysically relevant proton capture reaction Na22(p,γ)Mg23. In the indirect determination of the resonance strength of the lowest states, which were not accessible by direct methods, some of the spin-parity-assignments remained experimentally uncertain. We have investigated these states with shell model, Coulomb displacement, and Thomas-Ehrman shift calculations. From the comparison of calculated and observed properties, we relate the lowest relevant resonance state at Ex=7643 keV to an excited 3/2+ state in accordance with a recent experimental determination by Jenkins From this we deduce significantly improved values for the Na22(p,γ)Mg23 reaction rate at stellar temperatures below T9=0.1 K.

Valence and spin states of iron are invisible in Earth’s lower mantle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jiachao; Dorfman, Susannah M.; Zhu, Feng

Heterogeneity in Earth’s mantle is a record of chemical and dynamic processes over Earth’s history. The geophysical signatures of heterogeneity can only be interpreted with quantitative constraints on effects of major elements such as iron on physical properties including density, compressibility, and electrical conductivity. However, deconvolution of the effects of multiple valence and spin states of iron in bridgmanite (Bdg), the most abundant mineral in the lower mantle, has been challenging. Here we show through a study of a ferric-iron-only (Mg 0.46Fe 3+0.53)(Si 0.49Fe 3+ 0.51)O 3 Bdg that Fe 3+ in the octahedral site undergoes a spin transition betweenmore » 43 and 53 GPa at 300 K. The resolved effects of the spin transition on density, bulk sound velocity, and electrical conductivity are smaller than previous estimations, consistent with the smooth depth profiles from geophysical observations. For likely mantle compositions, the valence state of iron has minor effects on density and sound velocities relative to major cation composition.« less

Valence and spin states of iron are invisible in Earth’s lower mantle

DOE PAGES

Liu, Jiachao; Dorfman, Susannah M.; Zhu, Feng; ...

2018-03-29

Heterogeneity in Earth’s mantle is a record of chemical and dynamic processes over Earth’s history. The geophysical signatures of heterogeneity can only be interpreted with quantitative constraints on effects of major elements such as iron on physical properties including density, compressibility, and electrical conductivity. However, deconvolution of the effects of multiple valence and spin states of iron in bridgmanite (Bdg), the most abundant mineral in the lower mantle, has been challenging. Here we show through a study of a ferric-iron-only (Mg 0.46Fe 3+0.53)(Si 0.49Fe 3+ 0.51)O 3 Bdg that Fe 3+ in the octahedral site undergoes a spin transition betweenmore » 43 and 53 GPa at 300 K. The resolved effects of the spin transition on density, bulk sound velocity, and electrical conductivity are smaller than previous estimations, consistent with the smooth depth profiles from geophysical observations. For likely mantle compositions, the valence state of iron has minor effects on density and sound velocities relative to major cation composition.« less

High-Yield Spin Labeling of Long RNAs for Electron Paramagnetic Resonance Spectroscopy.

PubMed

Kerzhner, Mark; Matsuoka, Hideto; Wuebben, Christine; Famulok, Michael; Schiemann, Olav

2018-05-10

Site-directed spin labeling is a powerful tool for investigating the conformation and dynamics of biomacromolecules such as RNA. Here we introduce a spin labeling strategy based on click chemistry in solution that, in combination with enzymatic ligation, allows highly efficient labeling of complex and long RNAs with short reaction times and suppressed RNA degradation. With this approach, a 34-nucleotide aptamer domain of the preQ1 riboswitch and an 81-nucleotide TPP riboswitch aptamer could be labeled with two labels in several positions. We then show that conformations of the preQ1 aptamer and its dynamics can be monitored in the absence and presence of Mg 2+ and a preQ1 ligand by continuous wave electron paramagnetic resonance spectroscopy at room temperature and pulsed electron-electron double resonance spectroscopy (PELDOR or DEER) in the frozen state.

A critical comparison of electrical methods for measuring spin-orbit torques

NASA Astrophysics Data System (ADS)

Zhang, Xuanzi; Hung, Yu-Ming; Rehm, Laura; Kent, Andrew D.

Direct (DC) and alternating current (AC) transport measurements of spin-orbit torques (SOTs) in heavy metal-ferromagnet heterostructure with perpendicular magnetic anisotropy have been proposed and demonstrated. A DC method measures the change of perpendicular magnetization component while an AC method probes the first and second harmonic magnetization oscillation in responses to an AC current (~1 kHz). Here we conduct both types of measurements on β-Ta/CoFeB/MgO in the form of patterned Hall bars (20 μm linewidth) and compare the results. Experiments results are qualitatively in agreement with a macro spin model including Slonzewski-like and a field-like SOTs. However, the effective field from the ac method is larger than that obtained from the DC method. We discuss the possible origins of the discrepancy and its implications for quantitatively determining SOTs. Research supported by the SRC-INDEX program, NSF-DMR-1309202 and NYU-DURF award.

High spin structure and intruder configurations in 31P

NASA Astrophysics Data System (ADS)

Ionescu-Bujor, M.; Iordachescu, A.; Napoli, D. R.; Lenzi, S. M.; Mărginean, N.; Otsuka, T.; Utsuno, Y.; Ribas, R. V.; Axiotis, M.; Bazzacco, D.; Bizzeti-Sona, A. M.; Bizzeti, P. G.; Brandolini, F.; Bucurescu, D.; Cardona, M. A.; De Angelis, G.; De Poli, M.; Della Vedova, F.; Farnea, E.; Gadea, A.; Hojman, D.; Kalfas, C. A.; Kröll, Th.; Lunardi, S.; Martínez, T.; Mason, P.; Pavan, P.; Quintana, B.; Alvarez, C. Rossi; Ur, C. A.; Vlastou, R.; Zilio, S.

2006-02-01

The nucleus 31P has been studied in the 24Mg(16O,2αp) reaction with a 70-MeV 16O beam. A complex level scheme extended up to spins 17/2+ and 15/2-, on positive and negative parity, respectively, has been established. Lifetimes for the new states have been investigated by the Doppler shift attenuation method. Two shell-model calculations have been performed to describe the experimental data, one by using the code ANTOINE in a valence space restricted to the sd shell, and the other by applying the Monte Carlo shell model in a valence space including the sd-fp shells. The latter calculation indicates that intruder excitations, involving the promotion of a T=0 proton-neutron pair to the fp shell, play a dominant role in the structure of the positive-parity high-spin states of 31P.

Spin-glass behaviors in carrier polarity controlled Fe{sub 3−x}Ti{sub x}O{sub 4} semiconductor thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamahara, H., E-mail: yamahara@bioxide.t.u-tokyo.ac.jp; Seki, M.; Adachi, M.

2015-08-14

Carrier-type control of spin-glass (cluster spin-glass) is studied in order to engineer basic magnetic semiconductor elements using the memory functions of spin-glass. A key of carrier-polarity control in magnetite is the valence engineering between Fe(II) and Fe(III) that is achieved by Ti(IV) substitution. Single phases of (001)-oriented Fe{sub 3−x}Ti{sub x}O{sub 4} thin films have been obtained on spinel MgAl{sub 2}O{sub 4} substrates by pulsed laser deposition. Thermoelectric power measurements reveal that Ti-rich films (x = 0.8) show p-type conduction, while Ti-poor films (x = 0.6–0.75) show n-type conduction. The systematic Fe(III) reduction to Fe(II) followed by Ti(IV) substitution in the octahedral sublattice is confirmedmore » by the X-ray absorption spectra. All of the Fe{sub 3−x}Ti{sub x}O{sub 4} films (x = 0.6–0.8) exhibit ferrimagnetism above room temperature. Next, the spin-glass behaviors of Ti-rich Fe{sub 2.2}Ti{sub 0.8}O{sub 4} film are studied, since this magnetically diluted system is expected to exhibit the spin-glass behaviors. The DC magnetization and AC susceptibility measurements for the Ti-rich Fe{sub 2.2}Ti{sub 0.8}O{sub 4} film reveal the presence of the spin glass phase. Thermal- and magnetic-field-history memory effects are observed and are attributed to the long time-decay nature of remanent magnetization. The detailed analysis of the time-dependent thermoremanent magnetization reveals the presence of the cluster spin glass state.« less

Electronic transition and electrical transport properties of delafossite CuCr1-xMgxO2 (0 ≤ x ≤ 12%) films prepared by the sol-gel method: A composition dependence study

NASA Astrophysics Data System (ADS)

Han, M. J.; Duan, Z. H.; Zhang, J. Z.; Zhang, S.; Li, Y. W.; Hu, Z. G.; Chu, J. H.

2013-10-01

Highly transparent CuCr1-xMgxO2 (0 ≤ x ≤ 12%) films were prepared on (001) sapphire substrates by sol-gel method. The microstructure, phonon modes, optical band gap, and electrical transport properties have been systematically discussed. It was found that Mg-doping improved the crystal quality and enhanced the (00l) preferred orientation. The spectral transmittance of films approaches about 70%-75% in the visible-near-infrared wavelength region. With increasing Mg-composition, the optical band gap first declines and climbs up due to the band gap renormalization and Burstein-Moss effect. The direct and indirect band gaps of CuCr0.94Mg0.06O2 film are 3.00 and 2.56 eV, respectively. In addition, it shows a crossover from the thermal activation behavior to that of three-dimensional variable range hopping from temperature-dependent electrical conductivity. The crossover temperature decreases with increasing Mg-doping composition, which can be ascribed to the change of spin-charge coupling between the hole and the local spin at Cr site. It should be noted that the electrical conductivity of CuCr1-xMgxO2 films becomes larger with increasing x value. The highest electrical conductivity of 3.85 S cm-1 at room temperature for x = 12% is four-order magnitude larger than that (8.81 × 10-4 S cm-1) for pure CuCrO2 film. The high spectral transmittance and larger conductivity indicate that Mg-doped CuCrO2 films are promising for optoelectronic device applications.

Precessional Instability in Binary Black Holes with Aligned Spins.

PubMed

Gerosa, Davide; Kesden, Michael; O'Shaughnessy, Richard; Klein, Antoine; Berti, Emanuele; Sperhake, Ulrich; Trifirò, Daniele

2015-10-02

Binary black holes on quasicircular orbits with spins aligned with their orbital angular momentum have been test beds for analytic and numerical relativity for decades, not least because symmetry ensures that such configurations are equilibrium solutions to the spin-precession equations. In this work, we show that these solutions can be unstable when the spin of the higher-mass black hole is aligned with the orbital angular momentum and the spin of the lower-mass black hole is antialigned. Spins in these configurations are unstable to precession to large misalignment when the binary separation r is between the values r(ud±)=(√(χ(1))±√(qχ(2)))(4)(1-q)(-2)M, where M is the total mass, q≡m(2)/m(1) is the mass ratio, and χ(1) (χ(2)) is the dimensionless spin of the more (less) massive black hole. This instability exists for a wide range of spin magnitudes and mass ratios and can occur in the strong-field regime near the merger. We describe the origin and nature of the instability using recently developed analytical techniques to characterize fully generic spin precession. This instability provides a channel to circumvent astrophysical spin alignment at large binary separations, allowing significant spin precession prior to merger affecting both gravitational-wave and electromagnetic signatures of stellar-mass and supermassive binary black holes.

Multi-photon Rabi oscillations in high spin paramagnetic impurity

NASA Astrophysics Data System (ADS)

Bertaina, S.; Groll, N.; Chen, L.; Chiorescu, I.

2011-10-01

We report on multiple photon monochromatic quantum oscillations (Rabi oscillations) observed by pulsed EPR (Electron Paramagnetic Resonance) of Mn2+ (S = 5/2) impurities in MgO. We find that when the microwave magnetic field is similar or large than the anisotropy splitting, the Rabi oscillations have a spectrum made of many frequencies not predicted by the S = l/2 Rabi model. We show that these new frequencies come from multiple photon coherent manipulation of the multi-level spin impurity. We develop a model based on the crystal field theory and the rotating frame approximation, describing the observed phenomenon with a very good agreement.

Spin singlet and spin triplet pairing correlations on shape evolution in s d -shell N =Z Nuclei

NASA Astrophysics Data System (ADS)

Ha, Eunja; Cheoun, Myung-Ki; Sagawa, H.

2018-02-01

We study the shape evolution of N =Z nuclei 24Mg,28Si, and 32S in the axially symmetric deformed Woods-Saxon model, taking into account both T =0 and T =1 pairing interactions. We find the coexistence of T =0 and T =1 superfluidity phases in the large deformation region | β2|>0.3 in these three nuclei. The interplay between the two pairing interactions has an important effect on determining the deformation of the ground states in these nuclei. The self-energy contributions from the pairing correlations to the single particle (s.p.) energies are also examined.

Laser balancing system for high material removal rates

NASA Technical Reports Server (NTRS)

Jones, M. G.; Georgalas, G.; Ortiz, A. L.

1984-01-01

A laser technique to remove material in excess of 10 mg/sec from a spinning rotor is described. This material removal rate is 20 times greater than previously reported for a surface speed of 30 m/sec. Material removal enhancement was achieved by steering a focused laser beam with moving optics to increase the time of laser energy interaction with a particular location on the circumferential surface of a spinning rotor. A neodymium:yttrium aluminum garnet (Nd:YAG) pulse laser was used in this work to evaluate material removal for carbon steel, 347 stainless steel, Inconal 718, and titanium 6-4. This technique is applicable to dynamic laser balancing.

Kobayashi-Kondo-Maskawa-'t Hooft interaction in pentaquarks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dmitrasinovic, V.

2005-05-01

We review critically the predictions of pentaquarks in the quark model, in particular, those based on the flavor-spin-dependent (Glozman-Riska) hyperfine interaction and the color-spin (one-gluon-exchange Fermi-Breit) one. We include the antiquark interactions and find that: (1) the exotic SU(3) multiplets are not substantially affected in the flavor-spin model, whereas some of the nonexotic multiplets are; and (2) the variational upper bound on the {xi}{sup --}-{theta}{sup +} mass difference in the color-spin hyperfine interaction model is substantially reduced. This leads us to the U{sub A}(1) symmetry breaking Kobayashi-Kondo-Maskawa-'tHooft interaction. We discuss some of its phenomenological consequences for pentaquarks.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruhman, Jonathan; Kozii, Vladyslav; Fu, Liang

In this work, we study how an inversion-breaking quantum critical point affects the ground state of a one-dimensional electronic liquid with repulsive interaction and spin-orbit coupling. We find that regardless of the interaction strength, the critical fluctuations always lead to a gap in the electronic spin sector. The origin of the gap is a two-particle backscattering process, which becomes relevant due to renormalization of the Luttinger parameter near the critical point. The resulting spin-gapped state is topological and can be considered as a one-dimensional version of a spin-triplet superconductor. Interestingly, in the case of a ferromagnetic critical point, the Luttingermore » parameter is renormalized in the opposite manner, such that the system remains nonsuperconducting.« less

Theory of Tunneling Spectroscopy in a Mn12 Single-Electron Transistor by Density-Functional Theory Methods

NASA Astrophysics Data System (ADS)

Michalak, Ł.; Canali, C. M.; Pederson, M. R.; Paulsson, M.; Benza, V. G.

2010-01-01

We consider tunneling transport through a Mn12 molecular magnet using spin density functional theory. A tractable methodology for constructing many-body wave functions from Kohn-Sham orbitals allows for the determination of spin-dependent matrix elements for use in transport calculations. The tunneling conductance at finite bias is characterized by peaks representing transitions between spin multiplets, separated by an energy on the order of the magnetic anisotropy. The energy splitting of the spin multiplets and the spatial part of their many-body wave functions, describing the orbital degrees of freedom of the excess charge, strongly affect the electronic transport, and can lead to negative differential conductance.

Impact of Tunnel-Barrier Strength on Magnetoresistance in Carbon Nanotubes

NASA Astrophysics Data System (ADS)

Morgan, Caitlin; Misiorny, Maciej; Metten, Dominik; Heedt, Sebastian; Schäpers, Thomas; Schneider, Claus M.; Meyer, Carola

2016-05-01

We investigate magnetoresistance in spin valves involving CoPd-contacted carbon nanotubes. Both the temperature and bias-voltage dependence clearly indicate tunneling magnetoresistance as the origin. We show that this effect is significantly affected by the tunnel-barrier strength, which appears to be one reason for the variation between devices previously detected in similar structures. Modeling the data by means of the scattering matrix approach, we find a nontrivial dependence of the magnetoresistance on the barrier strength. Furthermore, an analysis of the spin precession observed in a nonlocal Hanle measurement yields a spin lifetime of τs=1.1 ns , a value comparable with those found in silicon- or graphene-based spin-valve devices.

Theory of tunneling spectroscopy in a Mn12 single-electron transistor by density-functional theory methods.

PubMed

Michalak, Ł; Canali, C M; Pederson, M R; Paulsson, M; Benza, V G

2010-01-08

We consider tunneling transport through a Mn12 molecular magnet using spin density functional theory. A tractable methodology for constructing many-body wave functions from Kohn-Sham orbitals allows for the determination of spin-dependent matrix elements for use in transport calculations. The tunneling conductance at finite bias is characterized by peaks representing transitions between spin multiplets, separated by an energy on the order of the magnetic anisotropy. The energy splitting of the spin multiplets and the spatial part of their many-body wave functions, describing the orbital degrees of freedom of the excess charge, strongly affect the electronic transport, and can lead to negative differential conductance.

Spin-dependent dwell times of electron tunneling through double- and triple-barrier structures

NASA Astrophysics Data System (ADS)

Erić, Marko; Radovanović, Jelena; Milanović, Vitomir; Ikonić, Zoran; Indjin, Dragan

2008-04-01

We have analyzed the influence of Dresselhaus and Rashba spin-orbit couplings (caused by the bulk inversion asymmetry and the structural asymmetry, respectively) on electron tunneling through a double- and triple-barrier structures, with and without an externally applied electric field. The results indicate that the degree of structural asymmetry and external electric field can greatly affect the dwell times of electrons with opposite spin orientation. This opens up the possibilities of obtaining efficient spin separation in the time domain. The material system of choice is AlxGa1-xSb, and the presented model takes into account the position dependence of material parameters, as well as the effects of band nonparabolicity.

Is spin transport through molecules really occurring in organic spin valves? A combined magnetoresistance and inelastic electron tunnelling spectroscopy study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galbiati, Marta; Tatay, Sergio; Delprat, Sophie

2015-02-23

Molecular and organic spintronics is an emerging research field which combines the versatility of chemistry with the non-volatility of spintronics. Organic materials have already proved their potential as tunnel barriers (TBs) or spacers in spintronics devices showing sizable spin valve like magnetoresistance effects. In the last years, a large effort has been focused on the optimization of these organic spintronics devices. Insertion of a thin inorganic tunnel barrier (Al{sub 2}O{sub 3} or MgO) at the bottom ferromagnetic metal (FM)/organic interface seems to improve the spin transport efficiency. However, during the top FM electrode deposition, metal atoms are prone to diffusemore » through the organic layer and potentially short-circuit it. This may lead to the formation of a working but undesired FM/TB/FM magnetic tunnel junction where the organic plays no role. Indeed, establishing a protocol to demonstrate the effective spin dependent transport through the organic layer remains a key issue. Here, we focus on Co/Al{sub 2}O{sub 3}/Alq{sub 3}/Co junctions and show that combining magnetoresistance and inelastic electron tunnelling spectroscopy measurements one can sort out working “organic” and short-circuited junctions fabricated on the same wafer.« less

Electron spin polarization in realistic trajectories around the magnetic node of two counter-propagating, circularly polarized, ultra-intense lasers

NASA Astrophysics Data System (ADS)

Del Sorbo, D.; Seipt, D.; Thomas, A. G. R.; Ridgers, C. P.

2018-06-01

It has recently been suggested that two counter-propagating, circularly polarized, ultra-intense lasers can induce a strong electron spin polarization at the magnetic node of the electromagnetic field that they setup (Del Sorbo et al 2017 Phys. Rev. A 96 043407). We confirm these results by considering a more sophisticated description that integrates over realistic trajectories. The electron dynamics is weakly affected by the variation of power radiated due to the spin polarization. The degree of spin polarization differs by approximately 5% if considering electrons initially at rest or already in a circular orbit. The instability of trajectories at the magnetic node induces a spin precession associated with the electron migration that establishes an upper temporal limit to the polarization of the electron population of about one laser period.

First Principles Study on Topological-Phase Transition in Ferroelectric Oxides

NASA Astrophysics Data System (ADS)

Yamauchi, Kunihiko; Barone, Paolo; Picozzi, Silvia

Graphene is known as a 2D topological insulator with zero energy gap and Dirac cone. In this study, we theoretically designed a honeycomb structure of Au ions embedded in a ferroelectric host oxide, in order to exploit structural distortions to control topological properties. We show that the polar structural distortion induces the emergence of spin-valley coupling, together with a topological transition from a quantum spin-Hall insulating phase to a trivial band insulator. The phase transition also affects the Berry curvature and spin-valley selection rules. Analogously to graphene, the microscopic origin of this topological phase is ascribed to a spin-valley-sublattice coupling, which arises from the interplay between trigonal crystal field and an ``effective'' spin-orbit interaction due to virtual excitations between eg and t2g states of transition-metal ions.

Laser-Heated DAC Mössbauer Study of Lower Mantle Phases: Spin Transitions and Implications for Mantle Heterogeneity

NASA Astrophysics Data System (ADS)

McCammon, C. A.; Dubrovinsky, L. S.; Potapkin, V.; Glazyrin, K.; Prescher, C.; Kupenko, I.; Chumakov, A.; Rüffer, R.; Kantor, A.; Kantor, I.; Smirnov, G. V.; Popov, S.

2011-12-01

57Fe Mössbauer spectroscopy measured in the energy domain remains one of the best methods to determine iron valence and the nature of spin transitions in lower mantle phases, but up until now measurements at high P,T using a diamond anvil cell (DAC) could only be made using external heating and hence were limited to a maximum of around 800 K. Higher temperatures are possible through laser heating; however conventional radioactive sources have limited intensity and essentially no possibilities for focusing in a laboratory setting. To overcome these limitations we have developed an energy domain synchrotron Mössbauer source (SMS) on beamline ID18 at the European Synchrotron Radiation Facility, enabling rapid collection of high quality energy domain Mössbauer spectra. Combined with a portable double-sided laser heating system, SMS spectra can be collected on iron-containing phases at P,T conditions up to those close to the base of the lower mantle in less than one hour. In the current study we performed SMS measurements on several compositions of (Mg,Fe)(Si,Al)O3 perovskite (Pv) as well as Mg0.8Fe0.2O (Fp) up to 122 GPa and 2500 K. All Mössbauer spectra at high pressure and room temperature are consistent with previous observations: a high-spin (HS) to intermediate-spin (IS) transition of Fe2+(Pv) starting at around 30 GPa, a HS to low-spin (LS) transition of Fe2+(Fp) starting at around 50 GPa, and no spin transition in Fe3+(Pv) up to at least 100 GPa. At high temperature all Fe2+ components show the expected strong decrease in both centre shift and quadrupole splitting, which provides an independent measure of temperature based on the Debye model, and shows clearly the strong temperature gradient in one-sided versus double-sided laser heating experiments. Preliminary fitting of the high P,T Mössbauer spectra is consistent with predominantly IS Fe2+ (Pv), HS Fe3+ (Pv) and mixed HS-LS Fe2+ (Fp). The relative proportion of Fe3+ (Pv) does not appear to change significantly on heating, and all of the original Mössbauer spectra are recovered after cooling. Based on our results, Fe2+ in silicate perovskite is inferred to be predominantly in the IS state throughout the lower mantle while Fe3+ remains in the HS state, implying that seismic velocity anomalies in the main part of the lower mantle cannot be attributed to iron spin transitions in silicate perovskite.

Training Level Does Not Affect Auditory Perception of The Magnitude of Ball Spin in Table Tennis.

PubMed

Santos, Daniel P R; Barbosa, Roberto N; Vieira, Luiz H P; Santiago, Paulo R P; Zagatto, Alessandro M; Gomes, Matheus M

2017-01-01

Identifying the trajectory and spin of the ball with speed and accuracy is critical for good performance in table tennis. The aim of this study was to analyze the ability of table tennis players presenting different levels of training/experience to identify the magnitude of the ball spin from the sound produced when the racket hit the ball. Four types of "forehand" contact sounds were collected in the laboratory, defined as: Fast Spin (spinning ball forward at 140 r/s); Medium Spin (105 r/s); Slow Spin (84 r/s); and Flat Hit (less than 60 r/s). Thirty-four table tennis players of both sexes (24 men and 10 women) aged 18-40 years listened to the sounds and tried to identify the magnitude of the ball spin. The results revealed that in 50.9% of the cases the table tennis players were able to identify the ball spin and the observed number of correct answers (10.2) was significantly higher (χ 2 = 270.4, p <0.05) than the number of correct answers that could occur by chance. On the other hand, the results did not show any relationship between the level of training/experience and auditory perception of the ball spin. This indicates that auditory information contributes to identification of the magnitude of the ball spin, however, it also reveals that, in table tennis, the level of training does not interfere with the auditory perception of the ball spin.

Spin transition of ferric iron in the NAL phase: Implications for the seismic heterogeneities of subducted slabs in the lower mantle

NASA Astrophysics Data System (ADS)

Wu, Ye; Wu, Xiang; Lin, Jung-Fu; McCammon, Catherine A.; Xiao, Yuming; Chow, Paul; Prakapenka, Vitali B.; Yoshino, Takashi; Zhai, Shuangmeng; Qin, Shan

2016-01-01

Al-rich phases (NAL: new hexagonal aluminous phase and CF: calcium-ferrite phase) are believed to constitute 10 ∼ 30 wt% of subducted mid-ocean ridge basalt (MORB) in the Earth's lower mantle. In order to understand the effects of iron on compressibility and elastic properties of the NAL phase, we have studied two single-crystal samples (Fe-free Na1.14Mg1.83Al4.74Si1.23O12 and Fe-bearing Na0.71Mg2.05Al4.62Si1.162+0.009Fe 3+0.17Fe O12) using synchrotron nuclear forward scattering (NFS) and X-ray diffraction (XRD) combined with diamond anvil cells up to 86 GPa at room temperature. A pressure-induced high-spin (HS) to low-spin (LS) transition of the octahedral Fe3+ in the Fe-bearing NAL is observed at approximately 30 GPa by NFS. Compared to the Fe-free NAL, the Fe-bearing NAL undergoes a volume reduction of 1.0% (∼1.2 Å3) at 33 ∼ 47 GPa as supported by XRD, which is associated with the spin transition of the octahedral Fe3+. The fits of Birch-Murnaghan equation of state (B-M EoS) to P- V data yield unit-cell volume at zero pressure V0 = 183.1 (1) Å3 and isothermal bulk modulus KT0 = 233 (6) GPa with a pressure derivative KT0 ‧ = 3.7 (2) for the Fe-free NAL; V0-HS = 184.76 (6) Å3 and KT0-HS = 238 (1) GPa with KT0- HS ‧ = 4 (fixed) for the Fe-bearing NAL. The bulk sound velocities (VΦ) of the Fe-free and Fe-bearing NAL phase are approximately 6% larger than those of Al, Fe-bearing bridgmanite and calcium silicate perovskite in the lower mantle, except for the spin transition region where a notable softening of VΦ with a maximum reduction of 9.4% occurs in the Fe-bearing NAL at 41 GPa. Considering the high volume proportion of the NAL phase in subducted MORB, the distinct elastic properties of the Fe-bearing NAL phase across the spin transition reported here may provide an alternative plausible explanation for the observed seismic heterogeneities of subducted slabs in the lower mantle at depths below 1200 km.

How does relativity affect magnetically induced currents?

PubMed

Berger, R J F; Repisky, M; Komorovsky, S

2015-09-21

Magnetically induced probability currents in molecules are studied in relativistic theory. Spin-orbit coupling (SOC) enhances the curvature and gives rise to a previously unobserved current cusp in AuH or small bulge-like distortions in HgH2 at the proton positions. The origin of this curvature is magnetically induced spin-density arising from SOC in the relativistic description.

Relativistic effects on the bonding and properties of the hydrides of platinum

NASA Technical Reports Server (NTRS)

Dyall, Kenneth G.

1993-01-01

The ground state of PtH2 and several low-lying states of PtH(+) and PtH have been studied at the all-electron self-consistent-field level of theory to examine the importance of relativistic effects. The results of calculations based on Dirac-Hartree-Fock theory, nonrelativistic theory, and the spin-free no-pair relativistic approximation of Hess are compared to separate the effects of the spin-free terms and the spin-orbit terms of the Hamiltonian on the relativistic corrections to the molecular properties. Comparison is also made between first-order perturbation theory including the one-electron spin-free terms and the method of Hess to determine the size of effects beyond first order. It is found that the spin-orbit interaction significantly affects the properties and energetics of these molecules because of the participation of the Pt 5d orbitals in the bonding, and that effects beyond first order in perturbation theory are large. Any treatment of Pt compounds will have to include both the spin-free and spin-orbit interactions for an accurate description.

Spin-Mechanical Inertia in Antiferromagnet

NASA Astrophysics Data System (ADS)

Cheng, Ran; Wu, Xiaochuan; Xiao, Di

Interplay between spin dynamics and mechanical motions is responsible for numerous striking phenomena, which has shaped a rapidly expanding field known as spin-mechanics. The guiding principle of this field has been the conservation of angular momentum that involves both quantum spins and classical mechanical rotations. However, in an antiferromagnet, the macroscopic magnetization vanishes while the order parameter (Néel order) does not carry an angular momentum. It is therefore not clear whether the order parameter dynamics has any mechanical consequence as its ferromagnetic counterparts. Here we demonstrate that the Néel order dynamics affects the mechanical motion of a rigid body by modifying its inertia tensor in the presence of strong magnetocrystalline anisotropy. This effect depends on temperature when magnon excitations are considered. Such a spin-mechanical inertia can produce measurable consequences at nanometer scales. Our discovery establishes spin-mechanical inertia as an essential ingredient to properly describe spin-mechanical effects in AFs, which supplements the known governing physics from angular momentum conservation. This work was supported by the DOE, Basic Energy Sciences, Grant No. DE-SC0012509. D.X. also acknowledges support from a Research Corporation for Science Advancement Cottrell Scholar Award.

IR Studies of the Spin-Nuclear Conversion in the Vicinity of alpha α - beta β - Transition in Cryodeposited Methane Films

NASA Astrophysics Data System (ADS)

Drobyshev, A.; Aldiyarov, A.; Sokolov, D.; Shinbayeva, A.

2017-06-01

Solid methane belongs to a group of crystals containing hydrogen atoms, whose macroscopic properties are greatly influenced by the spin interaction of hydrogen nuclei. In particular, the methane molecule, which has four protons with spin I=1/2, has three total spin modifications: para-, ortho- and meta-states with three values of the total spin moments of 0, 1 and 2, respectively. Equilibrium concentrations of these modifications and relaxation times are dependent on the temperature, affecting the observed thermal properties of solid methane, such as thermal conductivity, specific heat, thermal expansion. In this paper, we attempt to explain the peculiarities of thin film growth of methane at cryogenic temperatures from the viewpoint of spin-nuclear transformations. Our observations of absorption intensity at a frequency corresponding to 1/2 of the absorption band amplitude of deformation vibrations record a step-like change in the position of the absorption band during the sample deposition process. The observed phenomenon, in our opinion, is the demonstration of spin transformations during deposition.

Quantum interference measurement of spin interactions in a bio-organic/semiconductor device structure

DOE PAGES

Deo, Vincent; Zhang, Yao; Soghomonian, Victoria; ...

2015-03-30

Quantum interference is used to measure the spin interactions between an InAs surface electron system and the iron center in the biomolecule hemin in nanometer proximity in a bio-organic/semiconductor device structure. The interference quantifies the influence of hemin on the spin decoherence properties of the surface electrons. The decoherence times of the electrons serve to characterize the biomolecule, in an electronic complement to the use of spin decoherence times in magnetic resonance. Hemin, prototypical for the heme group in hemoglobin, is used to demonstrate the method, as a representative biomolecule where the spin state of a metal ion affects biologicalmore » functions. The electronic determination of spin decoherence properties relies on the quantum correction of antilocalization, a result of quantum interference in the electron system. Spin-flip scattering is found to increase with temperature due to hemin, signifying a spin exchange between the iron center and the electrons, thus implying interactions between a biomolecule and a solid-state system in the hemin/InAs hybrid structure. The results also indicate the feasibility of artificial bioinspired materials using tunable carrier systems to mediate interactions between biological entities.« less

Influences of mass Chlorophyll-a blends using P3HT:PCBM for efficiency of organic solar cells

NASA Astrophysics Data System (ADS)

Lestari, E.; Supriyanto, A.; Iriani, Y.; Ramelan, A. H.; Nurosyid, F.

