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Sample records for colossal magnetoresistive manganites

  1. Nodal Quasiparticle in Pseudogapped Colossal Magnetoresistive Manganites

    SciTech Connect

    Mannella, N.

    2010-06-02

    A characteristic feature of the copper oxide high-temperature superconductors is the dichotomy between the electronic excitations along the nodal (diagonal) and antinodal (parallel to the Cu-O bonds) directions in momentum space, generally assumed to be linked to the d-wave symmetry of the superconducting state. Angle-resolved photoemission measurements in the superconducting state have revealed a quasiparticle spectrum with a d-wave gap structure that exhibits a maximum along the antinodal direction and vanishes along the nodal direction. Subsequent measurements have shown that, at low doping levels, this gap structure persists even in the high-temperature metallic state, although the nodal points of the superconducting state spread out in finite Fermi arcs. This is the so-called pseudogap phase, and it has been assumed that it is closely linked to the superconducting state, either by assigning it to fluctuating superconductivity or by invoking orders which are natural competitors of d-wave superconductors. Here we report experimental evidence that a very similar pseudogap state with a nodal-antinodal dichotomous character exists in a system that is markedly different from a superconductor: the ferromagnetic metallic groundstate of the colossal magnetoresistive bilayer manganite La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7}. Our findings therefore cast doubt on the assumption that the pseudogap state in the copper oxides and the nodal-antinodal dichotomy are hallmarks of the superconductivity state.

  2. Nodal quasiparticle in pseudogapped colossal magnetoresistive manganites

    NASA Astrophysics Data System (ADS)

    Mannella, N.; Yang, W. L.; Zhou, X. J.; Tanaka, K.; Zheng, H.; Mitchell, J. F.; Zaanen, J.; Devereaux, T. P.; Nagaosa, N.; Hussain, Z.; Shen, Z. X.

    2006-03-01

    In this talk, the result of a recent angle-resolved photoemission spectroscopy (ARPES) investigation which allowed elucidating the controversial nature of the ferromagnetic metallic groundstate in the prototypical colossal magnetoresistive manganite bilayer compound La1.2Sr1.8Mn2O7 will be discussed [1]. The distribution of spectral weight in momentum space exhibits a nodal--antinodal dichotomous character. Quasiparticle excitations have been detected for the first time along the nodal direction (i.e. diagonal), and they are found to determine the metallic transport properties of this compound. The weight of the quasiparticle peak diminishes rapidly while crossing over to the antinodal (i.e. parallel to the Mn--O bonds) parallel sections of the Fermi surface, with the spectra strongly resembling those found in heavily underdoped cuprates high temperature superconductors (HTSC) such as Ca2-xNaxCuO2Cl2 [2]. This dichotomy between the electronic excitations along the nodal and antinodal directions in momentum space was so far considered a characteristic unique feature of the copper oxide HTSC. These findings therefore cast doubt on the assumption that the pseudogap state in the cuprate HTSC and the nodal-antinodal dichotomy are hallmarks of the superconductivity state. [1] N. Mannella et al., Nature 438, 474 (2005) [2] K. M Shen et al., Science 307, 901 (2005).

  3. Topological end states in two-orbital double-exchange model for colossal magnetoresistive manganites

    NASA Astrophysics Data System (ADS)

    Li, Yang; Dong, Shuai; Kou, Su-Peng

    2016-02-01

    Manganites are famous mostly for the colossal magnetoresistive effect, which involves the phase separation between ferromagnetic phase and charge-ordered C E -type antiferromagnetic phases. Furthermore, manganites contain some typical magnetic ferroelectrics, e.g., E -type antiferromagnetic o -HoMnO3 . Here we re-examined these zigzag-winding antiferromagnetic phases (C E -type and E -type antiferromagnets) from the topological perspective. Our theoretical analysis proved that the E -type phase is a weak topological insulator belonging to the Z class. In momentum space, we classify the symmetries of this phase, and find the three symmetry operators for the chiral, particle-hole, and time-reversal symmetry. The C E -type phase can be described by the Duffin-Kemmer-Petiau algebra, implying that it is a different class of topological insulator and hence extends the existing classification. The corresponding topological end states are demonstrated via numerical calculations, which may implicate the experimental observed ferromagnetic edge states in manganite strips [Nat. Commun. 6, 6179 (2015), 10.1038/ncomms7179] and may play a crucial role in the colossal magnetoresistive effect.

  4. Coexistence of orbital and CE-AFM orders in colossal magnetoresistance manganites: A symmetry perspective

    NASA Astrophysics Data System (ADS)

    Ribeiro, J. L.

    2016-07-01

    The complex interplay between order parameters of different nature that dominates the physics of colossal magnetoresistance manganites is analysed from a symmetry based perspective. Phenomenological energies are given for the different competing phases. It is shown that the general trends observed in different systems, such as the mutual exclusion of orbital order and A-AFM order and the related stabilization of the CE-AFM order, stem to large extend from the symmetry of the parameters involved. The possible stabilization of complex phases where charge and orbital order coexist with magnetic and ferroelectric states is also anticipated.

  5. Origin of colossal magnetoresistance in LaMnO3 manganite

    PubMed Central

    Baldini, Maria; Muramatsu, Takaki; Sherafati, Mohammad; Mao, Ho-kwang; Malavasi, Lorenzo; Postorino, Paolo; Satpathy, Sashi; Struzhkin, Viktor V.

    2015-01-01

    Phase separation is a crucial ingredient of the physics of manganites; however, the role of mixed phases in the development of the colossal magnetoresistance (CMR) phenomenon still needs to be clarified. We report the realization of CMR in a single-valent LaMnO3 manganite. We found that the insulator-to-metal transition at 32 GPa is well described using the percolation theory. Pressure induces phase separation, and the CMR takes place at the percolation threshold. A large memory effect is observed together with the CMR, suggesting the presence of magnetic clusters. The phase separation scenario is well reproduced, solving a model Hamiltonian. Our results demonstrate in a clean way that phase separation is at the origin of CMR in LaMnO3. PMID:26272923

  6. First Order Colossal Magnetoresistance Transitions in the Two-Orbital Model for Manganites

    SciTech Connect

    Sen, Cengiz; Alvarez, Gonzalo; Dagotto, Elbio R

    2010-01-01

    Large-scale Monte Carlo simulation results for the two-orbital model for manganites, including Jahn- Teller lattice distortions, are presented here. At hole density x 1=4 and in the vicinity of the region of competition between the ferromagnetic metallic and spin-charge-orbital ordered insulating phases, the colossal magnetoresistance (CMR) phenomenon is observed with a magnetoresistance ratio 10 000%. Our main result is that this CMR transition is found to be of first order in some portions of the phase diagram, in agreement with early results from neutron scattering, specific heat, and magnetization, thus solving a notorious discrepancy between experiments and previous theoretical studies. The first order characteristics of the transition survive, and are actually enhanced, when weak quenched disorder is introduced.

  7. Complex state found in the colossal magnetoresistance regime of models for manganites

    SciTech Connect

    Sen, Cengiz; Liang, Shuhua; Dagotto, Elbio R

    2012-01-01

    The colossal magnetoresistance (CMR) effect of manganites is widely believed to be caused by the competition between a ferromagnetic (FM) metallic state induced by the double-exchange mechanism and an insulator with complex spin, charge, and orbital order. Recent computational studies in small clusters have indeed reported a CMR precisely near the frontier between those two states at a realistic hole density x = 1/4. However, the detailed characteristics of the competing insulator were not fully understood in those previous investigations. This insulator is expected to display special properties that lead to the CMR; otherwise any competition between ferromagnetic and antiferromagnetic states would induce such an effect, which is not the case experimentally. In this report, the competing insulator at electronic density x = 1/4 and in the CMR regime is studied in detail using the double-exchange two-orbital model with Jahn-Teller lattice distortions on two-dimensional clusters, employing a careful large-scale cooling down process in the Monte Carlo simulations to avoid being trapped in metastable states. Our investigations show that this competing insulator has an unexpected complex structure, involving diagonal stripes with alternating regions displaying FM and CE-like order. The level of complexity of this new state even surpasses that of the recently unveiled spin-orthogonal-stripe states and their associated high degeneracy. This new state complements the long-standing scenario of phase separation, since the alternating FM-CE pattern appears even in the clean limit. The present and recent investigations are also in agreement with the many glassy characteristics of the CMR state found experimentally, due to the high degeneracy of the insulating states involved in the process. Results for the spin-structure factor of the new states are also here provided to facilitate the analysis of neutron scattering experiments for these materials.

  8. Magnetorefractive effect in manganites with a colossal magnetoresistance in the visible spectral region

    SciTech Connect

    Sukhorukov, Yu. P. Telegin, A. V.; Granovsky, A. B. Gan'shina, E. A.; Zhukov, A.; Gonzalez, J.; Caicedo, J. M.; Bessonov, V. D.; Kaul', A. R.; Gorbenko, O. Yu.; Korsakov, I. E.

    2012-01-15

    The magnetotransmission, magnetoreflection, and magnetoresistance of the La{sub 0.7}Ca{sub 0.3}MnO{sub 3} and La{sub 0.9}Ag{sub 0.1}MnO{sub 3} epitaxial films have been investigated. It has been found that the films exhibit a significant magnetorefractive effect in the case of reflection and transmission of light in the fundamental absorption region both in the vicinity of the Curie temperature and at low temperatures. It has been shown that the magnetorefractive effect in the infrared spectral region of the manganites is determined by a high-frequency response to magnetoresistance, whereas the magnetorefractive effect in the visible spectral region of these materials is associated with a change in the electronic structure in response to a magnetic field, which, in turn, leads to a change in the electron density of states, the probability of interband optical transitions, and the shift of light absorption bands. The obtained values of the magnetotransmittance and magnetoreflectance in the visible spectral region are less than those observed in the infrared region of the spectrum, but they are several times greater than the linear magneto-optical effects. As a result, the magnetorefractive effect, which is a nongyrotropic phenomenon, makes it possible to avoid the use of light analyzers and polarizers in optical circuits.

  9. Chemical Ordering Modulated Electronic Phase Separation and Macroscopic Properties in Colossal Magnetoresistance Manganites

    NASA Astrophysics Data System (ADS)

    Zhu, Yinyan; Du, Kai; Yin, Lifeng; Shen, Jian; Low-dimensional material physics Team

    Using unit cell by unit cell superlattice growth technique, we determine the role of chemical ordering of the Pr dopant in a colossal magnetoresistance (La1-yPry)1-x CaxMnO3 (LPCMO) system, which has been well known for its large length scale electronic phase separation (EPS) phenomena. Our experimental results show that the chemical ordering of Pr leads to dramatic reduction of the length scale of EPS. Moreover, compared to the conventional Pr-disordered LPCMO system, the Pr-ordered LPCMO system has ~100 K higher metal-insulator transition temperature. We have further investigated the n-dependence of the physical properties of the (LCMO)2n/(PCMO)n superlattices. Magnetic and transport measurements indicate that the physical properties change nonmonotonically with increasing n, reaching a minimum for both the Curie temperature and the meta-insulator transition temperature. The crossover thickness thus reflects the characteristic correlation length scale along the vertical direction of the superlattice. For superlattices with n smaller than the correlation length, we combine MFM studies and model calculations to explain the weakened ferromagnetism and metallicity with increasing n.

  10. Experimental Evidence of the Origin of Nanophase Separation in Low Hole-Doped Colossal Magnetoresistant Manganites.

    PubMed

    Cortés-Gil, Raquel; Ruiz-González, M Luisa; González-Merchante, Daniel; Alonso, José M; Hernando, Antonio; Trasobares, Susana; Vallet-Regí, María; Rojo, Juan M; González-Calbet, José M

    2016-01-13

    While being key to understanding their intriguing physical properties, the origin of nanophase separation in manganites and other strongly correlated materials is still unclear. Here, experimental evidence is offered for the origin of the controverted phase separation mechanism in the representative La1-xCaxMnO3 system. For low hole densities, direct evidence of Mn(4+) holes localization around Ca(2+) ions is experimentally provided by means of aberration-corrected scanning transmission electron microscopy combined with electron energy loss spectroscopy. These localized holes give rise to the segregated nanoclusters, within which double exchange hopping between Mn(3+) and Mn(4+) remains restricted, accounting for the insulating character of perovskites with low hole density. This localization is explained in terms of a simple model in which Mn(4+) holes are bound to substitutional divalent Ca(2+) ions.

  11. Colossal piezoresistance in manganites.

    NASA Astrophysics Data System (ADS)

    Tosado, Jacob; Lopez, Josymir; Dhakal, Tara; Biswas, Amlan

    2007-03-01

    We have studied the effect of the application of direct mechanical stress on thin films of the hole-doped manganese oxide (manganite) (La1-yPry)1-xCaxMnO3 (LPCMO). The two competing phases in manganites are the pseudocubic ferromagnetic metallic (FMM) phase and the orthorhombic charge-ordered insulating (COI) phase. Due to the different structures of the FMM and COI phases, manganites are susceptible to mechanical stresses. The traditional methods of applying stress on oxide thin films result in different growth modes which makes it difficult to quantify the strain in the thin film. Using a calibrated screw we applied direct mechanical stress on the substrate and measured the change in the phase diagram of the manganite as a function of strain. Our results show that the effect of strain is the largest in the fluid phase separated region of the phase diagram^2, where we observe a strain-induced change in resistance of about 5 orders of magnitude. [2] Tara Dhakal, et. al, Cond-mat/0607502.

  12. Temperature dependent evolution of the electronic and local atomic structure in the cubic colossal magnetoresistive manganite La1-xSrxMnO3

    SciTech Connect

    Arenholz, Elke; Mannella, N.; Booth, C.H.; Rosenhahn, A.; Sell, B.C.; Nambu, A.; Marchesini, S.; Mun, B. S.; Yang, S.-H.; Watanabe, M.; Ibrahim, K.; Arenholz, E.; Young, A.; Guo, J.; Tomioka, Y.; Fadley, C.S.