2017-02-01

Organic solar cells have been made using the material poly (3-hexylthiophene)(P3HT), [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM), and Chlorophyll-a with blend metods. Active layer of P3HT:PCBM:Chlorophyll-a are deposited using spin coating with rotary speed of 2500 rpm for 10 seconds and subsequently heated at 1000C for 10 min. Mass of chlorophyll-a are 0.1 mg, 0.2 mg, and 0.3 mg. Thin layers are characterized by UV-Visible Spectrometer Lamda 25 for optical properties and Keithley 2602 for electrical properties. From the UV-Vis showed that absorbance of P3HT:PCBM:Chlorophyll-a are 400-614nm and 620-700 nm. Efficiency of P3HT:PCBM:Chlorophyll-a for mass chlorophyll 0.1 mg, 0.2 mg, and 0.3 mg are 2.68 x 10-2 %, 3.93 x 10-2 %, and 8.79 x 10-2 % respectively.

A spin labelling study of immunomodulating peptidoglycan monomer and adamantyltripeptides entrapped into liposomes.

PubMed

Frkanec, Ruza; Noethig-Laslo, Vesna; Vranesić, Branka; Mirosavljević, Krunoslav; Tomasić, Jelka

2003-04-01

The interaction of immunostimulating compounds, the peptidoglycan monomer (PGM) and structurally related adamantyltripeptides (AdTP1 and AdTP2), respectively, with phospholipids in liposomal bilayers were investigated by electron paramagnetic resonance spectroscopy. (1). The fatty acids bearing the nitroxide spin label at different positions along the acyl chain were used to investigate the interaction of tested compounds with negatively charged multilamellar liposomes. Electron spin resonance (ESR) spectra were studied at 290 and 310 K. The entrapment of the adamantyltripeptides affected the motional properties of all spin labelled lipids, while the entrapment of PGM had no effect. (2). Spin labelled PGM was prepared and the novel compound bearing the spin label attached via the amino group of diaminopimelic acid was chromatographically purified and chemically characterized. The rotational correlation time of the spin labelled molecule dissolved in buffer at pH 7.4 was studied as a function of temperature. The conformational change was observed above 300 K. The same effect was observed with the spin labelled PGM incorporated into liposomes. Such effect was not observed when the spin labelled PGM was studied at alkaline pH, probably due to the hydrolysis of PGM molecule. The study of possible interaction with liposomal membrane is relevant to the use of tested compounds incorporated into liposomes, as adjuvants in vivo.

Gate fidelity and coherence of an electron spin in an Si/SiGe quantum dot with micromagnet

DOE PAGES

Kawakami, Erika; Jullien, Thibaut; Scarlino, Pasquale; ...

2016-10-03

The gate fidelity and the coherence time of a quantum bit (qubit) are important benchmarks for quantum computation. We construct a qubit using a single electron spin in an Si/SiGe quantum dot and control it electrically via an artificial spin-orbit field from a micromagnet. We measure an average single-qubit gate fidelity of ~99% using randomized benchmarking, which is consistent with dephasing from the slowly evolving nuclear spins in the substrate. The coherence time measured using dynamical decoupling extends up to ~400 μs for 128 decoupling pulses, with no sign of saturation. We find evidence that the coherence time is limitedmore » by noise in the 10-kHz to 1-MHz range, possibly because charge noise affects the spin via the micromagnet gradient. Furthermore, this work shows that an electron spin in an Si/SiGe quantum dot is a good candidate for quantum information processing as well as for a quantum memory, even without isotopic purification.« less

Heat capacity peak at the quantum critical point of the transverse Ising magnet CoNb2O6

PubMed Central

Liang, Tian; Koohpayeh, S. M.; Krizan, J. W.; McQueen, T. M.; Cava, R. J.; Ong, N. P.

2015-01-01

The transverse Ising magnet Hamiltonian describing the Ising chain in a transverse magnetic field is the archetypal example of a system that undergoes a transition at a quantum critical point (QCP). The columbite CoNb2O6 is the closest realization of the transverse Ising magnet found to date. At low temperatures, neutron diffraction has observed a set of discrete collective spin modes near the QCP. Here, we ask if there are low-lying spin excitations distinct from these relatively high-energy modes. Using the heat capacity, we show that a significant band of gapless spin excitations exists. At the QCP, their spin entropy rises to a prominent peak that accounts for 30% of the total spin degrees of freedom. In a narrow field interval below the QCP, the gapless excitations display a fermion-like, temperature-linear heat capacity below 1 K. These novel gapless modes are the main spin excitations participating in, and affected by, the quantum transition. PMID:26146018

Gate fidelity and coherence of an electron spin in an Si/SiGe quantum dot with micromagnet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kawakami, Erika; Jullien, Thibaut; Scarlino, Pasquale

The gate fidelity and the coherence time of a quantum bit (qubit) are important benchmarks for quantum computation. We construct a qubit using a single electron spin in an Si/SiGe quantum dot and control it electrically via an artificial spin-orbit field from a micromagnet. We measure an average single-qubit gate fidelity of ~99% using randomized benchmarking, which is consistent with dephasing from the slowly evolving nuclear spins in the substrate. The coherence time measured using dynamical decoupling extends up to ~400 μs for 128 decoupling pulses, with no sign of saturation. We find evidence that the coherence time is limitedmore » by noise in the 10-kHz to 1-MHz range, possibly because charge noise affects the spin via the micromagnet gradient. Furthermore, this work shows that an electron spin in an Si/SiGe quantum dot is a good candidate for quantum information processing as well as for a quantum memory, even without isotopic purification.« less

Pressure driven spin transition in siderite and magnesiosiderite single crystals.

PubMed

Weis, Christopher; Sternemann, Christian; Cerantola, Valerio; Sahle, Christoph J; Spiekermann, Georg; Harder, Manuel; Forov, Yury; Kononov, Alexander; Sakrowski, Robin; Yavaş, Hasan; Tolan, Metin; Wilke, Max

2017-11-28

Iron-bearing carbonates are candidate phases for carbon storage in the deep Earth and may play an important role for the Earth's carbon cycle. To elucidate the properties of carbonates at conditions of the deep Earth, we investigated the pressure driven magnetic high spin to low spin transition of synthetic siderite FeCO 3 and magnesiosiderite (Mg 0.74 Fe 0.26 )CO 3 single crystals for pressures up to 57 GPa using diamond anvil cells and x-ray Raman scattering spectroscopy to directly probe the iron 3d electron configuration. An extremely sharp transition for siderite single crystal occurs at a notably low pressure of 40.4 ± 0.1 GPa with a transition width of 0.7 GPa when using the very soft pressure medium helium. In contrast, we observe a broadening of the transition width to 4.4 GPa for siderite with a surprising additional shift of the transition pressure to 44.3 ± 0.4 GPa when argon is used as pressure medium. The difference is assigned to larger pressure gradients in case of argon. For magnesiosiderite loaded with argon, the transition occurs at 44.8 ± 0.8 GPa showing similar width as siderite. Hence, no compositional effect on the spin transition pressure is observed. The spectra measured within the spin crossover regime indicate coexistence of regions of pure high- and low-spin configuration within the single crystal.

Investigating spin-transfer torques induced by thermal gradients in magnetic tunnel junctions by using micro-cavity ferromagnetic resonance

NASA Astrophysics Data System (ADS)

Cansever, H.; Narkowicz, R.; Lenz, K.; Fowley, C.; Ramasubramanian, L.; Yildirim, O.; Niesen, A.; Huebner, T.; Reiss, G.; Lindner, J.; Fassbender, J.; Deac, A. M.

2018-06-01

Similar to electrical currents flowing through magnetic multilayers, thermal gradients applied across the barrier of a magnetic tunnel junction may induce pure spin-currents and generate ‘thermal’ spin-transfer torques large enough to induce magnetization dynamics in the free layer. In this study, we describe a novel experimental approach to observe spin-transfer torques induced by thermal gradients in magnetic multilayers by studying their ferromagnetic resonance response in microwave cavities. Utilizing this approach allows for measuring the magnetization dynamics on micron/nano-sized samples in open-circuit conditions, i.e. without the need of electrical contacts. We performed first experiments on magnetic tunnel junctions patterned into 6  ×  9 µm2 ellipses from Co2FeAl/MgO/CoFeB stacks. We conducted microresonator ferromagnetic resonance (FMR) under focused laser illumination to induce thermal gradients in the layer stack and compared them to measurements in which the sample was globally heated from the backside of the substrate. Moreover, we carried out broadband FMR measurements under global heating conditions on the same extended films the microstructures were later on prepared from. The results clearly demonstrate the effect of thermal spin-torque on the FMR response and thus show that the microresonator approach is well suited to investigate thermal spin-transfer-driven processes for small temperatures gradients, far below the gradients required for magnetic switching.

Perpendicular magnetic anisotropy at transition metal/oxide interfaces and applications

NASA Astrophysics Data System (ADS)

Dieny, B.; Chshiev, M.

2017-04-01

Spin electronics is a rapidly expanding field stimulated by a strong synergy between breakthrough basic research discoveries and industrial applications in the fields of magnetic recording, magnetic field sensors, nonvolatile memories [magnetic random access memories (MRAM) and especially spin-transfer-torque MRAM (STT-MRAM)]. In addition to the discovery of several physical phenomena (giant magnetoresistance, tunnel magnetoresistance, spin-transfer torque, spin-orbit torque, spin Hall effect, spin Seebeck effect, etc.), outstanding progress has been made on the growth and nanopatterning of magnetic multilayered films and nanostructures in which these phenomena are observed. Magnetic anisotropy is usually observed in materials that have large spin-orbit interactions. However, in 2002 perpendicular magnetic anisotropy (PMA) was discovered to exist at magnetic metal/oxide interfaces [for instance Co (Fe )/alumina ]. Surprisingly, this PMA is observed in systems where spin-orbit interactions are quite weak, but its amplitude is remarkably large—comparable to that measured at Co /Pt interfaces, a reference for large interfacial anisotropy (anisotropy˜1.4 erg /cm2=1.4 mJ /m2 ). Actually, this PMA was found to be very common at magnetic metal/oxide interfaces since it has been observed with a large variety of amorphous or crystalline oxides, including AlOx, MgO, TaOx, HfOx, etc. This PMA is thought to be the result of electronic hybridization between the oxygen and the magnetic transition metal orbit across the interface, a hypothesis supported by ab initio calculations. Interest in this phenomenon was sparked in 2010 when it was demonstrated that the PMA at magnetic transition metal/oxide interfaces could be used to build out-of-plane magnetized magnetic tunnel junctions for STT-MRAM cells. In these systems, the PMA at the CoFeB /MgO interface can be used to simultaneously obtain good memory retention, thanks to the large PMA amplitude, and a low write current, thanks to a relatively weak Gilbert damping. These two requirements for memories tend to be difficult to reconcile since they rely on the same spin-orbit coupling. PMA-based approaches have now become ubiquitous in the designs for perpendicular STT-MRAM, and major microelectronics companies are actively working on their development with the first goal of addressing embedded FLASH and static random access memory-type of applications. Scalability of STT-MRAM devices based on this interfacial PMA is expected to soon exceed the 20-nm nodes. Several very active new fields of research also rely on interfacial PMA at magnetic metal/oxide interfaces, including spin-orbit torques associated with Rashba or spin Hall effects, record high speed domain wall propagation in buffer/magnetic metal/oxide-based magnetic wires, and voltage-based control of anisotropy. This review deals with PMA at magnetic metal/oxide interfaces from its discovery, by examining the diversity of systems in which it has been observed and the physicochemical methods through which the key roles played by the electronic hybridization at the metal/oxide interface were elucidated. The physical origins of the phenomenon are also covered and how these are supported by ab initio calculations is dealt with. Finally, some examples of applications of this interfacial PMA in STT-MRAM are listed along with the various emerging research topics taking advantage of this PMA.

Optically-pumped spin-exchange polarized electron source

NASA Astrophysics Data System (ADS)

Pirbhai, Munir Hussein

Polarized electron beams are an indispensable probe of spin-dependent phenomena in fields of atomic and molecular physics, magnetism and biophysics. While their uses have become widespread, the standard source based on negative electron affinity gallium arsenide (GaAs) remains technically complicated. This has hindered progress on many experiments involving spin-polarized electrons, especially those using target gas loads, which tend to adversely affect the performance of GaAs sources. A robust system based on an alternative way to make polarized electron beams has been devised in this study, which builds on previous work done in our lab. It involves spin-exchange collisions between free, unpolarized electrons and oriented rubidium atoms in the presence of a quenching gas. This system has less stringent vacuum requirements than those of GaAs sources, and is capable of operating in background pressures of ~1mTorr. Beams with ~24% polarization and 4μA of current have been recorded, which is comparable to the performance obtained with the earlier version built in our lab. The present system is however not as unstable as in the previous work, and has the potential to be developed into a "turn-key" source of polarized electron beams. It has also allowed us to undertake a study to find factors which affect the beam polarization in this scheme of producing polarized electrons. Such knowledge will help us to design better optically-pumped spin-exchange polarized electron sources.

Emotion dynamics and tinnitus: Daily life data from the “TrackYourTinnitus” application

PubMed Central

Probst, Thomas; Pryss, Rüdiger; Langguth, Berthold; Schlee, Winfried

2016-01-01

It is well established that emotions influence tinnitus, but the role of emotion dynamics remains unclear. The present study investigated emotion dynamics in N = 306 users of the “TrackYourTinnitus” application who completed the Mini-Tinnitus Questionnaire (Mini-TQ) at one assessment point and provided complete data on at least five assessment points for the following state variables: tinnitus loudness, tinnitus distress, arousal, valence. The repeated arousal and valence ratings were used for two operationalizations of emotion dynamics: intra-individual variability of affect intensity (pulse) as well as intra-individual variability of affect quality (spin). Pearson correlation coefficients showed that the Mini-TQ was positively correlated with pulse (r = 0.19; p < 0.05) as well as with spin (r = 0.12; p < 0.05). Multilevel models revealed the following results: increases in tinnitus loudness were more strongly associated with increases in tinnitus distress at higher levels of pulse as well as at higher levels of spin (both p < 0.05), whereby increases in tinnitus loudness correlated even stronger with increases in tinnitus distress when both pulse as well as spin were high (p < 0.05). Moreover, increases in spin were associated with a less favorable time course of tinnitus loudness (p < 0.05). To conclude, equilibrating emotion dynamics might be a potential target in the prevention and treatment of tinnitus. PMID:27488227

Relativistic quasiparticle band structures of Mg2Si, Mg2Ge, and Mg2Sn: Consistent parameterization and prediction of Seebeck coefficients

NASA Astrophysics Data System (ADS)

Shi, Guangsha; Kioupakis, Emmanouil

2018-02-01

We apply density functional and many-body perturbation theory calculations to consistently determine and parameterize the relativistic quasiparticle band structures of Mg2Si, Mg2Ge, and Mg2Sn, and predict the Seebeck coefficient as a function of doping and temperature. The quasiparticle band gaps, including spin-orbit coupling effects, are determined to be 0.728 eV, 0.555 eV, and 0.142 eV for Mg2Si, Mg2Ge, and Mg2Sn, respectively. The inclusion of the semicore electrons of Mg, Ge, and Sn in the valence is found to be important for the accurate determination of the band gaps of Mg2Ge and Mg2Sn. We also developed a Luttinger-Kohn Hamiltonian and determined a set of band parameters to model the near-edge relativistic quasiparticle band structure consistently for all three compounds that can be applied for thermoelectric device simulations. Our calculated values for the Seebeck coefficient of all three compounds are in good agreement with the available experimental data for a broad range of temperatures and carrier concentrations. Our results indicate that quasiparticle corrections are necessary for the accurate determination of Seebeck coefficients at high temperatures at which bipolar transport becomes important.

Effect of the stellar spin history on the tidal evolution of close-in planets

NASA Astrophysics Data System (ADS)

Bolmont, E.; Raymond, S. N.; Leconte, J.; Matt, S. P.

2012-08-01

Context. The spin rate of stars evolves substantially during their lifetime, owing to the evolution of their internal structure and to external torques arising from the interaction of stars with their environments and stellar winds. Aims: We investigate how the evolution of the stellar spin rate affects, and is affected by, planets in close orbits via star-planet tidal interactions. Methods: We used a standard equilibrium tidal model to compute the orbital evolution of single planets orbiting both Sun-like stars and very low-mass stars (0.1 M⊙). We tested two stellar spin evolution profiles, one with fast initial rotation (1.2 day rotation period) and one with slow initial rotation (8 day period). We tested the effect of varying the stellar and planetary dissipations, and the planet's mass and initial orbital radius. Results: For Sun-like stars, the different tidal evolution between initially rapidly and slowly rotating stars is only evident for extremely close-in gas giants orbiting highly dissipative stars. However, for very low-mass stars the effect of the initial rotation of the star on the planet's evolution is apparent for less massive (1 M⊕) planets and typical dissipation values. We also find that planetary evolution can have significant effects on the stellar spin history. In particular, when a planet falls onto the star, it can cause the star to spin up. Conclusions: Tidal evolution allows us to differentiate between the early behaviors of extremely close-in planets orbiting either a rapidly rotating star or a slowly rotating star. The early spin-up of the star allows the close-in planets around fast rotators to survive the early evolution. For planets around M-dwarfs, surviving the early evolution means surviving on Gyr timescales, whereas for Sun-like stars the spin-down brings about late mergers of Jupiter planets. In the light of this study, we can say that differentiating one type of spin evolution from another given the present position of planets can be very tricky. Unless we can observe some markers of former evolution, it is nearly impossible to distinguish the two very different spin profiles, let alone intermediate spin-profiles. Nevertheless, some conclusions can still be drawn about statistical distributions of planets around fully convective M-dwarfs. If tidal evolution brings about a merger late in the stellar history, it can also entail a noticeable acceleration of the star at late ages, so that it is possible to have old stars that spin rapidly. This raises the question of how the age of stars can be more tightly constrained.

Effect of heavy metal layer thickness on spin-orbit torque and current-induced switching in Hf|CoFeB|MgO structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akyol, Mustafa; Jiang, Wanjun; Yu, Guoqiang

We study the heavy metal layer thickness dependence of the current-induced spin-orbit torque (SOT) in perpendicularly magnetized Hf broken vertical bar CoFeB broken vertical bar MgO multilayer structures. The damping-like (DL) current-induced SOT is determined by vector anomalous Hall effect measurements. A non-monotonic behavior in the DL-SOT is found as a function of the thickness of the heavy-metal layer. The sign of the DL-SOT changes with increasing the thickness of the Hf layer in the trilayer structure. As a result, in the current-driven magnetization switching, the preferred direction of switching for a given current direction changes when the Hf thicknessmore » is increased above similar to 7 nm. Although there might be a couple of reasons for this unexpected behavior in DL-SOT, such as the roughness in the interfaces and/or impurity based electric potential in the heavy metal, one can deduce a roughness dependence sign reversal in DL-SOT in our trilayer structure.« less

Effect of heavy metal layer thickness on spin-orbit torque and current-induced switching in Hf|CoFeB|MgO structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akyol, Mustafa; Department of Physics, University of Çukurova, Adana 01330; Jiang, Wanjun

We study the heavy metal layer thickness dependence of the current-induced spin-orbit torque (SOT) in perpendicularly magnetized Hf|CoFeB|MgO multilayer structures. The damping-like (DL) current-induced SOT is determined by vector anomalous Hall effect measurements. A non-monotonic behavior in the DL-SOT is found as a function of the thickness of the heavy-metal layer. The sign of the DL-SOT changes with increasing the thickness of the Hf layer in the trilayer structure. As a result, in the current-driven magnetization switching, the preferred direction of switching for a given current direction changes when the Hf thickness is increased above ∼7 nm. Although there might bemore » a couple of reasons for this unexpected behavior in DL-SOT, such as the roughness in the interfaces and/or impurity based electric potential in the heavy metal, one can deduce a roughness dependence sign reversal in DL-SOT in our trilayer structure.« less

Time and spatial evolution of spin-orbit torque-induced magnetization switching in W/CoFeB/MgO structures with various sizes

NASA Astrophysics Data System (ADS)

Zhang, Chaoliang; Fukami, Shunsuke; DuttaGupta, Samik; Sato, Hideo; Ohno, Hideo

2018-04-01

We study spin-orbit torque (SOT) switching in W/CoFeB/MgO structures with various dot sizes (120-3500 nm) using pulsed current of various widths τ (800 ps-100 ms) to examine the time and spatial evolution of magnetization switching. We show that the switching behavior and the resultant threshold switching current density J th strongly depend on device size and pulse width. The switching mode in a 3500 nm dot device changes from probabilistic switching to reproducible partial switching as τ decreases. At τ = 800 ps, J th becomes more than 3 times larger than that in the long-pulse regime. A decrease in dot size to 700 nm does not significantly change the switching characteristics, suggesting that domain-wall propagation among the nucleated multiple domains governs switching. In contrast, devices with further reduced size (120 nm) show normal full switching with increasing probability with current and insignificant dependence of J th on τ, indicating that nucleation governs switching.

Spin-orbit torque induced magnetization switching in Ta/Co{sub 20}Fe{sub 60}B{sub 20}/MgO structures under small in-plane magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, Jiangwei, E-mail: caojw@lzu.edu.cn; Zheng, Yuqiang; Su, Xianpeng

2016-04-25

Spin-orbit torque (SOT)-induced magnetization switching under small in-plane magnetic fields in as-deposited and annealed Ta/CoFeB/MgO structures is studied. For the as-deposited samples, partial SOT-induced switching behavior is observed under an in-plane field of less than 100 Oe. Conversely, for the annealed samples, an in-plane field of 10 Oe is large enough to achieve full deterministic magnetization switching. The Dzyaloshinskii-Moriya interaction at the Ta/CoFeB interface is believed to be the main reason for the discrepancy of the requisite in-plane magnetic fields for switching in the as-deposited and annealed samples. In addition, asymmetric field dependence behavior of SOT-induced magnetization switching is observed in themore » annealed samples. Deterministic magnetization switching in the absence of an external magnetic field is obtained in the annealed samples, which is extremely important to develop SOT-based magnetoresistive random access memory.« less

Current-induced spin-orbit torque switching of perpendicularly magnetized Hf|CoFeB|MgO and Hf|CoFeB|TaO{sub x} structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akyol, Mustafa; Department of Physics, University of Çukurova, Adana 01330; Yu, Guoqiang

2015-04-20

We study the effect of the oxide layer on current-induced perpendicular magnetization switching properties in Hf|CoFeB|MgO and Hf|CoFeB|TaO{sub x} tri-layers. The studied structures exhibit broken in-plane inversion symmetry due to a wedged CoFeB layer, resulting in a field-like spin-orbit torque (SOT), which can be quantified by a perpendicular (out-of-plane) effective magnetic field. A clear difference in the magnitude of this effective magnetic field (H{sub z}{sup FL}) was observed between these two structures. In particular, while the current-driven deterministic perpendicular magnetic switching was observed at zero magnetic bias field in Hf|CoFeB|MgO, an external magnetic field is necessary to switch the CoFeBmore » layer deterministically in Hf|CoFeB|TaO{sub x}. Based on the experimental results, the SOT magnitude (H{sub z}{sup FL} per current density) in Hf|CoFeB|MgO (−14.12 Oe/10{sup 7} A cm{sup −2}) was found to be almost 13× larger than that in Hf|CoFeB|TaO{sub x} (−1.05 Oe/10{sup 7} A cm{sup −2}). The CoFeB thickness dependence of the magnetic switching behavior, and the resulting  H{sub z}{sup FL} generated by in-plane currents are also investigated in this work.« less

Influence of longitudinal spin fluctuations on the phase transition features in chiral magnets

NASA Astrophysics Data System (ADS)

Belemuk, A. M.; Stishov, S. M.

2018-04-01

Using the classical Monte Carlo calculations, we investigate the effects of longitudinal spin fluctuations on the helimagnetic transition in a Heisenberg magnet with the Dzyaloshinskii-Moriya interaction. We use variable spin amplitudes in the framework of the spin-lattice Hamiltonian. It is this kind of fluctuations that naturally occur in an itinerant system. We show that the basic features of the helical phase transition are not changed much by the longitudinal spin fluctuations though the transition temperature Tc and the fluctuation hump seen in specific heat at T >Tc is significantly affected. We report thermodynamic and structural effects of these fluctuations. By increasing the system size in the Monte Carlo modeling, we are able to reproduce the ring shape scattering intensity above the helimagnetic transition temperature Tc, which transforms into the spiral spots seen below Tc in the neutron scattering experiments.

Misrepresentation and distortion of research in biomedical literature

PubMed Central

Boutron, Isabelle; Ravaud, Philippe

2018-01-01

Publication in peer-reviewed journals is an essential step in the scientific process. However, publication is not simply the reporting of facts arising from a straightforward analysis thereof. Authors have broad latitude when writing their reports and may be tempted to consciously or unconsciously “spin” their study findings. Spin has been defined as a specific intentional or unintentional reporting that fails to faithfully reflect the nature and range of findings and that could affect the impression the results produce in readers. This article, based on a literature review, reports the various practices of spin from misreporting by “beautification” of methods to misreporting by misinterpreting the results. It provides data on the prevalence of some forms of spin in specific fields and the possible effects of some types of spin on readers’ interpretation and research dissemination. We also discuss why researchers would spin their reports and possible ways to avoid it. PMID:29531025

Studies on entanglement entropy for Hubbard model with hole-doping and external magnetic field [rapid communication

NASA Astrophysics Data System (ADS)

Yao, K. L.; Li, Y. C.; Sun, X. Z.; Liu, Q. M.; Qin, Y.; Fu, H. H.; Gao, G. Y.

2005-10-01

By using the density matrix renormalization group (DMRG) method for the one-dimensional (1D) Hubbard model, we have studied the von Neumann entropy of a quantum system, which describes the entanglement of the system block and the rest of the chain. It is found that there is a close relation between the entanglement entropy and properties of the system. The hole-doping can alter the charge charge and spin spin interactions, resulting in charge polarization along the chain. By comparing the results before and after the doping, we find that doping favors increase of the von Neumann entropy and thus also favors the exchange of information along the chain. Furthermore, we calculated the spin and entropy distribution in external magnetic filed. It is confirmed that both the charge charge and the spin spin interactions affect the exchange of information along the chain, making the entanglement entropy redistribute.

Computational investigation of spin-polarization in cobalt/graphite superlattices

NASA Astrophysics Data System (ADS)

Goto, Kim F.; Hill, Nicola A.; Sanvito, Stefano

2003-03-01

We present results of a computational investigation of the magnetic properties of cobalt/ graphite superlattices. This work was motivated by experimental data showing spin injection into carbon nanotubes via cobalt contacts [1] as well as the discovery of a magnetic meteorite made from graphite and magnetic particles, in which part of the magnetization is on the carbon atoms [2]. Using density functional theory within the local spin-density approximation (the SIESTA implementation), we show that cobalt induces both n-doping and a magnetic moment in the graphite layers adjacent to the cobalt-carbon interface. We also show that the magnetic properties are strongly affected by the orientation of the graphite. Finally, implications for spin injection and spin-polarized transport are discussed. [1] K. Tsukagoshi, B.W. Alphenaar, and H. Ago, Nature (London) 401, 572 (1999) [2] J.M.D. Coey, M. Venkatesan, C.B. Fitzgerald, A.P. Douvalis and I.S. Sanders, Nature (London) 420, 156 (2002)

The dangerous flat spin and the factors affecting it

NASA Technical Reports Server (NTRS)

Fuchs, Richard; Schmidt, Wilhelm

1931-01-01

This report deals first with the fundamental data required for the investigation. These are chiefly the aerodynamic forces and moments acting on an airplane in a flat spin. It is shown that these forces and moments depend principally on the angle of attack and on the rotation about the path axis, and can therefore either be measured in a wind tunnel or calculated from wind-tunnel measurements of lift, drag and moment about the leading edge of the wing of an airplane model at rest. The lift, drag and moments about the span axis are so greatly altered by the rapid rotation in a flat spin, that they can no longer be regarded as independent of rotation. No substantial change in the angles of attack and glide occurring in a flat spin is involved. The cross-wind force, as compared with the lift and drag, can be disregarded in a flat spin.

Silk screen based dual spin-filter module for perfusion culture of adherent and non-adherent mammalian cells.

PubMed

Kamthan, Shweta; Gomes, James; Roychoudhury, Pradip K

2014-08-01

Spin-filters have been primarily used for producing therapeutic proteins from mammalian cells. However, disposability and/or high filter clogging of the existing spin-filter systems affect the process economy and productivity. Hence, to address these drawbacks a reusable dual spin-filter module for perfusion culture of adherent and non-adherent mammalian cells was designed. Two non-woven Bombyx mori silk layers were used as filter screen; the outer layer was conducive to cell attachment whilst the inner was non-conducive. Adherent cells can be cultured either in suspended mode using its inner single module or as monolayer of cells using its dual concentric module. We achieved 30 % higher urokinase productivity as compared to the stainless-steel spin-filter during perfusion experiments of adherent human kidney cells in suspended mode. This was due to the hydrophobic and negatively-charged silk screen that allows clog-free perfusion culture for prolonged periods.

Low-energy Model for Strongly Correlated Oxides

NASA Astrophysics Data System (ADS)

Liu, Shiu

We provide a detailed derivation of the low-energy model for site-diluted strongly correlated oxides, an example being Zn-diluted La2CuO 4, in the limit of low doping together with a study of the ground-state properties of that model. The generally complicated Hamiltonian on the energy scale of the most relevant atomic orbitals is systematically downfolded to an effective model containing only spin-spin interactions using several techniques. In our study, beginning with the site-diluted three-band Hubbard model for La2ZnxCu(1- x)O4, we first determine the hybridized electronic states of CuO4 and ZnO4 plaquettes within the CuO2 planes utilizing Wannier-orthogonalization of oxygen orbitals and cell-perturbation of the Hamiltonian of each plaquett. Qualitatively, we find that the hybridization of zinc and oxygen orbitals can result in an impurity state with the energy epsilon, which is lower than the effective Hubbard gap U. Then we apply canonical transformation in the limit of the effective hopping integral t << epsilon, U, to obtain the low-energy, spin-only Hamiltonian, which includes terms of the order t2/U, t4/epsilon3, and t 4/Uepsilon2. In other words, besides the usual diluted nearest-neighbor superexchange J-terms of order t2/U, the low-energy model contains impurity-mediated, further-neighbor frustrating interactions among the Cu spins surrounding Zn-sites in an otherwise unfrustrated antiferromagnetic background. These terms, denoted as J'Zn and J''Zn , are of order t4/epsilon3 and can be substantial when epsilon ˜ U/2, the latter value corresponding to the realistic CuO2 parameters. The other further-neighbor Cu spin interactions are of order t 4/U3, which are neglected in both pure and diluted systems, because they are much lesser than J'Zn and J''Zn and independent of impurity concentration. In order to verify this spin-only model, we subsequently apply the T-matrix approach to study the effect of impurities on the antiferromagnetic order parameter. Previous theoretical T-matrix and quantum Monte Carlo (QMC) studies, which include only the dilution effect of impurities, show a large discrepancy with experimental neutron scattering and nuclear quadrupole resonance (NQR) data in the doping dependence of the staggered magnetization at low doping. We demonstrate that this discrepancy is eliminated by including zinc orbitals in the three-band Hubbard model and by including impurity-induced frustrations into the effective spin model with realistic CuO2 parameters. Recent experimental study shows a significantly stronger suppression of spin stiffness in the case of Zn-doped La2CuO4 compared to the Mg-doped case and thus gives a strong support to our theory. Different site-diluting dopants with different electron configurations affect the magnetism of the whole system differently. We argue that the available impurity orbitals are crucial in deriving theoretical models for the site-diluted systems and the proposed impurity-induced frustrations should be important in other strongly correlated oxides and charge-transfer insulators.

Direct measurement of the long-range p -d exchange coupling in a ferromagnet-semiconductor Co/CdMgTe/CdTe quantum well hybrid structure

NASA Astrophysics Data System (ADS)

Akimov, I. A.; Salewski, M.; Kalitukha, I. V.; Poltavtsev, S. V.; Debus, J.; Kudlacik, D.; Sapega, V. F.; Kopteva, N. E.; Kirstein, E.; Zhukov, E. A.; Yakovlev, D. R.; Karczewski, G.; Wiater, M.; Wojtowicz, T.; Korenev, V. L.; Kusrayev, Yu. G.; Bayer, M.

2017-11-01

The exchange interaction between magnetic ions and charge carriers in semiconductors is considered to be a prime tool for spin control. Here, we solve a long-standing problem by uniquely determining the magnitude of the long-range p -d exchange interaction in a ferromagnet-semiconductor (FM-SC) hybrid structure where a 10-nm-thick CdTe quantum well is separated from the FM Co layer by a CdMgTe barrier with a thickness on the order of 10 nm. The exchange interaction is manifested by the spin splitting of acceptor bound holes in the effective magnetic field induced by the FM. The exchange splitting is directly evaluated using spin-flip Raman scattering by analyzing the dependence of the Stokes shift ΔS on the external magnetic field B . We show that in a strong magnetic field, ΔS is a linear function of B with an offset of Δp d=50 -100 μ eV at zero field from the FM induced effective exchange field. On the other hand, the s -d exchange interaction between conduction band electrons and FM, as well as the p -d contribution for free valence band holes, are negligible. The results are well described by the model of indirect exchange interaction between acceptor bound holes in the CdTe quantum well and the FM layer mediated by elliptically polarized phonons in the hybrid structure.

Powder-XRD and (14) N magic angle-spinning solid-state NMR spectroscopy of some metal nitrides.

PubMed

Kempgens, Pierre; Britton, Jonathan

2016-05-01

Some metal nitrides (TiN, ZrN, InN, GaN, Ca3 N2 , Mg3 N2 , and Ge3 N4 ) have been studied by powder X-ray diffraction (XRD) and (14) N magic angle-spinning (MAS) solid-state NMR spectroscopy. For Ca3 N2 , Mg3 N2 , and Ge3 N4 , no (14) N NMR signal was observed. Low speed (νr  = 2 kHz for TiN, ZrN, and GaN; νr  = 1 kHz for InN) and 'high speed' (νr  = 15 kHz for TiN; νr  = 5 kHz for ZrN; νr  = 10 kHz for InN and GaN) MAS NMR experiments were performed. For TiN, ZrN, InN, and GaN, powder-XRD was used to identify the phases present in each sample. The number of peaks observed for each sample in their (14) N MAS solid-state NMR spectrum matches perfectly well with the number of nitrogen-containing phases identified by powder-XRD. The (14) N MAS solid-state NMR spectra are symmetric and dominated by the quadrupolar interaction. The envelopes of the spinning sidebands manifold are Lorentzian, and it is concluded that there is a distribution of the quadrupolar coupling constants Qcc 's arising from structural defects in the compounds studied. Copyright © 2015 John Wiley & Sons, Ltd.

Enhancing the Bounce of a Ball

ERIC Educational Resources Information Center

Cross, Rod

2010-01-01

In sports such as baseball, softball, golf, and tennis, a common objective is to hit the ball as fast or as far as possible. Another common objective is to hit the ball so that it spins as fast as possible, since the trajectory of the ball through the air is strongly affected by ball spin. In an attempt to enhance both the coefficient of…

Theoretical Studies of the Spin Hamiltonian Parameters and Local Distortions for Cu2+ in Alkaline Earth Lead Zinc Phosphate Glasses

NASA Astrophysics Data System (ADS)

Wang, Bo-Kun; Wu, Shao-Yi; Yuan, Zi-Yi; Liu, Zi-Xuan; Jiang, Shi-Xin; Liu, Zheng; Yao, Zi-Jian; Teng, Bao-Hua; Wu, Ming-He

2016-08-01

The spin Hamiltonian parameters and local structures are theoretically studied for Cu2+-doped alkaline earth lead zinc phosphate (RPPZ, R=Mg, Ca, Sr, and Ba) glasses based on the high-order perturbation calculations for a tetragonally elongated octahedral 3d9 cluster. The relative elongation ratios are found to be ρ≈3.2%, 4.4%, 4.6%, and 3.3% for R=Mg, Ca, Sr, and Ba, respectively, because of the Jahn-Teller effect. The whole decreasing crystal-field strength Dq and orbital reduction factor k from Mg to Sr are ascribed to the weakening electrostatic coulombic interactions and the increasing probability of productivity of nonbridge oxygen (and hence increasing Cu2+-O2- electron cloud admixtures) under PbO addition, respectively, with increasing alkali earth ionic radius. The anomalies (the largest Dq and the next highest k among the systems) for R=Ba are attributed to the cross linkage of this large cation in the network. The overall increasing order (Mg≤Ba

Tunable multiphoton Rabi oscillations in an electronic spin system

NASA Astrophysics Data System (ADS)

Bertaina, S.; Groll, N.; Chen, L.; Chiorescu, I.

2011-10-01

We report on multiphoton Rabi oscillations and controlled tuning of a multilevel system at room temperature (S=5/2 for Mn2+:MgO) in and out of a quasiharmonic level configuration. The anisotropy is much smaller than the Zeeman splittings, e.g., the six-level scheme shows only a small deviation from an equidistant diagram. This allows us to tune the spin dynamics by compensating for the cubic anisotropy with either a precise static-field orientation or a microwave field intensity. Using the rotating-frame approximation, the experiments are explained very well by both an analytical model and a generalized numerical model. The calculated multiphoton Rabi frequencies are in excellent agreement with the experimental data.

The structure of Al-23 and astrophysical consequences

NASA Astrophysics Data System (ADS)

Zhai, Yongjun

Motivated by existing nuclear astrophysics problems, the b-decay of the proton rich nucleus 23 Al was studied for the first time with pure samples which were obtained by using the 1 H( 24 Mg, 23 Al)2n reaction and the MARS recoil separator at Texas A&M University. b and b-g coincidence measurements were made with a fast tape-transport system, scintillator, BGO and HPGe g detectors. The experiment allowed us to measure absolute b branching ratios and to determine log ft values for transitions to final states in 23 Mg, including the isobaric analog state (IAS), and, therefore, to determine unambiguously the spin and parity of the 23 Al ground state to be J p = 5/2 + . This work excludes the large increases in the radiative proton capture cross section for the reaction 22 Mg(p,g) 23 Al at astrophysical energies, which were implied by claims that the spin and parity of the 23 Al ground state were J p = 1/2 + . More precise half life and mass determinations of 23 Al were obtained from the experimental data. The log ft for the Fermi transition to its isobaric analog state in 23 Mg was also determined for the first time. This IAS and a state 16 keV below it were observed, well separated in the same experiment for the first time. The b- decay scheme of the proton rich nucleus 23 Al was established. We can now solve a number of inconsistencies in the literature, exclude strong isospin mixing claimed before, and obtain a new determination of the resonance strength. The IAS and the state 16 keV below it are resonances in the 22 Na(p,g) 23 Mg reaction at energies that are important in novae. This second state turns out to be the resonance that gives the most important contribution in the depletion of 22Na from novae. Both of the reactions of 22 Mg(p,g) 23 Al and 22 Na(p,g) 23 Mg have been suggested as possible candidates for diverting some of the flux in oxygen-neon novae explosions from the A=22 into the A=23 mass chain.

Predicition and Discovery of High Tunneling Magnetoresistance in Magnetic Tunnel Junctions with Crystalline Barriers

NASA Astrophysics Data System (ADS)

Butler, William

2005-03-01

Tunneling magnetoresistance in excess of 200% has recently been observed in magnetic tunnel junctions using bcc Fe or bcc CoFe electrodes with crystalline MgO tunnel barriers[1,2]. These results demonstrate that tunneling magnetoresistance depends on more than the ``electrode polarization''. This talk will describe the calculations that predicted high TMR in these and other systems[3,4,5]. These calculations helped us to understand certain principles that may lead to high TMR through coherent electron tunneling. They can be briefly summarized as follows: (1) If the symmetry of a Bloch state can be preserved as electrons cross the interfaces between the electrode and the tunnel barrier, this be used to advantage for spin filtering. (2) Evanescent states of different symmetries decay at different rates in the barrier. (3) Interfacial bonding can be very important in determining the probability that an electron can traverse the interface. (4) Electrons of disallowed symmetry cannot propagate in an electrode. Once these simple principles are understood, simple band codes can be used to screen and to develop heterostructures with the proper symmetries to obtain high TMR. [1] S. S. P. Parkin, C. Kaiser, A. Panchula, P. M. Rice, B. Hughes, M. Samant AND S.-H. Yang, ``Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers,'' Nature Materials, Advance Online Publication [2] S. Yuasa, T. Nagahama, A. Fukushima, Y. Suzuki, K. Ando, ``Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions,'' Nature Materials, Advance Online Publication [3] W. H. Butler, X.-G. Zhang, T. C. Schulthess, and J. M. MacLaren, ``Spin-dependent tunneling conductance of Fe | MgO | Fe sandwiches'' Phys. Rev. B 63, 054416 (2001) [4] J. Mathon, A. Umerski, ``Theory of tunneling magnetoresistance of an epitaxial Fe/MgO/Fe(001) junction,'' Phys. Rev. B 63, 220403(R) (2001). [5] X.-G. Zhang, and W. H. Butler, ``Large magnetoresistance in bcc Co/MgO/Co and FeCo/MgO/FeCo tunnel junctions,'' Phys. Rev. B 70, 172407 (2004)

Atomic origin of the spin-polarization of the Co2FeAl Heusler compound

NASA Astrophysics Data System (ADS)

Liang, Jaw-Yeu; Lam, Tu-Ngoc; Lin, Yan-Cheng; Chang, Shu-Jui; Lin, Hong-Ji; Tseng, Yuan-Chieh

2016-02-01

Using synchrotron x-ray techniques, we studied the Co2FeAl spin-polarization state that generates the half-metallicity of the compound during an A2 (low-spin)  →  B2 (high-spin) phase transition. Given the advantage of element specificity of x-ray techniques, we could fingerprint the structural and magnetic cross-reactions between Co and Fe within a complex Co2FeAl structure deposited on a MgO (0 0 1) substrate. X-ray diffraction and extended x-ray absorption fine structure investigations determined that the Co atoms preferably populate the (1/4,1/4,1/4) and (3/4,3/4,3/4) sites during the development of the B2 phase. X-ray magnetic spectroscopy showed that although the two magnetic elements were ferromagnetically coupled, they interacted in a competing manner via a charge-transfer effect, which enhanced Co spin polarization at the expense of Fe spin polarization during the phase transition. This means that the spin-polarization of Co2FeAl was electronically dominated by Fe in A2 whereas the charge transfer turned the dominance to Co upon B2 formation. Helicity-dependent x-ray absorption spectra also revealed that only the minority state of Co/Fe was involved in the charge-transfer effect whereas the majority state was independent of it. Despite an overall increase of Co2FeAl magnetization, the charge-transfer effect created an undesired trade-off during the Co-Fe exchange interactions, because of the presence of twice as many X sites (Co) as Y sites (Fe) in the Heusler X 2 YZ formula. This suggests that the spin-polarization of Co2FeAl is unfortunately regulated by compromising the enhanced X (Co) sites and the suppressed Y (Fe) sites, irrespective of the development of the previously known high-spin-polarization phase of B2. This finding provides a possible cause for the limited half-metallicity of Co2FeAl discovered recently. Electronic tuning between the X and Y sites is necessary to further increase the spin-polarization, and likely the half-metallicity as well, of the compound.

A nuclear magnetic resonance spectrometer concept for hermetically sealed magic angle spinning investigations on highly toxic, radiotoxic, or air sensitive materials.

PubMed

Martel, L; Somers, J; Berkmann, C; Koepp, F; Rothermel, A; Pauvert, O; Selfslag, C; Farnan, I

2013-05-01

A concept to integrate a commercial high-resolution, magic angle spinning nuclear magnetic resonance (MAS-NMR) probe capable of very rapid rotation rates (70 kHz) in a hermetically sealed enclosure for the study of highly radiotoxic materials has been developed and successfully demonstrated. The concept centres on a conventional wide bore (89 mm) solid-state NMR magnet operating with industry standard 54 mm diameter probes designed for narrow bore magnets. Rotor insertion and probe tuning take place within a hermetically enclosed glovebox, which extends into the bore of the magnet, in the space between the probe and the magnet shim system. Oxygen-17 MAS-NMR measurements demonstrate the possibility of obtaining high quality spectra from small sample masses (~10 mg) of highly radiotoxic material and the need for high spinning speeds to improve the spectral resolution when working with actinides. The large paramagnetic susceptibility arising from actinide paramagnetism in (Th(1-x)U(x))O2 solid solutions gives rise to extensive spinning sidebands and poor resolution at 15 kHz, which is dramatically improved at 55 kHz. The first (17)O MAS-NMR measurements on NpO(2+x) samples spinning at 55 kHz are also reported. The glovebox approach developed here for radiotoxic materials can be easily adapted to work with other hazardous or even air sensitive materials.

Size dependence of vortex-type spin torque oscillation in a Co2Fe0.4Mn0.6Si Heusler alloy disk

NASA Astrophysics Data System (ADS)

Seki, T.; Kubota, T.; Yamamoto, T.; Takanashi, K.

2018-02-01

This paper reports the systematic investigation of vortex-type spin torque oscillation in circular disks of highly spin-polarized Co2Fe0.4Mn0.6Si (CFMS) Heusler alloys. We fabricated the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices with various disk diameters (D) using the layer stack of CFMS/Ag3Mg/CFMS. The gyrotropic motion of the vortex core was successfully excited for the CFMS circular disks with 0.2 µm  ⩽  D  ⩽  0.3 µm. The CPP-GMR device with D  =  0.2 µm exhibited the Q factor of more than 5000 and the large output power of 0.4 nW owing to the high coherency of vortex dynamics and the high spin-polarization of CFMS. However, the Q factor was remarkably decreased as D was reduced from 0.2 µm to 0.14 µm. The comparison with the calculated resonance frequencies suggested that this degradation of the Q factor was due to the transition of the oscillation mode from the vortex mode to other modes such as the low-coherent out-of-plane precession mode. The present experimental results also suggest that there exists an adequate disk size for the enhanced Q factor of the vortex-type spin torque oscillation.

Predictions of the shear response of (Mg,Fe)SiO3 post-perovskite

NASA Astrophysics Data System (ADS)

Metsue, A.; Tsuchiya, T.

2011-12-01

Observation of seismic data put in forth evidence of a spatial anisotropy in the seismic wave velocities in the D'' layer, the lowermost part of the mantle. (Mg,Fe)SiO3 post-perovskite (PPv) is thought to be the most abundant phase in this part of the mantle, and this mineral exhibits a strong elastic anisotropy and may contribute significantly to the seismic anisotropy in the D'' layer. However, the seismic anisotropy cannot be expressed at the rock scale if the orientations of the grains are distributed randomly. Consequently, the formation of lattice preferred orientations with an anisotropic mechanism of plasticity, such as dislocation creep, can cause the seismic anisotropy in the D'' layer. Some experiments have been done on the plasticity of pure and Fe-bearing MgSiO3 post-perovskite and lead to textures of deformation dominated by the (100) and (110) slip planes (Merkel et al., 2007) and by the (001) slip plane (Miyagi et al., 2010). On the other hand, theoretical calculations on the dislocations mobility on pure MgSiO3 (Carrez et al., 2007; Metsue et al., 2009) suggested a texture dominated by the (010) slip plane. A first step to understanding the mechanisms of plasticity and, therefore, the shear wave splitting occurring in the deep Earth is to test the response of the PPv phase to a plastic shear in a geophysical relevant composition. In this study, we present new results from first-principles calculations on the shear response of pure and ferrous iron-bearing MgSiO3 PPv. The originality of this work is the use of internally consistent LSDA+U formalism to accurately describe the local interactions between the d-states of iron. About 8% of iron is incorporated in the high spin state as a Mg substitution defect, since several studies suggest that iron is in the high spin in the D'' layer pressure range (Stackhouse et al., 2006; Metsue and Tsuchiya, 2011). We also performed the calculations for incorporated iron in the low spin state if an eventual spin transition of Fe occurs. The response of the PPv to a plastic shear is investigated at 120 GPa through the calculations of the Generalized Stacking Faults (GSF) energy in pure and iron-bearing systems for ten potential {hkl} slip systems, since these latter are not well constrained for the PPv phase. The GSF energies are obtained by shearing homogeneously half of an infinite crystal over the other half for every slip plane and give the value of the ideal shear stress (ISS), which can be defined as the theoretical elastic limit of the crystal. The [100](001) slip system in pure and iron-bearing phases exhibits the lowest ISS and may play an important role in the plastic deformation of the PPv phase. The activation of this slip system is compatible with the observed shear wave splitting VSH>VSV. We show that incorporation of iron decreases the GSF energy and the ISS of all slip systems. We discuss the plastic anisotropy of pure and iron-bearing phases from the values of the ISS and the orientation of applied tensile stress. Our results suggest that the incorporation of ferrous iron in the PPv phase has a limited effect on its plastic anisotropy.

Thermal Entanglement in XXZ Heisenberg Model for Coupled Spin-Half and Spin-One Triangular Cell

NASA Astrophysics Data System (ADS)

Najarbashi, Ghader; Balazadeh, Leila; Tavana, Ali

2018-01-01

In this paper, we investigate the thermal entanglement of two-spin subsystems in an ensemble of coupled spin-half and spin-one triangular cells, (1/2, 1/2, 1/2), (1/2, 1, 1/2), (1, 1/2, 1) and (1, 1, 1) with the XXZ anisotropic Heisenberg model subjected to an external homogeneous magnetic field. We adopt the generalized concurrence as the measure of entanglement which is a good indicator of the thermal entanglement and the critical points in the mixed higher dimensional spin systems. We observe that in the near vicinity of the absolute zero, the concurrence measure is symmetric with respect to zero magnetic field and changes abruptly from a non-null to null value for a critical magnetic field that can be signature of a quantum phase transition at finite temperature. The analysis of concurrence versus temperature shows that there exists a critical temperature, that depends on the type of the interaction, i.e. ferromagnetic or antiferromagnetic, the anisotropy parameter and the strength of the magnetic field. Results show that the pairwise thermal entanglement depends on the third spin which affects the maximum value of the concurrence at absolute zero and at quantum critical points.

Thermoelastic enhancement of the magnonic spin Seebeck effect in thin films and bulk samples

NASA Astrophysics Data System (ADS)

Chotorlishvili, L.; Wang, X.-G.; Toklikishvili, Z.; Berakdar, J.

2018-04-01

A nonuniform temperature profile may generate a pure spin current in magnetic films, as observed, for instance, in the spin Seebeck effect. In addition, thermally induced elastic deformations may set in that could affect the spin current. A self-consistent theory of the magnonic spin Seebeck effect including thermally activated magnetoelastic effects is presented, and analytical expressions for the thermally activated deformation tensor and dispersion relations for coupled magnetoelastic modes are obtained. We derive analytical results for bulk (three-dimensional) systems and thin magnetic (two-dimensional) films. We observe that the displacement vector and the deformation tensor in bulk systems decay asymptotically as u ˜1 /R2 and ɛ ˜1 /R3 , respectively, while the decays in thin magnetic films proceed slower, following u ˜1 /R and ɛ ˜1 /R2 . The dispersion relations evidence a strong anisotropy in the magnetic excitations. We observe that a thermoelastic steady-state deformation may lead to both an enchantment and a reduction of the gap in the magnonic spectrum. The reduction of the gap increases the number of magnons contributing to the spin Seebeck effect and offers new possibilities for the thermoelastic control of the spin Seebeck effect.

Heisenberg necklace model in a magnetic field

DOE PAGES

Tsvelik, A. M.; Zaliznyak, I. A.

2016-08-26

Here, we study the low-energy sector of the Heisenberg necklace model. Using the field-theory methods, we estimate how the coupling of the electronic spins with the paramagnetic Kondo spins affects the overall spin dynamics and evaluate its dependence on a magnetic field. We are motivated by the experimental realizations of the spin-1/2 Heisenberg chains in SrCuO 2 and Sr 2CuO 3 cuprates, which remain one-dimensional Luttinger liquids down to temperatures much lower than the in-chain exchange coupling J. We also consider the perturbation of the energy spectrum caused by the interaction γ with nuclear spins (I=3/2) present on the samemore » sites. We find that the resulting necklace model has a characteristic energy scale, Λ~J 1/3(γI) 2/3, at which the coupling between (nuclear) spins of the necklace and the spins of the Heisenberg chain becomes strong. Furthermore, this energy scale is insensitive to a magnetic field B. For μBB>Λ we find two gapless bosonic modes that have different velocities, whose ratio at strong fields approaches a universal number, 2√+1.« less

Demonstration of an adaptive response to preconditioning Frankliniella occidentalis (Pergande) to sublethal doses of spinosad: a hormetic-dose response.

PubMed

Gong, Youhui; Xu, Baoyun; Zhang, Youjun; Gao, Xiwu; Wu, Qingjun

2015-07-01

Sublethal doses of some insecticides have been reported to either stimulate or reduce the survival and fecundity of insects. Many sublethal-effect studies have been conducted after exposure of only one generation to sublethal insecticides, and there is little information about the sublethal effects on insects after long-term exposure to sublethal insecticides. In this study, changes in biological characteristics were investigated in spinosad-susceptible (Spin-S) and sublethal-spinosad-treated (Spin-Sub) strains of Frankliniella occidentalis (Pergande) after exposure to their corresponding sublethal concentrations of spinosad. The results showed that for the Spin-S strain, the LC10 concentration of spinosad slightly affected the biotic fitness both in parents and offspring of F. occidentalis. The LC25 concentration of spinosad prolonged the development time, reduced the fecundity, and significantly reduced the intrinsic rate of increase, the net reproductive rate and the finite rate of increase in the Spin-S strain. However, the negative effects were not as pronounced in the offspring (F1 generation) as in the parent generation. For the Spin-Sub strain, the LC10 and LC25 concentrations of spinosad had little negative effect on the development and fecundity, and no significant difference was found between the effects of the LC10 and LC25 treatments on the Spin-Sub strain. The Spin-Sub strain exhibited a shorter developmental time, and larger intrinsic rates of increase and net reproductive rates, compared with the corresponding treatments of the Spin-S strain. These findings combined with our previous studies suggest that the biotic fitness increased in the Spin-Sub strain and the strain became more adaptable to sublethal doses of spinosad, compared with the Spin-S strain. Physiological and biochemical adaptation may contribute to these changes after long treatment times at sublethal doses.

Giant strain control of magnetoelectric effect in Ta|Fe|MgO

PubMed Central

Odkhuu, Dorj

2016-01-01

The exploration of electric field controlled magnetism has come under scrutiny for its intriguing magnetoelectric phenomenon as well as technological advances in spintronics. Herein, the tremendous effect of an epitaxial strain on voltage-controlled perpendicular magnetic anisotropy (VPMA) is demonstrated in a transition-metal|ferromagnet|MgO (TM|FM|MgO) heterostructure from first-principles electronic structure computation. By tuning the epitaxial strain in Ta|Fe|MgO as a model system of TM|FM|MgO, we find distinctly different behaviours of VPMA from V- to Λ-shape trends with a substantially large magnetoelectric coefficient, up to an order of 103 fJV−1m−1. We further reveal that the VPMA modulation under strain is mainly governed by the inherently large spin-orbit coupling of Ta 5d–Fe 3d hybridized orbitals at the TM|FM interface, although the Fe 3d–O 2p hybridization at the FM|MgO interface is partly responsible in determining the PMA of Ta|Fe|MgO. These results suggest that the control of epitaxial strain enables the engineering of VPMA, and provides physical insights for the divergent behaviors of VPMA and magnetoelectric coefficients found in TM|FM|MgO experiments. PMID:27597448

Re-examining the transition into the N = 20 island of inversion: Structure of 30Mg

NASA Astrophysics Data System (ADS)

Fernández-Domínguez, B.; Pietras, B.; Catford, W. N.; Orr, N. A.; Petri, M.; Chartier, M.; Paschalis, S.; Patterson, N.; Thomas, J. S.; Caamaño, M.; Otsuka, T.; Poves, A.; Tsunoda, N.; Achouri, N. L.; Angélique, J.-C.; Ashwood, N. I.; Banu, A.; Bastin, B.; Borcea, R.; Brown, J.; Delaunay, F.; Franchoo, S.; Freer, M.; Gaudefroy, L.; Heil, S.; Labiche, M.; Laurent, B.; Lemmon, R. C.; Macchiavelli, A. O.; Negoita, F.; Paul, E. S.; Rodríguez-Tajes, C.; Roussel-Chomaz, P.; Staniou, M.; Taylor, M. J.; Trache, L.; Wilson, G. L.

2018-04-01

Intermediate energy single-neutron removal from 31Mg has been employed to investigate the transition into the N = 20 island of inversion. Levels up to 5 MeV excitation energy in 30Mg were populated and spin-parity assignments were inferred from the corresponding longitudinal momentum distributions and γ-ray decay scheme. Comparison with eikonal-model calculations also permitted spectroscopic factors to be deduced. Surprisingly, the 02+ level in 30Mg was found to have a strength much weaker than expected in the conventional picture of a predominantly 2 p - 2 h intruder configuration having a large overlap with the deformed 31Mg ground state. In addition, negative parity levels were identified for the first time in 30Mg, one of which is located at low excitation energy. The results are discussed in the light of shell-model calculations employing two newly developed approaches with markedly different descriptions of the structure of 30Mg. It is concluded that the cross-shell effects in the region of the island of inversion at Z = 12 are considerably more complex than previously thought and that np - nh configurations play a major role in the structure of 30Mg.

Laser cooling of MgCl and MgBr in theoretical approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wan, Mingjie; Shao, Juxiang; Huang, Duohui

Ab initio calculations for three low-lying electronic states (X{sup 2}Σ{sup +}, A{sup 2}Π, and 2{sup 2}Π) of MgCl and MgBr molecules, including spin-orbit coupling, are performed using multi-reference configuration interaction plus Davidson correction method. The calculations involve all-electronic basis sets and Douglas–Kroll scalar relativistic correction. Spectroscopic parameters well agree with available theoretical and experimental data. Highly diagonally distributed Franck-Condon factors f{sub 00} for A{sup 2}Π{sub 3/2,1/2} (υ′ = 0) → X{sup 2}Σ{sup +}{sub 1/2} (υ″ = 0) are determined for both MgCl and MgBr molecules. Suitable radiative lifetimes τ of A{sup 2}Π{sub 3/2,1/2} (υ′ = 0) states for rapid lasermore » cooling are also obtained. The proposed laser drives A{sup 2}Π{sub 3/2} (υ′ = 0) → X{sup 2}Σ{sup +}{sub 1/2} (υ″ = 0) transition by using three wavelengths (main pump laser λ{sub 00}; two repumping lasers λ{sub 10} and λ{sub 21}). These results indicate the probability of laser cooling MgCl and MgBr molecules.« less

Odd-Parity Superconductivity near an Inversion Breaking Quantum Critical Point in One Dimension

DOE PAGES

Ruhman, Jonathan; Kozii, Vladyslav; Fu, Liang

2017-05-31

In this work, we study how an inversion-breaking quantum critical point affects the ground state of a one-dimensional electronic liquid with repulsive interaction and spin-orbit coupling. We find that regardless of the interaction strength, the critical fluctuations always lead to a gap in the electronic spin sector. The origin of the gap is a two-particle backscattering process, which becomes relevant due to renormalization of the Luttinger parameter near the critical point. The resulting spin-gapped state is topological and can be considered as a one-dimensional version of a spin-triplet superconductor. Interestingly, in the case of a ferromagnetic critical point, the Luttingermore » parameter is renormalized in the opposite manner, such that the system remains nonsuperconducting.« less

Properties of low-lying intruder states in 34Al and 34Si populated in the beta-decay of 34Mg

NASA Astrophysics Data System (ADS)

Licǎ, R.; Rotaru, F.; Negoitǎ, F.; Grévy, S.; Mǎrginean, N.; Desagne, Ph.; Stora, T.; Borcea, C.; Borcea, R.; Cǎlinescu, S.; Daugas, J. M.; Filipescu, D.; Kuti, I.; Fraile, L. M.; Franchoo, S.; Gheorghe, I.; Ghitǎ, D. G.; Mǎrginean, R.; Mihai, C.; Mourface, P.; Morel, P.; Mrazek, J.; Negret, A.; Pietreanu, D.; Sava, T.; Sohler, D.; Stǎnoiu, M.; Stefan, I.; Şuvǎilǎ, R.; Toma, S.; Ur, C. A.

2015-02-01

The results of the IS530 experiment at ISOLDE revealed new information concerning several nuclei close to the N ≈ 20 'Island of Inversion' - 34Mg , 34Al , 34Si . The half-life of 34Mg was found to be three times larger than the adopted value (63(1) ms instead of 20(10) ms). The beta-gamma spectroscopy of 34Mg performed for the first time in this experiment, led to the first experimental level scheme for 34Al , also showing that the full beta strength goes through the predicted 1+ isomer in 34Al [1] and/or excited states that deexcite to it. The subsequent beta-decay of the 1+ isomer in 34Al allowed the observation of new gamma lines in 34Si , (tentatively) associated with low-spin high-energy excited states previously unobserved.

Ballistic Analysis of New Military Grade Magnesium Alloys for Armor Applications

NASA Astrophysics Data System (ADS)

Jones, Tyrone L.; Kondoh, Katsuyoshi

Since 2006, the U.S. Army has been evaluating magnesium (Mg) alloys for ballistic structural applications. While Mg-alloys have been used in military structural applications since WWII, very little research has been done to improve its mediocre ballistic performance. The Army's need for ultra-lightweight armor systems has led to research and development of high strength, high ductility Mg-alloys. The U.S. Army Research Laboratory contracted through International Technology Center-Pacific Contract Number FA-5209-09-P-0158 with the Joining and Welding Research Instituteof Osaka University to develop the next generation of high strength, high ductility Mg-alloys using a novel Spinning Water Atomization Process for rapid solidification. New alloys AMX602 and ZAXE1711 in extruded bar form were characterized for microstructure, mechanical, and ballistic response. Significant increases in ballistic performance were evident when compared to the baseline alloy AZ31B.

Proton threshold states in the {sup 22}Na(p,{gamma}){sup 23}Mg reaction and astrophysical implications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Comisel, H.; Hategan, C.; Graw, G.

Proton threshold states in {sup 23}Mg are important for the astrophysically relevant proton capture reaction {sup 22}Na(p,{gamma}){sup 23}Mg. In the indirect determination of the resonance strength of the lowest states, which were not accessible by direct methods, some of the spin-parity-assignments remained experimentally uncertain. We have investigated these states with shell model, Coulomb displacement, and Thomas-Ehrman shift calculations. From the comparison of calculated and observed properties, we relate the lowest relevant resonance state at E{sub x}=7643 keV to an excited 3/2{sup +} state in accordance with a recent experimental determination by Jenkins et al. From this we deduce significantly improvedmore » values for the {sup 22}Na(p,{gamma}){sup 23}Mg reaction rate at stellar temperatures below T{sub 9}=0.1 K.« less

Dextromethorphan/quinidine: in pseudobulbar affect.

PubMed

Garnock-Jones, Karly P

2011-05-01

Pseudobulbar affect is characterized by uncontrollable, inappropriate laughing and/or crying that is either unrelated or out of proportion to the emotions felt by the patient and occurs in patients with neurological disorders, such as amyotrophic lateral sclerosis (ALS), multiple sclerosis or traumatic brain injury. Dextromethorphan/quinidine is indicated in the US for the treatment of pseudobulbar affect. Dextromethorphan, when its metabolism is inhibited by the coadministration of quinidine, has been shown to have a positive effect on the symptoms of pseudobulbar affect. Dextromethorphan/quinidine 20 mg/10 mg twice daily was associated with a significantly greater decrease in the rate of pseudobulbar affect episodes per day (primary endpoint) than placebo in the 12-week, randomized, double-blind, placebo-controlled, multicentre STAR trial (Safety, Tolerability, And efficacy Results trial of AVP-923 in PBA [pseudobulbar affect]) involving patients with pseudobulbar affect and ALS or multiple sclerosis. Moreover, the mean change from baseline in Center for Neurologic Study-Lability Scale score at 12 weeks was significantly greater among recipients of dextromethorphan/quinidine 20 mg/10 mg twice daily than those receiving placebo. Dextromethorphan/quinidine 20 mg/10 mg twice daily was generally well tolerated. The drug has been shown to cause dosage-dependent corrected QT interval (QTc) prolongation; however, in the STAR trial, dextromethorphan/quinidine 20 mg/10 mg twice daily appeared to be well tolerated with regard to QTc prolongation.

230% room-temperature magnetoresistance in CoFeB /MgO/CoFeB magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Djayaprawira, David D.; Tsunekawa, Koji; Nagai, Motonobu; Maehara, Hiroki; Yamagata, Shinji; Watanabe, Naoki; Yuasa, Shinji; Suzuki, Yoshishige; Ando, Koji

2005-02-01

Magnetoresistance (MR) ratio up to 230% at room temperature (294% at 20 K) has been observed in spin-valve-type magnetic tunnel junctions (MTJs) using MgO tunnel barrier layer fabricated on thermally oxidized Si substrates. We found that such a high MR ratio can be obtained when the MgO barrier layer was sandwiched with amorphous CoFeB ferromagnetic electrodes. Microstructure analysis revealed that the MgO layer with (001) fiber texture was realized when the MgO layer was grown on amorphous CoFeB rather than on polycrystalline CoFe. Since there have been no theoretical studies on the MTJs with a crystalline tunnel barrier and amorphous electrodes, the detailed mechanism of the huge tunneling MR effect observed in this study is not clear at the present stage. Nevertheless, the present work is of paramount importance in realizing high-density magnetoresistive random access memory and read head for ultra high-density hard-disk drives into practical use.

Research for Brazing Materials of High-Temperature Thermoelectric Modules with CoSb3 Thermoelectric Materials

NASA Astrophysics Data System (ADS)

Lee, Yu Seong; Kim, Suk Jun; Kim, Byeong Geun; Lee, Soonil; Seo, Won-Seon; Kim, Il-Ho; Choi, Soon-Mok

2017-05-01

Metallic glass (MG) can be a candidate for an alternative brazing material of high-temperature thermoelectric modules, since we can expect both a lower brazing temperature and a high operating temperature for the junction from the MG brazers. Another advantage of MG powders is their outstanding oxidation resistance, namely, high-temperature durability in atmosphere. We fabricated three compositions of Al-based MGs—Al-Y-Ni, Al-Y-Ni-Co, and Al-Y-Ni-Co-La—by using the melt spinning process, and their T gs were 273°C, 264°C, and 249°C, respectively. The electrical resistivity of the Al-Y-Ni MG ribbon dropped significantly after annealing at 300°C. The electrical resistivity of crystallized Al-Y-Ni reduced down to 0.03 mΩ cm, which is an order of magnitude lower than that of the amorphous one. After the MG ribbons were pulverized to sub-100 μm, the average particle size was about 400 μm.