    2007-12-06

    We have studied the temperature-dependent evolution of the electronic and local atomic structure in the cubic colossal magnetoresistive manganite La{sub 1-x}Sr{sub x}MnO{sub 3} (x= 0.3-0.4) with core and valence level photoemission (PE), x-ray absorption spectroscopy (XAS), x-ray emission spectroscopy (XES), resonant inelastic x-ray scattering (RIXS), extended x-ray absorption fine structure (EXAFS) spectroscopy and magnetometry. As the temperature is varied across the Curie temperature T{sub c}, our PE experiments reveal a dramatic change of the electronic structure involving an increase in the Mn spin moment from {approx} 3 {micro}B to {approx} 4 {micro}B, and a modification of the local chemical environment of the other constituent atoms indicative of electron localization on the Mn atom. These effects are reversible and exhibit a slow-timescale {approx}200 K-wide hysteresis centered at T{sub c}. Based upon the probing depths accessed in our PE measurements, these effects seem to survive for at least 35-50 {angstrom} inward from the surface, while other consistent signatures for this modification of the electronic structure are revealed by more bulk sensitive spectroscopies like XAS and XES/RIXS. We interpret these effects as spectroscopic fingerprints for polaron formation, consistent with the presence of local Jahn-Teller distortions of the MnO{sub 6} octahedra around the Mn atom, as revealed by the EXAFS data. Magnetic susceptibility measurements in addition show typical signatures of ferro-magnetic clusters formation well above the Curie temperature.

  13. Colossal Magnetoresistive Manganite Based Fast Bolometric X-ray Sensors for Total Energy Measurements of Free Electron Lasers

    SciTech Connect

    Yong, G J; Kolagani, R M; Adhikari, S; Mundle, R M; Cox, D W; Davidson III, A L; Liang, Y; Drury, O B; Hau-Riege, S P; Gardner, C; Ables, E; Bionta, R M; Friedrich, S

    2008-12-17

    Bolometric detectors based on epitaxial thin films of rare earth perovskite manganites have been proposed as total energy monitors for X-ray pulses at the Linac Coherent Light Source free electron laser. We demonstrate such a detector scheme based on epitaxial thin films of the perovskite manganese oxide material Nd{sub 0.67}Sr{sub x0.33}MnO{sub 3}, grown by pulsed laser deposition on buffered silicon substrates. The substrate and sensor materials are chosen to meet the conflicting requirements of radiation hardness, sensitivity, speed and linearity over a dynamic range of three orders of magnitude. The key challenge in the material development is the integration of the sensor material with Si. Si is required to withstand the free electron laser pulse impact and to achieve a readout speed three orders of magnitude faster than conventional cryoradiometers for compatibility with the Linac Coherent Light Source pulse rate. We discuss sensor material development and the photoresponse of prototype devices. This Linac Coherent Light Source total energy monitor represents the first practical application of manganite materials as bolometric sensors.

  14. Direct observation of current-induced conductive path in colossal-electroresistance manganite thin films

    NASA Astrophysics Data System (ADS)

    Wei, Wengang; Zhu, Yinyan; Bai, Yu; Liu, Hao; Du, Kai; Zhang, Kai; Kou, Yunfang; Shao, Jian; Wang, Wenbin; Hou, Denglu; Dong, Shuai; Yin, Lifeng; Shen, Jian

    2016-01-01

    Manganites are known to often show colossal electroresistance (CER) in addition to colossal magnetoresistance. The (La1-yP ry) 1 -xC axMn O3 (LPCMO) system has a peculiar CER behavior in that little change of magnetization occurs. We use a magnetic force microscope to uncover the CER mechanism in the LPCMO system. In contrast to the previous belief that current reshapes the ferromagnetic metallic (FMM) domains, we show that the shape of the FMM domains remain virtually unchanged after passing electric current. Instead, it is the appearance of a tiny fraction of FMM "bridges" that is responsible for the CER behavior.

  15. Role of structurally and magnetically modified nanoclusters in colossal magnetoresistance

    PubMed Central

    Tao, Jing; Niebieskikwiat, Dario; Jie, Qing; Schofield, Marvin A.; Wu, Lijun; Li, Qiang; Zhu, Yimei

    2011-01-01

    It is generally accepted that electronic and magnetic phase separation is the origin of many of exotic properties of strongly correlated electron materials, such as colossal magnetoresistance (CMR), an unusually large variation in the electrical resistivity under applied magnetic field. In the simplest picture, the two competing phases are those associated with the material state on either side of the phase transition. Those phases would be paramagnetic insulator and ferromagnetic metal for the CMR effect in doped manganites. It has been speculated that a critical component of the CMR phenomenon is nanoclusters with quite different properties than either of the terminal phases during the transition. However, the role of these nanoclusters in the CMR effect remains elusive because the physical properties of the nanoclusters are hard to measure when embedded in bulk materials. Here we show the unexpected behavior of the nanoclusters in the CMR compound La1-xCaxMnO3 (0.4 ≤ x < 0.5) by directly correlating transmission electron microscopy observations with bulk measurements. The structurally modified nanoclusters at the CMR temperature were found to be ferromagnetic and exhibit much higher electrical conductivity than previously proposed. Only at temperatures much below the CMR transition, the nanoclusters are antiferromagnetic and insulating. These findings substantially alter the current understanding of these nanoclusters on the material’s functionality and would shed light on the microscopic study on the competing spin-lattice-charge orders in strongly correlated systems. PMID:22160678

  16. Sub-200 Oe giant magnetoresistance in manganite tunnel junctions

    SciTech Connect

    Xiao, G.; Li, X.W.; Gong, G.Q.; Gupta, A.; Sun, J.Z.

    1998-12-31

    Metallic manganite oxides, La{sub 1{minus}x}D{sub x}MnO{sub 3} (D = Sr, Ca, etc.), display colossal magnetoresistance (CMR) near their magnetic phase transition temperatures ({Tc}) when subject to a Tesla-scale magnetic field. This phenomenal effect is the result of the strong interplay inherent in this class of materials among electronic structure, magnetic ordering, and lattice dynamics. Though fundamentally interesting, the CMR effect achieved only at large fields poses severe technological challenges to potential applications in magnetoelectronic devices, where low field sensitivity is crucial. Among the objectives of the research effort involving manganite materials is to reduce the field scale of MR by designing and fabricating tunnel junctions and other structures rich in magnetic domain walls. The junction electrodes were made of doped manganite epitaxial films, and the insulating barrier of SrTiO{sub 3}. The interfacial epitaxy has been imaged by using high-resolution transmission electron microscopy (TEM). The authors have used self-aligned lithographic process to pattern the junctions to micron scale in size. Large MR values close to 250% at low fields of a few tens of Oe have been observed. The mechanism of the spin-dependent transport is due to the spin-polarized tunneling between the half-metallic electrodes, in which the spins of the conduction electrons are nearly fully polarized. The authors present results of field and temperature dependence of MR in these structures and discuss the electronic structure of the manganite inferred from tunneling measurement. Results of large MR at low fields due to the grain-boundary effect is also presented.

  17. Magnetic mesocrystal-assisted magnetoresistance in manganite.

    PubMed

    Yang, Jan-Chi; He, Qing; Zhu, Yuan-Min; Lin, Jheng-Cyuan; Liu, Heng-Jui; Hsieh, Ying-Hui; Wu, Ping-Chun; Chen, Yen-Lin; Lee, Shang-Fan; Chin, Yi-Ying; Lin, Hong-Ji; Chen, Chien-Te; Zhan, Qian; Arenholz, Elke; Chu, Ying-Hao

    2014-11-12

    Mesocrystal, a new class of crystals as compared to conventional and well-known single crystals and polycrystalline systems, has captured significant attention in the past decade. Recent studies have been focused on the advance of synthesis mechanisms as well as the potential on device applications. In order to create further opportunities upon functional mesocrystals, we fabricated a self-assembled nanocomposite composed of magnetic CoFe2O4 mesocrystal in Sr-doped manganites. This combination exhibits intriguing structural and magnetic tunabilities. Furthermore, the antiferromagnetic coupling of the mesocrystal and matrix has induced an additional magnetic perturbation to spin-polarized electrons, resulting in a significantly enhanced magnetoresistance in the nanocomposite. Our work demonstrates a new thought toward the enhancement of intrinsic functionalities assisted by mesocrystals and advanced design of novel mesocrystal-embedded nanocomposites.

  18. Anisotropic magnetoresistance in manganites: experiment and theory.

    PubMed

    Fuhr, J D; Granada, M; Steren, L B; Alascio, B

    2010-04-14

    We present measurements of the anisotropic magnetoresistance (AMR) of La(0.75)Sr(0.25)MnO(3) films deposited on (001) SrTiO(3) substrates, and a model that describes the experimental results. The model, based on the electronic structure of manganites plus the spin-orbit coupling, correctly accounts for the dependence of the AMR on the direction of the current to the crystalline axes. We measure an AMR of the order of 10(-3) for the current I parallel to the [100] axis of the crystal and vanishing AMR for I , in agreement with the model predictions. Further, we calculate the planar Hall effect and show its connection to AMR.

  19. Large magnetic entropy change in the colossal magnetoresistance material La 2/3Ca 1/3MnO 3

    NASA Astrophysics Data System (ADS)

    Sun, Young; Xu, Xiaojun; Zhang, Yuheng

    2000-09-01

    In this paper, we present a study of magnetocaloric effect in the colossal magnetoresistance material La 2/3Ca 1/3MnO 3. From the measurements of temperature dependence of magnetization under various magnetic fields, we have discovered a large magnetic entropy change associated with the ferromagnetic-paramagnetic transition. This result suggests that perovskite manganites are suitable candidates as working substances in magnetic refrigeration technology.

  20. Magnetoresistive properties of nanostructured magnetic metals, manganites, and magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Solin, N. I.; Romashev, L. N.; Naumov, S. V.; Saranin, A. A.; Zotov, A. V.; Olyanich, D. A.; Kotlyar, V. G.; Utas, O. A.

    2016-02-01

    We consider methods for controlling magnetoresistive parameters of magnetic metal superlattices, manganites, and magnetic semiconductors. By reducing the thickness of ferromagnetic layers in superlattices (e.g., Fe layers in Fe/Cr superlattices), it is possible to form superparamagnetic clustered-layered nanostructures with a magnetoresistance weakly depending on the direction of the external magnetic field, which is very important for applications of such type of materials. Producing Mn vacancies and additionally annealing lanthanum manganites in the oxygen atmosphere, it is possible to increase their magnetoresistance by more than four orders of magnitude. By changing the thickness of p- n junction in the structure of ferromagnetic semiconductors, their magnetoresistance can be increased by 2-3 orders of magnitude.

  1. Colossal elastoresistance, electroresistance and magnetoresistance in Pr0.5Sr0.5MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Chen, Liping; Guo, Xuexiang; Gao, J.

    2016-05-01

    Pr0.5Sr0.5MnO3 thin films on substrates of (001)-oriented LaAlO3 were epitaxially grown by pulsed laser deposition. It was found that a substrate-induced strain of ~1.3% brings a great resistivity change of ~98% at 25 K. We studied the dependence of resistivity on the applied electric current and magnetic field. In the greatly strained films of 60 nm thickness the electroresistance ER=[ρ(I1 μA)-ρ(I1000 μA)]/ρ(I1 μA) reaches ~70% at T=25 K, much higher than ER~7% in the strain-relaxed films of 400 nm thickness, implying the strain effect on ER. Also the magnetoresistance of the film falls with strain-relaxation. Therefore the electric properties of the film could be efficiently modified by strain, electric current and magnetic field. All of them may be explained by the effect on the percolative phase separation and competition in the half-doped manganite material. The manganite films located at phase boundary are expected to be an ideal compound for providing practical colossal effects of elastoresistance, electroresistance and magnetoresistance due to the multiphase coexistence.

  2. Griffiths phase and colossal magnetoresistance in Nd0.5Sr0.5MnO3 oxygen-deficient thin films

    NASA Astrophysics Data System (ADS)

    Solin, N. I.; Korolyov, A. V.; Medvedev, Yu. V.; Nikolaenko, Yu. M.; Khokhlov, V. A.; Prokhorov, A. Yu.; Levchenko, G. G.

    2013-05-01

    This work is devoted to study the influence of the Griffiths phase in colossal magnetoresistance manganites. Griffiths-phase-like behavior of the paramagnetic susceptibility χ0 is observed in Nd0.5Sr0.5MnO3 oxygen-deficient thin films fabricated by magnetron sputtering deposition. In Nd0.5Sr0.5MnO3-δ films with oxygen deficiency for ТG≈260-280 K>T>TC=138 K (ТG and ТС—Griffiths and Curie temperatures, respectively), paramagnetic matrix consists of a magnetic phase with short-range order (˜1-1.5 nm) (which is responsible for the colossal magnetoresistance (CMR) above ТС), and is embedded in this matrix region with long-range ferromagnetic order (≫10 nm), responsible for the Griffiths phase-like behavior of the paramagnetic susceptibility. Electrical resistivity is caused by carrier tunneling between the localized states and obeys the Efros-Shklovskii law. Magnetic resistivity is caused by change of the localized state sizes under the magnetic field. The temperature and magnetic field dependencies of size of the phase inhomogeneity inclusions, found from measurements of magneto-transport properties, can be satisfactorily described by the model of thermodynamic phase separation into metallic droplets of small radius in a paramagnetic matrix. Intrinsic nanoscale inhomogeneities caused by thermodynamic phase separation, rather than the Griffiths phase, determine the electrical resistivity and colossal magnetoresistance of the films. In half-doped manganites, the nature of long-range ordered magnetic phases may be related, besides the chemical heterogeneity, to proximity to a ferromagnetic-antiferromagnetic boundary at the phase diagram as well. The results are in good agreement with the model of existence of an analog of Griffiths phase temperature in half-doped manganites.

  3. Current dependence of colossal anisotropic magnetoresistance in La 0.3 Pr 0.4 Ca 0.3 MnO 3 microbridges

    NASA Astrophysics Data System (ADS)

    Jeon, J.; Jung, J.; Chow, K. H.