Detecting higher spin fields through statistical anisotropy in the CMB and galaxy power spectra

NASA Astrophysics Data System (ADS)

Bartolo, Nicola; Kehagias, Alex; Liguori, Michele; Riotto, Antonio; Shiraishi, Maresuke; Tansella, Vittorio

2018-01-01

Primordial inflation may represent the most powerful collider to test high-energy physics models. In this paper we study the impact on the inflationary power spectrum of the comoving curvature perturbation in the specific model where massive higher spin fields are rendered effectively massless during a de Sitter epoch through suitable couplings to the inflaton field. In particular, we show that such fields with spin s induce a distinctive statistical anisotropic signal on the power spectrum, in such a way that not only the usual g2 M-statistical anisotropy coefficients, but also higher-order ones (i.e., g4 M,g6 M,…,g(2 s -2 )M and g(2 s )M) are nonvanishing. We examine their imprints in the cosmic microwave background and galaxy power spectra. Our Fisher matrix forecasts indicate that the detectability of gL M depends very weakly on L : all coefficients could be detected in near future if their magnitudes are bigger than about 10-3.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gavriliuk, A.G.; Lin, J.F.; Lyubutin, I.S.

The effect of the experimental conditions on the shape of the nuclear resonant forward scattering (NFS) from (Mg{sub 0.75}Fe{sub 0.25})O magnesiowustite has been studied at high pressures up to 100 GPa in diamond anvil cells by the method of the NFS of synchrotron radiation from the Fe-57 nuclei at room temperature. The behavior of the system in the electronic transition of the Fe{sup 2+} ion from the high-spin to low-spin state (spin crossover) near 62 GPa is analyzed as a function of the sample thickness, degree of nonhydrostaticity, and focusing and collimation conditions of a synchrotron beam. It is foundmore » that the inclusion of dynamical beats associated with the sample thickness is very important in the approximation of the experimental NFS spectra. It is shown that the electronic transition occurs in a much narrower pressure range ({+-}6 GPa) rather than in a broad range as erroneously follows from experiments with thick samples under strongly nonhydrostatic conditions.« less

Double-pinned magnetic tunnel junction sensors with spin-valve-like sensing layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Z. H.; Huang, L.; Feng, J. F., E-mail: jiafengfeng@iphy.ac.cn

2015-08-07

MgO magnetic tunnel junction (MTJ) sensors with spin-valve-like sensing layers of Ir{sub 22}Mn{sub 78} (6)/Ni{sub 80}Fe{sub 20} (t{sub NiFe} = 20–70)/Ru (0.9)/Co{sub 40}Fe{sub 40}B{sub 20} (3) (unit: nm) have been fabricated. A linear field dependence of magnetoresistance for these MTJ sensors was obtained by carrying out a two-step field annealing process. The sensitivity and linear field range can be tuned by varying the thickness of NiFe layer and annealing temperature, and a high sensitivity of 37%/mT has been achieved in the MTJ sensors with 70 nm NiFe at the optimum annealing temperature of 230 °C. Combining the spin-valve-like sensing structure and a soft magneticmore » NiFe layer, MTJ sensors with relatively wide field sensing range have been achieved and could be promising for showing high sensitivity magnetic field sensing applications.« less

Interfacial Dzyaloshinskii-Moriya Interaction: Effect of 5 d Band Filling and Correlation with Spin Mixing Conductance

NASA Astrophysics Data System (ADS)

Ma, Xin; Yu, Guoqiang; Tang, Chi; Li, Xiang; He, Congli; Shi, Jing; Wang, Kang L.; Li, Xiaoqin

2018-04-01

The Dzyaloshinskii-Moriya interaction (DMI) at the heavy metal (HM) and ferromagnetic metal (FM) interface has been recognized as a key ingredient in spintronic applications. Here we investigate the chemical trend of DMI on the 5 d band filling (5 d3- 5 d10 ) of the HM element in HM/FM (FM =CoFeB ,Co )/MgO multilayer thin films. DMI is quantitatively evaluated by measuring asymmetric spin wave dispersion using Brillouin light scattering. Sign reversal and 20 times modification of the DMI coefficient D have been measured as the 5 d HM element is varied. The chemical trend can be qualitatively understood by considering the 5 d and 3 d bands alignment at the HM/FM interface and the subsequent orbital hybridization around the Fermi level. Furthermore, a correlation is observed between DMI and effective spin mixing conductance at the HM/FM interfaces. Our results provide new insights into the interfacial DMI for designing future spintronic devices.

First-principles study of high spin-polarization and thermoelectric efficiency of ferromagnetic CoFeCrAs quaternary Heusler alloy

NASA Astrophysics Data System (ADS)

Bhat, Tahir Mohiuddin; Gupta, Dinesh C.

2018-03-01

The ground state properties along with thermodynamic and thermoelectric properties of quaternary CoFeCrAs alloy within the ordered LiMgPdSn-type structure have been investigated by employing first-principles calculations. The alloy offers half-metallic ferromagnet character with an indirect band gap of 1.12 eV in the minority spin state with total spin magnetic moment of 4μB and follows Slater-Pauling relation. Effects on various properties of the material has been studied by the variation of the pressure and temperature. CoFeCrAs tenders large value of the Grüneisen parameter and small value for the thermal expansion coefficient. The materials present high Seebeck coefficient and huge power factor with the room temperature value of ∼-40 μV/K and 18 (1014 μWcm-1 K-2 s-1) respectively, which make CoFeCrAs promising candidate for efficient thermoelectric material.

Homoepitaxial graphene tunnel barriers for spin transport

NASA Astrophysics Data System (ADS)

Friedman, Adam

Tunnel barriers are key elements for both charge-and spin-based electronics, offering devices with reduced power consumption and new paradigms for information processing. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, interface stability, and electronic states that severely complicate fabrication and compromise performance. Graphene is the perfect tunnel barrier. It is an insulator out-of-plane, possesses a defect-free, linear habit, and is impervious to interdiffusion. Nonetheless, true tunneling between two stacked graphene layers is not possible in environmental conditions (magnetic field, temperature, etc.) usable for electronics applications. However, two stacked graphene layers can be decoupled using chemical functionalization. We demonstrate successful tunneling, charge, and spin transport with a fluorinated graphene tunnel barrier on a graphene channel. We show that while spin transport stops short of room temperature, spin polarization efficiency values are the highest of any graphene spin devices. We also demonstrate that hydrogenation of graphene can also be used to create a tunnel barrier. We begin with a four-layer stack of graphene and hydrogenate the top few layers to decouple them from the graphene transport channel beneath. We demonstrate successful tunneling by measuring non-linear IV curves and a weakly temperature dependent zero-bias resistance. We demonstrate lateral transport of spin currents in non-local spin-valve structures and determine spin lifetimes with the non-local Hanle effect to be commensurate with previous studies. The measured spin polarization efficiencies for hydrogenated graphene are higher than most oxide tunnel barriers on graphene, but not as high as with fluorinated graphene tunnel barriers. However, here we show that spin transport persists up to room temperature. Our results for the hydrogenated graphene tunnel barriers are compared with fluorinated tunnel barriers and we discuss the possibility that magnetic moments in the graphene tunnel barriers affect the spin transport of our devices.

Homoepitaxial graphene tunnel barriers for spin transport

NASA Astrophysics Data System (ADS)

Friedman, Adam L.; van't Erve, Olaf M. J.; Robinson, Jeremy T.; Whitener, Keith E.; Jonker, Berend T.

2016-05-01

Tunnel barriers are key elements for both charge-and spin-based electronics, offering devices with reduced power consumption and new paradigms for information processing. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, interface stability, and electronic states that severely complicate fabrication and compromise performance. Graphene is the perfect tunnel barrier. It is an insulator out-of-plane, possesses a defect-free, linear habit, and is impervious to interdiffusion. Nonetheless, true tunneling between two stacked graphene layers is not possible in environmental conditions usable for electronics applications. However, two stacked graphene layers can be decoupled using chemical functionalization. Here, we demonstrate that hydrogenation or fluorination of graphene can be used to create a tunnel barrier. We demonstrate successful tunneling by measuring non-linear IV curves and a weakly temperature dependent zero-bias resistance. We demonstrate lateral transport of spin currents in non-local spin-valve structures, and determine spin lifetimes with the non-local Hanle effect. We compare the results for hydrogenated and fluorinated tunnel and we discuss the possibility that ferromagnetic moments in the hydrogenated graphene tunnel barrier affect the spin transport of our devices.

Correlation Analysis between Spin, Velocity Shear, and Vorticity of Baryonic and Dark Matter Halos

NASA Astrophysics Data System (ADS)

Liu, Li-li

2017-04-01

Based on the cosmological hydrodynamic simulations, we investigate the correlations between the spin, velocity shear and vorticity in dark matter halos, as well as the relationship between the baryonic matter and the dark matter. We find that (1) the difference between the vorticity of baryonic matter and that of dark matter is evident on the scales of < 0.2 h-1 Mpc; (2) the vorticity of baryonic matter exhibits a stronger correlation with the tensor of velocity shear than the vorticity of dark matter does; and (3) the spinning direction of small-mass dark matter halos tends to be parallel to the direction of their host filaments, while the spinning direction of massive dark matter halos tends to be perpendicular to the direction of their host filaments, and the intensity of this kind correlation depends on the size of simulation box, and the simulation accuracy. These factors may cause the relationship between the the spins of dark matter halos and those of galaxies to be complicated, and affect the correlation between the galaxy spins and the nearby large-scale structures.

Magnon Valve Effect between Two Magnetic Insulators.

PubMed

Wu, H; Huang, L; Fang, C; Yang, B S; Wan, C H; Yu, G Q; Feng, J F; Wei, H X; Han, X F

2018-03-02

The key physics of the spin valve involves spin-polarized conduction electrons propagating between two magnetic layers such that the device conductance is controlled by the relative magnetization orientation of two magnetic layers. Here, we report the effect of a magnon valve which is made of two ferromagnetic insulators (YIG) separated by a nonmagnetic spacer layer (Au). When a thermal gradient is applied perpendicular to the layers, the inverse spin Hall voltage output detected by a Pt bar placed on top of the magnon valve depends on the relative orientation of the magnetization of two YIG layers, indicating the magnon current induced by the spin Seebeck effect at one layer affects the magnon current in the other layer separated by Au. We interpret the magnon valve effect by the angular momentum conversion and propagation between magnons in two YIG layers and conduction electrons in the Au layer. The temperature dependence of the magnon valve ratio shows approximately a power law, supporting the above magnon-electron spin conversion mechanism. This work opens a new class of valve structures beyond the conventional spin valves.

Magnon Valve Effect between Two Magnetic Insulators

NASA Astrophysics Data System (ADS)

Wu, H.; Huang, L.; Fang, C.; Yang, B. S.; Wan, C. H.; Yu, G. Q.; Feng, J. F.; Wei, H. X.; Han, X. F.

2018-03-01

The key physics of the spin valve involves spin-polarized conduction electrons propagating between two magnetic layers such that the device conductance is controlled by the relative magnetization orientation of two magnetic layers. Here, we report the effect of a magnon valve which is made of two ferromagnetic insulators (YIG) separated by a nonmagnetic spacer layer (Au). When a thermal gradient is applied perpendicular to the layers, the inverse spin Hall voltage output detected by a Pt bar placed on top of the magnon valve depends on the relative orientation of the magnetization of two YIG layers, indicating the magnon current induced by the spin Seebeck effect at one layer affects the magnon current in the other layer separated by Au. We interpret the magnon valve effect by the angular momentum conversion and propagation between magnons in two YIG layers and conduction electrons in the Au layer. The temperature dependence of the magnon valve ratio shows approximately a power law, supporting the above magnon-electron spin conversion mechanism. This work opens a new class of valve structures beyond the conventional spin valves.

EPR spin probe and spin label studies of some low molecular and polymer micelles

NASA Astrophysics Data System (ADS)

Wasserman, A. M.; Kasaikin, V. A.; Timofeev, V. P.

1998-12-01

The rotational mobility of spin probes of different shape and size in low molecular and polymer micelles has been studied. Several probes having nitroxide fragment localized either in the vicinity of micelle interface or in the hydrocarbon core have been used. Upon increasing the number of carbon atoms in hydrocarbon chain of detergent from 7 to 13 (sodium alkyl sulfate micelles) or from 12 to 16 (alkyltrimethylammonium bromide micelles) the rotational mobility of spin probes is decreased by the factor 1.5-2.0. The spin probe rotational mobility in polymer micelles (the complexes of alkyltrimethylammonium bromides and polymethacrylic or polyacrylic acids) is less than mobility in free micelles of the same surfactants. The study of EPR-spectra of spin labeled polymethacrylic acid (PMA) indicated that formation of water soluble complexes of polymer and alkyltrimethylammonium bromides in alkaline solutions (pH 9) does not affect the polymer segmental mobility. On the other hand, the polymer complexes formation in slightly acidic water solution (pH 6) breaks down the compact PMA conformation, thus increasing the polymer segmental mobility. Possible structures of polymer micelles are discussed.

Measurement of cross relaxation between two selected nuclei by synchronous nutation of magnetization in nuclear magnetic resonance

NASA Astrophysics Data System (ADS)

Burghardt, Irene; Konrat, Robert; Boulat, Benoit; Vincent, Sébastien J. F.; Bodenhausen, Geoffrey

1993-01-01

A novel technique is described that allows one to measure cross-relaxation rates (Overhauser effects) between two selected nuclei in high-resolution NMR. The two chosen sites are irradiated simultaneously with the sidebands of an amplitude-modulated radio-frequency field, so that their magnetization vectors are forced to undergo a simultaneous motion, which is referred to as ``synchronous nutation.'' From the time-dependence observed for different initial conditions, one may derive cross-relaxation rates, and hence determine internuclear distances. The scalar interactions between the selected spins and other spins belonging to the same coupling network are effectively decoupled. Furthermore, cross relaxation to other spins in the environment does not affect the transient response of the selected spins, which are therefore in effect isolated from their environment in terms of dipolar interactions. The method is particularly suitable to study cases where normal Overhauser effects are perturbed by spin-diffusion effects due to the presence of further spins. The technique is applied to the protein bovine pancreatic trypsin inhibitor.

Spin transport properties of n-polyacene molecules (n = 1–15) connected to Ni surface electrodes: Theoretical analysis

PubMed Central

Caliskan, S.; Laref, A.

2014-01-01

Using non-equilibrium Green function formalism in conjunction with density functional theory, we explore the spin-polarized transport characteristics of several planar n-acene molecules suspended between two semi-infinite Ni electrodes via the thiol group. We examine the spin-dependence transport on Ni-n-acenes-Ni junctions, while the number of fused benzene rings varies between 1 and 15. Intriguingly, the induced magnetic moments of small acene molecules are higher than that of longer acene rings. The augmentation of fused benzene rings affects both the magnetic and transport features, such as the transmission function and conductance owing to their coupling to the Ni surface contacts via the anchoring group. The interplay between the spin-polarized transport properties, structural configuration and molecular electronic is a fortiori essential in these attractive molecular devices. Thus, this can conduct to the engineering of the electron spin transport in atomistic and molecular junctions. These prominent molecules convincingly infer that the molecular spin valves can conduct to thriving molecular devices. PMID:25482076

Boosting spin-caloritronic effects by attractive correlations in molecular junctions.

PubMed

Weymann, Ireneusz

2016-01-25

In nanoscopic systems quantum confinement and interference can lead to an enhancement of thermoelectric properties as compared to conventional bulk materials. For nanostructures, such as molecules or quantum dots coupled to external leads, the thermoelectric figure of merit can reach or even exceed unity. Moreover, in the presence of external magnetic field or when the leads are ferromagnetic, an applied temperature gradient can generate a spin voltage and an associated spin current flow in the system, which makes such nanostructures particularly interesting for future thermoelectric applications. In this study, by using the numerical renormalization group method, we examine the spin-dependent thermoelectric transport properties of a molecular junction involving an orbital level with attractive Coulomb correlations coupled to ferromagnetic leads. We analyze how attractive correlations affect the spin-resolved transport properties of the system and find a nontrivial dependence of the conductance and tunnel magnetoresistance on the strength and sign of those correlations. We also demonstrate that attractive correlations can lead to an enhancement of the spin thermopower and the figure of merit, which can be controlled by a gate voltage.

A systematic study of 25Mg NMR in paramagnetic transition metal oxides: applications to Mg-ion battery materials.

PubMed

Lee, Jeongjae; Seymour, Ieuan D; Pell, Andrew J; Dutton, Siân E; Grey, Clare P

2016-12-21

Rechargeable battery systems based on Mg-ion chemistries are generating significant interest as potential alternatives to Li-ion batteries. Despite the wealth of local structural information that could potentially be gained from Nuclear Magnetic Resonance (NMR) experiments of Mg-ion battery materials, systematic 25 Mg solid-state NMR studies have been scarce due to the low natural abundance, low gyromagnetic ratio, and significant quadrupole moment of 25 Mg (I = 5/2). This work reports a combined experimental 25 Mg NMR and first principles density functional theory (DFT) study of paramagnetic Mg transition metal oxide systems Mg 6 MnO 8 and MgCr 2 O 4 that serve as model systems for Mg-ion battery cathode materials. Magnetic parameters, hyperfine shifts and quadrupolar parameters were calculated ab initio using hybrid DFT and compared to the experimental values obtained from NMR and magnetic measurements. We show that the rotor assisted population transfer (RAPT) pulse sequence can be used to enhance the signal-to-noise ratio in paramagnetic 25 Mg spectra without distortions in the spinning sideband manifold. In addition, the value of the predicted quadrupolar coupling constant of Mg 6 MnO 8 was confirmed using the RAPT pulse sequence. We further apply the same methodology to study the NMR spectra of spinel compounds MgV 2 O 4 and MgMn 2 O 4 , candidate cathode materials for Mg-ion batteries.

MgO NPs synthesis, capping and enhanced free radical effect on the bacteria and its cell morphology

NASA Astrophysics Data System (ADS)

Kushwaha, Amisha; Bagchi, T.

2018-05-01

Magnesium Oxide Nanoparticles (MgO NPs) commonly known as Magnesia is a white powder, hygroscopic material. MgO NPs were synthesized through four methods Co-precipitation method (Co-PM), Solution combustion (S-CoM) and Sol-gel method with starch (So-GSM) and CTAB (So-GCM), classified as template dependent and template independent method using magnesium nitrate hexahydrate (Mg(NO3).6H2O) as the precursor and comparative analysis was done through DLS. The order of hydrodynamic diameters of four different synthesis method of MgO NPs is Co-PM LA-MgO NPs> MgO NPs responding.

Representing massive gravitons, as a way to quantify early universe magnetic field contributions to space-time, created by non linear electrodynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beckwith, Andrew Walcott, E-mail: Rwill9955b@gmail.com

We review a relationship between cosmological vacuum energy and massive gravitons as given by Garattini and also the nonlinear electrodynamics of Camara et.al (2004) for a non singular universe and NLED. . In evaluating the Garattini result, we find that having the scale factor close to zero due to a given magnetic field value in, an early universe magnetic field affects how we would interpret Garattini’s linkage of the ‘cosmological constant’ value and non zero graviton mass.. We close as to how these initial conditions affect the issue of an early universe initial pressure and its experimental similarities and differencesmore » with results by Corda and Questa as to negative pressure at the surface of a star. Note, that in theDupays et.al. article , the star in question is rapidly spinning, which is not. assumed in the Camara et.al article , for an early universe. Also, Corda and Questa do not assume a spinning star. We conclude with a comparison between the Lagrangian Dupays and other authors bring up for non linear electrodynamics which is for rapidly spinning neutron stars , and a linkage between the Goldstone theorem and NLED. Our conclusion is for generalizing results seen in the Dupays neutron star Lagrangian with conditions which may confirm C. A. Escobar and L. F. Urrutia’s work on the Goldstone theorem and non linear electrodynamics, for some future projects we have in mind. If the universe does not spin, then we will stick with the density analogy given by adapting density as proportional to one over the fourth power of the minimum value of the scale factor as computed by adaptation of the Camara et.al.(2004) theory for non spinning universes. What may happen is that the Camara (2004) density and Quintessential density are both simultaneously satisfied, which would put additional restrictions on the magnetic field, which is one of our considerations, regardless if a universe spins, akin to spinning neutron stars. The spinning universe though may allow for easier reconciliation of the ‘Goldstone’ behavior of gravity and NLED though.« less

Investigation of Spinning and Tumbling Characteristics of a 1/20-Scale Model of the Consolidated Vultee XFY-1 Airplane in the Free-Spinning Tunnel, TED No. NACA DE 370

NASA Technical Reports Server (NTRS)

Lee, Henry A.

1952-01-01

An investigation has been conducted in the Langley 20-foot free-spinning tunnel on a l/20-scale model of the Consolidated Vultee XFY-1 airplane with a windmilling propeller simulated to determine the effects of control setting and movements upon the erect spin and recovery characteristics for a range of airplane-loading conditions. The effects on the model's spin-recovery characteristics of removing the lower vertical tail, removing the gun pods, and fixing the rudders at neutral were also investigated briefly. The investigation included determination of the size parachute required for emergency recovery from demonstration spins. The tumbling tendencies of the model were also investigated. Brief static force tests were made to determine the aerodynamic characteristics in pitch at high angles of attack. The investigation indicated that the spin and recovery characteristics of the airplane with propeller windmilling will be satisfactory for all loading conditions if recovery is attempted by full rudder reversal accompanied by simultaneous movement of the stick laterally to full with the spin (stick right in a right spin) and longitudinally to neutral. Inverted spins should be satisfactorily terminated by fully reversing the rudder followed immediately by moving the stick laterally towards the forward rudder pedal and longitudinally to neutral. Removal of the gun pods or fixing the rudders at neutral will not adversely affect the airplane's spin-recovery characteristics, but removal of the lower vertical tail will result in unsatisfactory spin-recovery characteristics. The model-test results showed that a 13.3-foot wing-tip conventional parachute (drag coefficient approximately 0.7) should be effective as an emergency spin-recovery device during demonstration spins of the airplane. It was indicated that the airplane should not tumble and that no unusual longitudinal-trim characteristics should be obtained for the center-of-gravity positions investigated.

MDMA ‘ecstasy’ increases cerebral cortical perfusion determined by bolus-tracking arterial spin labelling (btASL) MRI

PubMed Central

Rouine, J; Gobbo, O L; Campbell, M; Gigliucci, V; Ogden, I; McHugh Smith, K; Duffy, P; Behan, B; Byrne, D; Kelly, M E; Blau, C W; Kerskens, C M; Harkin, A

2013-01-01

Background and Purpose The purpose of this study was to assess cerebral perfusion changes following systemic administration of the recreational drug 3,4-methylendioxymethamphetamine (MDMA ‘ecstasy’) to rats. Experimental Approach Cerebral perfusion was quantified using bolus-tracking arterial spin labelling (btASL) MRI. Rats received MDMA (20 mg·kg−1; i.p.) and were assessed 1, 3 or 24 h later. Rats received MDMA (5 or 20 mg·kg−1; i.p.) and were assessed 3 h later. In addition, rats received MDMA (5 or 10 mg·kg−1; i.p.) or saline four times daily over 2 consecutive days and were assessed 8 weeks later. Perfusion-weighted images were generated in a 7 tesla (7T) MRI scanner and experimental data was fitted to a quantitative model of cerebral perfusion to generate mean transit time (MTT), capillary transit time (CTT) and signal amplitude. Key Results MDMA reduces MTT and CTT and increases amplitude in somatosensory and motor cortex 1 and 3 h following administration, indicative of an increase in perfusion. Prior exposure to MDMA provoked a long-term reduction in cortical 5-HT concentration, but did not produce a sustained effect on cerebral cortical perfusion. The response to acute MDMA challenge (20 mg·kg−1; i.p.) was attenuated in these animals indicating adaptation in response to prior MDMA exposure. Conclusions and Implications MDMA provokes changes in cortical perfusion, which are quantifiable by btASL MRI, a neuroimaging tool with translational potential. Future studies are directed towards elucidation of the mechanisms involved and correlating changes in cerebrovascular function with potential behavioural deficits associated with drug use. PMID:23517012

Study on glass-forming ability and hydrogen storage properties of amorphous Mg{sub 60}Ni{sub 30}La{sub 10−x}Co{sub x} (x = 0, 4) alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lv, Peng; Wang, Zhong-min, E-mail: zmwang@guet.edu.cn; Zhang, Huai-gang

2013-12-15

Mg{sub 60}Ni{sub 30}La{sub 10−x}Co{sub x} (x = 0, 4) amorphous alloys were prepared by rapid solidification, using a melt-spinning technique. X-ray diffraction and differential scanning calorimetry analysis were employed to measure their microstructure, thermal stability and glass-forming ability, and hydrogen storage properties were studied by means of PCTPro2000. Based on differential scanning calorimetry results, their glass-forming ability and thermal stability were investigated by Kissinger method, Lasocka curves and atomic cluster model, respectively. The results indicate that glass-forming ability, thermal properties and hydrogen storage properties in the Mg-rich corner of Mg–Ni–La–Co system alloys were enhanced by Co substitution for La. Itmore » can be found that the smaller activation energy (ΔΕ) and frequency factor (υ{sub 0}), the bigger value of B (glass transition point in Lasocka curves), and higher glass-forming ability of Mg–Ni–La–Co alloys would be followed. In addition, atomic structure parameter (λ), deduced from atomic cluster model is valuable in the design of Mg–Ni–La–Co system alloys with good glass-forming ability. With an increase of Co content from 0 to 4, the hydrogen desorption capacity within 4000 s rises from 2.25 to 2.85 wt.% at 573 K. - Highlights: • Amorphous Mg{sub 60}Ni{sub 30}La{sub 10−x}Co{sub x} (x = 0 and 4) alloys were produced by melt spinning. • The GFA and hydrogen storage properties were enhanced by Co substitution for La. • With an increase of Co content, the hydrogen desorption capacity rises at 573 K.« less

Isotopically Heavy Low-Spin Iron in Ferropericlase at the Core-Mantle Boundary

NASA Astrophysics Data System (ADS)

Yang, H.; Lin, J. F.; Dauphas, N.; Bi, W.; Zhao, J.

2016-12-01

The iron isotope fractionation between metal and silicate at high pressure is of great interest for it is potentially responsible for the iron isotopic difference between the 2 main iron reservoir —the mantle and the core and therefore vital for estimating the bulk iron isotopic composition of the Earth. In 2009, Polyakov pioneered the use of NRIXS(Nuclear Resonant Inelastic X-ray Scat- tering) technique to investigate iron isotope fractionation at core-mantle boundary. This synchr- otron-based technique is excellent in that it can be applied to samples loaded in DACs with tens of um in size and one doesn't needs to put minerals together to reach isotope exchange equilib- rium. However, the NRIXS data used in Polyakov(2009) was scanned over a limited energy range and thus is not suitable for isotope fractionation at high pressure: the phonon modes shift with increasing pressure and a scanned energy range over 100meV is necessary. Recently, Shahar and co-workers(2016) used NRIXS with a wider energy scan range and DFT simulation to estimate the light element alloying effect on iron bonding environment at high pressure. They found that C or H may not be a major light element in the core considering only bridgmanite as a proxy of the mantle, but another lower mantle mineral ferropericlase was not taken into account. Here we report newly collected NRIXS data at sector-3 of the Advanced Photon Source. >95% 57Fe enriched powder ferropericlase((Fe0.25,Mg0.75)O) was loaded in 3-fold panoramic DACs us- ing Be gasket and c-BN insert as windows for X-ray fluorescence. The NRIXS spectra of ferroperic- lase were measured up to 94GPa across the spin transition zone. We found that the spin state of iron dramatically influences its force constants at high pressure. Low-spin iron force constants incr- ease 3 times faster than high-spin iron with pressure. Assuming linear relationship between force constants and pressure, this will lead to a fractionation of 0.147 (delta57Fe/54Fe) between ferrop- ericlase and iron metal at the core-mantle boundary conditions (4000K and 135GPa). The partition coefficient KD of Fe/Mg between bridgmanite and ferropericlase decreases with the spin transition of iron, therefore the ferropericlase would be a major iron carrier at the core-mantle boundary and fur- ther emphasize the results here.

Dirac cones in artificial structures of 3d transitional-metals doped Mg-Al spinels

NASA Astrophysics Data System (ADS)

Lu, Yuan; Feng, Min; Shao, Bin; Zuo, Xu

2014-05-01

Motivated by recent theoretical predications for Dirac cone in two-dimensional (2D) triangular lattice [H. Ishizuka, Phys. Rev. Lett. 109, 237207 (2012)], first-principles studies are performed to predict Dirac cones in artificial structures of 3d transitional-metals (TM = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) doped Mg-Al spinels. In investigated artificial structures, TM dopants substitute specific positions of the B sub-lattice in Mg-Al spinel, and form a quasi-2D triangular lattice in the a-b plane. Calculated results illustrate the existence of the spin-polarized Dirac cones formed in d-wave bands at (around) the K-point in the momentum space. The study provides a promising route for engineering Dirac physics in condensed matters.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kostylev, M.

In this work, we derive the interface exchange boundary conditions for the classical linear dynamics of magnetization in ferromagnetic layers with the interface Dzyaloshinskii-Moriya interaction (IDMI). We show that IDMI leads to pinning of dynamic magnetization at the interface. An unusual peculiarity of the IDMI-based pinning is that its scales as the spin-wave wave number. We incorporate these boundary conditions into an existing numerical model for the dynamics of the Damon-Eshbach spin wave in ferromagnetic films. IDMI affects the dispersion and the frequency non-reciprocity of the travelling Damon-Eshbach spin wave. For a broad range of film thicknesses L and wavemore » numbers, the results of the numerical simulations of the spin wave dispersion are in a good agreement with a simple analytical expression, which shows that the contribution of IDMI to the dispersion scales as 1/L, similarly to the effect of other types of interfacial anisotropy. Suggestions to experimentalists how to detect the presence of IDMI in a spin wave experiment are given.« less

Influence of Molecular Oxygen on Ortho-Para Conversion of Water Molecules

NASA Astrophysics Data System (ADS)

Valiev, R. R.; Minaev, B. F.

2017-07-01

The mechanism of influence of molecular oxygen on the probability of ortho-para conversion of water molecules and its relation to water magnetization are considered within the framework of the concept of paramagnetic spin catalysis. Matrix elements of the hyperfine ortho-para interaction via the Fermi contact mechanism are calculated, as well as the Maliken spin densities on water protons in H2O and O2 collisional complexes. The mechanism of penetration of the electron spin density into the water molecule due to partial spin transfer from paramagnetic oxygen is considered. The probability of ortho-para conversion of the water molecules is estimated by the quantum chemistry methods. The results obtained show that effective ortho-para conversion of the water molecules is possible during the existence of water-oxygen dimers. An external magnetic field affects the ortho-para conversion rate given that the wave functions of nuclear spin sublevels of the water protons are mixed in the complex with oxygen.

Perforated cenosphere-supported pH-sensitive spin probes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fomenko, E.V.; Bobko, A.A.; Salanov, A.N.

2008-03-15

Porous supports with an accessible internal volume and a shell providing the diffusive migration of pH-sensitive spin probes were obtained for the first time from hollow aluminosilicate cenospheres isolated from the coal fly ash. Using the methods of scanning electron microscopy and electron spin resonance, the morphology of different porous cenosphere modifications and its influence on the diffusion of spin probes from the internal volume were studied. When supporting aqueous solutions of a radical, the characteristic diffusion time for the mesoporous structure of the support is longer by a factor of 3-5 than that for the macroporous structure. Ferrospinel inmore » a content of 6 wt.% do not virtually affect the diffusion rate of spin probes. A constant rate of radical migration of similar to 1 {mu} mol min{sup -1}, determined by radical solubility in water, is achieved when a radical in the solid aggregate state is supported on the magnetic cenospheres.« less

Solid-state dynamic nuclear polarization at 263 GHz: spectrometer design and experimental results†

PubMed Central

Rosay, Melanie; Tometich, Leo; Pawsey, Shane; Bader, Reto; Schauwecker, Robert; Blank, Monica; Borchard, Philipp M.; Cauffman, Stephen R.; Felch, Kevin L.; Weber, Ralph T.; Temkin, Richard J.; Griffin, Robert G.; Maas, Werner E.