    2016-09-01

    The effect of the bias current on the in-plane colossal anisotropic magnetoresistance (C-AMR) is investigated in spatially confined La 0.3 Pr 0.4 Ca 0.3 MnO 3 microbridges. Dramatic increases of the C-AMR are found when the bias current is reduced. For example, in one of the samples, the C-AMR changed from ˜900% to over ˜24 000% as the current is decreased from 1 μA to 10 nA. The results indicate that the bias current can be used to manipulate the C-AMR in spatially confined manganite thin films via changes to the nature of the anisotropic percolation within the samples.

  4. Crystallinity and magnetoresistance in calcium doped lanthanum manganites

    SciTech Connect

    Gillman, E.S.; Dahmen, K.H.

    1998-12-31

    Thin films of calcium doped lanthanum manganites La{sub 1{minus}x}Ca{sub x}MnO{sub 3} (LCMO) with x {approximately} 0.41 have been prepared on LaAlO{sub 3}(001) (LAO) Y-stabilized ZrO{sub 2}(001) (YSZ), and Al{sub 2}O{sub 3}(0001) (SAP) substrates by liquid delivery metal-organic chemical vapor deposition (LD-MOCVD). The films on YSZ and SAP substrates have a textured, polycrystalline morphology with a preferred orientation of (110). The films on LAO show a single-crystalline morphology and a (100) orientation. Transport measurements show the polycrystalline films have a resistance peak approximately 60 K lower than the films on LAO and, in general, have a much higher overall resistance. The magnetoresistance (MR) ratio ([R(H) - R(0)]/R(H)) is sharply peaked near the maximum in resistance for the films on LAO, while the polycrystalline films show a noticeable absence of this sharply peaked behavior and a flat, rather large ({approximately} 100%) MR ratio over a large temperature range. These results will be discussed in terms of grain boundary scattering, crystallite size, and magnetization.

  5. Spin Seebeck Effect and Thermal Colossal Magnetoresistance in Graphene Nanoribbon Heterojunction

    PubMed Central

    Ni, Yun; Yao, Kailun; Fu, Huahua; Gao, Guoying; Zhu, Sicong; Wang, Shuling

    2013-01-01

    Spin caloritronics devices are very important for future development of low-power-consumption technology. We propose a new spin caloritronics device based on zigzag graphene nanoribbon (ZGNR), which is a heterojunction consisting of single-hydrogen-terminated ZGNR (ZGNR-H) and double-hydrogen-terminated ZGNR (ZGNR-H2). We predict that spin-up and spin-down currents flowing in opposite directions can be induced by temperature difference instead of external electrical bias. The thermal spin-up current is considerably large and greatly improved compared with previous work in graphene. Moreover, the thermal colossal magnetoresistance is obtained in our research, which could be used to fabricate highly-efficient spin caloritronics MR devices. PMID:23459307

  6. Actively tunable Fano resonances based on colossal magneto-resistant metamaterials.

    PubMed

    Tian, Jie-Bing; Yan, Chang-Chun; Wang, Cheng; Han, Ying; Zou, Rong-Yuan; Li, Dong-Dong; Xu, Zheng-Ji; Zhang, Dao-Hua

    2015-04-01

    In this Letter, a periodic structure in which each unit cell consists of one manganese oxide (La(0.7)Ca(0.3)MnO(3)) strip and two gold strips is designed. By simulating the electromagnetic responses of the structure, we confirm that Fano resonances can be actively controlled in the infrared region by modulating the intensity of the external magnetic field applied to the structure. This is due to the colossal magneto-resistance of the La(0.7)Ca(0.3)MnO(3) material. Furthermore, a transmission phase can also be effectively tuned. The phase has a shift of ΔΦ=1.05  rad at a frequency of 130 THz when the intensity of the external magnetic field varies from 5083 to 5193  kA/m. Such a tunable method has potential applications in controllable photoelectric elements. PMID:25831314

  7. Colossal positive magnetoresistance in surface-passivated oxygen-deficient strontium titanite

    PubMed Central

    David, Adrian; Tian, Yufeng; Yang, Ping; Gao, Xingyu; Lin, Weinan; Shah, Amish B.; Zuo, Jian-Min; Prellier, Wilfrid; Wu, Tom

    2015-01-01

    Modulation of resistance by an external magnetic field, i.e. magnetoresistance effect, has been a long-lived theme of research due to both fundamental science and device applications. Here we report colossal positive magnetoresistance (CPMR) (>30,000% at a temperature of 2 K and a magnetic field of 9 T) discovered in degenerate semiconducting strontium titanite (SrTiO3) single crystals capped with ultrathin SrTiO3/LaAlO3 bilayers. The low-pressure high-temperature homoepitaxial growth of several unit cells of SrTiO3 introduces oxygen vacancies and high-mobility carriers in the bulk SrTiO3, and the three-unit-cell LaAlO3 capping layer passivates the surface and improves carrier mobility by suppressing surface-defect-related scattering. The coexistence of multiple types of carriers and inhomogeneous transport lead to the emergence of CPMR. This unit-cell-level surface engineering approach is promising to be generalized to others oxides, and to realize devices with high-mobility carriers and interesting magnetoelectronic properties. PMID:25975606

  8. Positive magnetoresistance of single-crystal bilayer manganites (La{sub 1−z}Nd{sub z}){sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7} (z = 0, 0.1)

    SciTech Connect

    Shaykhutdinov, K. A.; Petrov, M. I.; Terent'ev, K. I.; Semenov, S. V.; Popkov, S. I.; Nikitin, S. E.

    2015-04-28

    We investigate magnetoresistance, ρ{sub c}, of single-crystal bilayer lanthanum manganites (La{sub 1−z}Nd{sub z}){sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7} (z = 0 and 0.1) at a transport current flowing along the crystal c axis and in external magnetic fields applied parallel to the crystal c axis or ab plane. It is demonstrated that the La{sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7} manganite exhibits the positive magnetoresistance effect in the magnetic field applied in the ab sample plane at the temperatures T < 60 K, along with the negative magnetoresistance typical of all the substituted lanthanum manganites. In the (La{sub 0.9}Nd{sub 0.1}){sub 1.4}Sr{sub 1.6}Mn{sub 2}O{sub 7} sample, the positive magnetoresistance effect is observed at temperatures of 60–80 K in an applied field parallel to the c axis. The mechanism of this effect is shown to be fundamentally different from the colossal magnetoresistance effect typical of lanthanum manganites. The positive magnetoresistance originates from spin-dependent tunneling of carriers between the manganese-oxygen bilayers and can be explained by features of the magnetic structure of the investigated compounds.

  9. The effect of band Jahn-Teller distortion on the magnetoresistivity of manganites: a model study.

    PubMed

    Rout, G C; Panda, Saswati; Behera, S N

    2011-10-01

    We present a model study of magnetoresistance through the interplay of magnetisation, structural distortion and external magnetic field for the manganite systems. The manganite system is described by the Hamiltonian which consists of the s-d type double exchange interaction, Heisenberg spin-spin interaction among the core electrons, and the static and dynamic band Jahn-Teller (JT) interaction in the e(g) band. The relaxation time of the e(g) electron is found from the imaginary part of the Green's function using the total Hamiltonian consisting of the interactions due to the electron and phonon. The calculated resistivity exhibits a peak in the pure JT distorted insulating phase separating the low temperature metallic ferromagnetic phase and the high temperature paramagnetic phase. The resistivity is suppressed with the increase of the external magnetic field. The e(g) electron band splitting and its effect on magnetoresistivity is reported here.

  10. Atomic scale studies of La/Sr ordering in colossal magnetoresistant La2-2xSr1+2xMn2O7 single crystals

    SciTech Connect

    Roldan, Manuel A.; Oxley, Mark P.; Li, Qing'an A.; Zheng, Hong; Gray, Kenneth E.; Mitchell, John F.; Pennycook, Stephen J.; Varela, Maria

    2014-09-29

    In this study, it is unclear whether chemical order (or disorder) is in any way connected to double exchange, electronic phase separation, or charge ordering (CO) in manganites. In this work, we carry out an atomic resolution study of the colossal magnetoresistant manganite La2–2xSr1+2xMn2O7 (LSMO). We combine aberration-corrected electron microscopy and spectroscopy with spectroscopic image simulations, to analyze cation ordering at the atomic scale in real space in a number of LSMO single crystals. We compare three different compositions within the phase diagram: a ferromagnetic metallic material (x=0.36), an insulating, antiferromagnetic charge ordered (AF-CO) compound (x=0.5), which also exhibits orbital ordering, and an additional AF sample (x=0.56). Detailed image simulations are essential to accurately quantify the degree of chemical ordering of these samples. We find a significant degree of long-range chemical ordering in all cases, which increases in the AF-CO range. However, the degree of ordering is never complete nor can it explain the strongly correlated underlying ordering phenomena. Our results show that chemical ordering over distinct crystallographic sites is not needed for electronic ordering phenomena to appear in manganites, and cannot by itself explain the complex electronic behavior of LSMO.

  11. Atomic scale studies of La/Sr ordering in colossal magnetoresistant La2-2xSr1+2xMn2O7 single crystals

    DOE PAGESBeta

    Roldan, Manuel A.; Oxley, Mark P.; Li, Qing'an A.; Zheng, Hong; Gray, Kenneth E.; Mitchell, John F.; Pennycook, Stephen J.; Varela, Maria

    2014-09-29

    In this study, it is unclear whether chemical order (or disorder) is in any way connected to double exchange, electronic phase separation, or charge ordering (CO) in manganites. In this work, we carry out an atomic resolution study of the colossal magnetoresistant manganite La2–2xSr1+2xMn2O7 (LSMO). We combine aberration-corrected electron microscopy and spectroscopy with spectroscopic image simulations, to analyze cation ordering at the atomic scale in real space in a number of LSMO single crystals. We compare three different compositions within the phase diagram: a ferromagnetic metallic material (x=0.36), an insulating, antiferromagnetic charge ordered (AF-CO) compound (x=0.5), which also exhibits orbitalmore » ordering, and an additional AF sample (x=0.56). Detailed image simulations are essential to accurately quantify the degree of chemical ordering of these samples. We find a significant degree of long-range chemical ordering in all cases, which increases in the AF-CO range. However, the degree of ordering is never complete nor can it explain the strongly correlated underlying ordering phenomena. Our results show that chemical ordering over distinct crystallographic sites is not needed for electronic ordering phenomena to appear in manganites, and cannot by itself explain the complex electronic behavior of LSMO.« less

  12. Atomic scale studies of La/Sr ordering in colossal magnetoresistant La(2-2x)Sr(1+2x)Mn2O7 single crystals.

    PubMed

    Roldan, Manuel A; Oxley, Mark P; Li, Qing'an; Zheng, Hong; Gray, K E; Mitchell, J F; Pennycook, Stephen J; Varela, María

    2014-12-01

    To date, it is unclear whether chemical order (or disorder) is in any way connected to double exchange, electronic phase separation, or charge ordering (CO) in manganites. In this work, we carry out an atomic resolution study of the colossal magnetoresistant manganite La(2-2x)Sr(1+2x)Mn2O7 (LSMO). We combine aberration-corrected electron microscopy and spectroscopy with spectroscopic image simulations, to analyze cation ordering at the atomic scale in real space in a number of LSMO single crystals. We compare three different compositions within the phase diagram: a ferromagnetic metallic material (x=0.36), an insulating, antiferromagnetic charge ordered (AF-CO) compound (x=0.5), which also exhibits orbital ordering, and an additional AF sample (x=0.56). Detailed image simulations are essential to accurately quantify the degree of chemical ordering of these samples. We find a significant degree of long-range chemical ordering in all cases, which increases in the AF-CO range. However, the degree of ordering is never complete nor can it explain the strongly correlated underlying ordering phenomena. Our results show that chemical ordering over distinct crystallographic sites is not needed for electronic ordering phenomena to appear in manganites, and cannot by itself explain the complex electronic behavior of LSMO.

  13. Absence of colossal magnetoresistance in the oxypnictide PrMnAsO0.95F0.05.

    PubMed

    Wildman, Eve J; Sher, Falak; Mclaughlin, Abbie C

    2015-03-16

    We have recently reported a new mechanism of colossal magnetoresistance (CMR) in electron doped manganese oxypnictides NdMnAsO1-xFx. Magnetoresistances of up to -95% at 3 K have been observed. Here we show that upon replacing Nd for Pr, the CMR is surprisingly no longer present. Instead a sizable negative magnetoresistance is observed for PrMnAsO0.95F0.05 below 35 K (MR7T (12 K) = -13.4% for PrMnAsO0.95F0.05). A detailed neutron and synchrotron X-ray diffraction study of PrMnAsO0.95F0.05 has been performed, which shows that a structural transition, Ts, occurs at 35 K from tetragonal P4/nmm to orthorhombic Pmmn symmetry. The structural transition is driven by the Pr 4f electrons degrees of freedom. The sizable -MR observed below the transition most likely arises due to a reduction in magnetic and/or multipolar scattering upon application of a magnetic field. PMID:25713929

  14. Paramagnetic spin correlations in colossal magnetoresistive La0.7Ca0.3MnO3

    SciTech Connect

    Helton, Joel S; Stone, Matthew B; Shulyatev, Dmitry A; Mukovskii, Yakov M; Lynn, J. W.

    2012-01-01

    Neutron spectroscopy measurements reveal dynamic spin correlations throughout the Brillouin zone in the colossal magnetoresistive system La0.7Ca0.3MnO3 at 265 K (1.03 TC). The longwavelength behavior is consistent with spin diffusion, yet an additional and unexpected component of the scattering is also observed in low-energy constant-E measurements which takes the form of ridges of strong scattering running along (H 0 0) and equivalent directions. Well defined Q-space correlations are observed in constant-E scans at energies up to at least 28 meV, suggesting robust short-range spin correlations in the paramagnetic phase.

  15. Colossal magnetoresistance accompanied with magnetorelaxor behavior in phase-separated Ca1-xCexMnO3 thin films and CaMnO3/Ca0.92Ce0.08MnO3 superlattices

    NASA Astrophysics Data System (ADS)

    Xiang, P.-H.; Yamada, H.; Sawa, A.; Akoh, H.

    2010-03-01

    We report on the transport properties of electron-doped manganite Ca1-xCexMnO3 (CCMO, 0≤x≤0.08) films and superlattices composed of insulating layers CaMnO3 (CMO) and Ca0.92Ce0.08MnO3 (CCMO8), deposited on nearly lattice-matched NdAlO3 substrates. The CCMO (x =0.06 and 0.07) films show colossal magnetoresistance (CMR) accompanied with magnetorelaxor behavior, which can be ascribed to the phase separation of canted G-type antiferromagnetic metal and C-type antiferromagnetic insulator. The (CMO)m/(CCMO8)n superlattices with 4≤m, n ≤8 (unit cells) resemble the solid-solution CCMO (x =0.06 and 0.07) films in CMR and magnetorelaxor behavior, suggesting that the phase separation takes place in the superlattices. The CMR and magnetorelaxor behavior of the (CMO)m/(CCMO8)n superlattices strongly depend on the thicknesses of constituent CMO and CCMO8 layers. The origin of the phase separation in the superlattices is discussed in terms of the charge transfer and the phase competition at the interfaces.

  16. Electric field induced metal-insulator transition and colossal magnetoresistance in CdCr2S4

    NASA Astrophysics Data System (ADS)

    Sun, C. P.; Lin, C. C.; Her, J. L.; Taran, S.; Chou, C. C.; Chan, C. L.; Huang, C. L.; Berger, H.; Yang, H. D.

    2008-03-01

    Multiferroic ordering existing in a single material is a recent hot topic in the field of condensed matter physics due to its potential application in device control. The chromium chalcogenide spinel CdCr2S4 is one of the attractive materials investigated by Hemberger et al. recently.[1] Based on the electrical measurement, there is no discontinuity through the ferromagnetic ordering at TC ˜ 85K.[2] We measure the temperature dependent resistance under various electric fields to investigate the electrical properties of the present material. To our knowledge, we first observe the electric field induced metal-insulator transition in this material around TC. Moreover, a colossal magnetoresistance (CMR), which is comparable to that of manganese-based CMR material, is also observed near TC. The origin for these properties is discussed. [1] J. Hemberger, P. Lunkenheimer, R. Fichtl, H.-A. Krug von Nidda, V. Tsurkan, A. Loidl, Nature 434, 364 (2006). [2] P. K. Baltzer, H. W. Lehmann, and M. Robbins, Phys. Rev. Lett. 15, 493 (1965).

  17. Wigner Crystal and Colossal Magnetoresistance in InSb Doped with Mn

    PubMed Central

    Obukhov, S. A.; Tozer, S. W.; Coniglio, W. A.

    2015-01-01

    We report magnetotransport investigation of nonmagnetic InSb single crystal doped with manganese at Mn concentration NMn ~ 1,5 × 1017 cm−3 in the temperature range T = 300 K–40 mK, magnetic field B = 0–25T and hydrostatic pressure P = 0–17 kbar. Resistivity saturation was observed in the absence of magnetic field at temperatures below 200 mK while applied increasing external magnetic field induced colossal drop of resistivity (by factor 104) at B ~ 4T with further gigantic resistivity increase (by factor 104) at 15T. Under pressure, P = 17 kbar, resistivity saturation temperature increased up to 1,2 K. Existing models are discussed in attempt to explain resistivity saturation, dramatic influence of magnetic field and pressure on resistivity with the focus on possible manifestation of three dimensional Wigner crystal formed in InSb by light electrons and heavy holes. PMID:26307952

  18. Wigner Crystal and Colossal Magnetoresistance in InSb Doped with Mn

    NASA Astrophysics Data System (ADS)

    Obukhov, S. A.; Tozer, S. W.; Coniglio, W. A.

    2015-08-01

    We report magnetotransport investigation of nonmagnetic InSb single crystal doped with manganese at Mn concentration NMn ~ 1,5 × 1017 cm-3 in the temperature range T = 300 K-40 mK, magnetic field B = 0-25T and hydrostatic pressure P = 0-17 kbar. Resistivity saturation was observed in the absence of magnetic field at temperatures below 200 mK while applied increasing external magnetic field induced colossal drop of resistivity (by factor 104) at B ~ 4T with further gigantic resistivity increase (by factor 104) at 15T. Under pressure, P = 17 kbar, resistivity saturation temperature increased up to 1,2 K. Existing models are discussed in attempt to explain resistivity saturation, dramatic influence of magnetic field and pressure on resistivity with the focus on possible manifestation of three dimensional Wigner crystal formed in InSb by light electrons and heavy holes.

  19. Hall effect within the colossal magnetoresistive semimetallic state of MoTe2

    NASA Astrophysics Data System (ADS)

    Zhou, Qiong; Rhodes, D.; Zhang, Q. R.; Tang, S.; Schönemann, R.; Balicas, L.

    2016-09-01

    Here, we report a systematic study on the Hall effect of the semimetallic state of bulk MoTe2, which was recently claimed to be a candidate for a novel type of Weyl semimetallic state. The temperature (T ) dependence of the carrier densities and of their mobilities, as estimated from a numerical analysis based on the isotropic two-carrier model, indicates that its exceedingly large and nonsaturating magnetoresistance may be attributed to a near perfect compensation between the densities of electrons and holes at low temperatures. A sudden increase in hole density, with a concomitant rapid increase in the electron mobility below T ˜40 K, leads to comparable densities of electrons and holes at low temperatures suggesting a possible electronic phase transition around this temperature.

  20. Extraordinary colossal magnetoresistance in La 0.67Ca 0.33Mn 1- xCr xO 3 ( x⩽0.3)

    NASA Astrophysics Data System (ADS)

    Sun, Young; Tong, Wei; Xu, Xiaojun; Zhang, Yuheng

    2001-06-01

    The magnetic and magnetotransport properties of La 0.67Ca 0.33Mn 1- xCr xO 3 ( x⩽0.3) perovskites have been studied. It was found that Cr doping is impotent in driving Curie temperature Tc but brings about cluster glass behaviors. Moreover, the substitution with Cr on Mn sites introduces extraordinary electrical transport and colossal magnetoresistance (CMR) behavior, characterized by double peaks. As a result, the temperature range of CMR response is greatly broadened. These results suggest that Cr doping could be a potent way in tuning CMR.

  1. Magnetoresistive properties of cerium doped La0.7Ca0.3MnO3 manganites

    NASA Astrophysics Data System (ADS)

    Chihoub, R.; Amira, A.; Mahamdioua, N.; Altintas, S. P.; Varilci, A.; Terzioglu, C.

    2016-07-01

    In this work, the effect of doping by tetravalent Ce4+on the structural and magnetoresistive properties of La0.7-xCexCa0.3MnO3 polycrystalline manganites is presented. Samples with x=0, 0.1, 0.2 and 0.3 are prepared by solid state reaction method and characterized. For all doping levels, the X ray diffraction (XRD) analysis shows that the doping element is not completely soluble in the manganite. The cell parameters values, which decrease with Ce content, are refined in the orthorhombic system by taking into account the unreacted CeO2 phase. The observation by scanning electron microscopy (SEM) reveals a change in the morphology of the grains and the porosity of the samples by doping. The temperature dependence of magnetization curves shows a transition from paramagnetic to ferromagnetic state in all samples. A decrease of the Curie temperature Tc with doping is revealed. The resistivity of the samples increases with Ce content and shows a clear metal to insulator transition when measured as a function of temperature. The doping also decreases the temperature Tp of this transition, in accordance with the evolution of Tc values. The calculated magnetoresistance (MR) for a magnetic field of 5T increases gradually from 39.52% for x=0 to 66.18% for x=0.3.

  2. Magnetic anisotropy and anisotropic magnetoresistance in strongly phase separated manganite thin films

    NASA Astrophysics Data System (ADS)

    Kandpal, Lalit M.; Singh, Sandeep; Kumar, Pawan; Siwach, P. K.; Gupta, Anurag; Awana, V. P. S.; Singh, H. K.

    2016-06-01

    The present study reports the impact of magnetic anisotropy (MA) on magnetotransport properties such as the magnetic transitions, magnetic liquid behavior, glass transition and anisotropic magnetoresistance (AMR) in epitaxial film (thickness 42 nm) of strongly phase separated manganite La5/8-yPryCa3/8MnO3 (y≈0.4). Angle dependent magnetization measurement confirms the out-of-plane magnetic anisotropy with the magnetic easy axes aligned in the plane of the film and the magnetic hard axis along the normal to the film plane. The more prominent divergence between the zero filed cooled (ZFC) and field cooled warming (FCW) and the stronger hysteresis between the field cooled cooling (FCC) and FCW magnetization for H ∥ shows the weakening of the magnetic liquid along the magnetic hard axis. The peak at Tp≈42 K in FCW magnetization, which characterizes the onset of spin freezing shifts down to Tp≈18 K as the field direction is switched from the easy axes (H ∥) to the hard axis (H ⊥). The glass transition, which appears at Tg≈28 K for H ∥ disappears for H ⊥. The easy axis magnetization (M∣∣) appears to saturate around H~20 kOe, but the hard axis counterpart (M⊥) does not show such tendency even up to H=50 kOe. MA appears well above the ferromagnetic (FM) transition at T≈170 K, which is nearly the same as the Neel temperature (TN) of M⊥ - T . The temperature dependent resistivity measured at H=10 kOe applied along the easy axis (ρ|| - T) and the hard axis (ρ⊥ - T) shows insulator metal transition (IMT) at ≈106 K and ≈99 K in the cooling cycle, respectively. The large difference between ρ⊥ - T and ρ|| - T during the cooling cycle and in the vicinity of IMT results in huge AMR of ≈-142% and -115%. The observed properties have been explained in terms of the MA induced variation in the relative fraction of the coexisting magnetic phases.

  3. Competition entre les phases ferromagnetique metallique et ordre de charges a l'interface de manganites a magnetoresistance colossale

    NASA Astrophysics Data System (ADS)

    Laverdiere, Jonathan

    Dans la these qui suit, l'interaction entre deux manganites a magnetoresistance colossale domines par des phases antagonistes est etudiee a l'interface de bicouches. Un manganite isolant anti-ferromagnetique presentant une phase d'ordre de charges a basse temperature et un manganite metallique domine par les interactions ferromagnetiques. L'objectif est de verifier si l'interaction entre ces deux manganites est susceptible de soit 1) affaiblir la stabilite de l'ordre de charges ou soit 2) de rendre la phase metallique plus resistive afin d'ameliorer les proprietes de magnetoresistance colossale. Deux series de bicouches ont ete preparees par depot par ablation laser pulse et analysees avec une combinaison de plusieurs methodes experimentales telles que la mesure de resistance electrique, la spectroscopie Raman, la mesure d'aimantation et la diffraction des rayons X. Dans la premiere serie de bicouches, la configuration utilisee consiste en une couche tampon ferromagnetique sur laquelle une couche de manganite a ordre de charges est deposee. Il s'est avere que la phase d'ordre de charges n'est pas destabilisee par la phase ferromagnetique metallique dans une couche d'ordre de charges aussi mince que 10 nm. Les mesures de resistance montrent que la phase isolante demeure difficile a rendre metallique sous l'application d'un champ magnetique. La spectroscopie Raman montre egar lement une phase d'ordre de charges tres stable et suggere que les contraintes mecaniques appliquees par la couche tampon sont responsables de cette stabilite, malgre la presence de la phase ferromagnetique a proximite. Dans la deuxieme serie de bicouches, la configuration utilisee consiste en une couche tampon presentant de l'ordre de charges sur laquelle une couche ferromagnetique metallique est deposee. La diminution de l'epaisseur de la couche ferromagnetique metallique se repercute sur une diminution de la temperature de Curie et de la transition metal-isolant. Entre 4 et 5 nm, la

  4. Giant intrinsic tunnel magnetoresistance in manganite thin films etched with antidot arrays

    SciTech Connect

    Li, Hui; Li, Lin; Li, Long; Liang, Haixing; Cheng, Long; Zhai, Xiaofang; Zeng, Changgan

    2014-02-24

    Huge intrinsic tunnel magnetoresistance effects at low field are demonstrated in macroscopic La{sub 0.33}Pr{sub 0.34}Ca{sub 0.33}MnO{sub 3} thin films etched with periodic antidot arrays, and a highest magnetoresistance ratio (about 1600%) is achieved at 58 K. Such giant tunnel magnetoresistance effect might originate from delicate phase separation and coherent transport under the applied periodic spatial confinement. Strong transport fluctuation is also revealed in such systems due to phase competition. Our findings pave a way to realize tunnel magnetoresistance devices based on electronically phase separated materials with spatial modulations.

  5. Colossal thermoelectric power in charge ordered lanthanum calcium manganites (La{sub 0.5}Ca{sub 0.5}MnO{sub 3})

    SciTech Connect

    Joy, Lija K.; Anantharaman, M. R.; Shanmukharao Samatham, S.; Ganesan, V.; Thomas, Senoy; Al-Harthi, Salim; Liebig, A.; Albrecht, M.

    2014-12-07

    Lanthanum calcium manganites (La{sub 0.5}Ca{sub 0.5}MnO{sub 3}) with a composition close to charge ordering, synthesized by high energy ball milling, was found to exhibit colossal thermoelectric power. Thermoelectric power (TEP) data was systematically analyzed by dividing the entire temperature range (5 K–300 K) into three different regimes to explore different scattering mechanisms involved. Mandal's model has been applied to explain TEP data in the region below the Curie temperature (T{sub C}). It has been found that the variation of thermoelectric power with temperature is pronounced when the system enters the charge ordered region at T < 200 K. For temperatures lower than 120 K, due to the co-existence of charge ordered state with a spin-glass state, the variation of thermoelectric power is maximum and exhibited a peak value of −80 mV/K at 58 K. This has been explained by incorporating Kondo properties of the spin-glass along with magnon scattering. FC-ZFC magnetization measurements indicate the existence of a glassy state in the region corresponding to a maximum value of thermoelectric power. Phonon drag contribution instead of spin-glass contribution is taken into account to explain TEP in the region 120 K < T < T{sub C}. Mott's polaronic contribution of charge carriers are considered to interpret TEP in the high temperature region (T > T{sub C}). The optimal Mn{sup 4+}-Mn{sup 3+} concentration in charge ordered La{sub 0.5}Ca{sub 0.5}MnO{sub 3} was examined by X-ray Photoelectron Spectroscopy analysis which confirms the charge ordered nature of this compound.