2015-01-01

Dynamic Nuclear Polarization (DNP) experiments transfer polarization from electron spins to nuclear spins with microwave irradiation of the electron spins for enhanced sensitivity in nuclear magnetic resonance (NMR) spectroscopy. Design and testing of a spectrometer for magic angle spinning (MAS) DNP experiments at 263 GHz microwave frequency, 400 MHz 1H frequency is described. Microwaves are generated by a novel continuous-wave gyrotron, transmitted to the NMR probe via a transmission line, and irradiated on a 3.2 mm rotor for MAS DNP experiments. DNP signal enhancements of up to 80 have been measured at 95 K on urea and proline in water–glycerol with the biradical polarizing agent TOTAPOL. We characterize the experimental parameters affecting the DNP efficiency: the magnetic field dependence, temperature dependence and polarization build-up times, microwave power dependence, sample heating effects, and spinning frequency dependence of the DNP signal enhancement. Stable system operation, including DNP performance, is also demonstrated over a 36 h period. PMID:20449524

Ground-state properties of neutron-rich Mg isotopes

NASA Astrophysics Data System (ADS)

Watanabe, S.; Minomo, K.; Shimada, M.; Tagami, S.; Kimura, M.; Takechi, M.; Fukuda, M.; Nishimura, D.; Suzuki, T.; Matsumoto, T.; Shimizu, Y. R.; Yahiro, M.

2014-04-01

We analyze recently measured total reaction cross sections for 24-38Mg isotopes incident on 12C targets at 240 MeV/nucleon by using the folding model and antisymmetrized molecular dynamics (AMD). The folding model well reproduces the measured reaction cross sections, when the projectile densities are evaluated by the deformed Woods-Saxon (def-WS) model with AMD deformation. Matter radii of 24-38Mg are then deduced from the measured reaction cross sections by fine tuning the parameters of the def-WS model. The deduced matter radii are largely enhanced by nuclear deformation. Fully microscopic AMD calculations with no free parameter well reproduce the deduced matter radii for 24-36Mg, but still considerably underestimate them for 37,38Mg. The large matter radii suggest that 37,38Mg are candidates for deformed halo nucleus. AMD also reproduces other existing measured ground-state properties (spin parity, total binding energy, and one-neutron separation energy) of Mg isotopes. Neutron-number (N) dependence of deformation parameter is predicted by AMD. Large deformation is seen from 31Mg with N =19 to a drip-line nucleus 40Mg with N =28, indicating that both the N =20 and 28 magicities disappear. N dependence of neutron skin thickness is also predicted by AMD.

Losses Disguised as Wins Affect Game Selection on Multiline Slots.

PubMed

Graydon, Candice; Stange, Madison; Dixon, Mike J

2018-05-05

Multiline slots are exciting games that contain features which make them alluring. One such feature is a loss disguised as a win (LDW); wherein, players win less than they wager (e.g., bet 2 dollars, win back 50 cents), but this net loss is disguised by flashing graphics and winning sounds. Research to date concludes that LDWs are both rewarding and reinforcing. Here, we investigated whether LDWs affect players' game selection. Thirty-two undergraduate students with experience playing slot machines played 100 spins on four games-two had positive payback percentages (115%) and two had negative payback percentages (85%) after 100 spins. For each payback percentage condition, there was a game with no LDWs and a game with a moderate number of LDWs. For the 100 spins, players could choose to play whichever game they wished. They then rated their preference for each game following the 100-spins and chose a game to continue playing. The majority of players preferred playing the positive payback percentage game with LDWs and chose to continue playing this game over the three other games. We conclude that in addition to LDWs being reinforcing and rewarding, LDWs do in fact influence game selection. We conclude that responsible gambling initiatives should educate players about LDWs.

Role of the Heavy Metal's Crystal Phase in Oscillations of Perpendicular Magnetic Anisotropy and the Interfacial Dzyaloshinskii-Moriya Interaction in W /Co -Fe -B /MgO Films

NASA Astrophysics Data System (ADS)

Kim, Gyu Won; Samardak, Alexander S.; Kim, Yong Jin; Cha, In Ho; Ognev, Alexey V.; Sadovnikov, Alexandr V.; Nikitov, Sergey A.; Kim, Young Keun

2018-06-01

The interfacial Dzyaloshinskii-Moriya interaction (IDMI) generally arises in "heavy-metal-ferromagnet" (HM-FM) heterostructures due the strong spin-orbit coupling in HMs and plays a crucial role in the nucleation of Dzyaloshinskii domain walls and Skyrmions that can be efficiently moved by spin-orbit torques. We study the IDMI in W /Co -Fe -B /MgO /Ta films with perpendicular magnetic anisotropy for different crystal structures and thicknesses of W layers treated by postsputtering annealing at 300 °C and 400 °C . We employ Brillouin light scattering spectroscopy to precisely measure the energy density and sign of the IDMI. We reveal two peaks associated with the IDMI: one for the amorphouslike phase of W, and another for α -W . The samples with pure β -W underlayers show the smallest values of IDMI. The sign of the IDMI is positive for all samples with the observed maximum effective and surface values of Deff=0.88 erg /cm2 and Ds=0.51 ×10-7 erg /cm , respectively. We report on the oscillating behavior of the IDMI as a function of thickness, which correlates with the surface anisotropy energy demonstrating common spin-orbit coupling and a robust dependence on the structural properties of the materials used. We ascribe the oscillations of the surface anisotropy and the IDMI mainly to the near inversely proportional dependence on the squared interatomic distance between the HM and FM atoms promoted by the thickness-driven crystal phase formation of W.

Muon spin relaxation study of spin dynamics in the extended kagome systems YBaCo 4 O 7 + δ   ( δ = 0 , 0.1 )

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, S.; Lee, Wonjun; Lee, K. J.

Here, we present muon spin relaxation (μSR) measurements of the extended kagome systems YBaCo 4O 7+δ (δ = 0,0.1), comprising two interpenetrating kagome sublattice of Co(I) 3+ (S = 3/2) and a triangle sublattice of Co(II) 2+ (S = 2). The zero- and longitudinal-field μ SR spectra of the stoichiometric compound YBaCo 4O 7 unveil that the triangular subsystem orders at TN = 101 K. In contrast, the muon spin relaxation rate pertaining to the kagome subsystem shows persistent spin dynamics down to T = 20 K and then a sublinear decrease λ(T ) ~ T 0.66(5) on cooling towardsmore » T = 4 K. In addition, the introduction of interstitial oxygen (δ = 0.1) is found to drastically affect the magnetism. For the fast-cooling experiment (>10 K/min), YBaCo 4O 7.1 enters a regime characterized by persistent spin dynamics below 90 K. For the slow-cooling experiment (1 K/min), evidence is obtained for the phase separation into interstitial oxygen-poor and oxygen-rich regions with distinct correlation times. The observed temperature, cooling rate, and oxygen content dependencies of spin dynamics are discussed in terms of a broad range of spin-spin correlation times, relying on a different degree of frustration between the kagome and triangle sublattices as well as of oxygen migration.« less

Isotropic and anisotropic regimes of the field-dependent spin dynamics in Sr 2 IrO 4 : Raman scattering studies

DOE PAGES

Gim, Y.; Sethi, A.; Zhao, Q.; ...

2016-01-11

A major focus of experimental interest in Sr 2IrO 4 has been to clarify how the magnetic excitations of this strongly spin-orbit coupled system differ from the predictions of an isotropic 2D spin-1/2 Heisenberg model and to explore the extent to which strong spin-orbit coupling affects the magnetic properties of iridates. Here, we present a high-resolution inelastic light (Raman) scattering study of the low energy magnetic excitation spectrum of Sr 2IrO 4 and doped Eu-doped Sr 2IrO 4 as functions of both temperature and applied magnetic field. We show that the high-field (H > 1.5 T) in-plane spin dynamics ofmore » Sr 2IrO 4 are isotropic and governed by the interplay between the applied field and the small in-plane ferromagnetic spin components induced by the Dzyaloshinskii-Moriya interaction. However, the spin dynamics of Sr 2IrO 4 at lower fields (H < 1.5 T) exhibit important effects associated with interlayer coupling and in-plane anisotropy, including a spin-flop transition at Hc in Sr 2IrO 4 that occurs either discontinuously or via a continuous rotation of the spins, depending upon the in-plane orientation of the applied field. Furthermore, these results show that in-plane anisotropy and interlayer coupling effects play important roles in the low-field magnetic and dynamical properties of Sr 2IrO 4.« less

Muon spin relaxation study of spin dynamics in the extended kagome systems YBaCo 4 O 7 + δ   ( δ = 0 , 0.1 )

DOE PAGES

Lee, S.; Lee, Wonjun; Lee, K. J.; ...

2018-03-15

Here, we present muon spin relaxation (μSR) measurements of the extended kagome systems YBaCo 4O 7+δ (δ = 0,0.1), comprising two interpenetrating kagome sublattice of Co(I) 3+ (S = 3/2) and a triangle sublattice of Co(II) 2+ (S = 2). The zero- and longitudinal-field μ SR spectra of the stoichiometric compound YBaCo 4O 7 unveil that the triangular subsystem orders at TN = 101 K. In contrast, the muon spin relaxation rate pertaining to the kagome subsystem shows persistent spin dynamics down to T = 20 K and then a sublinear decrease λ(T ) ~ T 0.66(5) on cooling towardsmore » T = 4 K. In addition, the introduction of interstitial oxygen (δ = 0.1) is found to drastically affect the magnetism. For the fast-cooling experiment (>10 K/min), YBaCo 4O 7.1 enters a regime characterized by persistent spin dynamics below 90 K. For the slow-cooling experiment (1 K/min), evidence is obtained for the phase separation into interstitial oxygen-poor and oxygen-rich regions with distinct correlation times. The observed temperature, cooling rate, and oxygen content dependencies of spin dynamics are discussed in terms of a broad range of spin-spin correlation times, relying on a different degree of frustration between the kagome and triangle sublattices as well as of oxygen migration.« less

Optimization of transversal relaxation of nitroxides for pulsed electron-electron double resonance spectroscopy in phospholipid membranes.

PubMed

Dastvan, Reza; Bode, Bela E; Karuppiah, Muruga Poopathi Raja; Marko, Andriy; Lyubenova, Sevdalina; Schwalbe, Harald; Prisner, Thomas F

2010-10-28

Pulsed electron-electron double resonance (PELDOR) spectroscopy is increasingly applied to spin-labeled membrane proteins. However, after reconstitution into liposomes, spin labels often exhibit a much faster transversal relaxation (T(m)) than in detergent micelles, thus limiting application of the method in lipid bilayers. In this study, the main reasons for enhanced transversal relaxation in phospholipid membranes were investigated systematically by use of spin-labeled derivatives of stearic acid and phosphatidylcholine as well as spin-labeled derivatives of the channel-forming peptide gramicidin A under the conditions typically employed for PELDOR distance measurements. Our results clearly show that dephasing due to instantaneous diffusion that depends on dipolar interaction among electron spins is an important contributor to the fast echo decay in cases of high local concentrations of spin labels in membranes. The main difference between spin labels in detergent micelles and membranes is their local concentration. Consequently, avoiding spin clustering and suppressing instantaneous diffusion is the key step for maximizing PELDOR sensitivity in lipid membranes. Even though proton spin diffusion is an important relaxation mechanism, only in samples of low local concentrations does deuteration of acyl chains and buffer significantly prolong T(m). In these cases, values of up to 7 μs have been achieved. Furthermore, our study revealed that membrane composition and labeling position in the membrane can also affect T(m), either by promoting the segregation of spin-labeled species or by altering their exposure to matrix protons. Effects of other experimental parameters including temperature (<50 K), presence of oxygen, and cryoprotectant type are negligible under our experimental conditions.

Quantitative detection of the respective concentrations of chiral compounds with weak measurements

NASA Astrophysics Data System (ADS)

Xie, Linguo; Qiu, Xiaodong; Luo, Lan; Liu, Xiong; Li, Zhaoxue; Zhang, Zhiyou; Du, Jinglei; Wang, Deqiang

2017-11-01

In this letter, we determine the respective concentrations of glucose and fructose in the mixed chiral solution by simultaneously measuring the optical rotation angle (ORA) and the refractive index change (RIC) with weak measurements. The photonic spin Hall effect (PSHE) serves as a probe in our scheme. The measurement of ORA is based on the high sensitivity of the amplification factor to the polarization state in weak measurements. The measurement of RIC is based on the rapid variation of spin splitting of the PSHE. The measurement precision of the respective concentrations can be achieved to be 0.02 mg/ml. This method can detect traces of enantiomeric impurities and has a potential application in chiral sensing.

General pharmacological properties of YJA 20379-1, a novel proton pump inhibitor with antiulcer activities.

PubMed

Lee, E B; Cho, S I; Cheon, S A; Chang, M S; Kim, K B; Sohn, S K; Chung, Y K

1999-12-01

The general pharmacological properties of YJA 20379-1 (2-amino-4,5-dihydro-8-phenylimidazo[2,1-b]thiazolo[4,5-g]benzo thi azole), a novel proton pump inhibitor with antiulcer activities, were investigated in mice, rats, guinea pig and rabbits. YJA 20379-1 at oral doses of 50, 100 and 200 mg/kg did not affect the general behaviour, hexobarbital hypnosis, motor coordination and body temperature in mice. The drug does not have analgesic and anticonvulsant action at 200 mg/kg p.o. The locomotor activity was not affected at 100 mg/kg p.o., but at 200 mg/kg, the activity was suppressed. YJA 20379-1 (at 2 x 10(-4) g/ml) did neither produce any contraction nor relaxation of isolated organs such as rat fundus, rat uterus, guinea pig ileum and guinea pig vas deferens, and the drug did not antagonize the contractile response to several spasmogens, such as histamine, acetylcholine, serotonin and oxytocin, and the drug up to 200 mg/kg p.o. did not affect pupil size of mice. The intestinal propulsion in mice was not affected up to 200 mg/kg p.o. The gastric emptying in rats was not affected at 100 mg/kg p.o., even if retardation in gastric emptying occurred at 200 mg/kg. YJA 20379-1 did not show anti-inflammatory action nor did it affect urinary excretion up to 200 mg/kg p.o. From these results, it is suggested that YJA 20379-1 at the high dose of 100 mg/kg p.o. may not exert any adverse effects.

All-optical spin switching: A new frontier in femtomagnetism — A short review and a simple theory

NASA Astrophysics Data System (ADS)

Zhang, G. P.; Latta, T.; Babyak, Z.; Bai, Y. H.; George, Thomas F.

2016-08-01

Using an ultrafast laser pulse to manipulate the spin degree of freedom has broad technological appeal. It allows one to control the spin dynamics on a femtosecond time scale. The discipline, commonly called femtomagnetism, started with the pioneering experiment by Beaurepaire and coworkers in 1996, who showed subpicosecond demagnetization occurs in magnetic Ni thin films. This finding has motivated extensive research worldwide. All-optical helicity-dependent spin switching (AO-HDS) represents a new frontier in femtomagnetism, where a single ultrafast laser pulse can permanently switch spin without any assistance from a magnetic field. This review summarizes some of the crucial aspects of this new discipline: key experimental findings, leading mechanisms, controversial issues, and possible future directions. The emphasis is on our latest investigation. We first develop the all-optical spin switching (AOS) rule that determines how the switchability depends on the light helicity. This rule allows one to understand microscopically how the spin is reversed and why the circularly polarized light appears more powerful than the linearly polarized light. Then we invoke our latest spin-orbit coupled harmonic oscillator model to simulate single spin reversal. We consider both continuous wave (cw) excitation and pulsed laser excitation. The results are in a good agreement with the experimental result (a MatLab code is available upon request from the author). We then extend the code to include the exchange interaction among different spin sites. We show where the “inverse-Faraday field” comes from and how the laser affects the spin reversal nonlinearly. Our hope is that this review will motivate new experimental and theoretical investigations and discussions.

Weak Localization and Antilocalization in Topological Materials with Impurity Spin-Orbit Interactions

PubMed Central

Hankiewicz, Ewelina M.; Culcer, Dimitrie

2017-01-01

Topological materials have attracted considerable experimental and theoretical attention. They exhibit strong spin-orbit coupling both in the band structure (intrinsic) and in the impurity potentials (extrinsic), although the latter is often neglected. In this work, we discuss weak localization and antilocalization of massless Dirac fermions in topological insulators and massive Dirac fermions in Weyl semimetal thin films, taking into account both intrinsic and extrinsic spin-orbit interactions. The physics is governed by the complex interplay of the chiral spin texture, quasiparticle mass, and scalar and spin-orbit scattering. We demonstrate that terms linear in the extrinsic spin-orbit scattering are generally present in the Bloch and momentum relaxation times in all topological materials, and the correction to the diffusion constant is linear in the strength of the extrinsic spin-orbit. In topological insulators, which have zero quasiparticle mass, the terms linear in the impurity spin-orbit coupling lead to an observable density dependence in the weak antilocalization correction. They produce substantial qualitative modifications to the magnetoconductivity, differing greatly from the conventional Hikami-Larkin-Nagaoka formula traditionally used in experimental fits, which predicts a crossover from weak localization to antilocalization as a function of the extrinsic spin-orbit strength. In contrast, our analysis reveals that topological insulators always exhibit weak antilocalization. In Weyl semimetal thin films having intermediate to large values of the quasiparticle mass, we show that extrinsic spin-orbit scattering strongly affects the boundary of the weak localization to antilocalization transition. We produce a complete phase diagram for this transition as a function of the mass and spin-orbit scattering strength. Throughout the paper, we discuss implications for experimental work, and, at the end, we provide a brief comparison with transition metal dichalcogenides. PMID:28773167

Hyperfine interaction and its effects on spin dynamics in organic solids

NASA Astrophysics Data System (ADS)

Yu, Z. G.; Ding, Feizhi; Wang, Haobin

2013-05-01

Hyperfine interaction (HFI) and spin-orbit coupling are two major sources that affect electron spin dynamics. Here we present a systematic study of the HFI and its role in organic spintronic applications. For electron spin dynamics in disordered π-conjugated organics, the HFI can be characterized by an effective magnetic field whose modular square is a weighted sum of contact and dipolar contributions. We determine the effective HFI fields of some common π-conjugated organics studied in the literature via first-principles calculations. Most of them are found to be less than 2 mT. While the H atoms are the major source of the HFI in organics containing only the C and H atoms, many organics contain other nuclear spins, such as Al and N in tris-(8-hydroxyquinoline) aluminum, that contribute to the total HFI. Consequently, the deuteration effect on the HFI in the latter may be much weaker than in the former. The HFI gives rise to multiple resonance peaks in electron spin resonance. In disordered organic solids, these individual resonances are unresolved, leading to a broad peak whose width is proportional to the effective HFI field. As electrons hop among adjacent organic molecules, they experience a randomly varying local HFI field, inducing electron spin relaxation and diffusion. This is analyzed rigorously based on master equations. Electron spin relaxation undergoes a crossover along the ratio between the electron hopping rate η¯ and the Larmor frequency Ω of the HFI field. The spin relaxation rate increases (decreases) with η¯ when η¯≪Ω (η¯≫Ω). A coherent beating of electron spin at Ω is possible when the external field is small compared to the HFI. In this regime, the magnetic field is found to enhance the spin relaxation.

Spin dynamics of paramagnetic centers with anisotropic g tensor and spin of ½

PubMed Central

Maryasov, Alexander G.

2012-01-01

The influence of g tensor anisotropy on spin dynamics of paramagnetic centers having real or effective spin of 1/2 is studied. The g anisotropy affects both the excitation and the detection of EPR signals, producing noticeable differences between conventional continuous-wave (cw) EPR and pulsed EPR spectra. The magnitudes and directions of the spin and magnetic moment vectors are generally not proportional to each other, but are related to each other through the g tensor. The equilibrium magnetic moment direction is generally parallel to neither the magnetic field nor the spin quantization axis due to the g anisotropy. After excitation with short microwave pulses, the spin vector precesses around its quantization axis, in a plane that is generally not perpendicular to the applied magnetic field. Paradoxically, the magnetic moment vector precesses around its equilibrium direction in a plane exactly perpendicular to the external magnetic field. In the general case, the oscillating part of the magnetic moment is elliptically polarized and the direction of precession is determined by the sign of the g tensor determinant (g tensor signature). Conventional pulsed and cw EPR spectrometers do not allow determination of the g tensor signature or the ellipticity of the magnetic moment trajectory. It is generally impossible to set a uniform spin turning angle for simple pulses in an unoriented or ‘powder’ sample when g tensor anisotropy is significant. PMID:22743542

Pin-Hole Free Perovskite Film for Solar Cells Application Prepared by Controlled Two-Step Spin-Coating Method

NASA Astrophysics Data System (ADS)

Bahtiar, A.; Rahmanita, S.; Inayatie, Y. D.

2017-05-01

Morphology of perovskite film is a key important for achieving high performance perovskite solar cells. Perovskite films are commonly prepared by two-step spin-coating method. However, pin-holes are frequently formed in perovskite films due to incomplete conversion of lead-iodide (PbI2) into perovskite CH3NH3PbI3. Pin-holes in perovskite film cause large hysteresis in current-voltage curve of solar cells due to large series resistance between perovskite layer-hole transport material. Moreover, crystal structure and grain size of perovskite crystal are also other important parameters for achieving high performance solar cells, which are significantly affected by preparation of perovskite film. We studied the effect of preparation of perovskite film using controlled spin-coating parameters on crystal structure and morphological properties of perovskite film. We used two-step spin-coating method for preparation of perovskite film with varied spinning speed, spinning time and temperature of spin-coating process to control growth of perovskite crystal aimed to produce high quality perovskite crystal with pin-hole free and large grain size. All experiment was performed in air with high humidity (larger than 80%). The best crystal structure, pin-hole free with large grain crystal size of perovskite film was obtained from film prepared at room temperature with spinning speed 1000 rpm for 20 seconds and annealed at 100°C for 300 seconds.

Spin dynamics of paramagnetic centers with anisotropic g tensor and spin of 1/2

NASA Astrophysics Data System (ADS)

Maryasov, Alexander G.; Bowman, Michael K.

2012-08-01

The influence of g tensor anisotropy on spin dynamics of paramagnetic centers having real or effective spin of 1/2 is studied. The g anisotropy affects both the excitation and the detection of EPR signals, producing noticeable differences between conventional continuous-wave (cw) EPR and pulsed EPR spectra. The magnitudes and directions of the spin and magnetic moment vectors are generally not proportional to each other, but are related to each other through the g tensor. The equilibrium magnetic moment direction is generally parallel to neither the magnetic field nor the spin quantization axis due to the g anisotropy. After excitation with short microwave pulses, the spin vector precesses around its quantization axis, in a plane that is generally not perpendicular to the applied magnetic field. Paradoxically, the magnetic moment vector precesses around its equilibrium direction in a plane exactly perpendicular to the external magnetic field. In the general case, the oscillating part of the magnetic moment is elliptically polarized and the direction of precession is determined by the sign of the g tensor determinant (g tensor signature). Conventional pulsed and cw EPR spectrometers do not allow determination of the g tensor signature or the ellipticity of the magnetic moment trajectory. It is generally impossible to set a uniform spin turning angle for simple pulses in an unoriented or 'powder' sample when g tensor anisotropy is significant.

Conductance of a quantum wire at low electron density

NASA Astrophysics Data System (ADS)

Matveev, Konstantin

2006-03-01

We study the transport of electrons through a long quantum wire connecting two bulk leads. As the electron density in the wire is lowered, the Coulomb interactions lead to short-range crystalline ordering of electrons. In this Wigner crystal state the spins of electrons form an antiferromagnetic Heisenberg spin chain with exponentially small exchange coupling J. Inhomogeneity of the electron density due to the coupling of the wire to the leads results in violation of spin-charge separation in the device. As a result the spins affect the conductance of the wire. At zero temperature the low-energy spin excitations propagate freely through the wire, and its conductance remains 2e^2/h. At finite temperature some of the spin excitations are reflected by the wire and contribute to its resistance. Since the energy of the elementary excitations in the spin chain (spinons) cannot exceed πJ/2, the conductance of the wire acquires an exponentially small negative correction δG - (-πJ/2T) at low temperatures T J. At higher temperatures, T J, most of the spin excitations in the leads are reflected by the wire, and the conductance levels off at a new universal value e^2/h. This result is consistent with experimental observations of a mini-plateau of conductance at e^2/h in quantum wires in the absence of magnetic field.

Evaluating Graphene as a Channel Material in Spintronic Logic Devices

NASA Astrophysics Data System (ADS)

Anugrah, Yoska

Spintronics, a class of devices that exploit the spin properties of electrons in addition to the charge properties, promises the possibility for nonvolatile logic and memory devices that operate at low power. Graphene is a material in which the spin orientation of electrons can be conserved over a long distance, which makes it an attractive channel material in spintronics devices. In this dissertation, the properties of graphene that are interesting for spintronics applications are explored. A robust fabrication process is described for graphene spin valves using Al2O3 tunnel tunnel barriers and Co ferromagnetic contacts. Spin transport was characterized in both few-layer exfoliated and single-layer graphene, and spin diffusion lengths and spin relaxation times were extracted using the nonlocal spin valve geometry and Hanle measurements. The effect of input-output asymmetry on the spin transport was investigated. The effect of an applied drift electric field on spin transport was investigated and the spin diffusion length was found to be tunable by a factor of 8X (suppressed to 1.6 microm and enhanced to 13 microm from the intrinsic length of 4.6 microm using electric field of +/-1800 V/cm). A mechanism to induce asymmetry without excess power dissipation is also described which utilizes a double buried-gate structure to tune the Fermi levels on the input and output sides of a graphene spin logic device independently. It was found that different spin scattering mechanisms were at play in the two halves of a small graphene strip. This suggests that the spin properties of graphene are strongly affected by its local environment, e.g. impurities, surface topography, defects. Finally, two-dimensional materials beyond graphene have been explored as spin channels. One such material is phosphorene, which has low spin-orbit coupling and high mobility, and the interface properties of ferromagnets (cobalt and permalloy) with this material were explored. This work could potentially enable spin injection without the need for a physical tunnel barrier to solve the conductivity mismatch problem inherent to graphene.

Origin of the spin Seebeck effect in compensated ferrimagnets

PubMed Central

Geprägs, Stephan; Kehlberger, Andreas; Coletta, Francesco Della; Qiu, Zhiyong; Guo, Er-Jia; Schulz, Tomek; Mix, Christian; Meyer, Sibylle; Kamra, Akashdeep; Althammer, Matthias; Huebl, Hans; Jakob, Gerhard; Ohnuma, Yuichi; Adachi, Hiroto; Barker, Joseph; Maekawa, Sadamichi; Bauer, Gerrit E. W.; Saitoh, Eiji; Gross, Rudolf; Goennenwein, Sebastian T. B.; Kläui, Mathias

2016-01-01

Magnons are the elementary excitations of a magnetically ordered system. In ferromagnets, only a single band of low-energy magnons needs to be considered, but in ferrimagnets the situation is more complex owing to different magnetic sublattices involved. In this case, low lying optical modes exist that can affect the dynamical response. Here we show that the spin Seebeck effect (SSE) is sensitive to the complexities of the magnon spectrum. The SSE is caused by thermally excited spin dynamics that are converted to a voltage by the inverse spin Hall effect at the interface to a heavy metal contact. By investigating the temperature dependence of the SSE in the ferrimagnet gadolinium iron garnet, with a magnetic compensation point near room temperature, we demonstrate that higher-energy exchange magnons play a key role in the SSE. PMID:26842873

Voltage- and Light-Controlled Spin Properties of a Two-Dimensional Hole Gas in p-Type GaAs/AlAs Resonant Tunneling Diodes

NASA Astrophysics Data System (ADS)

Galeti, H. V. A.; Galvão Gobato, Y.; Brasil, M. J. S. P.; Taylor, D.; Henini, M.

2018-03-01

We have investigated the spin properties of a two-dimensional hole gas (2DHG) formed at the contact layer of a p-type GaAs/AlAs resonant tunneling diode (RTD). We have measured the polarized-resolved photoluminescence of the RTD as a function of bias voltage, laser intensity and external magnetic field up to 15T. By tuning the voltage and the laser intensity, we are able to change the spin-splitting from the 2DHG from almost 0 meV to 5 meV and its polarization degree from - 40% to + 50% at 15T. These results are attributed to changes of the local electric field applied to the two-dimensional gas which affects the valence band and the hole Rashba spin-orbit effect.

Quantum gates controlled by spin chain soliton excitations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cuccoli, Alessandro, E-mail: cuccoli@fi.infn.it; Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, I-50019 Sesto Fiorentino; Nuzzi, Davide

2014-05-07

Propagation of soliton-like excitations along spin chains has been proposed as a possible way for transmitting both classical and quantum information between two distant parties with negligible dispersion and dissipation. In this work, a somewhat different use of solitons is considered. Solitons propagating along a spin chain realize an effective magnetic field, well localized in space and time, which can be exploited as a means to manipulate the state of an external spin (i.e., a qubit) that is weakly coupled to the chain. We have investigated different couplings between the qubit and the chain, as well as different soliton shapes,more » according to a Heisenberg chain model. It is found that symmetry properties strongly affect the effectiveness of the proposed scheme, and the most suitable setups for implementing single qubit quantum gates are singled out.« less

Hydrogenation thermodynamics of melt-spun magnesium rich Mg-Ni nanocrystalline alloys with the addition of multiwalled carbon nanotubes and TiF3

NASA Astrophysics Data System (ADS)

Hou, Xiaojiang; Hu, Rui; Zhang, Tiebang; Kou, Hongchao; Li, Jinshan

2016-02-01

Based on the complexity of hydrogen absorption/desorption process and from the perspective of overall control, the as-cast Mg-10wt%Ni (Mg10Ni) alloy has been successively optimized by melt-spinning and surface catalyzed to realize the internal refinement as well as surface modification. The isothermal hydrogenation behavior of modified Mg-rich alloys has been investigated in this work. The results indicate that melt-spun Mg10Ni catalyzed by multiwalled carbon nanotubes (MWCNTs) coupling with TiF3 possesses superior activation properties and can absorb 6.23 wt% at 250 °C under 2.5 MPa. It is worth mentioning that the hydrogenation capacities of Mg10Ni-MWCNTs-TiF3 are 5.93 wt% and 5.99 wt% within the initial 1 min and 5 min, respectively. Meanwhile, the catalytic effect of MWCNTs and TiF3 has been discussed. The improved activation performance as well as the thermodynamics properties of Mg10Ni catalyzed by MWCNTs and TiF3 is attributed to the synergistic effect on dissociation of H2 molecules, diffusion of H-atoms and heterogeneous nucleation of hydrides.

Detection of MgCn in IRC + 10216: A new metal-bearing free radical

NASA Technical Reports Server (NTRS)

Ziurys, L. M.; Apponi, A. J.; Guelin, M.; Cernicharo, J.

1995-01-01

A new metal-containing molecule, MgCN, has been detected toward the late-type star IRC + 10216, using the NRAO 12 m and IRAM 30 m telescopes. The N = 11 approaches 10, 10 approaches 9, and 9 approaches 8 transtions of this species which has a (sup 2)Sigma(sup +) ground state, have been observed in the outer envelope of this object at 3 mm. For the N = 11 approaches 10 transitions, the two spin-rotation components are clearly resolved and conclusively identify this new radical. These measurements imply a column of density for MgCN of N(sub tot) approximately 10(exp 12)/sq cm in the outer shell, which corresponds to a fractional abundance of f approximately 7x10(exp -10). This molecule, the metastable isomer of MgNC, is the third metal-bearing species thus far identified in the outer shell of IRC + 10216, and its detection implies a ratio of MgNC/MgCN approximately 22/1. MgCN may be formed through a reaction scheme involving magnesium and HNC or CN, both prominent outer shell molecules, or through synthesis on grains.

High-resolution F T spectrum of A 2 Π r - X 2 Σ + band system of MgCl

NASA Astrophysics Data System (ADS)

Saksena, M. D.; Deo, M. N.; Sunanda, K.; Behere, S. H.; Jadhav, Ashok

2011-03-01

The emission spectrum of the A 2 Π r - X 2 Σ + band system of MgCl molecule (360-380 nm) has been recorded on BOMEM DA8 Fourier transform spectrometer at an apodized resolution of 0.035 cm-1. The spectra have been excited under flowing conditions in a demountable stainless steel hollow cathode lamp (400 V, 250 mA) containing anhydrous MgCl2 and Ar. The resulting spectra are very intense and the 0-0, 1-1, 1-0 bands of A 2 Π 1/2- X 2 Σ + sub-transition and the 0-0 band of A 2 Π 3/2- X 2 Σ + sub-transition have been rotationally analyzed. Improved molecular constants have been derived using a least-squares fit program in which optical data of earlier analyzed 0-1 and 0-2 bands ( A 2 Π 1/2- X 2 Σ +) was also included. The Λ-doubling constants in the v' = 0, 1 levels of the A 2 Π 1/2 sub-state are as expected, i.e. p 1 > p 0, where as it is found that the spin-doubling constants of the v″ = 0, 1 and 2 levels of the ground state X 2 Σ +, decrease with the increase in v, i.e. γ 0 > γ 1 > γ 2. This is indicative of the presence of some nearby state, influencing the spin-doubling.

Perpendicular magnetic anisotropy and magnetization dynamics in oxidized CoFeAl films

PubMed Central

Wu, Di; Zhang, Zhe; Li, Le; Zhang, Zongzhi; Zhao, H. B.; Wang, J.; Ma, B.; Jin, Q. Y.