  6. Colossal magnetoresistance in amino-functionalized graphene quantum dots at room temperature: manifestation of weak anti-localization and doorway to spintronics.

    PubMed

    Roy, Rajarshi; Thapa, Ranjit; Kumar, Gundam Sandeep; Mazumder, Nilesh; Sen, Dipayan; Sinthika, S; Das, Nirmalya S; Chattopadhyay, Kalyan K

    2016-04-21

    In this work, we have demonstrated the signatures of localized surface distortions and disorders in functionalized graphene quantum dots (fGQD) and consequences in magneto-transport under weak field regime (∼1 Tesla) at room temperature. Observed positive colossal magnetoresistance (MR) and its suppression is primarily explained by weak anti-localization phenomenon where competitive valley (inter and intra) dependent scattering takes place at room temperature under low magnetic field; analogous to low mobility disordered graphene samples. Furthermore, using ab-initio analysis we show that sub-lattice sensitive spin-polarized ground state exists in the GQD as a result of pz orbital asymmetry in GQD carbon atoms with amino functional groups. This spin polarized ground state is believed to help the weak anti-localization dependent magneto transport by generating more disorder and strain in a GQD lattice under applied magnetic field and lays the premise for future graphene quantum dot based spintronic applications.

  7. A New Concept for Non-Volatile Memory: The Electric-Pulse Induced Resistive Change Effect in Colossal Magnetoresistive Thin Films

    NASA Technical Reports Server (NTRS)

    Liu, S. Q.; Wu, N. J.; Ignatiev, A.

    2001-01-01

    A novel electric pulse-induced resistive change (EPIR) effect has been found in thin film colossal magnetoresistive (CMR) materials, and has shown promise for the development of resistive, nonvolatile memory. The EPIR effect is induced by the application of low voltage (< 4 V) and short duration (< 20 ns) electrical pulses across a thin film sample of a CMR material at room temperature and under no applied magnetic field. The pulse can directly either increase or decrease the resistance of the thin film sample depending on pulse polarity. The sample resistance change has been shown to be over two orders of magnitude, and is nonvolatile after pulsing. The sample resistance can also be changed through multiple levels - as many as 50 have been shown. Such a device can provide a way for the development of a new kind of nonvolatile multiple-valued memory with high density, fast write/read speed, low power-consumption, and potential high radiation-hardness.

  8. A Variable Temperature Synchrotron X-ray Diffraction Study of Colossal Magnetoresistant NdMnAsO0.95F0.05

    PubMed Central

    Wildman, E. J.; Mclaughlin, A. C.

    2016-01-01

    The recent discovery of high temperature superconductivity in Fe arsenides has invigorated research into transition metal pnictides. Colossal magnetoresistance (CMR) has recently been reported for NdMnAsO1-xFx for x = 0.05–0.08, with a maximum magnetoresistance achieved at low temperature (MR9T(3 K)) = −95%). This appears to be a novel mechanism of CMR, which is as a result of a second order phase transition in field from an insulating antiferromagnet to a semiconducting paramagnet. Here we report a variable temperature synchrotron X-ray powder diffraction study of the CMR oxypnictide NdMnAsO0.95F0.05 between 4 K–290 K. An excellent fit to the tetragonal unit cell with space group P4/nmm is obtained over the entire temperature range, with no change in crystal structure detected down to 4 K. A coupling of the lattice and magnetic order is observed, where subtle discontinuities in the temperature variation of a and the c/a ratio are apparent as the Nd spins order antiferromagnetically and the Mn moments reorient into the basal plane at TSR. The results suggest that very small changes in lattice parameters effect the coupling between lattice, electronic and magnetic degrees of freedom. PMID:26875693

  9. A Variable Temperature Synchrotron X-ray Diffraction Study of Colossal Magnetoresistant NdMnAsO0.95F0.05.

    PubMed

    Wildman, E J; Mclaughlin, A C

    2016-01-01

    The recent discovery of high temperature superconductivity in Fe arsenides has invigorated research into transition metal pnictides. Colossal magnetoresistance (CMR) has recently been reported for NdMnAsO1-xFx for x = 0.05-0.08, with a maximum magnetoresistance achieved at low temperature (MR9T(3 K)) = -95%). This appears to be a novel mechanism of CMR, which is as a result of a second order phase transition in field from an insulating antiferromagnet to a semiconducting paramagnet. Here we report a variable temperature synchrotron X-ray powder diffraction study of the CMR oxypnictide NdMnAsO0.95F0.05 between 4 K-290 K. An excellent fit to the tetragonal unit cell with space group P4/nmm is obtained over the entire temperature range, with no change in crystal structure detected down to 4 K. A coupling of the lattice and magnetic order is observed, where subtle discontinuities in the temperature variation of a and the c/a ratio are apparent as the Nd spins order antiferromagnetically and the Mn moments reorient into the basal plane at TSR. The results suggest that very small changes in lattice parameters effect the coupling between lattice, electronic and magnetic degrees of freedom. PMID:26875693

  10. A Variable Temperature Synchrotron X-ray Diffraction Study of Colossal Magnetoresistant NdMnAsO0.95F0.05

    NASA Astrophysics Data System (ADS)

    Wildman, E. J.; McLaughlin, A. C.

    2016-02-01

    The recent discovery of high temperature superconductivity in Fe arsenides has invigorated research into transition metal pnictides. Colossal magnetoresistance (CMR) has recently been reported for NdMnAsO1-xFx for x = 0.05-0.08, with a maximum magnetoresistance achieved at low temperature (MR9T(3 K)) = -95%). This appears to be a novel mechanism of CMR, which is as a result of a second order phase transition in field from an insulating antiferromagnet to a semiconducting paramagnet. Here we report a variable temperature synchrotron X-ray powder diffraction study of the CMR oxypnictide NdMnAsO0.95F0.05 between 4 K-290 K. An excellent fit to the tetragonal unit cell with space group P4/nmm is obtained over the entire temperature range, with no change in crystal structure detected down to 4 K. A coupling of the lattice and magnetic order is observed, where subtle discontinuities in the temperature variation of a and the c/a ratio are apparent as the Nd spins order antiferromagnetically and the Mn moments reorient into the basal plane at TSR. The results suggest that very small changes in lattice parameters effect the coupling between lattice, electronic and magnetic degrees of freedom.

  11. Changes of the local distortions and colossal magnetoresistive properties of La(0.7)Ca(0.3)MnO(3) induced by Ti or Ga defects

    SciTech Connect

    Bridges, F.; Cao, D.; Anderson, M.; Ramirez, A.P.; Olapinski, M.; Subramanian, M.A.; Booth, C.H.; Kwei, G.

    2002-07-12

    The magnetoresistive properties of La0.7Ca0.3MnO3 change rapidly when Ti or Ga are substituted on the Mn site for concentrations, x, from 1 to 10 percent. The samples exhibit colossal magnetoresistance (CMR) and the resistivity increases dramatically with dopant concentration. The temperature of the resistivity peak, TR, shifts rapidly to lower temperatures with increasing x and the ferromagnetic transition broadens. However, the transition temperature, Tc, is only slightly suppressed. Consequently, TR occurs well below Tc for x above 2 percent. Investigations of these materials using Mn XAFS show that changes in the local structure, parametrized by the pair-distribution width, sigma, correlate well with Tc and the sample magnetization. For a given dopant, the resistivity peak occurs when sigma{sup 2} decreases below a critical value. Both dopants produce extended defects which increases the resistivity of the nearby materials considerably. The data suggest that even at x {approx}4 percent, most of the sites are slightly distorted at low T.

  12. Uniaxial magnetic anisotropy induced low field anomalous anisotropic magnetoresistance in manganite thin films

    NASA Astrophysics Data System (ADS)

    Liao, Zhaoliang; Huijben, Mark; Koster, Gertjan; Rijnders, Guus

    2014-09-01

    La2/3Sr1/3MnO3 films with uniaxial magnetic anisotropy were coherently grown on NdGaO3 (110) substrates. The uniaxial anisotropy has strong effect on magnetoresistance (MR). A positive MR was observed when the current is along magnetic easy axis under the current-field perpendicular geometry. In contrast, no positive MR is observed when current is along the magnetic hard axis regardless of the field direction. Our analysis indicates that the anomalous anisotropic MR effect arises from the uniaxial magnetic anisotropy caused stripe domains which contribute to strong anisotropic domain wall resistivity.

  13. Emergence of Complex States in CMR Manganites and High-Tc Cuprates

    NASA Astrophysics Data System (ADS)

    Dagotto, Elbio

    2005-03-01

    Recent developments in the context of theory and experiments for manganites and cuprates will be discussed. It will be argued that the presence of nanoscale phase separation is at the heart of the colossal magnetoresistance phenomenon [1]. Simulation results support this view, as well as experimental data. These effects are not limited to manganites, but they may appear in other compounds as well, such as the high-Tc cuprates. New results will be presented in this area, on the phenomenological competition between antiferromagnetism and d-wave superconductivity, suggesting the possibility of ``colossal'' effects in this context [2]. This is compatible with the recent discovery of ``giant proximity effects'' in Cu-oxides [3]. All this suggests that clustered or mixed-phase states could form a new paradigm for the understanding of compounds in condensed matter physics. Work in collaboration with G. Alvarez, M. Mayr, A. Moreo, C. Sen, and I. Sergienko, supported by NSF DMR. [1] A. Moreo et al., Science 283, 2034 (1999); E.D., T. Hotta and A. Moreo, Physics Reports 344,1 (2001); E.D., ``Nanoscale Phase Separation and Colossal Magnetoresistance'', Springer-Verlag, 2002. [2] G. Alvarez et al., cond-mat/0401474, PRB to appear. [3] I. Bozovic et al., Phys. Rev. Lett. 93, 157002 (2004)

  14. Magnetoresistance from quantum interference effects in ferromagnets

    PubMed

    Manyala; Sidis; DiTusa; Aeppli; Young; Fisk

    2000-04-01

    The desire to maximize the sensitivity of read/write heads (and thus the information density) of magnetic storage devices has stimulated interest in the discovery and design of new magnetic materials exhibiting magnetoresistance. Recent discoveries include the 'colossal' magnetoresistance in the manganites and the enhanced magnetoresistance in low-carrier-density ferromagnets. An important feature of these systems is that the electrons involved in electrical conduction are different from those responsible for the magnetism. The latter are localized and act as scattering sites for the mobile electrons, and it is the field tuning of the scattering strength that ultimately gives rise to the observed magnetoresistance. Here we argue that magnetoresistance can arise by a different mechanism in certain ferromagnets--quantum interference effects rather than simple scattering. The ferromagnets in question are disordered, low-carrier-density magnets where the same electrons are responsible for both the magnetic properties and electrical conduction. The resulting magnetoresistance is positive (that is, the resistance increases in response to an applied magnetic field) and only weakly temperature-dependent below the Curie point.

  15. Method of making active magnetic refrigerant, colossal magnetostriction and giant magnetoresistive materials based on Gd-Si-Ge alloys

    DOEpatents

    Gschneidner, Jr., Karl A.; Pecharsky, Alexandra O.; Pecharsky, Vitalij K.

    2003-07-08

    Method of making an active magnetic refrigerant represented by Gd.sub.5 (Si.sub.x Ge.sub.1-x).sub.4 alloy for 0.ltoreq.x.ltoreq.1.0 comprising placing amounts of the commercially pure Gd, Si, and Ge charge components in a crucible, heating the charge contents under subambient pressure to a melting temperature of the alloy for a time sufficient to homogenize the alloy and oxidize carbon with oxygen present in the Gd charge component to reduce carbon, rapidly solidifying the alloy in the crucible, and heat treating the solidified alloy at a temperature below the melting temperature for a time effective to homogenize a microstructure of the solidified material, and then cooling sufficiently fast to prevent the eutectoid decomposition and improve magnetocaloric and/or the magnetostrictive and/or the magnetoresistive properties thereof.

  16. Colossal magnetoresistance in amino-functionalized graphene quantum dots at room temperature: manifestation of weak anti-localization and doorway to spintronics

    NASA Astrophysics Data System (ADS)

    Roy, Rajarshi; Thapa, Ranjit; Kumar, Gundam Sandeep; Mazumder, Nilesh; Sen, Dipayan; Sinthika, S.; Das, Nirmalya S.; Chattopadhyay, Kalyan K.

    2016-04-01

    In this work, we have demonstrated the signatures of localized surface distortions and disorders in functionalized graphene quantum dots (fGQD) and consequences in magneto-transport under weak field regime (~1 Tesla) at room temperature. Observed positive colossal magnetoresistance (MR) and its suppression is primarily explained by weak anti-localization phenomenon where competitive valley (inter and intra) dependent scattering takes place at room temperature under low magnetic field; analogous to low mobility disordered graphene samples. Furthermore, using ab-initio analysis we show that sub-lattice sensitive spin-polarized ground state exists in the GQD as a result of pz orbital asymmetry in GQD carbon atoms with amino functional groups. This spin polarized ground state is believed to help the weak anti-localization dependent magneto transport by generating more disorder and strain in a GQD lattice under applied magnetic field and lays the premise for future graphene quantum dot based spintronic applications.In this work, we have demonstrated the signatures of localized surface distortions and disorders in functionalized graphene quantum dots (fGQD) and consequences in magneto-transport under weak field regime (~1 Tesla) at room temperature. Observed positive colossal magnetoresistance (MR) and its suppression is primarily explained by weak anti-localization phenomenon where competitive valley (inter and intra) dependent scattering takes place at room temperature under low magnetic field; analogous to low mobility disordered graphene samples. Furthermore, using ab-initio analysis we show that sub-lattice sensitive spin-polarized ground state exists in the GQD as a result of pz orbital asymmetry in GQD carbon atoms with amino functional groups. This spin polarized ground state is believed to help the weak anti-localization dependent magneto transport by generating more disorder and strain in a GQD lattice under applied magnetic field and lays the premise for

  17. Spin-dependent Seebeck Effect, Thermal Colossal Magnetoresistance and Negative Differential Thermoelectric Resistance in Zigzag Silicene Nanoribbon Heterojunciton

    PubMed Central

    Fu, Hua-Hua; Wu, Dan-Dan; Zhang, Zu-Quan; Gu, Lei

    2015-01-01

    Spin-dependent Seebeck effect (SDSE) is one of hot topics in spin caloritronics, which examine the relationships between spin and heat transport in materials. Meanwhile, it is still a huge challenge to obtain thermally induced spin current nearly without thermal electron current. Here, we construct a hydrogen-terminated zigzag silicene nanoribbon heterojunction, and find that by applying a temperature difference between the source and the drain, spin-up and spin-down currents are generated and flow in opposite directions with nearly equal magnitudes, indicating that the thermal spin current dominates the carrier transport while the thermal electron current is much suppressed. By modulating the temperature, a pure thermal spin current can be achieved. Moreover, a thermoelectric rectifier and a negative differential thermoelectric resistance can be obtained in the thermal electron current. Through the analysis of the spin-dependent transport characteristics, a phase diagram containing various spin caloritronic phenomena is provided. In addition, a thermal magnetoresistance, which can reach infinity, is also obtained. Our results put forward an effective route to obtain a spin caloritronic material which can be applied in future low-power-consumption technology. PMID:26000658

  18. Atomic-scale electrochemistry on the surface of a manganite

    DOE PAGESBeta

    Vasudevan, Rama K.; Tselev, Alexander; Baddorf, Arthur P.; Kalinin, Sergei V.

    2015-04-09

    The doped manganese oxides (manganites) have been widely studied for their colossal magnetoresistive effects, for potential applications in oxide spintronics, electroforming in resistive switching devices, and are materials of choice as cathodes in modern solid oxide fuel cells. However, little experimental knowledge of the dynamics of the surfaces of perovskite manganites at the atomic scale exists. Here, through in-situ scanning tunnelling microscopy (STM), we demonstrate atomic resolution on samples of La0.625Ca0.375MnO3 grown on (001) SrTiO3 by pulsed laser deposition (PLD). Furthermore, by applying triangular DC waveforms of increasing amplitude to the STM tip, and measuring the tunnelling current, we demonstratemore » the ability to both perform and monitor surface electrochemical processes at the atomic level, including, for the first time in a manganite, formation of single and multiple oxygen vacancies, disruption of the overlying manganite layers, and removal and deposition of individual atomic units or clusters. Our work paves the way for better understanding of surface oxygen reactions in these systems.« less

  19. Atomic-scale electrochemistry on the surface of a manganite

    SciTech Connect

    Vasudevan, Rama K.; Tselev, Alexander; Baddorf, Arthur P.; Kalinin, Sergei V.

    2015-04-09

    The doped manganese oxides (manganites) have been widely studied for their colossal magnetoresistive effects, for potential applications in oxide spintronics, electroforming in resistive switching devices, and are materials of choice as cathodes in modern solid oxide fuel cells. However, little experimental knowledge of the dynamics of the surfaces of perovskite manganites at the atomic scale exists. Here, through in-situ scanning tunnelling microscopy (STM), we demonstrate atomic resolution on samples of La0.625Ca0.375MnO3 grown on (001) SrTiO3 by pulsed laser deposition (PLD). Furthermore, by applying triangular DC waveforms of increasing amplitude to the STM tip, and measuring the tunnelling current, we demonstrate the ability to both perform and monitor surface electrochemical processes at the atomic level, including, for the first time in a manganite, formation of single and multiple oxygen vacancies, disruption of the overlying manganite layers, and removal and deposition of individual atomic units or clusters. Our work paves the way for better understanding of surface oxygen reactions in these systems.

  20. Nodal quasiparticle in pseudogapped colossal magnetoresistivemanganites

    SciTech Connect

    Mannella, Norman; Yang, Wanli L.; Zhou, Xing Jiang; Zheng, Hong; Mitchell, John F.; Zaanen, Jan; Devereaux, Thomas P.; Nagaosa, Naoto; Hussain, Zahid; Shen, Zhi-Xun

    2008-01-17

    A characteristic feature of the copper oxidehigh-temperaturesuperconductors is the dichotomy between the electronicexcitations along the nodal (diagonal) and antinodal (parallel to the CuO bonds) directions in momentum space, generally assumed to be linked tothe 'd-wave' symmetry of the superconducting state. Angle-resolvedphotoemission measurements in the superconducting state have revealed aquasiparticle spectrum with a d-wave gap structure that exhibits amaximum along the antinodal direction and vanishes along the nodaldirection1. Subsequent measurements have shown that, at low dopinglevels, this gap structure persists even in the high-temperature metallicstate, although the nodal points of the superconducting state spread outin finite 'Fermi arcs'2. This is the so-called pseudogap phase, and ithas been assumed that it is closely linked to the superconducting state,either by assigning it to fluctuating superconductivity3 or by invokingorders which are natural competitors of d-wave superconductors4, 5. Herewe report experimental evidence that a very similar pseudogap state witha nodal-antinodal dichotomous character exists in a system that ismarkedly different from a superconductor: the ferromagnetic metallicgroundstate of the colossal magnetoresistive bilayer manganiteLa1.2Sr1.8Mn2O7. Our findings therefore cast doubt on the assumption thatthe pseudogap state in the copper oxides and the nodal-antinodaldichotomy are hallmarks of the superconductivity state.

  1. The intrinsic electronic structure of bilayer manganites from Angle Resolved Photoemission

    NASA Astrophysics Data System (ADS)

    de Jong, Sanne; Kukreja, R.; Hossain, M. A.; Golden, M. S.; van Heumen, E.; Massee, F.; Huang, Y.; Boothroyd, A. T.; Pabhakaran, P.; Walter, A.; Bostwick, A.; Rotenberg, E.; Durr, H. A.

    2012-02-01

    The Colossal MagnetoResistant (CMR) manganites are one of the most studied condensed matter physics systems since decades. Yet, the mechanism behind the CMR effect and their electronic structure are still under hot debate. Recent angle resolved photoemission (ARPES) studies on the bilayer manganite La(2-2x)Sr(1+2x)Mn3O7, LSMO327, reported contradictory results [1]. Here we present an ARPES study unveiling the intrinsic k-- and temperature dependent electronic structure of LSMO327, while carefully steering away from the recently reported sample inhomogeneities [2] that have caused all the confusion. [4pt] [1] N. Mannella, Nature (2005); S. Sun Nature Phys. (2007); S. de Jong, PRB (2007)[0pt] [2] F. Massee, Nature Phys(2011)

  2. Atomic-scale electrochemistry on the surface of a manganite by scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Vasudevan, Rama K.; Tselev, Alexander; Gianfrancesco, Anthony G.; Baddorf, Arthur P.; Kalinin, Sergei V.

    2015-04-01

    The doped manganese oxides (manganites) have been widely studied for their colossal magnetoresistive effects, for potential applications in oxide spintronics, electroforming in resistive switching devices, and are materials of choice as cathodes in modern solid oxide fuel cells. However, little experimental knowledge of the dynamics of the surfaces of perovskite manganites at the atomic scale exists. Here, through in-situ scanning tunneling microscopy (STM), we demonstrate atomic resolution on samples of La0.625Ca0.375MnO3 grown on (001) SrTiO3 by pulsed laser deposition. Furthermore, by applying triangular DC waveforms of increasing amplitude to the STM tip, and measuring the tunneling current, we demonstrate the ability to both perform and monitor surface electrochemical processes at the atomic level, including formation of oxygen vacancies and removal and deposition of individual atomic units or clusters. Our work paves the way for better understanding of surface oxygen reactions in these systems.

  3. Nanoscale control of low-dimensional spin structures in manganites

    NASA Astrophysics Data System (ADS)

    Jing, Wang; Iftikhar, Ahmed Malik; Renrong, Liang; Wen, Huang; Renkui, Zheng; Jinxing, Zhang

    2016-06-01

    Due to the upcoming demands of next-generation electronic/magnetoelectronic devices with low-energy consumption, emerging correlated materials (such as superconductors, topological insulators and manganites) are one of the highly promising candidates for the applications. For the past decades, manganites have attracted great interest due to the colossal magnetoresistance effect, charge-spin-orbital ordering, and electronic phase separation. However, the incapable of deterministic control of those emerging low-dimensional spin structures at ambient condition restrict their possible applications. Therefore, the understanding and control of the dynamic behaviors of spin order parameters at nanoscale in manganites under external stimuli with low energy consumption, especially at room temperature is highly desired. In this review, we collected recent major progresses of nanoscale control of spin structures in manganites at low dimension, especially focusing on the control of their phase boundaries, domain walls as well as the topological spin structures (e.g., skyrmions). In addition, capacitor-based prototype spintronic devices are proposed by taking advantage of the above control methods in manganites. This capacitor-based structure may provide a new platform for the design of future spintronic devices with low-energy consumption. Project supported by the National Basic Research Program of China (Grant No. 2014CB920902), the National Natural Science Foundation of China (Grant Nos. 61306105 and 51572278), the Information Science and Technology (TNList) Cross-discipline Foundation from Tsinghua National Laboratory, China and the Fund from the State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China.

  4. First Order CMR Transitions in the Two-Orbital Model for Manganites

    SciTech Connect

    Sen, Cengiz; Alvarez, Gonzalo; Dagotto, Elbio R

    2010-01-01

    Large-scale Monte Carlo simulation results for the two-orbital model for manganites, including Jahn-Teller lattice distortions, are presented here. At hole density x=1/4 and in the vicinity of the region of competition between the ferromagnetic metallic and spin-charge-orbital ordered insulating phases, the colossal magnetoresistance (CMR) phenomenon is observed with a magnetoresistance ratio {approx}10,000%. Our main result is that this CMR transition is found to be of first order in some portions of the phase diagram, in agreement with early results from neutron scattering, specific heat, and magnetization, thus solving a notorious discrepancy between experiments and previous theoretical studies. The first order characteristics of the transition survive, and are actually enhanced, when weak quenched disorder is introduced.

  5. A new method of increasing thermopower in doped manganites

    NASA Astrophysics Data System (ADS)

    Koroleva, L. I.; Morozov, A. S.; Zhakina, E. S.; Batashev, I. K.; Balbashov, A. M.

    2016-06-01

    Thermopower, magnetothermopower, resistivity, magnetoresistance, and magnetization of singlecrystalline samples of the Sm1- x Sr x MnO3 system ( x = 0.15, 0.2, 0.25, 0.3) have been experimentally studied. These compositions consist of ferromagnetic clusters of the ferron type dispersed in the A-type antiferromagnetic matrix. Colossal thermo- and negative magnetothermopower values reaching 94.5% in a composition with x = 0.3 in the region of Curie point T C in a magnetic field of 1.323 T. This result implies that thermopower is mostly related to ferron-type clusters, since their breakage under the action of magnetic field or heating above T C leads to a sharp decrease in thermopower values. These results imply that thermopower in doped manganite semiconductors is determined by the concentration of impurity and volume of a sample.

  6. What Coexists with the Ferromagnetic Metallic Phase in Manganites?

    SciTech Connect

    Burkhardt, Mark H.; Hossain, M.A.; Sarkar, S.; Achkar, A.J.; Hawthorn, D.G.; Sutarto, R.; Chuang, 5 Y.-D.; Gonzalez, A.G.Cruz; Choi, Y.J.; Cheong, S.-W.; Durr, H.A.; Stohr, J.

    2012-07-25

    Colossal magnetoresistance, whereby the application of a magnetic field reduces the resistivity of a manganite by orders of magnitude, is generally believed to occur because of coexisting phases. Development of a complete theory to explain the phenomenon requires that the exact nature of these phases be known. We used resonant elastic soft x-ray scattering to examine the superlattice order that exists in La{sub 0.35}Pr{sub 0.275}Ca{sub 0.375}MnO{sub 3} above and below the Curie temperature. By measuring the resonance profile of the scattered x-rays at different values of q, we disentangle the contributions of orbital order and antiferromagnetism to the scattering signal above the Curie temperature. Below the Curie temperature, we see no signal from orbital order, and only antiferromagnetism coexists with the dominant ferromagnetic metallic phase.

  7. Colossal thermoelectric power in charge-ordered Li-doped La0.75Li0.25MnO3 manganite system

    NASA Astrophysics Data System (ADS)

    Taran, Subhrangsu; Sun, C. P.; Yang, H. D.; Chatterjee, S.

    2016-05-01

    A detail study of transport and magnetic properties of La1-xLixMnO3+δ (0.05 ≤ x ≤ 0.3) system synthesized by wet-chemical mixing route has been done. The room temperature x-ray powder diffraction (XRD) data show single phase behavior of all samples except x = 0.3. Rietveld refinement of XRD data shows structural transition from rhombohedral (R3-C) to orthorhombic (Pnma) symmetry occurs at the Li-doping level x > 0.2 with both the lattice parameter and unit-cell volume decrease with increase of `x'. All the samples show ferromagnetic (FM) behavior while metallic behavior are shown by the samples up to Li-concentration x = 0.2. With further Li doping i.e. for x = 0.25, the sample shows insulating behavior accompanied by charge-order transition around T ~ 225K. Metallic part of the resistivity data of the samples is best fitted with an expression ρ(T) = ρ0 + ρ4.5T4.5 + C/ sinh2(hvs/2kBT) containing small-polaron contribution (last term). Most interesting finding in the present study is the observation of large anomalous decrease in thermoelectric power (S) below 100K shown by the sample with x = 0.25. Probable mechanisms responsible for the observed colossal thermoelectric power have been discussed.