2015-01-01

Half-metallic Co-based full-Heusler alloys with perpendicular magnetic anisotropy (PMA), such as Co2FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3 nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability. In order to solve this issue, we fabricated oxidized Co50Fe25Al25 (CFAO) films with proper thicknesses without employing the MgO layer. The samples show controllable PMA by tuning the oxygen pressure (PO2) and CFAO thickness (tCFAO), large perpendicular anisotropy field of ~8.0 kOe can be achieved at PO2 = 12% for the sample of tCFAO = 2.1 nm or at PO2 = 7% for tCFAO = 2.8 nm. The loss of PMA at thick tCFAO or high PO2 results mainly from the formation of large amount of CoFe oxides, which are superparamagnetic at room temperature but become hard magnetic at low temperatures. The magnetic CFAO films, with strong PMA in a relatively wide thickness range and small intrinsic damping parameter below 0.028, would find great applications in developing advanced spintronic devices. PMID:26190066

Does performance level affect initial ball flight kinematics in finger and wrist-spin cricket bowlers?

PubMed

Spratford, Wayne; Whiteside, David; Elliott, Bruce; Portus, Marc; Brown, Nicholas; Alderson, Jacqueline

2018-03-01

Spin bowling plays a fundamental role within the game of cricket yet little is known about the initial ball kinematics in elite and pathway spin bowlers or their relationship to performance. Therefore, the purpose of this study was to record three-dimensional ball kinematics in a large and truly high level cohort of elite and pathway finger-spin (FS) and wrist-spin (WS) bowlers, identifying potential performance measures that can be subsequently used in future research. A 22-camera Vicon motion analysis system captured retro-reflective markers placed on the seam (static) and ball (dynamic) to quantify ball kinematics in 36 FS (12 elite and 24 pathway) and 20 WS (eight elite and 12 pathway) bowlers. Results indicated that FS bowlers delivered the ball with an increased axis of rotation elevation, while wrist-spin bowlers placed greater amounts of revolutions on the ball. It also highlighted that ball release (BR) velocity, revolutions and velocity/revolution index scores for both groups and seam stability for FS bowlers, and seam azimuth angle and spin axis elevation angle for WS bowlers, were discriminators of playing level. As such these variables could be used as indicators of performance (i.e. performance measures) in future research.

Giant interfacial perpendicular magnetic anisotropy in Fe/CuIn 1 -xGaxSe2 beyond Fe/MgO

NASA Astrophysics Data System (ADS)

Masuda, Keisuke; Kasai, Shinya; Miura, Yoshio; Hono, Kazuhiro

2017-11-01

We study interfacial magnetocrystalline anisotropies in various Fe/semiconductor heterostructures by means of first-principles calculations. We find that many of those systems show perpendicular magnetic anisotropy (PMA) with a positive value of the interfacial anisotropy constant Ki. In particular, the Fe/CuInSe 2 interface has a large Ki of ˜2.3 mJ /m2 , which is about 1.6 times larger than that of Fe/MgO known as a typical system with relatively large PMA. We also find that the values of Ki in almost all the systems studied in this work follow the well-known Bruno's relation, which indicates that minority-spin states around the Fermi level provide dominant contributions to the interfacial magnetocrystalline anisotropies. Detailed analyses of the local density of states and wave-vector-resolved anisotropy energy clarify that the large Ki in Fe/CuInSe 2 is attributed to the preferable 3 d -orbital configurations around the Fermi level in the minority-spin states of the interfacial Fe atoms. Moreover, we have shown that the locations of interfacial Se atoms are the key for such orbital configurations of the interfacial Fe atoms.

How current ginning processes affect fiber length uniformity index

USDA-ARS?s Scientific Manuscript database

There is a need to develop cotton ginning methods that improve fiber characteristics that are compatible with the newer and more efficient spinning technologies. A literature search produced recent studies that described how current ginning processes affect HVI fiber length uniformity index. Resul...

Ultra-senstitive magnesium oxide-based magnetic tunnel junctions for spintronic immunoassay

NASA Astrophysics Data System (ADS)

Shen, Weifeng

We systematically studied the spin-dependent tunnel properties of MgO-based magnetic tunnel junctions (MTJs). Utilizing the spin-coherent tunnel effects of the MgO (001) insulating layer, we have achieved large tunneling magnetoresistance (TMR) ratios (above 200%) at room temperature in optimized MTJ devices. We have shown that the MgO surface roughness, and therefore device magnetoresistance, depends strongly on the pressure of the Ar sputtering gas. We have investigated the characteristics of MgO-MTJs, including their dependence on barrier thickness and bias voltage, their thermal stability and resistance to electrostatic discharge (ESD). We have also fabricated MgO-MTJs with a synthetic antiferromagnetic (SAF) free layer, which exhibits a coherent, single-domain-like switching. Our data show that MgO-MTJs have superior properties for low-field magnetic field sensing applications as compared with conventional AlOx-based MTJs. Based on this giant TMR effect, we designed and developed ultra-sensitive magnetic tunnel junction (MTJ) sensors and sensor arrays for biomagnetic sensing applications. By integrating MTJ sensor arrays into microfluidic channels, we were able to detect the presence of moving, micron-size superparamagnetic beads in real time. We have obtained an average signal of 80 mV for a single Dynal M-280 bead, with a signal-to-noise ratio (SNR) of 24 dB. We also biologically treated the MTJ sensor array surfaces, and demonstrated the detection of 2.5 muM single strand target DNA labeled with 16-nm-diameter Fe3O 4 nanoparticles (NPs). Our measured signal of 72 muV indicates that the current system's detection limit for analyte DNA is better than 150 nM. We also demonstrated the detection of live HeLa cells labeled with Fe 3O4 nanoparticles, with an effective signal of 8 mV and a signal-to-noise ratio of 6 dB. These results represent an important milestone in the development of spintronics immunoassay technology: the detection of a single live cell labeled with magnetic nanoparticles. All the data show conclusively that MTJ sensors and sensor arrays are very promising candidates for future applications involving the accurate detection and identification of biomolecules tagged with magnetic labels.

Spin scattering asymmetric coefficients and enhanced specific interfacial resistance of fully epitaxial current-perpendicular-to-plane giant magnetoresistance spin valves using alternate monatomic layered [Fe/Co]n and a Ag spacer layer

NASA Astrophysics Data System (ADS)

Jung, J. W.; Shiozaki, R.; Doi, M.; Sahashi, M.

2011-04-01

Using current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) measurement, we have evaluated the bulk and interface spin scattering asymmetric coefficients, βF and γF/N and the specific interfacial resistance, AR*F/N, for exchange-biased spin-valves consisting of artificially ordered B2 structure Fe50Co50 and Ag spacer layer. Artificially epitaxial ordered Fe50Co50 superlattices have been successfully fabricated on MgO (001) substrate by alternate monatomic layer (AML) deposition at a substrate temperature of 75 °C. The structural properties of the full epitaxial trilayer, AML[Fe/Co]n/Ag/AML[Fe/Co]n, on the Ag electrode have been confirmed by in situ reflection high-energy electron diffraction and transmission electron diffraction microscopy. A considerably large resistance-area product change and MR ratio (ΔRA > 3 mΩμm2 and MR ratio ˜5%) were confirmed even at thin AML[Fe/Co]n layer at room temperature (RT) in our spin-valve elements. The estimated values of βF and γF/N were 0.80 and 0.84 ± 0.02, respectively, from the Valet-Fert theory analysis of ΔRA as a function of thickness of the ferromagnetic layer (3, 4, and 5 nm) on the basis of the two-current model.

Multifunctional Gadolinium-Doped Mesoporous TiO2 Nanobeads: Photoluminescence, Enhanced Spin Relaxation, and Reactive Oxygen Species Photogeneration, Beneficial for Cancer Diagnosis and Treatment.

PubMed

Imani, Roghayeh; Dillert, Ralf; Bahnemann, Detlef W; Pazoki, Meysam; Apih, Tomaž; Kononenko, Veno; Repar, Neža; Kralj-Iglič, Veronika; Boschloo, Gerrit; Drobne, Damjana; Edvinsson, Tomas; Iglič, Aleš

2017-05-01

Materials with controllable multifunctional abilities for optical imaging (OI) and magnetic resonant imaging (MRI) that also can be used in photodynamic therapy are very interesting for future applications. Mesoporous TiO 2 sub-micrometer particles are doped with gadolinium to improve photoluminescence functionality and spin relaxation for MRI, with the added benefit of enhanced generation of reactive oxygen species (ROS). The Gd-doped TiO 2 exhibits red emission at 637 nm that is beneficial for OI and significantly improves MRI relaxation times, with a beneficial decrease in spin-lattice and spin-spin relaxation times. Density functional theory calculations show that Gd 3+ ions introduce impurity energy levels inside the bandgap of anatase TiO 2 , and also create dipoles that are beneficial for charge separation and decreased electron-hole recombination in the doped lattice. The Gd-doped TiO 2 nanobeads (NBs) show enhanced ability for ROS monitored via • OH radical photogeneration, in comparison with undoped TiO 2 nanobeads and TiO 2 P25, for Gd-doping up to 10%. Cellular internalization and biocompatibility of TiO 2 @xGd NBs are tested in vitro on MG-63 human osteosarcoma cells, showing full biocompatibility. After photoactivation of the particles, anticancer trace by means of ROS photogeneration is observed just after 3 min irradiation. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Moessbauer spectroscopy of Mg(0.9)Fe(0.1)SiO3 perovskite

NASA Technical Reports Server (NTRS)

Jeanloz, Raymond; O'Neill, Bridget; Pasternak, Moshe P.; Taylor, R. D.; Bohlen, Steven R.

1992-01-01

Ambient pressure Moessbauer spectra of Mg(0.9)Fe-57(0.1)SiO3 perovskite synthesized at pressure-temperature conditions of about 50 GPa and 1700 K show that the iron is entirely high-spin Fe(2+) and appears to be primarily located in the octahedral site within the crystal structure. We observe broad Moessbauer lines, suggesting a distribution of electric-field gradients caused by disorder associated with the Fe ions. Also, the perovskite exhibits magnetic ordering at temperatures lower than 5 K, implying that there is a magnetic contribution to the absolute ('third-law') entropy of this phase.

Dimer self-organization of impurity ytterbium ions in synthetic forsterite single crystals

NASA Astrophysics Data System (ADS)

Tarasov, V. F.; Sukhanov, A. A.; Dudnikova, V. B.; Zharikov, E. V.; Lis, D. A.; Subbotin, K. A.

2017-07-01

Paramagnetic centers formed by impurity Yb3+ ions in synthetic forsterite (Mg2SiO4) grown by the Czochralski technique are studied by X-band CW and pulsed EPR spectroscopy. These centers are single ions substituting magnesium in two different crystallographic positions denoted M1 and M2, and dimer associates formed by two Yb3+ ions in nearby positions M1. It is established that there is a pronounced mechanism favoring self-organization of ytterbium ions in dimer associates during the crystal growth, and the mechanism of the spin-spin coupling between ytterbium ions in the associate has predominantly a dipole-dipole character, which makes it possible to control the energy of the spin-spin interaction by changing the orientation of the external magnetic field. The structural computer simulation of cluster ytterbium centers in forsterite crystals is carried out by the method of interatomic potentials using the GULP 4.0.1 code (General Utility Lattice Program). It is established that the formation of dimer associates in the form of a chain parallel to the crystallographic axis consisting of two ytterbium ions with a magnesium vacancy between them is the most energetically favorable for ytterbium ions substituting magnesium in the position M1.

Endotoxin-induced mortality in rats is reduced by nitrones

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamburger, S.A.; McCay, P.B.

The goal of these investigations was to determine if nitrone spin-trapping agents can alter mortality associated with endotoxemia in the rat. Reactive free radicals attack nitrone spin-trapping agents forming relatively reactive, persistent free radical spin adducts. We administered 85 mM (10 ml/kg) of alpha-phenyl N-tert-butyl nitrone (PBN), alpha-4-pyridyl-N-oxide N-tert-butyl nitrone (4-POBN), 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), or vehicle (saline i.p.) 30 min before endotoxin (25 mg/kg i.p.) or vehicle to Sprague-Dawley (SD) or Holtzman virus-free (HVF) rats (n = 10-17/group). All vehicle-treated rats receiving endotoxin were dead by 1 day. At 7 days, 83% of PBN-treated SD, 42% of PBN- or POBN-treated HVF,more » and 25% of DMPO-treated HVF rats were alive. The difference in survival of PBN-treated animals between strains may reflect the higher susceptibility of HVF rats to endotoxin. The observed reduction in mortality may be related to the well-established capacity of spin-trapping agents to capture reactive free radicals that may be generated in target tissues in response to endotoxin, and that would otherwise react with cell components and produce tissue injury.« less

Effect of 9. 6-GHz pulsed microwaves on the orb web spinning ability of the cross spider (Araneus diadematus)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liddle, C.G.; Putnam, J.P.; Lewter, O.L.

1986-01-01

Eight cross spiders (Araneus diadematus) were exposed overnight (16 h) during web-building activity to pulsed 9.6-GHz microwaves at average power densities of 10, 1, and 0.1 mW/sq. cm. (estimated SARs 40, 4, and 0.4 mW/g). Under these conditions, 9.6-GHz pulsed microwaves did not affect the web-spinning ability of the cross spider.

Nanostructured hydroxyapatite/poly(lactic-co-glycolic acid) composite coating for controlling magnesium degradation in simulated body fluid.

PubMed

Johnson, Ian; Akari, Khalid; Liu, Huinan

2013-09-20

Biodegradable magnesium (Mg) and its alloys have many attractive properties (e.g. comparable mechanical properties to cortical bone) for orthopedic implant applications, but they degrade too rapidly in the human body to meet clinical requirements. Nanostructured hydroxyapatite (nHA)/poly(lactic-co-glycolic acid) (PLGA) composite coatings provide synergistic properties for controlling degradation of Mg-based substrates and improving bone-implant integration. In this study, nHA/PLGA composites were spin coated onto Mg-based substrates and the results showed that the nHA/PLGA coatings retained nano-scale features with nHA dispersed in PLGA matrix. In comparison with non-coated Mg, the nHA/PLGA composite coated Mg increased the corrosion potential and decreased the corrosion current in revised simulated body fluid (rSBF). After 24 h of immersion in rSBF, increased calcium phosphate (CaP) deposition and formation of Mg-substituted CaP rosettes were observed on the surface of the nHA/PLGA coated Mg, indicating greater bioactivity. In contrast, no significant CaP was deposited on the PLGA coated Mg. Since both PLGA coating and nHA/PLGA coating showed some degree of delamination from Mg-based substrates during extended immersion in rSBF, the coating processing and properties should be further optimized in order to take full advantage of biodegradable Mg and nHA/PLGA nanocomposites for orthopedic applications.

Nanostructured hydroxyapatite/poly(lactic-co-glycolic acid) composite coating for controlling magnesium degradation in simulated body fluid

NASA Astrophysics Data System (ADS)

Johnson, Ian; Akari, Khalid; Liu, Huinan

2013-09-01

Biodegradable magnesium (Mg) and its alloys have many attractive properties (e.g. comparable mechanical properties to cortical bone) for orthopedic implant applications, but they degrade too rapidly in the human body to meet clinical requirements. Nanostructured hydroxyapatite (nHA)/poly(lactic-co-glycolic acid) (PLGA) composite coatings provide synergistic properties for controlling degradation of Mg-based substrates and improving bone-implant integration. In this study, nHA/PLGA composites were spin coated onto Mg-based substrates and the results showed that the nHA/PLGA coatings retained nano-scale features with nHA dispersed in PLGA matrix. In comparison with non-coated Mg, the nHA/PLGA composite coated Mg increased the corrosion potential and decreased the corrosion current in revised simulated body fluid (rSBF). After 24 h of immersion in rSBF, increased calcium phosphate (CaP) deposition and formation of Mg-substituted CaP rosettes were observed on the surface of the nHA/PLGA coated Mg, indicating greater bioactivity. In contrast, no significant CaP was deposited on the PLGA coated Mg. Since both PLGA coating and nHA/PLGA coating showed some degree of delamination from Mg-based substrates during extended immersion in rSBF, the coating processing and properties should be further optimized in order to take full advantage of biodegradable Mg and nHA/PLGA nanocomposites for orthopedic applications.

Field-controllable Spin-Hall Effect of Light in Optical Crystals: A Conoscopic Mueller Matrix Analysis.

PubMed

Samlan, C T; Viswanathan, Nirmal K

2018-01-31

Electric-field applied perpendicular to the direction of propagation of paraxial beam through an optical crystal dynamically modifies the spin-orbit interaction (SOI), leading to the demonstration of controllable spin-Hall effect of light (SHEL). The electro- and piezo-optic effects of the crystal modifies the radially symmetric spatial variation in the fast-axis orientation of the crystal, resulting in a complex pattern with different topologies due to the symmetry-breaking effect of the applied field. This introduces spatially-varying Pancharatnam-Berry type geometric phase on to the paraxial beam of light, leading to the observation of SHEL in addition to the spin-to-vortex conversion. A wave-vector resolved conoscopic Mueller matrix measurement and analysis provides a first glimpse of the SHEL in the biaxial crystal, identified via the appearance of weak circular birefringence. The emergence of field-controllable fast-axis orientation of the crystal and the resulting SHEL provides a new degree of freedom for affecting and controlling the spin and orbital angular momentum of photons to unravel the rich underlying physics of optical crystals and aid in the development of active photonic spin-Hall devices.

Hysteresis and change of transition temperature in thin films of Fe([Me{sub 2}Pyrz]{sub 3}BH){sub 2}, a new sublimable spin-crossover molecule

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davesne, V.; Gruber, M.; Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe

2015-05-21

Thin films of the spin-crossover (SCO) molecule Fe([Me{sub 2}Pyrz]{sub 3}BH){sub 2} (Fe-pyrz) were sublimed on Si/SiO{sub 2} and quartz substrates, and their properties investigated by X-ray absorption and photoemission spectroscopies, optical absorption, atomic force microscopy, and superconducting quantum interference device. Contrary to the previously studied Fe(phen){sub 2}(NCS){sub 2}, the films are not smooth but granular. The thin films qualitatively retain the typical SCO properties of the powder sample (SCO, thermal hysteresis, soft X-ray induced excited spin-state trapping, and light induced excited spin-state trapping) but present intriguing variations even in micrometer-thick films: the transition temperature decreases when the thickness is decreased,more » and the hysteresis is affected. We explain this behavior in the light of recent studies focusing on the role of surface energy in the thermodynamics of the spin transition in nano-structures. In the high-spin state at room temperature, the films have a large optical gap (∼5 eV), decreasing at thickness below 50 nm, possibly due to film morphology.« less

Electrical control of a long-lived spin qubit in a Si/SiGe quantum dot.

PubMed

Kawakami, E; Scarlino, P; Ward, D R; Braakman, F R; Savage, D E; Lagally, M G; Friesen, Mark; Coppersmith, S N; Eriksson, M A; Vandersypen, L M K

2014-09-01

Nanofabricated quantum bits permit large-scale integration but usually suffer from short coherence times due to interactions with their solid-state environment. The outstanding challenge is to engineer the environment so that it minimally affects the qubit, but still allows qubit control and scalability. Here, we demonstrate a long-lived single-electron spin qubit in a Si/SiGe quantum dot with all-electrical two-axis control. The spin is driven by resonant microwave electric fields in a transverse magnetic field gradient from a local micromagnet, and the spin state is read out in the single-shot mode. Electron spin resonance occurs at two closely spaced frequencies, which we attribute to two valley states. Thanks to the weak hyperfine coupling in silicon, a Ramsey decay timescale of 1 μs is observed, almost two orders of magnitude longer than the intrinsic timescales in GaAs quantum dots, whereas gate operation times are comparable to those reported in GaAs. The spin echo decay time is ~40 μs, both with one and four echo pulses, possibly limited by intervalley scattering. These advances strongly improve the prospects for quantum information processing based on quantum dots.

Interface roughness mediated phonon relaxation rates in Si quantum dots.

NASA Astrophysics Data System (ADS)

Ferdous, Rifat; Hsueh, Yuling; Klimeck, Gerhard; Rahman, Rajib

2015-03-01

Si QDs are promising candidates for solid-state quantum computing due to long spin coherence times. However, the valley degeneracy in Si adds an additional degree of freedom to the electronic structure. Although the valley and orbital indices can be uniquely identified in an ideal Si QD, interface roughness mixes valley and orbital states in realistic dots. Such valley-orbit coupling can strongly influence T1 times in Si QDs. Recent experimental measurements of various relaxation rates differ from previous predictions of phonon relaxation in ideal Si QDs. To understand how roughness affects different relaxation rates, for example spin relaxation due to spin-valley coupling, which is a byproduct of spin-orbit and valley-orbit coupling, we need to understand the effect of valley-orbit coupling on valley relaxation first. Using a full-band atomistic tight-binding description for both the system's electron and electron-phonon hamiltonian, we analyze the effect of atomic-scale interface disorder on phonon induced valley relaxation and spin relaxation in a Si QD. We find that, the valley splitting dependence of valley relaxation rate governs the magnetic field dependence of spin relaxation rate. Our results help understand experimentally measured relaxation times.

Irradiation of an Accretion Disc by a Jet: General Properties and Implications for Spin Measurements of Black Holes

NASA Technical Reports Server (NTRS)

T.Dauser; Garcia, J.; Wilms, J.; Boeck, M.; Brenneman, L. W.; Falanga, M.; Fukumura, Keigo; Reynolds, C. S.

2013-01-01

X-ray irradiation of the accretion disc leads to strong reflection features, which are then broadened and distorted by relativistic effects. We present a detailed, general relativistic approach to model this irradiation for different geometries of the primary X-ray source. These geometries include the standard point source on the rotational axis as well as more jet-like sources, which are radially elongated and accelerating. Incorporating this code in the RELLINE model for relativistic line emission, the line shape for any configuration can be predicted. We study how different irradiation geometries affect the determination of the spin of the black hole. Broad emission lines are produced only for compact irradiating sources situated close to the black hole. This is the only case where the black hole spin can be unambiguously determined. In all other cases the line shape is narrower, which could either be explained by a low spin or an elongated source. We conclude that for those cases and independent of the quality of the data, no unique solution for the spin exists and therefore only a lower limit of the spin value can be given

Biodegradable polymer for sealing porous PEO layer on pure magnesium: An in vitro degradation study

NASA Astrophysics Data System (ADS)

Alabbasi, Alyaa; Mehjabeen, Afrin; Kannan, M. Bobby; Ye, Qingsong; Blawert, Carsten

2014-05-01

An attempt was made to seal the porous silicate-based plasma electrolytic oxidation (PEO) layer on pure magnesium (Mg) with a biodegradable polymer, poly(L-lactide) (PLLA), to delay the localized degradation of magnesium-based implants in body fluid for better in-service mechanical integrity. Firstly, a silicate-based PEO coating on pure magnesium was performed using a pulsed constant current method. In order to seal the pores in the PEO layer, PLLA was coated using a two-step spin coating method. The performance of the PEO-PLLA Mg was evaluated using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The EIS results showed that the polarization resistance (Rp) of the PEO-PLLA Mg was close to two orders of magnitude higher than that of the PEO Mg. While the corrosion current density (icorr) of the pure Mg was reduced by 65% with the PEO coating, the PEO-PLLA coating reduced the icorr by almost 100%. As expected, the Rp of the PEO-PLLA Mg decreased with increase in exposure time. However, it was noted that the Rp of the PEO-PLLA Mg even after 100 h was six times higher than that of the PEO Mg after 48 h exposure, and did not show any visible localized attack.

The Effect of Propellant Variables on Slag in Subscale Spin Motors. Part 1; Design and Qualification of a Slag Discrimination Motor

NASA Technical Reports Server (NTRS)

Perkins, F. M.; Beus, R. W.; May, D. H.

1995-01-01

The formation, collection, and expulsion of aluminum oxide slag is known to affect the performance of many solid rocket motor systems. Slag expulsion, in particular, is believed to be capable of causing pressure and thrust perturbations. Propellant combustion studies, performed and documented by many investigators, have shown that variations in propellant raw materials and processing affect the nature of alumina droplets at the burning propellant surface, and hence, may affect the quantity of slag retained in the motor chamber, available for expulsion. Thiokol has completed an experimental and analytical evaluation to determine the effects of several material and process variables on Space SHuttle propellant and its propensity to 'slag'. This paper describes the test article, a small scale spin motor with special nozzle, designed and qualified as a slag discriminating tool for use in the evaluation.

Specificity of different organic nitrates to elicit NO formation in rabbit vascular tissues and organs in vivo.

PubMed Central

Mülsch, A.; Bara, A.; Mordvintcev, P.; Vanin, A.; Busse, R.

1995-01-01

1. In the present study we assessed the formation of nitric oxide (NO) from classical and thiol-containing organic nitrates in vascular tissues and organs of anaesthetized rabbits, and established a relationship between the relaxant response elicited by nitroglycerin (NTG) and NO formation in the rabbit isolated aorta. Furthermore, the effect of isolated cytochrome P450 on NO formation from organic nitrates was investigated. 2. Rabbits received diethyldithiocarbamate (DETC; 200 mg kg-1 initial bolus i.p. and 200 mg kg-1 during 20 min, i.v.) and either saline, or one of the following organic nitrates: nitroglycerin (NTG, 0.5 mg kg-1), isosorbide dinitrate (ISDN), N-(3-nitratopivaloyl)-L-cysteine ethylester (SPM 3672), S-carboxyethyl-N-(3-nitratopivaloyl)-L-cysteine ethylester (SPM 5185), at 10 mg kg-1 each. After 20 min the animals were killed, blood vessels and organs were removed, and subsequently analyzed for spin-trapped NO by cryogenic electron spin resonance (e.s.r.) spectroscopy. 3. In the saline-treated control group, NO remained below the detection limit in all vessels and organs. In contrast, all of the nitrates tested elicited measurable NO formation, which was higher in organs (liver, kidney, heart, lung, spleen) (up to 4.8 nmol g-1 20 min-1) than in blood vessels (vena cava, mesenteric bed, femoral artery, aorta) (up to 0.7 nmol g-1 20 min-1). Classical organic nitrates (NTG, ISDN) formed NO preferentially in the mesenteric bed and the vena cava, while the SPM compounds elicited comparable NO formation in veins and arteries. 4. Using a similar spin trapping technique, NO formation was assessed in vitro in phenylephrine-precontracted rabbit aortic rings. The maximal relaxation elicited by a first exposure (10 min) to NTG (0.3 to 10 microM) was positively correlated (r = 0.8) with the net increase (NTG minus basal) of NO spin-trapped during a second exposure to the same concentration of NTG in the presence of DETC. 5. Cytochrome P450 purified from rabbit liver enhanced NO formation in a NADPH-dependent fashion from NTG, but not from the other nitrates, as assessed by activation of purified soluble guanylyl cyclase. 6. We conclude that the vessel selective action of different organic nitrates in vivo reflects differences in vascular NO formation. Thus, efficient preload reduction by classical organic nitrates can be accounted for by higher NO formation in venous capacitance as compared to arterial conductance and resistance vessels. In contrast, NO is released from cysteine-containing nitrates (SPMs) to a similar extent in arteries and veins, presumably independently of an organic nitrate-specific biotransformation. Limited tissue bioavailability of NTG and ISDN might account for low NO formation in the aorta, while true differences in biotransformation seem to account for differences in NO formation in the other vascular tissues. PMID:8590999

Pure spin polarized current through a full magnetic silicene junction

NASA Astrophysics Data System (ADS)

Lorestaniweiss, Zeinab; Rashidian, Zeinab

2018-06-01

Using the Landauer-Buttiker formula, we investigate electronic transport in silicene junction composed of ferromagnetic silicene. The direction of magnetization in the middle region may change in a plane perpendicular to the junction, whereas the magnetization direction keep fixed upward in silicene electrodes. We investigate how the various magnetization directions in the middle region affect the electronic transport. We demonstrate that conductance depends on the orientation of magnetizations in the middle region. It is found that by changing the direction of the magnetization in the middle region, a pure spin up current can be achieved. This achievement makes this full magnetic junction a good design for a full spin-up current polarizer.

Effect of preheating on fatigue resistance of gears in spin induction coil hardening process

NASA Astrophysics Data System (ADS)

Kumar, Pawan; Aggarwal, M. L.

2018-02-01

Spin hardening inductors are typically used for fine-sized teeth gear geometry. With the proper selection of several design parameters, only the gear teeth can be case surface hardened without affecting the other surface of gear. Preheating may be done to reach an adapted high austenitizing temperature in the root circle to avoid overheating of the tooth tip during final heating. The effect of preheating of gear on control of compressive residual stresses and case hardening has been experimentally discussed in this paper. Present work is about analysing single frequency mode, preheat hardening treatment and compressive residual stresses field for hardening process of spur gear using spin hardening inductors.

Electronic and spin dynamics in the insulating iron pnictide NaFe0.5Cu0.5As

NASA Astrophysics Data System (ADS)

Zhang, Shunhong; He, Yanjun; Mei, Jia-Wei; Liu, Feng; Liu, Zheng

2017-12-01

NaFe0.5Cu0.5As represents a rare exception in the metallic iron pnictide family, in which a small insulating gap is opened. Based on first-principles study, we provide a comprehensive theoretical characterization of this insulating compound. The Fe3 + spin degree of freedom is quantified as a quasi-one-dimensional (1D) S =5/2 Heisenberg model. The itinerant As hole state is downfolded to a px y-orbital hopping model on a square lattice. An orbital-dependent Hund's coupling between the spin and the hole is revealed. Several important material properties are analyzed, including (a) the factors affecting the small p -d charge-transfer gap; (b) the role of extra interchain Fe atoms; and (c) quasi-1D spin excitation in the Fe chains. The experimental manifestations of these properties are discussed.

Correlation between spin structure oscillations and domain wall velocities

PubMed Central

Bisig, André; Stärk, Martin; Mawass, Mohamad-Assaad; Moutafis, Christoforos; Rhensius, Jan; Heidler, Jakoba; Büttner, Felix; Noske, Matthias; Weigand, Markus; Eisebitt, Stefan; Tyliszczak, Tolek; Van Waeyenberge, Bartel; Stoll, Hermann; Schütz, Gisela; Kläui, Mathias

2013-01-01

Magnetic sensing and logic devices based on the motion of magnetic domain walls rely on the precise and deterministic control of the position and the velocity of individual magnetic domain walls in curved nanowires. Varying domain wall velocities have been predicted to result from intrinsic effects such as oscillating domain wall spin structure transformations and extrinsic pinning due to imperfections. Here we use direct dynamic imaging of the nanoscale spin structure that allows us for the first time to directly check these predictions. We find a new regime of oscillating domain wall motion even below the Walker breakdown correlated with periodic spin structure changes. We show that the extrinsic pinning from imperfections in the nanowire only affects slow domain walls and we identify the magnetostatic energy, which scales with the domain wall velocity, as the energy reservoir for the domain wall to overcome the local pinning potential landscape. PMID:23978905

Measuring Parameters of Massive Black Hole Binaries with Partially-Aligned Spins

NASA Technical Reports Server (NTRS)

Lang, Ryan N.; Hughes, Scott A.; Cornish, Neil J.

2010-01-01

It is important to understand how well the gravitational-wave observatory LISA can measure parameters of massive black hole binaries. It has been shown that including spin precession in the waveform breaks degeneracies and produces smaller expected parameter errors than a simpler, precession-free analysis. However, recent work has shown that gas in binaries can partially align the spins with the orbital angular momentum, thus reducing the precession effect. We show how this degrades the earlier results, producing more pessimistic errors in gaseous mergers. However, we then add higher harmonics to the signal model; these also break degeneracies, but they are not affected by the presence of gas. The harmonics often restore the errors in partially-aligned binaries to the same as, or better than/ those that are obtained for fully precessing binaries with no harmonics. Finally, we investigate what LISA measurements of spin alignment can tell us about the nature of gas around a binary,

Spin State Control of the Perovskite Rh/Co Oxides

PubMed Central

Terasaki, Ichiro; Shibasaki, Soichiro; Yoshida, Shin; Kobayashi, Wataru

2010-01-01

We show why and how the spin state of transition-metal ions affects the thermoelectric properties of transition-metal oxides by investigating two perovskite-related oxides. In the A-site ordered cobalt oxide Sr3YCo4O10.5, partial substitution of Ca for Sr acts as chemical pressure, which compresses the unit cell volume to drive the spin state crossover, and concomitantly changes the magnetization and thermopower. In the perovskite rhodium oxide LaRhO3, partial substitution of Sr for La acts as hole-doping, and the resistivity and thermopower decrease systematically with the Sr concentration. The thermopower remains large values at high temperatures (>150 μV/K at 800 K), which makes a remarkable contrast to La1−xSrxCoO3. We associate this with the stability of the low spin state of the Rh3+ ions.