  8. Fermi Surface of Three-Dimensional La1 -xSrxMnO3 Explored by Soft-X-Ray ARPES: Rhombohedral Lattice Distortion and its Effect on Magnetoresistance

    NASA Astrophysics Data System (ADS)

    Lev, L. L.; Krempaský, J.; Staub, U.; Rogalev, V. A.; Schmitt, T.; Shi, M.; Blaha, P.; Mishchenko, A. S.; Veligzhanin, A. A.; Zubavichus, Y. V.; Tsetlin, M. B.; Volfová, H.; Braun, J.; Minár, J.; Strocov, V. N.

    2015-06-01

    Electronic structure of the three-dimensional colossal magnetoresistive perovskite La1 -xSrxMnO3 has been established using soft-x-ray angle-resolved photoemission spectroscopy with its intrinsically sharp definition of three-dimensional electron momentum. The experimental results show much weaker polaronic coupling compared to the bilayer manganites and are consistent with the theoretical band structure including the empirical Hubbard parameter U. The experimental Fermi surface unveils the canonical topology of alternating three-dimensional electron spheres and hole cubes, with their shadow contours manifesting the rhombohedral lattice distortion. This picture has been confirmed by one-step photoemission calculations including displacement of the apical oxygen atoms. The rhombohedral distortion is neutral to the Jahn-Teller effect and thus polaronic coupling, but affects the double-exchange electron hopping and thus the colossal magnetoresistance effect.

  9. Investigation of magnetic transitions through ultrasonic measurements in double-layered CMR manganite La1.2Sr1.8Mn2O7

    NASA Astrophysics Data System (ADS)

    Reddy, Y. S.; Vishnuvardhan Reddy, C.

    2014-03-01

    A polycrystalline, double-layered, colossal magnetoresistive manganite La1.2Sr1.8Mn2O7 is synthesized by sol-gel process and its magnetic and ultrasonic properties were investigated in the temperature range 80-300 K. The sample has Curie temperature at 124 K, where the sample exhibits a transition from paramagnetic insulator to ferromagnetic metallic state. The longitudinal sound velocity measurements show a significant hardening of sound velocity below TC, which may be attributed to the coupling between ferromagnetic spins and longitudinal acoustic phonons. The magnetization and ultrasonic studies reveal the presence of secondary transition at ≈ 260 K in this sample. The present sound velocity measurement results confirm the reliability of ultrasonic investigations as an independent tool to probe magnetic transitions in manganites.

  10. Epitaxial stabilization of ultra thin films of electron doped manganites

    SciTech Connect

    Middey, S. Kareev, M.; Meyers, D.; Liu, X.; Cao, Y.; Tripathi, S.; Chakhalian, J.; Yazici, D.; Maple, M. B.; Ryan, P. J.; Freeland, J. W.

    2014-05-19

    Ultra-thin films of the electron doped manganite La{sub 0.8}Ce{sub 0.2}MnO{sub 3} were grown in a layer-by-layer growth mode on SrTiO{sub 3} (001) substrates by pulsed laser interval deposition. High structural quality and surface morphology were confirmed by a combination of synchrotron based x-ray diffraction and atomic force microscopy. Resonant X-ray absorption spectroscopy measurements confirm the presence of Ce{sup 4+} and Mn{sup 2+} ions. In addition, the electron doping signature was corroborated by Hall effect measurements. All grown films show a ferromagnetic ground state as revealed by both dc magnetization and x-ray magnetic circular dichroism measurements and remain insulating contrary to earlier reports of a metal-insulator transition. Our results hint at the possibility of electron-hole asymmetry in the colossal magnetoresistive manganite phase diagram akin to the high-T{sub c} cuprates.

  11. Interplay between electronic transport and magnetic order in ferromagnetic magnetic manganite thin films

    SciTech Connect

    Hundley, M.F.; Neumeier, J.J.; Heffner, R.H.; Jia, Q.X.; Wu, X.D.; Thompson, J.D.

    1997-05-01

    The transition metal oxides La{sub 1{minus}x}A{sub x}MnO{sub 3} (A = Ba, Ca, or Sr) order ferromagnetically with Curie temperatures ranging from as low as 50 K to well above room temperature. Magnetic order in these compounds results in a concomitant metal-insulator transition. The feature displayed by the manganites that is most important technologically is the extremely large negative magnetoresistance that achieves its largest values near the magnetic ordering temperature. Qualitatively, this colossal magnetoresistance (CMR) phenomenon involves the suppression of the relatively sharp maximum in the resistivity that is centered at T{sub C}. When considered collectively, the anomalous temperature-dependent transport properties, the CMR effect, and the magnetically ordered ground state indicate that a novel interplay between magnetism and electronic transport occurs in the manganites. General features of the magnetic-field and temperature-dependent electrical resistivity and magnetization as displayed by PLD-grown thin films are examined. Particular emphasis is placed on what these measurements tell us about the conduction process both above and below the magnetic ordering temperature.

  12. Bilayer splitting and c-axis coupling in CMR bilayer manganites

    SciTech Connect

    Jozwiak, Chris; Graf, Jeff; Zhou, Shuyun; Bostwick, Aaron; Rotenberg, Eli; Zheng, Hong; Mitchell, John; Lanzara, Alessandra

    2009-09-03

    By performing angle-resolved photoemission spectroscopy of the bilayer colossal magnetoresistive (CMR) manganite, La2-2xSr1+2xMn2O7, we provide the complete mapping of the Fermi-level spectral weight topology. Clear and unambiguous bilayer splitting of the in-plane 3dx2-y2 band, mapped throughout the Brillouin zone, and the full mapping of the 3d3z2-r2 band are reported. Peculiar doping and temperature dependencies of these bands imply that as transition from the ferromagnetic metallic phase approaches, either as a function of doping or temperature, coherence along the c-axis between planes within the bilayer is lost, resulting in reduced interplane coupling. These results suggest that interplane coupling plays a large role in the CMR transition.

  13. Manipulation of magnetic phase separation and orbital occupancy in manganites by strain engineering and electric field

    NASA Astrophysics Data System (ADS)

    Cui, Bin; Song, Cheng; Pan, Feng; Key Laboratory of Advanced Materials (MOE) Team

    2015-03-01

    The modification of electronic phases in correlated oxides is one of the core issues of condensed matter. We report the reversible control of ferromagnetic phase transition in manganite films by ionic liquid gating, replicating the La1-xSrxMnO3 (LSMO) phase diagram. The formation and annihilation of an insulating and magnetically hard phase in the soft magnetic matrix, which randomly nucleates and grows across the film, is directly observed under different gate voltages (VG) . The realization of reversible metal-insulator transition in colossal magnetoresistance materials can lead to the development of four-state memories. The orbital occupancy and magnetic anisotropy of LSMO films are manipulated by VG in a reversible and quantitative manner. Positive and negative VG increases and reduces the occupancy of the orbital and magnetic anisotropy that were initially favored by strain (irrespective of tensile and compressive), respectively. This finding fills in the blank of electrical manipulation of four degrees of freedom in correlated system.

  14. Phase separation of electrons strongly coupled with phonons in cuprates and manganites

    NASA Astrophysics Data System (ADS)

    Alexandrov, Sasha

    2009-03-01

    Recent advanced Monte Carlo simulations have not found superconductivity and phase separation in the Hubbard model with on-site repulsive electron-electron correlations. I argue that microscopic phase separations in cuprate superconductors and colossal magnetoresistance (CMR) manganites originate from a strong electron-phonon interaction (EPI) combined with unavoidable disorder. Attractive electron correlations, caused by an almost unretarded EPI, are sufficient to overcome the direct inter-site Coulomb repulsion in these charge-transfer Mott-Hubbard insulators, so that low energy physics is that of small polarons and small bipolarons. They form clusters localized by disorder below the mobility edge, but propagate as the Bloch states above the mobility edge. I identify the Froehlich EPI as the most essential for pairing and phase separation in superconducting layered cuprates. The pairing of oxygen holes into heavy bipolarons in the paramagnetic phase (current-carrier density collapse (CCDC)) explains also CMR and high and low-resistance phase coexistence near the ferromagnetic transition of doped manganites.

  15. Atomic-scale electrochemistry on the surface of a manganite by scanning tunneling microscopy

    SciTech Connect

    Vasudevan, Rama K. Tselev, Alexander; Baddorf, Arthur P.; Gianfrancesco, Anthony G.

    2015-04-06

    The doped manganese oxides (manganites) have been widely studied for their colossal magnetoresistive effects, for potential applications in oxide spintronics, electroforming in resistive switching devices, and are materials of choice as cathodes in modern solid oxide fuel cells. However, little experimental knowledge of the dynamics of the surfaces of perovskite manganites at the atomic scale exists. Here, through in-situ scanning tunneling microscopy (STM), we demonstrate atomic resolution on samples of La{sub 0.625}Ca{sub 0.375}MnO{sub 3} grown on (001) SrTiO{sub 3} by pulsed laser deposition. Furthermore, by applying triangular DC waveforms of increasing amplitude to the STM tip, and measuring the tunneling current, we demonstrate the ability to both perform and monitor surface electrochemical processes at the atomic level, including formation of oxygen vacancies and removal and deposition of individual atomic units or clusters. Our work paves the way for better understanding of surface oxygen reactions in these systems.

  16. Evaluation of the effect of various mechanisms on the magnetoresistance of lanthanum manganites La{sub 0.85}Sr{sub 0.15}MnO{sub 3} with activation-type conductivity

    SciTech Connect

    Gudin, S. A. Kurkin, M. I.; Neifel’d, E. A.; Korolev, A. V.; Gapontseva, N. N.; Ugryumova, N. A.

    2015-11-15

    A method is proposed that allows one to divide the magnetoresistance (MR) observed in manganites into three mechanisms: dimensional, orientational, and magnetic. The first two mechanisms are associated with the stratification of a substance into ferromagnetic and nonferromagnetic phases, which significantly differ in electric resistivity. The dimensional mechanism of MR is attributed to the effect of a magnetic field on the size of magnetic inclusions. The orientational mechanism of MR is determined by the dependence of electric resistivity on the mutual orientation of the magnetizations of magnetic inclusions. The magnetic mechanism of MR is determined by the properties of the magnetization of a ferromagnet, in particular, by the Curie–Weiss singularity on the temperature dependence of magnetic susceptibility at the Curie point. This mechanism exists in homogeneous substances, although its value may depend on the magnetic properties of inhomogeneities. The method is developed for substances with activation-type conductivity and is applied to the analysis of MR of La{sub 0.85}Sr{sub 0.15}MnO{sub 3} manganite near the Curie point, where the MR attains its maximum. The dimensional mechanism turns out to be dominant in magnetic fields H greater than the saturation field H{sub s} (H > H{sub s}). The orientational, dimensional, and magnetic mechanisms have a comparable effect on the MR for H < H{sub s}. The effect of the orientational mechanism on MR is relatively weak (does not exceed the third part of the total MR), although this mechanism determines the giant MR in multilayered metal films. The possibility of application of the method to the analysis of MR near the insulator–metal transition is analyzed.

  17. Competing-fluctuation-induced anomalous magnetocaloric effects in perovskite manganites

    NASA Astrophysics Data System (ADS)

    Sakai, Hideaki; Taguchi, Yasujiro; Tokura, Yoshinori

    2010-03-01

    A magnetocaloric (MC) effect refers to the isothermal entropy change induced by applying (or removing) a magnetic field to the materials, which is a performance index of the magnetic refrigeration technology. In this study, the variation of MC effects has been systematically investigated for colossal magnetoresistive manganites R0.6Sr0.4MnO3 (R=La-Gd) by controlling the R-dependent one-electron bandwidth. With decreasing the bandwidth, the temperature profile of entropy change exhibits a larger peak at the ferromagnetic transition temperature and a steeper drop below it, due to the first-order nature of the transition promoted by a competing charge-orbital ordering instability. For the smallest-bandwidth systems adjacent to the metal- insulator phase boundary, a rectangular-shaped profile for the entropy change emerges with an anomalously wide temperature range. Model calculations have indicated that the bicritical fluctuation enhanced in the phase-competing region has a strong impact on such MC features [1]. [1] H. Sakai et al., J. Phys. Soc. Jpn. 78, 113708 (2009).

  18. Evolution and sign control of square-wave-like anisotropic magneto-resistance in spatially confined La0.3Pr0.4Ca0.3MnO3/LaAlO3(001) manganite thin films

    NASA Astrophysics Data System (ADS)

    Alagoz, H. S.; Jeon, J.; Keating, S.; Chow, K. H.; Jung, J.

    2016-04-01

    We investigated magneto-transport properties of a compressively strained spatially confined La0.3Pr0.4Ca0.3MnO3 (LPCMO) thin film micro-bridge deposited on LaAlO3. Angular dependence of the magneto-resistance R(θ) of this bridge, where θ is the angle between the magnetic field and the current directions in the film plane, exhibits sharp positive and negative percolation jumps near TMIT. The sign and the magnitude of these jumps can be tuned using the magnetic field. Such behavior has not been observed in LPCMO micro-bridges subjected to tensile strain, indicating a correlation between the type of the lattice strain, the distribution of electronic domains, and the anisotropic magneto-resistance in spatially confined manganite systems.

  19. Scanning probe microscopy investigation of bilayered manganites

    NASA Astrophysics Data System (ADS)

    Huang, Junwei

    The bilayered manganite La2-2xSr 1+2xMn2O7, with x in the ferromagnetic compositional region, exhibits very interesting electronic and magnetic properties below the Curie temperature, such as a colossal magneto-resistance (CMR) effect. We have studied the microscopic electronic structure in the x = 0.32, 0.4 compounds at 80 K and 20 K by using a home-built low temperature scanning tunneling microscope (STM) and the evolution of the ferromagnetic domains with temperature and magnetic field in the x = 0.32 compound from 30 K to 110 K by using a home-built low temperature magnetic force microscope (MFM). STM topographic images show nano-sized patterns composed of Mn 3+-rich and Mn4+-rich regions in the mixed-valent matrix. Tunneling spectra I(V)& dIdV (V) show a gap and a tunneling asymmetry of the LDOS as a function of the sample bias voltage. By using current-imaging tunneling spectroscopy (CITS), we obtained a series of tunneling conductance maps which show the coexistence of localized electrons and itinerant electrons in this system. In the x = 0.32 compound, we observed a modulation with a wave vector of 16 A propagating along a-axis at 20K. This indicates the formation of a charge density wave as a result of Fermi surface nesting in this system. In MFM images, we observed that below 60 K, the ferromagnetic (FM) domains form stable treelike patterns and the domains are mainly oriented in the out-of-plane direction. As the temperature increases, the FM domains begin to experience a gradual change. This change becomes more and more rapid above 80 K. The FM domains change their magnetization from the out-of-plane direction to in-plane around 88 K. The in-plane FM domains completely disappear near T C. We also observed thermal hysteresis occurring in magnetic structures. We conclude that the formation of FM domains at low temperatures is determined by the energy associated with surface magnetic free poles and domain walls. At high temperatures, the two

  20. Temperature-dependent electronic structure of the colossal magnetoresistive manganite La{sub 0.7}Sr{sub 0.3}MnO{sub 3} from hard x-ray photoemission.