Revisiting spin-lattice relaxation time measurements for dilute spins in high-resolution solid-state NMR spectroscopy

NASA Astrophysics Data System (ADS)

Fu, Riqiang; Li, Jun; Cui, Jingyu; Peng, Xinhua

2016-07-01

Numerous nuclear magnetic resonance (NMR) measurements of spin-lattice relaxation times (T1S) for dilute spins such as 13C have led to investigations of the motional dynamics of individual functional groups in solid materials. In this work, we revisit the Solomon equations and analyze how the heteronuclear cross relaxation between the dilute S (e.g. 13C) and abundant I (e.g. 1H) spins affects the measured T1S values in solid-state NMR in the absence of 1H saturation during the recovery time. It is found theoretically that at the beginning of the S spin magnetization recovery, the existence of non-equilibrium I magnetization introduces the heteronuclear cross relaxation effect onto the recovery of the S spin magnetization and confirmed experimentally that such a heteronuclear cross relaxation effect results in the recovery overshoot phenomena for the dilute spins when T1S is on the same order of T1H, leading to inaccurate measurements of the T1S values. Even when T1S is ten times larger than T1H, the heteronuclear cross relaxation effect on the measured T1S values is still noticeable. Furthermore, this cross relaxation effect on recovery trajectory of the S spins can be manipulated and even suppressed by preparing the initial I and S magnetization, so as to obtain the accurate T1S values. A sample of natural abundance L-isoleucine powder has been used to demonstrate the T1S measurements and their corresponding measured T1C values under various experimental conditions.

Electronic structure and vacancy formation in La(1 - x) B(x) CoO3 (B=Mg,Ca,Ba and x=0.125)

NASA Astrophysics Data System (ADS)

Salawu, Omotayo; Gan, Liyong; Schwingenschlogl, Udo

2015-03-01

The LaCoO3 class of materials is of interest for cathodes of solid oxide fuel cells. Spin-polarized density functional theory is applied to cubic La0.75(Mg/Ca/Ba)0.125CoO3. The effect of this cation doping on the electronic and magnetic properties as well as oxygen vacancy formation energy is studied. Oxygen vacancies with proximity to the dopant are energetically favourable in most cases. We discuss the effect of distortions of the CoO6 octahedron on the electronic structure and the formation energy of oxygen vacancies. The order of formation oxygen is found to be Mg > Ca > Ba. Cation doping incorporates holes to the Co-O network which enhances the oxygen vacancy formation.

Effect of graphite oxide solution concentration on the properties of multilayer graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Umar, Marjoni Imamora Ali; Yap, Chi Chin; Awang, Rozidawati

2013-11-27

This paper reports the influence of graphite oxide (GO) solution concentration on the optical and electrical properties of multilayer graphene (MLG) films. Graphene oxide (GrO) films were deposited on the glass substrates by spin coating aqueous solutions of GO with different concentrations (7, 8, 9, 10 and 11 mg/ml). The GrO films were then thermally reduced at temperature of 500°C in argon flow for half an hour to form MLG films. Both the transmittance and sheet resistance decreased with the GO concentration from 8 mg/ml to 9 mg/ml, possibly due to thicker and uniform coverage of MLG over the substrate.more » However, the transmittance and sheet resistance increased rapidly as the GO concentration reached 11 mg/ml, which can be attributed to poor film quality. The MLG film obtained at concentration of 10 mg/ml showed the highest transmittance/sheet resistance ratio with 69 % transmittance and sheet resistance of 292 ± 63 kΩ/sq. The optimum MLG film was utilized as counter electrode in dye sensitized solar cells based on ZnO nanorods.« less

Structural, optical and NO2 gas sensing properties of ZnMgO thin films prepared by the sol gel method

NASA Astrophysics Data System (ADS)

Chebil, W.; Boukadhaba, M. A.; Madhi, I.; Fouzri, A.; Lusson, A.; Vilar, C.; Sallet, V.

2017-01-01

In this present work, ZnO and ZnMgO thin films prepared by a sol-gel process were deposited on glass substrates via spin coating technique. The structural, morphological and optical properties of the obtained films were investigated. X-ray diffraction study revealed that all layers exhibit a hexagonal wurtzite structure without any secondary phase segregation. The atomic force microscopy (AFM) depicts that the grains size of ours samples decreases as magnesium content increases. The absorption spectra obtained on ZnMgO thin films show a band gap tuning from 3.19 to 3.36 eV, which is also consistent with blue shifting of near-band edge PL emission, measured at low temperature. The incorporated amount of magnesium was calculated and confirmed by EDX. The gas sensing performances were tested in air containing NO2 for different operating temperatures. The experimental result exhibited that ZnMgO sensors shows a faster response and recovery time than the ZnO thin films. The resistivity and the sensor response as function of Mg content were also investigated.

Effect of clathrate hydrate formation and decomposition on NMR parameters in THF-D2O solution.

PubMed

Rousina-Webb, Alexander; Leek, Donald M; Ripmeester, John

2012-06-28

The NMR spin-lattice relaxation time (T(1)), spin-spin relaxation time (T(2)) and the diffusion coefficient D were measured for (1)H in a 1:17 mol % solution of tetrahydrofuran (THF) in D(2)O. The aim of the work was to clarify some earlier points raised regarding the utility of these measurements to convey structural information on hydrate formation and reformation. A number of irregularities in T(1) and T(2) measurements during hydrate processes reported earlier are explained in terms of the presence of interfaces and possible temperature gradients. We observe that T(1) and T(2) in solution are exactly the same before and after hydrate formation, thus confirming that the solution is isotropic. This is inconsistent with the presence of memory effects, at least those that may affect the dynamics to which T(1) and T(2) are sensitive. The measurement of the diffusion coefficient for a number of hours in the subcooled solution before nucleation proved invariant with time, again suggesting that the solution remains isotropic without affecting the guest dynamics and diffusion.

Origin of the butterfly-shaped magnetoresistance in reactive sputtered epitaxial Fe{sub 3}O{sub 4} films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, P.; Zhang, L. T.; Mi, W. B.

2009-08-01

Epitaxial Fe{sub 3}O{sub 4} thin films were synthesized by facing-target reactive sputtering Fe targets. The epitaxy of the Fe{sub 3}O{sub 4} film on MgO (100) was examined macroscopically using x-ray diffraction, including conventional theta-2theta scan, tilting 2theta scan, phi scan, and pole figure. The observed low-field butterfly-shaped magnetoresistance (MR) are explained by the primary fast rotation of the spins far away from antiphase boundaries and the high-field MR changing linearly with magnetic field can be understood by the gradual rotation of the spins near the antiphase boundaries. It is magnetocrystalline anisotropy that causes an increase in MR below Verwey transitionmore » temperature.« less

Magnetic resonance imaging and relaxometry to study water transport mechanisms in a commercially available gastrointestinal therapeutic system (GITS) tablet.

PubMed

Broadbent, Amber L; Fell, Rob J; Codd, Sarah L; Lightley, Kim A; Konagurthu, Sanjay; Koehler-King, Dory G; Seymour, Joseph D

2010-09-15

The hydration of 4 mg Cardura XL (Pfizer), a commercially available gastrointestinal therapeutic system (GITS) tablet, was investigated using magnetic resonance imaging (MRI). A short echo time (T(e)=2.81 ms) technique for MRI of the hydration of a GITS tablet was implemented. From the MR images, signal intensity profiles were generated and interpreted in the context of diffusive and osmotic transport mechanisms. A distinct transition from diffusive to osmotic transport was measured at a timescale relevant to the measured drug release time. Diffusion and osmotic rate coefficients for water in the drug and polymer sweller layers of the tablet were quantified. Spin-lattice T(1) and spin-spin T(2) relaxation times of the water signal from within the tablet were measured as a function of hydration time in order to incorporate the effects of relaxation into interpretation of signal intensity and provide unique information on the distribution of water in different physical and chemical environments within the tablet. Copyright 2010 Elsevier B.V. All rights reserved.

24Mg(p, α) 21Na reaction study for spectroscopy of 21Na

DOE PAGES

Cha, S. M.; Chae, K. Y.; Kim, A.; ...

2015-11-03

The Mg-24(p, alpha)Na-21 reaction was measured at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory in order to better constrain the spins and parities of the energy levels in Na-21 for the astrophysically important F-17(alpha, p)Ne-20 reaction rate calculation. 31-MeV proton beams from the 25-MV tandem accelerator and enriched Mg-24 solid targets were used. When recoiling He-4 particles from the Mg-24(p, alpha)Na-21 reaction we used a highly segmented silicon detector array to detect them; it measured the yields of He-4 particles over a range of angles simultaneously. A observed a new level at 6661 ± 5 keVmore » in the present work. The extracted angular distributions for the first four levels of Na-21 and the results from distorted wave Born approximation (DWBA) calculations were compared to verify and extract the angular momentum transfer.« less

Interactions among dietary boron, molybdenum, and magnesium in the chick

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hunt, C.D.; Nielsen, F.H.

The authors have previously reported that dietary B affects plasma Mo concentrations in chicks fed inadequate levels of Mg and cholecalciferol (vit. D/sub 3/). Because of this finding, they studied the effect of dietary Mo and Mg on the signs of B deficiency in vit. D/sub 3/ deprived chicks. In a fully crossed, 2 x 2 x 2 factorially arranged experiment, day-old cockerel chicks (19 per group) were fed a ground corn-casein-corn oil based diet (containing 0.850 mg B, 0.319 mg Mo, and 125 IU vit. D/sub 3//kg) supplemented with B at 0 or 3 mg/kg, Mo at 0 ormore » 20 mg/kg, and Mg at 300 or 500 mg/kg. After four weeks, B deprivation depressed growth and elevated the plasma glucose and the brain wt/body wt ratio. Low dietary Mo elevated the heart wt/body wt ratio. An interaction between B and Mg affected hemoglobin and plasma alkaline phosphatase and an interaction between B and Mo affected the heart wt/body wt and liver wt/body wt ratios. Mg deficiency gave usual signs including depressed growth, plasma alkaline phosphatase, glucose, and spleen and liver wt/body wt ratios and elevated hematocrit and brain wt/body wt ratio. The findings suggest that physiological levels of Mg and Mo affect B metabolism. The effects of low dietary Mo on vit. D/sub 3/ and/or Mg-deficient chicks needs to be elucidated.« less

Improved electrochemical properties of amorphous Mg 65Ni 27La 8 electrodes: Surface modification using graphite

NASA Astrophysics Data System (ADS)

Wu, D. C.; Li, Lu; Liang, G. Y.; Guo, Y. L.; Wu, H. B.

Amorphous Mg 65Ni 27La 8 alloy is prepared by melt-spinning. The alloy surface is modified using different contents of graphite to improve the performances of the Mg 65Ni 27La 8 electrodes. In detail, the electrochemical properties of (Mg 65Ni 27La 8) + xC (x = 0-0.4) electrodes are studied systematically, where x is the mass ratio of graphite to alloy. Experimental results reveal that the discharge capacity, cycle life, discharge potential characteristics and electrochemical kinetics of the electrodes are all improved. The surface modification enhances the electrocatalytic activity of the alloy, reduces the contact resistance of the electrodes and obstructs the formation of Mg(OH) 2 on the alloy surface. An optimal content of graphite has been obtained. The (Mg 65Ni 27La 8) + 0.25 C electrode has the largest discharge capacity of 827 mA h g -1, which is 1.47 times as large as that of the electrode without graphite, and the best electrochemical kinetics. Further increasing of graphite content will lead to the increase of contact resistance and activation energy for charge-transfer reaction of the electrode, resulting in the degradation of electrode performance.

An examination of slo-pitch pitching trajectories.

PubMed

Wu, Tom; Gervais, Pierre

2008-01-01

Many slo-pitch coaches and players believe that generating spin on a ball can affect its trajectory. The influence of air resistance on a ball that is thrown at a moderate speed and spin is unclear. The aim of this study was to examine the influence of spin on the ball's trajectory in slo-pitch pitching using both experimental results and ball flight simulations. Fourteen pitchers participated in the study, each of whom threw five backspin and topspin pitches each. Data were collected using standard three-dimensional videography. The horizontal velocity, vertical velocity, angular velocity, release height, and horizontal displacement of the backspin pitches were significantly higher than those of the topspin pitches. The ball flight simulations were developed to examine the influence of the ball spin, and it was concluded that the spin of the ball had a significant effect on the ball's vertical and horizontal displacements. Furthermore, our results suggest that a backspin pitch that reaches the maximum height allowable and lands in the front edge of the strike zone has the steepest slope. The present results add to our understanding of projectile motion and aerodynamics.

Robust thermal quantum correlation and quantum phase transition of spin system on fractal lattices

NASA Astrophysics Data System (ADS)

Xu, Yu-Liang; Zhang, Xin; Liu, Zhong-Qiang; Kong, Xiang-Mu; Ren, Ting-Qi

2014-06-01

We investigate the quantum correlation measured by quantum discord (QD) for thermalized ferromagnetic Heisenberg spin systems in one-dimensional chains and on fractal lattices using the decimation renormalization group approach. It is found that the QD between two non-nearest-neighbor end spins exhibits some interesting behaviors which depend on the anisotropic parameter Δ, the temperature T, and the size of system L. With increasing Δ continuously, the QD possesses a cuspate change at Δ = 0 which is a critical point of quantum phase transition (QPT). There presents the "regrowth" tendency of QD with increasing T at Δ < 0, in contrast to the "growth" of QD at Δ > 0. As the size of the system L becomes large, there still exists considerable thermal QD between long-distance end sites in spin chains and on the fractal lattices even at unentangled states, and the long-distance QD can spotlight the presence of QPT. The robustness of QD on the diamond-type hierarchical lattices is stronger than that in spin chains and Koch curves, which indicates that the fractal can affect the behaviors of quantum correlation.

Systematic evaluation of heteronuclear spin decoupling in solid-state NMR at the rotary-resonance conditions in the regime of fast magic-angle spinning

NASA Astrophysics Data System (ADS)

Sharma, Kshama; Madhu, P. K.; Agarwal, Vipin

2016-09-01

The performance of heteronuclear spin decoupling sequences in solid-state NMR severely degrades when the proton radiofrequency (RF) nutation frequencies (ν1) are close to or at multiples of magic-angle spinning (MAS) frequency (νr) that are referred to as rotary-resonance recoupling conditions (ν1 = n · νr). Recently, two schemes, namely, PISSARRO and rCWApA, have been shown to be less affected by the problem of MAS and RF interference, specifically at the n = 2 rotary-resonance recoupling condition, especially in the fast MAS regime. Here, we systematically evaluate the loss in intensity of several heteronuclear spin decoupling sequences at the n = 1, 2 conditions compared to high-power decoupling in the fast-MAS regime. We propose that in the fast-MAS regime (above 40 kHz) the entire discussion about RF and MAS interference can be avoided by using appropriate low-power decoupling sequences which give comparable performance to decoupling sequences with high-power 1H irradiation of ca.195 kHz.

Using Spin Correlations to Distinguish Zh from ZA at the International Linear Collider

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahlon, Gregory; /Penn State U., Mont Alto; Parke, Stephen J.

2006-06-01

We investigate how to exploit the spin information imparted to the Z boson in associated Higgs production at a future linear collider as an aid in distinguishing between CP-even and CP-odd Higgs bosons. We apply a generalized spin-basis analysis which allows us to study the possibilities offered by non-traditional choices of spin projection axis. In particular, we find that the Z bosons produced in association with a CP-even Higgs via polarized collisions are in a single transverse spin-state (> 90% purity) when we use the Zh-transverse basis, provided that the Z bosons are not ultra-relativistic (speed < 0.9c). This samemore » basis applied to the associated production of a CP-odd Higgs yields Z's that are an approximately equal mixture of longitudinal and transverse polarizations. We present a decay angular distribution which could be used to distinguish between the CP-even and CP-odd cases. Finally, we make a few brief remarks about how this distribution would be affected if the Higgs boson turns out to not be a CP-eigenstate.« less

Critical and compensation behavior of a mixed spin-3/2 and spin-5/2 Ising ferrimagnetic system in a graphene layer

NASA Astrophysics Data System (ADS)

Alzate-Cardona, J. D.; Sabogal-Suárez, D.; Restrepo-Parra, E.

2017-05-01

We have studied the magnetic properties of the mixed spin σ = ± 3/2, ± 1/2 and spin S = ± 5/2, ± 3/2, ± 1/2 Ising ferrimagnetic system in a graphene layer by means of Monte Carlo simulations. The effects of next-nearest neighbors exchange interactions and crystal field anisotropy on the critical and compensation behavior of the system have been investigated. The results show that, for a system with given values of the crystal field anisotropy and exchange interaction constants, a compensation point only exists if the values of the spins in the ground state are such that | S | > | σ | and Jσ is higher than a certain value Jσmin . It was shown that the relationship between Jσmin and JS is linear for a given value of the crystal field constant. The compensation and the critical temperature are very sensitive to the change of JS and Jσ, respectively, while the crystal field anisotropy affects both temperatures to a large extent.

Reorientation of the diagonal double-stripe spin structure at Fe 1+yTe bulk and thin-film surfaces

DOE PAGES

Hanke, Torben; Singh, Udai Raj; Cornils, Lasse; ...

2017-01-06

Here, establishing the relation between ubiquitous antiferromagnetism in the parent compounds of unconventional superconductors and their superconducting phase is important for understanding the complex physics in these materials. Going from bulk systems to thin films additionally affects their phase diagram. For Fe 1+yTe, the parent compound of Fe 1+ySe 1$-x$Tex superconductors, bulk-sensitive neutron diffraction revealed an in-plane oriented diagonal double-stripe antiferromagnetic spin structure. Here we show by spin-resolved scanning tunnelling microscopy that the spin direction at the surfaces of bulk Fe 1+yTe and thin films grown on the topological insulator Bi 2Te 3 is canted out of the high-symmetry directionsmore » of the surface unit cell resulting in a perpendicular spin component, keeping the diagonal double-stripe order. As the magnetism of the Fe d-orbitals is intertwined with the superconducting pairing in Fe-based materials, our results imply that the superconducting properties at the surface of the related superconducting compounds might be different from the bulk.« less

The spatial effect of protein deuteration on nitroxide spin-label relaxation: Implications for EPR distance measurement

PubMed Central

El Mkami, Hassane; Ward, Richard; Bowman, Andrew; Owen-Hughes, Tom; Norman, David G.

2014-01-01

Pulsed electron–electron double resonance (PELDOR) coupled with site-directed spin labeling is a powerful technique for the elucidation of protein or nucleic acid, macromolecular structure and interactions. The intrinsic high sensitivity of electron paramagnetic resonance enables measurement on small quantities of bio-macromolecules, however short relaxation times impose a limit on the sensitivity and size of distances that can be measured using this technique. The persistence of the electron spin-echo, in the PELDOR experiment, is one of the most crucial limitations to distance measurement. At a temperature of around 50 K one of the predominant factors affecting persistence of an echo, and as such, the sensitivity and measurable distance between spin labels, is the electron spin echo dephasing time (Tm). It has become normal practice to use deuterated solvents to extend Tm and recently it has been demonstrated that deuteration of the underlying protein significantly extends Tm. Here we examine the spatial effect of segmental deuteration of the underlying protein, and also explore the concentration and temperature dependence of highly deuterated systems. PMID:25310878

Reorientation of the diagonal double-stripe spin structure at Fe 1+yTe bulk and thin-film surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hanke, Torben; Singh, Udai Raj; Cornils, Lasse

Here, establishing the relation between ubiquitous antiferromagnetism in the parent compounds of unconventional superconductors and their superconducting phase is important for understanding the complex physics in these materials. Going from bulk systems to thin films additionally affects their phase diagram. For Fe 1+yTe, the parent compound of Fe 1+ySe 1$-x$Tex superconductors, bulk-sensitive neutron diffraction revealed an in-plane oriented diagonal double-stripe antiferromagnetic spin structure. Here we show by spin-resolved scanning tunnelling microscopy that the spin direction at the surfaces of bulk Fe 1+yTe and thin films grown on the topological insulator Bi 2Te 3 is canted out of the high-symmetry directionsmore » of the surface unit cell resulting in a perpendicular spin component, keeping the diagonal double-stripe order. As the magnetism of the Fe d-orbitals is intertwined with the superconducting pairing in Fe-based materials, our results imply that the superconducting properties at the surface of the related superconducting compounds might be different from the bulk.« less

Analytical Approach Validation for the Spin-Stabilized Satellite Attitude

NASA Technical Reports Server (NTRS)

Zanardi, Maria Cecilia F. P. S.; Garcia, Roberta Veloso; Kuga, Helio Koiti

2007-01-01

An analytical approach for spin-stabilized spacecraft attitude prediction is presented for the influence of the residual magnetic torques and the satellite in an elliptical orbit. Assuming a quadripole model for the Earth s magnetic field, an analytical averaging method is applied to obtain the mean residual torque in every orbital period. The orbit mean anomaly is used to compute the average components of residual torque in the spacecraft body frame reference system. The theory is developed for time variations in the orbital elements, giving rise to many curvature integrals. It is observed that the residual magnetic torque does not have component along the spin axis. The inclusion of this torque on the rotational motion differential equations of a spin stabilized spacecraft yields conditions to derive an analytical solution. The solution shows that the residual torque does not affect the spin velocity magnitude, contributing only for the precession and the drift of the spin axis of the spacecraft. The theory developed has been applied to the Brazilian s spin stabilized satellites, which are quite appropriated for verification and comparison of the theory with the data generated and processed by the Satellite Control Center of Brazil National Research Institute. The results show the period that the analytical solution can be used to the attitude propagation, within the dispersion range of the attitude determination system performance of Satellite Control Center of Brazil National Research Institute.

Multiple acquisitions via sequential transfer of orphan spin polarization (MAeSTOSO): How far can we push residual spin polarization in solid-state NMR?

NASA Astrophysics Data System (ADS)

Gopinath, T.; Veglia, Gianluigi

2016-06-01

Conventional multidimensional magic angle spinning (MAS) solid-state NMR (ssNMR) experiments detect the signal arising from the decay of a single coherence transfer pathway (FID), resulting in one spectrum per acquisition time. Recently, we introduced two new strategies, namely DUMAS (DUal acquisition Magic Angle Spinning) and MEIOSIS (Multiple ExperIments via Orphan SpIn operatorS), that enable the simultaneous acquisitions of multidimensional ssNMR experiments using multiple coherence transfer pathways. Here, we combined the main elements of DUMAS and MEIOSIS to harness both orphan spin operators and residual polarization and increase the number of simultaneous acquisitions. We show that it is possible to acquire up to eight two-dimensional experiments using four acquisition periods per each scan. This new suite of pulse sequences, called MAeSTOSO for Multiple Acquisitions via Sequential Transfer of Orphan Spin pOlarization, relies on residual polarization of both 13C and 15N pathways and combines low- and high-sensitivity experiments into a single pulse sequence using one receiver and commercial ssNMR probes. The acquisition of multiple experiments does not affect the sensitivity of the main experiment; rather it recovers the lost coherences that are discarded, resulting in a significant gain in experimental time. Both merits and limitations of this approach are discussed.

Highly anisotropic exchange interactions of j eff = 1 2 iridium moments on the fcc lattice in La 2 B IrO 6   ( B = Mg , Zn )

DOE PAGES

Aczel, A. A.; Cook, A. M.; Williams, T. J.; ...

2016-06-20

Here we have performed inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites Lamore » $$_2$$ZnIrO$$_6$$ and La$$_2$$MgIrO$$_6$$, which are characterized by A-type antiferromagnetic ground states. The powder inelastic neutron scattering data on these geometrically frustrated $$j_{\\rm eff}=1/2$$ Mott insulators provide clear evidence for gapped spin wave excitations with very weak dispersion. The INS results and thermodynamic data on these materials can be reproduced by conventional Heisenberg-Ising models with significant uniaxial Ising anisotropy and sizeable second-neighbor ferromagnetic interactions. Such a uniaxial Ising exchange interaction is symmetry-forbidden on the ideal fcc lattice, so that it can only arise from the weak crystal distortions away from the ideal fcc limit. This may suggest that even weak distortions in $$j_{\\rm eff}=1/2$$ Mott insulators might lead to strong exchange anisotropies. More tantalizingly, however, we find an alternative viable explanation of the INS results in terms of spin models with a dominant Kitaev interaction. In contrast to the uniaxial Ising exchange, the highly-directional Kitaev interaction is a type of exchange anisotropy which is symmetry-allowed even on the ideal fcc lattice. The Kitaev model has a magnon gap induced by quantum order-by-disorder, while weak anisotropies of the Kitaev couplings generated by the symmetry-lowering due to lattice distortions can pin the order and enhance the magnon gap. In conclusion, our findings highlight how even conventional magnetic orders in heavy transition metal oxides may be driven by highly-directional exchange interactions rooted in strong spin-orbit coupling.« less

The Adsorption of Dextranase onto Mg/Fe-Layered Double Hydroxide: Insight into the Immobilization

PubMed Central

Ding, Yi; Liu, Le; Fang, Yaowei; Zhang, Xu; Lyu, Mingsheng; Wang, Shujun

2018-01-01

We report the adsorption of dextranase on a Mg/Fe-layered double hydroxide (Mg/Fe-LDH). We focused the effects of different buffers, pH, and amino acids. The Mg/Fe-LDH was synthesized, and adsorption experiments were performed to investigate the effects. The maximum adsorption occurred in pH 7.0 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer, and the maximum dextranase adsorption uptake was 1.38 mg/g (416.67 U/mg); histidine and phenylalanine could affect the adsorption. A histidine tag could be added to the protein to increase the adsorption significantly. The performance features and mechanism were investigated with X-ray diffraction patterns (XRD) and Fourier transform infrared spectra (FTIR). The protein could affect the crystal structure of LDH, and the enzyme was adsorbed on the LDH surface. The main interactions between the protein and LDH were electrostatic and hydrophobic. Histidine and phenylalanine could significantly affect the adsorption. The hexagonal morphology of LDH was not affected after adsorption. PMID:29562655

Density functional theory study of small X-doped Mg(n) (X = Fe, Co, Ni, n = 1-9) bimetallic clusters: equilibrium structures, stabilities, electronic and magnetic properties.

PubMed

Kong, Fanjie; Hu, Yanfei

2014-03-01

The geometries, stabilities, and electronic and magnetic properties of Mg(n) X (X = Fe, Co, Ni, n = 1-9) clusters were investigated systematically within the framework of the gradient-corrected density functional theory. The results show that the Mg(n)Fe, Mg(n)Co, and Mg(n)Ni clusters have similar geometric structures and that the X atom in Mg(n)X clusters prefers to be endohedrally doped. The average atomic binding energies, fragmentation energies, second-order differences in energy, and HOMO-LUMO gaps show that Mg₄X (X = Fe, Co, Ni) clusters possess relatively high stability. Natural population analysis was performed and the results showed that the 3s and 4s electrons always transfer to the 3d and 4p orbitals in the bonding atoms, and that electrons also transfer from the Mg atoms to the doped atoms (Fe, Co, Ni). In addition, the spin magnetic moments were analyzed and compared. Several clusters, such as Mg₁,₂,₃,₄,₅,₆,₈,₉Fe, Mg₁,₂,₄,₅,₆,₈,₉Co, and Mg₁,₂,₅,₆,₇,₉Ni, present high magnetic moments (4 μ(B), 3 μ(B), and 2 μ(B), respectively).

Scheme for Quantum Computing Immune to Decoherence

NASA Technical Reports Server (NTRS)

Williams, Colin; Vatan, Farrokh

2008-01-01

A constructive scheme has been devised to enable mapping of any quantum computation into a spintronic circuit in which the computation is encoded in a basis that is, in principle, immune to quantum decoherence. The scheme is implemented by an algorithm that utilizes multiple physical spins to encode each logical bit in such a way that collective errors affecting all the physical spins do not disturb the logical bit. The scheme is expected to be of use to experimenters working on spintronic implementations of quantum logic. Spintronic computing devices use quantum-mechanical spins (typically, electron spins) to encode logical bits. Bits thus encoded (denoted qubits) are potentially susceptible to errors caused by noise and decoherence. The traditional model of quantum computation is based partly on the assumption that each qubit is implemented by use of a single two-state quantum system, such as an electron or other spin-1.2 particle. It can be surprisingly difficult to achieve certain gate operations . most notably, those of arbitrary 1-qubit gates . in spintronic hardware according to this model. However, ironically, certain 2-qubit interactions (in particular, spin-spin exchange interactions) can be achieved relatively easily in spintronic hardware. Therefore, it would be fortunate if it were possible to implement any 1-qubit gate by use of a spin-spin exchange interaction. While such a direct representation is not possible, it is possible to achieve an arbitrary 1-qubit gate indirectly by means of a sequence of four spin-spin exchange interactions, which could be implemented by use of four exchange gates. Accordingly, the present scheme provides for mapping any 1-qubit gate in the logical basis into an equivalent sequence of at most four spin-spin exchange interactions in the physical (encoded) basis. The complexity of the mathematical derivation of the scheme from basic quantum principles precludes a description within this article; it must suffice to report that the derivation provides explicit constructions for finding the exchange couplings in the physical basis needed to implement any arbitrary 1-qubit gate. These constructions lead to spintronic encodings of quantum logic that are more efficient than those of a previously published scheme that utilizes a universal but fixed set of gates.

La 139 NMR investigation of the charge and spin order in a La 1.885 Sr 0.115 CuO 4 single crystal

DOE PAGES

Arsenault, A.; Takahashi, S. K.; Imai, T.; ...

2018-02-14

139La NMR is suited for investigations into magnetic properties of La 2CuO 4 -based cuprates in the vicinity of their magnetic instabilities, owing to the modest hyperfine interactions between 139La nuclear spins and Cu electron spins. We report comprehensive 139La NMR measurements on a single-crystal sample of high-T c superconductor La 1.885 Sr 0.115 CuO 4 in a broad temperature range across the charge and spin order transitions (T charge ≃ 80 K, T neutron spin ≃ T c = 30 K). From the high-precision measurements of the linewidth for the nuclear spin I z = + 1 / 2 to -1/2 central transition, we show that paramagnetic line broadening sets in precisely at T charge due to enhanced spin correlations within the CuO 2 planes. Additional paramagnetic line broadening ensues below ~35 K, signaling that Cu spins in some segments of CuO 2 planes are on the verge of three-dimensional magnetic order. A static hyperfine magnetic field arising from ordered Cu moments along the ab plane, however, begins to develop only below Tmore » $$μSR\\atop{spin}$$ = 15 – 20 K, where earlier muon spin rotation measurements detected Larmor precession for a small volume fraction (~20 % ) of the sample. Based on the measurement of 139 La nuclear-spin-lattice relaxation rate 1/T 1, we also show that charge order triggers enhancement of low-frequency Cu spin fluctuations inhomogeneously; a growing fraction of 139 La sites is affected by enhanced low-frequency spin fluctuations toward the eventual magnetic order, whereas a diminishing fraction continues to exhibit a behavior analogous to the optimally superconducting phase even below T charge. In conclusion, these 139La NMR results corroborate our recent 63Cu NMR observation that a very broad, anomalous winglike signal gradually emerges below T charge, whereas the normally behaving, narrower main peak is gradually wiped out [T. Imai et al., Phys. Rev. B 96, 224508 (2017)]. Furthermore, we show that the enhancement of low-energy spin excitations in the low-temperature regime below Tneutron spin (≃ Tc) depends strongly on the magnitude and orientation of the applied magnetic field.« less

La 139 NMR investigation of the charge and spin order in a La 1.885 Sr 0.115 CuO 4 single crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arsenault, A.; Takahashi, S. K.; Imai, T.

139La NMR is suited for investigations into magnetic properties of La 2CuO 4 -based cuprates in the vicinity of their magnetic instabilities, owing to the modest hyperfine interactions between 139La nuclear spins and Cu electron spins. We report comprehensive 139La NMR measurements on a single-crystal sample of high-T c superconductor La 1.885 Sr 0.115 CuO 4 in a broad temperature range across the charge and spin order transitions (T charge ≃ 80 K, T neutron spin ≃ T c = 30 K). From the high-precision measurements of the linewidth for the nuclear spin I z = + 1 / 2 to -1/2 central transition, we show that paramagnetic line broadening sets in precisely at T charge due to enhanced spin correlations within the CuO 2 planes. Additional paramagnetic line broadening ensues below ~35 K, signaling that Cu spins in some segments of CuO 2 planes are on the verge of three-dimensional magnetic order. A static hyperfine magnetic field arising from ordered Cu moments along the ab plane, however, begins to develop only below Tmore » $$μSR\\atop{spin}$$ = 15 – 20 K, where earlier muon spin rotation measurements detected Larmor precession for a small volume fraction (~20 % ) of the sample. Based on the measurement of 139 La nuclear-spin-lattice relaxation rate 1/T 1, we also show that charge order triggers enhancement of low-frequency Cu spin fluctuations inhomogeneously; a growing fraction of 139 La sites is affected by enhanced low-frequency spin fluctuations toward the eventual magnetic order, whereas a diminishing fraction continues to exhibit a behavior analogous to the optimally superconducting phase even below T charge. In conclusion, these 139La NMR results corroborate our recent 63Cu NMR observation that a very broad, anomalous winglike signal gradually emerges below T charge, whereas the normally behaving, narrower main peak is gradually wiped out [T. Imai et al., Phys. Rev. B 96, 224508 (2017)]. Furthermore, we show that the enhancement of low-energy spin excitations in the low-temperature regime below Tneutron spin (≃ Tc) depends strongly on the magnitude and orientation of the applied magnetic field.« less

SPIN EVOLUTION OF ACCRETING YOUNG STARS. I. EFFECT OF MAGNETIC STAR-DISK COUPLING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matt, Sean P.; Greene, Thomas P.; Pinzon, Giovanni

2010-05-10

We present a model for the rotational evolution of a young, solar mass star interacting with an accretion disk. The model incorporates a description of the angular momentum transfer between the star and the disk due to a magnetic connection, and includes changes in the star's mass and radius and a decreasing accretion rate. The model also includes, for the first time in a spin evolution model, the opening of the stellar magnetic field lines, as expected to arise from twisting via star-disk differential rotation. In order to isolate the effect that this has on the star-disk interaction torques, wemore » neglect the influence of torques that may arise from open field regions connected to the star or disk. For a range of magnetic field strengths, accretion rates, and initial spin rates, we compute the stellar spin rates of pre-main-sequence stars as they evolve on the Hayashi track to an age of 3 Myr. How much the field opening affects the spin depends on the strength of the coupling of the magnetic field to the disk. For the relatively strong coupling (i.e., high magnetic Reynolds number) expected in real systems, all models predict spin periods of less than {approx}3 days, in the age range of 1-3 Myr. Furthermore, these systems typically do not reach an equilibrium spin rate within 3 Myr, so that the spin at any given time depends upon the choice of initial spin rate. This corroborates earlier suggestions that, in order to explain the full range of observed rotation periods of approximately 1-10 days, additional processes, such as the angular momentum loss from powerful stellar winds, are necessary.« less

The Mini-Social Phobia Inventory: psychometric properties in an adolescent general population sample.

PubMed

Ranta, Klaus; Kaltiala-Heino, Riittakerttu; Rantanen, Päivi; Marttunen, Mauri

2012-07-01

Onset of social phobia (SP) typically occurs in adolescence. Short screening instruments for its assessment are needed for use in primary health and school settings. The 3-item Mini-Social Phobia Inventory (SPIN) has demonstrated effectiveness in screening for generalized SP (GSP) in adults. This study examined the psychometrics of the Mini-SPIN in an adolescent general population sample. Three hundred fifty adolescents aged 12 to 17 years were clinically interviewed using the Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime Version for identification of SP and other Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Axis I disorders, blind to their Mini-SPIN status. Associations between SP; subclinical SP; other anxiety, depressive, and disruptive disorders; and Mini-SPIN scores were examined, and diagnostic efficiency statistics were calculated. The association between Mini-SPIN scores and the generalized subtype of SP was also examined. As in adults, the Mini-SPIN items differentiated subjects with SP from those without. A score of 6 points or greater was found optimal in predicting SP with a sensitivity of 86%, specificity of 84%, and positive and negative predictive values of 26% and 99%. The Mini-SPIN also possessed discriminative validity, as scores were higher for adolescents with SP than they were for those with depressive, disruptive, and other anxiety disorders. The Mini-SPIN was also able to differentiate adolescents with GSP from the rest of the sample. The Mini-SPIN has good psychometrics for screening SP in adolescents from general population and may have value in screening for GSP. Copyright © 2012 Elsevier Inc. All rights reserved.

Magnon rainbows filtered through phonon clouds

NASA Astrophysics Data System (ADS)

Boona, Stephen R.

2016-06-01

The study of heat flow in magnetic insulators is a topic of significant interest in spin caloritronics, especially for understanding the nuanced origins of the spin Seebeck effect (SSE). Recent work by Diniz and Costa (2016 New J. Phys. 18 052002) provides insight into this subject by presenting a microscopic model for the spectral dependence of magnon-phonon interactions in magnetic insulators, which has been a challenging puzzle for decades. Their new paper shows that phonon-mediated magnon-magnon interactions affect the lifetime of magnons differently depending on the magnon wavelength. As a result, low energy magnons transport spin more efficiently, and are more sensitive to applied magnetic fields. These results help explain some unexpected behavior in the SSE recently reported in several experiments.

Suppression of quantum phase interference in the molecular magnet Fe8 with dipolar-dipolar interaction

NASA Astrophysics Data System (ADS)

Chen, Zhi-De; Liang, J.-Q.; Shen, Shun-Qing

2002-09-01

Renormalized tunnel splitting with a finite distribution in the biaxial spin model for molecular magnets is obtained by taking into account the dipolar interaction of enviromental spins. Oscillation of the resonant tunnel splitting with a transverse magnetic field along the hard axis is smeared by the finite distribution, which subsequently affects the quantum steps of the hysteresis curve evaluated in terms of the modified Landau-Zener model of spin flipping induced by the sweeping field. We conclude that the dipolar-dipolar interaction drives decoherence of quantum tunneling in the molecular magnet Fe8, which explains why the quenching points of tunnel splitting between odd and even resonant tunneling predicted theoretically were not observed experimentally.

NMR longitudinal relaxation enhancement in metal halides by heteronuclear polarization exchange during magic-angle spinning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shmyreva, Anna A.; Safdari, Majid; Furó, István

2016-06-14

Orders of magnitude decrease of {sup 207}Pb and {sup 199}Hg NMR longitudinal relaxation times T{sub 1} upon magic-angle-spinning (MAS) are observed and systematically investigated in solid lead and mercury halides MeX{sub 2} (Me = Pb, Hg and X = Cl, Br, I). In lead(II) halides, the most dramatic decrease of T{sub 1} relative to that in a static sample is in PbI{sub 2}, while it is smaller but still significant in PbBr{sub 2}, and not detectable in PbCl{sub 2}. The effect is magnetic-field dependent but independent of the spinning speed in the range 200–15 000 Hz. The observed relaxation enhancementmore » is explained by laboratory-frame heteronuclear polarization exchange due to crossing between energy levels of spin-1/2 metal nuclei and adjacent quadrupolar-spin halogen nuclei. The enhancement effect is also present in lead-containing organometal halide perovskites. Our results demonstrate that in affected samples, it is the relaxation data recorded under non-spinning conditions that characterize the local properties at the metal sites. A practical advantage of fast relaxation at slow MAS is that spectral shapes with orientational chemical shift anisotropy information well retained can be acquired within a shorter experimental time.« less

Theory of Fast Optical Spin Rotation in a Quantum Dot Based on Geometric Phases and Trapped States

DTIC Science & Technology

2007-11-19

rules are not affected by anisotropic exchange [15,16]. Our proposal is based on the observation that from the four-level system of Fig. 1, different...lasers, which is a significant experi- mental simplification. It requires the ability to perform Rabi oscillations between spin and trion, which has been...y) is the Rabi frequency of the transition with polarization x (y). Now we choose the envelope to be ft secht. We require the popu- lation

Structural Evolution of Reversible Mg Insertion into a Bilayer Structure of V 2 O 5 · n H 2 O Xerogel Material

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sa, Niya; Kinnibrugh, Tiffany L.; Wang, Hao

Functional multivalent intercalation cathodes represent one of the largest hurdles in the development of Mg batteries. While there are many reports of Mg cathodes, many times the evidence of intercalation chemistry is only circumstantial. In this work, direct evidence of Mg intercalation into a bilayer structure of V2O5·nH2O xerogel is confirmed, and the nature of the Mg intercalated species is reported. The interlayer spacing of V2O5·nH2O contracts upon Mg intercalation and expands for Mg deintercalation due to the strong electrostatic interaction between the divalent cation and the cathode. A combination of NMR, pair distribution function (PDF) analysis, and X-ray absorptionmore » near edge spectroscopy (XANES) confirmed reversible Mg insertion into the V2O5·nH2O material, and structural evolution of Mg intercalation leads to the formation of multiple new phases. Structures of V2O5·nH2O with Mg intercalation were further supported by the first principle simulations. A solvent cointercalated Mg in V2O5·nH2O is observed for the first time, and the 25Mg magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy was used to elucidate the structure obtained upon electrochemical cycling. Specifically, existence of a well-defined Mg–O environment is revealed for the Mg intercalated structures. Information reported here reveals the fundamental Mg ion intercalation mechanism in a bilayer structure of V2O5·nH2O material and provides insightful design metrics for future Mg cathodes.« less

Probing Metal Carbonation Reactions of CO2 in a Model System Containing Forsterite and H2O Using Si-29, C-13 Magic Angle Sample Spinning NMR Spectroscopy

NASA Astrophysics Data System (ADS)

Hu, J.; Kwak, J.; Hoyt, D. W.; Sears, J. A.; Rosso, K. M.; Felmy, A. R.

2009-12-01

Ex situ solid state NMR have been used for the first time to study fundamental mineral carbonation processes and reaction extent relevant to geologic carbon sequestration using a model silicate mineral forsterite (Mg2SiO4)+scCO2 with and without H2O. Run conditions were 80C and 96 bar. Si-29 NMR clearly shows that in the absence of CO2, the role of H2O is to hydrolyze surface Mg-O-Si bonds to produce Mg2+, and mono- and oligomeric hydroxylated silica species. The surface hydrolysis products contain only Q0 (Si(OH)4) and Q1 (Si(OH)3OSi) species. An equilibrium between Q0, Q1 and Mg2+ with a saturated concentration equivalent to less than 3.2% of the Mg2SiO4 conversion is obtained at a reaction time of up to 7 days. Using scCO2 without H2O, no reaction is observed within 7 days. Using both scCO2 and H2O, the surface reaction products for silica are mainly Q3 (SiOH(OSi)3) species accompanied by a lesser amount of Q2 (Si(OH)2(OSi)2) and Q4 (Si(OSi)4). However, no Q0 and Q1 were detected, indicating the carbonic acid formation/deprotonation and magnesite (MgCO3) precipitation reactions are faster than the forsterite hydrolysis process. Thus it can be concluded that the Mg2SiO4 hydrolysis process is the rate limiting step of the overall mineral carbonation process. Si-29 NMR combined with XRD, TEM, SAED and EDX further reveal that the reaction is a surface reaction with the Mg2SiO4 crystallite in the core and with condensed Q2-Q4 species forming amorphous surface layers. C-13 MAS NMR identified a possible reaction intermediates as (MgCO3)4*Mg(OH)2*5H2O. However, at long reaction times only crystallite magnesite MgCO3 products are observed. This research is part of a broader effort at PNNL to develop experimental tools and fundamental insights into chemical transformations affecting subsurface CO2 reactive transport. Si-29 (left) and C-13 (right) MAS NMR spectra of Mg2SiO4 under various reaction conditions. Si-29 NMR reveals that in scCO2 without H2O, no reaction is observed (b). In H2O without scCO2, only surface hydrolysis products Q0 and Q1 are present (c). In a mixture of both H2O and scCO2, the products are Q2, Q3 and Q4 (d). C-13 NMR (e-f) reveals the formation of MgCO3 at long reaction times with (MgCO3)4*Mg(OH)2*5H2O as a possible reaction intermediate.

Morphology effects on spin-dependent transport and recombination in polyfluorene thin films

NASA Astrophysics Data System (ADS)

Miller, Richards; van Schooten, K. J.; Malissa, H.; Joshi, G.; Jamali, S.; Lupton, J. M.; Boehme, C.

2016-12-01

We have studied the role of spin-dependent processes on conductivity in polyfluorene (PFO) thin films by preforming continuous wave (cw) electrically detected magnetic resonance (EDMR) spectroscopy at temperatures between 10 K and room temperature using microwave frequencies between about 1 GHz and 20 GHz, as well as pulsed EDMR at the X band (10 GHz). Variable frequency EDMR allows us to establish the role of spin-orbit coupling in spin-dependent processes whereas pulsed EDMR allows for the observation of coherent spin motion effects. We used PFO for this study in order to allow for the investigation of the effects of microscopic morphological ordering since this material can adopt two distinct intrachain morphologies: an amorphous (glassy) phase, in which monomer units are twisted with respect to each other, and an ordered (β) phase, where all monomers lie within one plane. In thin films of organic light-emitting diodes, the appearance of a particular phase can be controlled by deposition parameters and solvent vapor annealing, and is verified by electroluminescence spectroscopy. Under bipolar charge-carrier injection conditions, we conducted multifrequency cw EDMR, electrically detected Rabi spin-beat experiments, and Hahn echo and inversion-recovery measurements. Coherent echo spectroscopy reveals electrically detected electron-spin-echo envelope modulation due to the coupling of the carrier spins to nearby nuclear spins. Our results demonstrate that, while conformational disorder can influence the observed EDMR signals, including the sign of the current changes on resonance as well as the magnitudes of local hyperfine fields and charge-carrier spin-orbit interactions, it does not qualitatively affect the nature of spin-dependent transitions in this material. In both morphologies, we observe the presence of at least two different spin-dependent recombination processes. At room temperature and 10 K, polaron-pair recombination through weakly spin-spin coupled intermediate charge-carrier pair states is dominant, while at low temperatures, additional signatures of spin-dependent charge transport through the interaction of polarons with triplet excitons are seen in the half-field resonance of a triplet spin-1 species. This additional contribution arises since triplet lifetimes are increased at lower temperatures. We tentatively conclude that spectral broadening induced by hyperfine coupling is slightly weaker in the more ordered β-phase than in the glassy phase since protons are more evenly spaced, whereas broadening effects due to spin-orbit coupling, which impacts the distribution of g -factors, appear to be somewhat more significant in the β-phase.

Spin-Dependent Transport through Chiral Molecules Studied by Spin-Dependent Electrochemistry

PubMed Central

2016-01-01

Conspectus Molecular spintronics (spin + electronics), which aims to exploit both the spin degree of freedom and the electron charge in molecular devices, has recently received massive attention. Our recent experiments on molecular spintronics employ chiral molecules which have the unexpected property of acting as spin filters, by way of an effect we call “chiral-induced spin selectivity” (CISS). In this Account, we discuss new types of spin-dependent electrochemistry measurements and their use to probe the spin-dependent charge transport properties of nonmagnetic chiral conductive polymers and biomolecules, such as oligopeptides, L/D cysteine, cytochrome c, bacteriorhodopsin (bR), and oligopeptide-CdSe nanoparticles (NPs) hybrid structures. Spin-dependent electrochemical measurements were carried out by employing ferromagnetic electrodes modified with chiral molecules used as the working electrode. Redox probes were used either in solution or when directly attached to the ferromagnetic electrodes. During the electrochemical measurements, the ferromagnetic electrode was magnetized either with its magnetic moment pointing “UP” or “DOWN” using a permanent magnet (H = 0.5 T), placed underneath the chemically modified ferromagnetic electrodes. The spin polarization of the current was found to be in the range of 5–30%, even in the case of small chiral molecules. Chiral films of the l- and d-cysteine tethered with a redox-active dye, toludin blue O, show spin polarizarion that depends on the chirality. Because the nickel electrodes are susceptible to corrosion, we explored the effect of coating them with a thin gold overlayer. The effect of the gold layer on the spin polarization of the electrons ejected from the electrode was investigated. In addition, the role of the structure of the protein on the spin selective transport was also studied as a function of bias voltage and the effect of protein denaturation was revealed. In addition to “dark” measurements, we also describe photoelectrochemical measurements in which light is used to affect the spin selective electron transport through the chiral molecules. We describe how the excitation of a chromophore (such as CdSe nanoparticles), which is attached to a chiral working electrode, can flip the preferred spin orientation of the photocurrent, when measured under the identical conditions. Thus, chirality-induced spin polarization, when combined with light and magnetic field effects, opens new avenues for the study of the spin transport properties of chiral molecules and biomolecules and for creating new types of spintronic devices in which light and molecular chirality provide new functions and properties. PMID:27797176

Charge transfer transitions in optical spectra of NicMg1-cO oxides

NASA Astrophysics Data System (ADS)

Churmanov, V. N.; Sokolov, V. I.; Pustovarov, V. A.; Gruzdev, N. B.; Uimin, M. A.; Byzov, I. V.; Druzhinin, A. V.; Korolyov, A. V.; Kim, G. A.; Zatsepin, A. F.; Kuznetsova, J. A.

2017-04-01

Radiative recombination with charge transfer was observed in NicMg1-cO (c = 0.008) oxides over the 8-300 K temperature range. This recombination occurs as a result of strong hybridization of the Ni2+ ion 3d-states and the band states. The charge transfer radiation excitation spectrum shows vibrational LO repeats of two exciton lines having charge transfer energy intervals of about 35 meV. The NiO nanocrystal absorption spectrum shows two weak peaks with energies of 3.510 and 3.543 eV, which are highly dependent on temperature. They are interpreted as charge transfer excitons at the edge of NiO fundamental absorption. The distance between the charge transfer exciton lines in the NicMg1-cO oxide spectra are caused by spin-orbit splitting of the valence band peak that was formed by the p-states of the oxygen ion.

Reducing orbital eccentricity of precessing black-hole binaries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buonanno, Alessandra; Taracchini, Andrea; Kidder, Lawrence E.

2011-05-15

Building initial conditions for generic binary black-hole evolutions which are not affected by initial spurious eccentricity remains a challenge for numerical-relativity simulations. This problem can be overcome by applying an eccentricity-removal procedure which consists of evolving the binary black hole for a couple of orbits, estimating the resulting eccentricity, and then restarting the simulation with corrected initial conditions. The presence of spins can complicate this procedure. As predicted by post-Newtonian theory, spin-spin interactions and precession prevent the binary from moving along an adiabatic sequence of spherical orbits, inducing oscillations in the radial separation and in the orbital frequency. For single-spinmore » binary black holes these oscillations are a direct consequence of monopole-quadrupole interactions. However, spin-induced oscillations occur at approximately twice the orbital frequency, and therefore can be distinguished and disentangled from the initial spurious eccentricity which occurs at approximately the orbital frequency. Taking this into account, we develop a new eccentricity-removal procedure based on the derivative of the orbital frequency and find that it is rather successful in reducing the eccentricity measured in the orbital frequency to values less than 10{sup -4} when moderate spins are present. We test this new procedure using numerical-relativity simulations of binary black holes with mass ratios 1.5 and 3, spin magnitude 0.5, and various spin orientations. The numerical simulations exhibit spin-induced oscillations in the dynamics at approximately twice the orbital frequency. Oscillations of similar frequency are also visible in the gravitational-wave phase and frequency of the dominant l=2, m=2 mode.« less

ESR evidence for radical production from the reaction of ozone with unsaturated lipids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Church, D.F.; McAdams, M.L..; Pryor, W.A.

1991-03-15

The authors report electron spin resonance (ESR) spin trapping evidence for radical production by the reaction of ozone with unsaturated compounds. Soy and egg phosphatidylcholine liposomes, fatty acid emulsions, and homogeneous aqueous solutions of 3-hexenoic acid were treated with ozone in the presence of the spin trap {alpha}-phenyl-N-tert-butyl nitrone (PBN). Under these conditions, they observe spin adducts resulting from the trapping of both organic carbon- and oxygen-centered radicals. When the lipid-soluble antioxidant alpha-tocopherol is included in the liposomal systems, the formation of spin adducts is completely inhibited. The authors suggest that radicals giving rise to these spin adducts arise formmore » the rapid decomposition of the 1,2,3-trioxolane intermediate that is initially formed when ozone reacts with the carbon-carbon double bonds of the substrates. These free radicals are not formed by the decomposition of the Criegee ozonide, since little of the ozonide is formed in the presence of water. Although hydrogen peroxide is the predominate peroxidic product of the ozone/alkene reaction, its decomposition is not responsible for the observed radical production since neither catalase nor iron chelators significantly affect the spin adduct yield. The radical yield is approximately 1%. Since a polyunsaturated fatty acid (PUFA) such as linoleic acid produces much higher concentrations of spin trappable radicals than does the monounsaturated fatty oleic acid, the results also suggest that sites in the lung containing higher levels of PUFA may be an important target for radical formation.« less

Thin-Film Photoluminescent Properties and the Atomistic Model of Mg2TiO4 as a Non-rare Earth Matrix Material for Red-Emitting Phosphor

NASA Astrophysics Data System (ADS)

Huang, Chieh-Szu; Chang, Ming-Chuan; Huang, Cheng-Liang; Lin, Shih-kang

2016-12-01

Thin-film electroluminescent devices are promising solid-state lighting devices. Red light-emitting phosphor is the key component to be integrated with the well-established blue light-emitting diode chips for stimulating natural sunlight. However, environmentally hazardous rare-earth (RE) dopants, e.g. Eu2+ and Ce2+, are commonly used for red-emitting phosphors. Mg2TiO4 inverse spinel has been reported as a promising matrix material for "RE-free" red light luminescent material. In this paper, Mg2TiO4 inverse spinel is investigated using both experimental and theoretical approaches. The Mg2TiO4 thin films were deposited on Si (100) substrates using either spin-coating with the sol-gel process, or radio frequency sputtering, and annealed at various temperatures ranging from 600°C to 900°C. The crystallinity, microstructures, and photoluminescent properties of the Mg2TiO4 thin films were characterized. In addition, the atomistic model of the Mg2TiO4 inverse spinel was constructed, and the electronic band structure of Mg2TiO4 was calculated based on density functional theory. Essential physical and optoelectronic properties of the Mg2TiO4 luminance material as well as its optimal thin-film processing conditions were comprehensively reported.

Control of single-spin magnetic anisotropy by exchange coupling

NASA Astrophysics Data System (ADS)

Oberg, Jenny C.; Calvo, M. Reyes; Delgado, Fernando; Moro-Lagares, María; Serrate, David; Jacob, David; Fernández-Rossier, Joaquín; Hirjibehedin, Cyrus F.

2014-01-01

The properties of quantum systems interacting with their environment, commonly called open quantum systems, can be affected strongly by this interaction. Although this can lead to unwanted consequences, such as causing decoherence in qubits used for quantum computation, it can also be exploited as a probe of the environment. For example, magnetic resonance imaging is based on the dependence of the spin relaxation times of protons in water molecules in a host's tissue. Here we show that the excitation energy of a single spin, which is determined by magnetocrystalline anisotropy and controls its stability and suitability for use in magnetic data-storage devices, can be modified by varying the exchange coupling of the spin to a nearby conductive electrode. Using scanning tunnelling microscopy and spectroscopy, we observe variations up to a factor of two of the spin excitation energies of individual atoms as the strength of the spin's coupling to the surrounding electronic bath changes. These observations, combined with calculations, show that exchange coupling can strongly modify the magnetic anisotropy. This system is thus one of the few open quantum systems in which the energy levels, and not just the excited-state lifetimes, can be renormalized controllably. Furthermore, we demonstrate that the magnetocrystalline anisotropy, a property normally determined by the local structure around a spin, can be tuned electronically. These effects may play a significant role in the development of spintronic devices in which an individual magnetic atom or molecule is coupled to conducting leads.

The spin evolution of nascent neutron stars

NASA Astrophysics Data System (ADS)

Watts, Anna L.; Andersson, Nils

2002-07-01

The loss of angular momentum owing to unstable r-modes in hot young neutron stars has been proposed as a mechanism for achieving the spin rates inferred for young pulsars. One factor that could have a significant effect on the action of the r-mode instability is fallback of supernova remnant material. The associated accretion torque could potentially counteract any gravitational-wave-induced spin-down, and accretion heating could affect the viscous damping rates and hence the instability. We discuss the effects of various external agents on the r-mode instability scenario within a simple model of supernova fallback on to a hot young magnetized neutron star. We find that the outcome depends strongly on the strength of the magnetic field of the star. Our model is capable of generating spin rates for young neutron stars that accord well with initial spin rates inferred from pulsar observations. The combined action of r-mode instability and fallback appears to cause the spin rates of neutron stars born with very different spin rates to converge, on a time-scale of approximately 1 year. The results suggest that stars with magnetic fields <=1013G could emit a detectable gravitational wave signal for perhaps several years after the supernova event. Stars with higher fields (magnetars) are unlikely to emit a detectable gravitational wave signal via the r-mode instability. The model also suggests that the r-mode instability could be extremely effective in preventing young neutron stars from going dynamically unstable to the bar-mode.

Materials physics of half-metallic magnetic oxide films by pulsed laser deposition: Controlling the crystal structure and near-surface properties of strontium iron molybdenum oxide and chromium oxide films

NASA Astrophysics Data System (ADS)

Jalili, Helia

The idea of half-metallic ferromagnets was first introduced by de Groot et al. in 1983 based on their calculations. The density of state at the Fermi level for half-metallic ferromagnet is completely polarized, meaning that only one of the spin up or spin down channel exists and has metallic behaviour while the other spin channel behaves as a semiconductor or insulator. This unusual electronic structure can be seen in different materials including Sr2FeMoO6, CrO2 and Mn-based Heusler alloys. The high spin polarization degree of the half-metallic ferromagnets makes them a perfect candidate to be used as a spin-injector/detector in spin-based electronics device (spintronics). However, the degree of spin polarization of these materials, particularly in the multilayered structure spintronic devices, strongly depends on the surface/interface quality and the presence of defects, which was the subject of the present study. Pulsed laser deposition (PLD) has been used to grow two examples of the half-metallic ferromagnets, namely, Sr2FeMoO6 and CrO2. The effects of the growth conditions (deposition temperature, gas pressure, laser power, target-to-substrate distance, post-annealing) and of the substrate lattice mismatch and thickness evolution have been studied. By optimizing the growth conditions, nanocrystalline Sr2FeMoO6 films have been grown on a Si(100) substrate for the first time. This single-phase Sr 2FeMoO6 film was obtained at a temperature as low as 600°C, and it exhibits a high saturation magnetic moment of 3.4 muB per formula unit at 77 K. By using glancing-incidence X-ray diffraction with different incident beam angles, the crystal structure of the film was sampled as a function of depth. Despite the lack of good lattice matching with the Si substrate, a preferential orientation of the nanocrystals in the film was observed for the as-grown Sr2FeMoO6 films thicker than 60 nm. Furthermore, effects of the deposition temperature on the epitaxial growth of the Sr2FeMoO6 films on MgO(001) have been studied by means of high-resolution X-ray diffraction. The film grown at 800°C was post-annealed in oxygen, producing epitaxial films of SrMoO4 on top of the Sr2FeMoO6 film. The corresponding magnetization data showed that the post-annealing treatment lowered the saturation magnetic moment from 3.4 muB per formula unit (or /f.u.) for the as-grown Sr2FeMoO6 film to 1.4 muB/f.u. after annealing. X-ray photoemission measurements as a function of sputtering time further revealed the presence of SrMoO4 on both the as-grown and annealed films, and their corresponding depth profiles indicated a thicker SrMoO 4 overlayer on the annealed film. The intensity ratios of the 3d features of Mo4+, Mo5+, and Mo6+ for Sr 2FeMoO6 remained unchanged with sputtering depth (after 160 s of sputtering), supporting the conclusion that the observed secondary phase (SrMoO4) was formed predominantly on the surface and not in the sub-grain boundaries of the as-grown Sr2FeMoO6 film. The epitaxial growth evolution of Sr2FeMoO6 films of different thickness on substrates of MgO(001), SrTiO3(100) and LaAlO3(100) have also been studied. For each thickness, surface morphology, grain size, film epitaxy, and crystal quality were determined by atomic force microscopy and X-ray diffraction (o-2theta scan and reciprocal space mapping). For thicker films (˜120 nm), high resolution X-ray diffraction studies revealed that SrMoO4 and other parasitic phases tend to forms on SrTiO3 and LaAlO3 substrates, but not on those grown on MgO substrates. As a second part of the project, single-phase CrO2 nanostructured thin films have been grown for the first time directly on MgO(001) by PLD from a metallic Cr target in an O2 environment. X-ray diffraction shows that these films are strained and consist of CrO2 crystallites with two possible epitaxial relationships to the substrate: either CrO 2(110) or CrO2(200) is parallel to MgO(001). X-ray photoemission further confirms that the films are primarily CrO2 covered with a thin CrO3 overlayer, and indicates its complete synthesis without any residual metallic Cr.

Theoretical study of hyperfine coupling constants and electron spin g factors for X2Σ diatomics from Groups 1 and 2

NASA Astrophysics Data System (ADS)

Bruna, Pablo J.; Grein, Friedrich

The ESR parameters of the cations Be 2 + , Mg 2 + , Ca 2 + , BeMg + , BeCa + , MgCa + and the mixed radicals ZBe, ZMg, ZCa (Z = Li, Na, K), all having a X 2 Σu + (1 σg 2 1 σu )/X 2 Sigma + (1 σ2 2 σ) ground state, have been studied theoretically. The A iso and A dip constants have been calculated with UHF, CISD, MP2, B3LYP, PW91PW91 wavefunctions, and 6-311+G(2df) basis sets. The electron spin g factors (magnetic moment μs) have been evaluated from correlated (MRDCI) wavefunctions, using a Hamiltonian based on Breit-Pauli theory with perturbation expansions up to second order, and 6-311+ G(2d) basis sets. As expected for s-rich radicals, the hyperfine spectra are governed by the A iso terms. Both Δg|| and Δg Υ̂values are negative, but Δg|| lies close to zero. For Δg Υ̂, the coupling with 1 2 Π(u) dominates the sum-over-states expansions. Although the singly occupied MOs (SOMO) are mostly of s character, the | Δg Υ̂| are relatively large, up to 5200 ppm for cationic, and up to 7850 ppm for neutral radicals. These large values are caused by low excitation energies and high magnetic transition moments, the latter due to the fact that the σ*( s - s ) SOMO has the same nodal properties as a p σorbital. Of the radicals considered here, an ESR spectrum is available only for Mg2+. Our theoretical A iso of-287 MHz reproduces well the matrix result (-291 MHz). Calculated values of-10 ppm for Deltag|| and of-1280 ppm for Deltag Υ̂give an average < Δg> =-860 ppm that lies within the experimental range of-600( ±300) ppm in Ne, and of-1300( ±500) ppm in Ar matrices.

Landscape determinants of exchangeable calcium and magnesium in Ozark Highland forest soils

Treesearch

John M. Kabrick; Keith W. Goyne; Zhaofei Fan; Dennis Meinert

2011-01-01

Exchangeable base cations, particularly Ca and Mg, largely govern soil acidity and, consequently, plant species composition in temperate forests. Although studies have identified soil and terrain characteristics affecting exchangeable Ca and Mg, few studies have identified the relative importance of factors affecting Ca and Mg distribution across landscapes. Objectives...

Coulomb spin liquid in anion-disordered pyrochlore Tb 2Hf 2O 7

DOE PAGES

Sibille, Romain; Lhotel, Elsa; Hatnean, Monica Ciomaga; ...

2017-10-12

Here, the charge ordered structure of ions and vacancies characterizing rare-earth pyrochlore oxides serves as a model for the study of geometrically frustrated magnetism. The organization of magnetic ions into networks of corner-sharing tetrahedra gives rise to highly correlated magnetic phases with strong fluctuations, including spin liquids and spin ices. It is an open question how these ground states governed by local rules are affected by disorder. Here we demonstrate in the pyrochlore Tb 2Hf 2O 7, that the vicinity of the disordering transition towards a defective fluorite structure translates into a tunable density of anion Frenkel disorder while cationsmore » remain ordered. Quenched random crystal fields and disordered exchange interactions can therefore be introduced into otherwise perfect pyrochlore lattices of magnetic ions. We show that disorder can play a crucial role in preventing long-range magnetic order at low temperatures, and instead induces a strongly fluctuating Coulomb spin liquid with defect-induced frozen magnetic degrees of freedom.« less

Electronic spin polarization in the Majorana bound state in one-dimensional wires

NASA Astrophysics Data System (ADS)

Val'kov, V. V.; Aksenov, S. V.

2017-10-01

We have studied the effect of magnetic field and disorder on the electronic z-spin polarization at the ends of the one-dimensional wire with strong Rashba spin-orbit coupling deposited on an s-wave superconductor. It was shown that in the topologically nontrivial phase the polarization as well as the energy of the Majorana bound state oscillate as a function of the magnetic field. Despite being substantially nonzero in the low transversal and longitudinal fields the polarization at one of the wire's ends is significantly suppressed at a certain range of the magnitudes and angles of the canted magnetic field. Thus, in this case the polarization cannot be regarded as a local order parameter. However, the sum of the absolute values of the polarization at both ends remains significantly nonzero. It was demonstrated that Anderson disorder does not seriously affect observed properties but leads to the appearance of the additional areas with weak spin polarization at the high magnetic fields.

Magnetization switching in ferromagnets by adsorbed chiral molecules without current or external magnetic field.

PubMed

Ben Dor, Oren; Yochelis, Shira; Radko, Anna; Vankayala, Kiran; Capua, Eyal; Capua, Amir; Yang, See-Hun; Baczewski, Lech Tomasz; Parkin, Stuart Stephen Papworth; Naaman, Ron; Paltiel, Yossi

2017-02-23

Ferromagnets are commonly magnetized by either external magnetic fields or spin polarized currents. The manipulation of magnetization by spin-current occurs through the spin-transfer-torque effect, which is applied, for example, in modern magnetoresistive random access memory. However, the current density required for the spin-transfer torque is of the order of 1 × 10 6  A·cm -2 , or about 1 × 10 25 electrons s -1 cm -2 . This relatively high current density significantly affects the devices' structure and performance. Here we demonstrate magnetization switching of ferromagnetic thin layers that is induced solely by adsorption of chiral molecules. In this case, about 10 13 electrons per cm 2 are sufficient to induce magnetization reversal. The direction of the magnetization depends on the handedness of the adsorbed chiral molecules. Local magnetization switching is achieved by adsorbing a chiral self-assembled molecular monolayer on a gold-coated ferromagnetic layer with perpendicular magnetic anisotropy. These results present a simple low-power magnetization mechanism when operating at ambient conditions.