    SciTech Connect

    Offi, F.; Mannella, N.; Pardini, T.; Panaccione, G.; Fondacaro, A.; Torelli, P.; West, M. W.; Mitchell, J. F.; Fadley, C. S.; Univ. Roma Tre; LBNL; Stanford Univ.; Univ. Tennessee; Univ. California at Davis; Lab. Nazionale TASC-INFM-CNR; ESRF; LURE, Centre Univ. Paris Sud; Julich Research Center; Univ. Hamburg

    2008-01-01

    We have studied in situ fractured surfaces of single-crystal La{sub 0.7}Sr{sub 0.3}MnO{sub 3} with hard x-ray photoemission (HXPS) at an excitation energy of 7.7 keV. These more bulk-sensitive measurements reveal low-binding-energy satellites in the Mn 2p{sub 3/2}, 3s, and 3p core spectra that are in agreement with previously observed satellites in Mn 2p{sub 3/2} for other strongly correlated materials, and which have been interpreted in terms of nonlocalized screening effects. The Mn 3s spectrum is consistent with recent soft x-ray measurements [N. Mannella et al., Phys. Rev. Lett. 92, 166401 (2004)] in showing an increased multiplet splitting at temperatures 100 K or more above the Curie temperature, although the magnitude of the effect is somewhat reduced. The valence-band spectra exhibit significant enhancement of intensity at such higher temperatures that we interpret as evidence of localization of Mn 3d-derived charge, which is in agreement with the multiplet splitting change and prior soft x-ray work. Additional aspects of HXPS for the study of complex materials are thus demonstrated.

  1. Composition dependence of electronic, magnetic, transport and morphological properties of mixed valence manganite thin films

    DOE PAGESBeta

    Singh, Surendra; Freeland, J. W.; Fitzsimmons, Michael R.; Jeen, H.; Biswas, A.

    2016-07-27

    Mixed-valence manganese oxides present striking properties like the colossal magnetoresistance, metal-insulator transition (MIT) that may result from coexistence of ferromagnetic, metallic and insulating phases. Percolation of such phase coexistence in the vicinity of MIT leads to first-order transition in these manganites. However the length scales over which the electronic and magnetic phases are separated across MIT which appears compelling for bulk systems has been elusive in (La1-yPry)1-xCaxMnO3 films. Here we show the in-plane length scale over which charge and magnetism are correlated in (La0.4Pr0.6)1-xCaxMnO3 films with x = 0.33 and 0.375, across the MIT temperature. We combine electrical transport (resistance)more » measurements, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and specular/off-specular x-ray resonant magnetic scattering (XRMS) measurements as a function of temperature to elucidate relationships between electronic, magnetic and morphological structure of the thin films. Using off-specular XRMS we obtained the charge-charge and charge-magnetic correlation length of these LPCMO films across the MIT. We observed different charge-magnetic correlation length for two films which increases below the MIT. The different correlation length shown by two films may be responsible for different macroscopic (transport and magnetic) properties.« less

  2. Composition dependence of charge and magnetic length scales in mixed valence manganite thin films.

    PubMed

    Singh, Surendra; Freeland, J W; Fitzsimmons, M R; Jeen, H; Biswas, A

    2016-01-01

    Mixed-valence manganese oxides present striking properties like the colossal magnetoresistance, metal-insulator transition (MIT) that may result from coexistence of ferromagnetic, metallic and insulating phases. Percolation of such phase coexistence in the vicinity of MIT leads to first-order transition in these manganites. However the length scales over which the electronic and magnetic phases are separated across MIT which appears compelling for bulk systems has been elusive in (La1-yPry)1-xCaxMnO3 films. Here we show the in-plane length scale over which charge and magnetism are correlated in (La0.4Pr0.6)1-xCaxMnO3 films with x = 0.33 and 0.375, across the MIT temperature. We combine electrical transport (resistance) measurements, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and specular/off-specular x-ray resonant magnetic scattering (XRMS) measurements as a function of temperature to elucidate relationships between electronic, magnetic and morphological structure of the thin films. Using off-specular XRMS we obtained the charge-charge and charge-magnetic correlation length of these LPCMO films across the MIT. We observed different charge-magnetic correlation length for two films which increases below the MIT. The different correlation length shown by two films may be responsible for different macroscopic (transport and magnetic) properties. PMID:27461993

  3. Composition dependence of charge and magnetic length scales in mixed valence manganite thin films

    NASA Astrophysics Data System (ADS)

    Singh, Surendra; Freeland, J. W.; Fitzsimmons, M. R.; Jeen, H.; Biswas, A.

    2016-07-01

    Mixed-valence manganese oxides present striking properties like the colossal magnetoresistance, metal-insulator transition (MIT) that may result from coexistence of ferromagnetic, metallic and insulating phases. Percolation of such phase coexistence in the vicinity of MIT leads to first-order transition in these manganites. However the length scales over which the electronic and magnetic phases are separated across MIT which appears compelling for bulk systems has been elusive in (La1‑yPry)1‑xCaxMnO3 films. Here we show the in-plane length scale over which charge and magnetism are correlated in (La0.4Pr0.6)1‑xCaxMnO3 films with x = 0.33 and 0.375, across the MIT temperature. We combine electrical transport (resistance) measurements, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and specular/off-specular x-ray resonant magnetic scattering (XRMS) measurements as a function of temperature to elucidate relationships between electronic, magnetic and morphological structure of the thin films. Using off-specular XRMS we obtained the charge-charge and charge-magnetic correlation length of these LPCMO films across the MIT. We observed different charge-magnetic correlation length for two films which increases below the MIT. The different correlation length shown by two films may be responsible for different macroscopic (transport and magnetic) properties.

  4. Composition dependence of charge and magnetic length scales in mixed valence manganite thin films

    PubMed Central

    Singh, Surendra; Freeland, J. W.; Fitzsimmons, M. R.; Jeen, H.; Biswas, A.

    2016-01-01

    Mixed-valence manganese oxides present striking properties like the colossal magnetoresistance, metal-insulator transition (MIT) that may result from coexistence of ferromagnetic, metallic and insulating phases. Percolation of such phase coexistence in the vicinity of MIT leads to first-order transition in these manganites. However the length scales over which the electronic and magnetic phases are separated across MIT which appears compelling for bulk systems has been elusive in (La1−yPry)1−xCaxMnO3 films. Here we show the in-plane length scale over which charge and magnetism are correlated in (La0.4Pr0.6)1−xCaxMnO3 films with x = 0.33 and 0.375, across the MIT temperature. We combine electrical transport (resistance) measurements, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and specular/off-specular x-ray resonant magnetic scattering (XRMS) measurements as a function of temperature to elucidate relationships between electronic, magnetic and morphological structure of the thin films. Using off-specular XRMS we obtained the charge-charge and charge-magnetic correlation length of these LPCMO films across the MIT. We observed different charge-magnetic correlation length for two films which increases below the MIT. The different correlation length shown by two films may be responsible for different macroscopic (transport and magnetic) properties. PMID:27461993

  5. Large magnetoresistance in non-magnetic silver chalcogenides and new class of magnetoresistive compounds

    DOEpatents

    Saboungi, Marie-Louis; Price, David C. L.; Rosenbaum, Thomas F.; Xu, Rong; Husmann, Anke

    2001-01-01

    The heavily-doped silver chalcogenides, Ag.sub.2+.delta. Se and Ag.sub.2+.delta. Te, show magnetoresistance effects on a scale comparable to the "colossal" magnetoresistance (CMR) compounds. Hall coefficient, magnetoconductivity, and hydrostatic pressure experiments establish that elements of narrow-gap semiconductor physics apply, but both the size of the effects at room temperature and the linear field dependence down to fields of a few Oersteds are surprising new features.

  6. Surprising resistivity decrease in manganites with constant electronic density.

    PubMed

    Cortés-Gil, R; Ruiz-González, M L; Alonso, J M; Martínez, J L; Hernando, A; Vallet-Regí, M; González-Calbet, J M

    2013-12-01

    A decrease of eight orders of magnitude in the resistance of (La0.5Ca0.5)zMnO3 has been detected when the electronic density is kept constant while the calcium content is modified by introducing cationic vacancies. This effect is related to the disappearance of the charge ordering state and the emergence of an antiferromagnetic–ferromagnetic transition. Moreover, high values of the colossal magnetoresistance above room temperature are attained. PMID:24200948

  7. Unusual ferromagnetism enhancement in ferromagnetically optimal manganite La0.7−yCa0.3+yMn1−yRuyO3 (0≤y<0.3): the role of Mn-Ru t2g super-exchange

    PubMed Central

    Liu, M. F.; Du, Z. Z.; Xie, Y. L.; Li, X.; Yan, Z. B.; Liu, J. –M.

    2015-01-01

    The eg-orbital double-exchange mechanism as the core of physics of colossal magnetoresistance (CMR) manganites is well known, which usually covers up the role of super-exchange at the t2g-orbitals. The role of the double-exchange mechanism is maximized in La0.7Ca0.3MnO3, leading to the concurrent metal-insulator transition and ferromagnetic transition as well as CMR effect. In this work, by a set of synchronous Ru-substitution and Ca-substitution experiments on La0.7–yCa0.3+yMn1–yRuyO3, we demonstrate that the optimal ferromagnetism in La0.7Ca0.3MnO3 can be further enhanced. It is also found that the metal-insulator transition and magnetic transition can be separately modulated. By well-designed experimental schemes with which the Mn3+-Mn4+ double-exchange is damaged as weakly as possible, it is revealed that this ferromagnetism enhancement is attributed to the Mn-Ru t2g ferromagnetic super-exchange. The present work allows a platform on which the electro-transport and magnetism of rare-earth manganites can be controlled by means of the t2g-orbital physics of strongly correlated transition metal oxides. PMID:25909460

  8. Model of the magnetorefractive effect in manganites within the effective medium theory

    NASA Astrophysics Data System (ADS)

    Yurasov, A. N.; Telegin, A. V.; Sukhorukov, Yu. P.

    2016-04-01

    The magnetorefractive effect (MRE) in manganites has been studied within the effective medium theory. The MRE has been calculated in manganites La1- x K x MnO3 ( x = 0.1 and 0.15) for light transmission and reflection. Good agreement with experimental results demonstrates direct relation of the MRE to the magnetoresistance and optical properties of manganites with various substitution levels. It has been shown that the MRE can exceed 10% in the near- and mid-IR region near the magnetic phase transition and can change sign during light transmission and reflection in the region of phonon modes. The results make it possible to recommend the MRE as a contactless method for studying magnetoresistive materials and for developing sensors and microelectronic elements.

  9. Superconducting Clusters and Colossal Effects in Underdoped Cuprates

    NASA Astrophysics Data System (ADS)

    Alvarez, Gonzalo; Mayr, Matthias; Moreo, Adriana

    2005-03-01

    Phenomenological models for the antiferromagnetic vs. d-wave superconductivity competition in cuprates are studied[1] using conventional Monte Carlo techniques. The analysis suggests that cuprates may show a variety of different behaviors in the very underdoped regime: local coexistence, stripes, or, if disorder is present, states with nanoscale superconducting clusters. The transition from an antiferromagnetic to a superconducting state does not seem universal. In particular, inhomogeneous states lead to the possibility of colossal effects in some cuprates, analogous of those in manganites. Under suitable conditions, non-superconducting Cu-oxides could rapidly[2] become superconducting by the influence of weak perturbations that align the randomly oriented phases of the superconducting clusters in the mixed state. Consequences of these ideas for angle resolved photoemission and scanning tunneling microscopy experiments[3] will also discussed. [1] Alvarez et al., cond-mat/0401474, to appear in PRB. [2] I. Bozovic et al., PRL 93, 157002, (2004) [3] A. Ino et al., PRB 62, 4127 (2000); K. Lang et al, Nature 415, 412 (2002). Research performed in part at the Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy under Contract DE-AC05-00OR22725.

  10. Studies on magneto-resistance, magnetization and thermoelectric power of Cr substituted La0.65Ca0.35Mn1-xCrxO3 (0≤x≤0.07) manganites

    NASA Astrophysics Data System (ADS)

    Manjunatha, S. O.; Rao, Ashok; Babu, P. D.; Tarachand; Okram, G. S.

    2015-10-01

    A systematic investigation has been carried out on effect of Cr-doping on structural, magneto-resistance, magnetic and thermoelectric power properties of La0.65Ca0.35Mn1-xCrxO3 compounds. Samples were prepared using conventional solid state reaction method. The XRD analysis using Rietveld refinement reveals that the samples are single phased. Temperature dependent electrical resistivity measurements show the existence of the expected metal-insulator transition (TMI) which is followed by a small hump at temperatures lower than TMI. With the application of magnetic field, resistivity of all the samples is found to decrease and TMI is observed to shift towards higher temperature. This is attributed to induced magnetic ordering of the localized t2g spins and increased electron transfer integral between Mn3+/Mn4+ via oxygen by the application of magnetic field. MR% is observed to increase with the increasing Cr concentration. Magnetic studies show that the Curie temperature, TC and magnetic moment decreases with Cr-content which is consistent with the electrical studies. Electrical resistivity and thermoelectric power data have been analyzed using theoretical models and both suggest that the small polaron hopping (SPH) model is operative in the high temperature insulating region for the entire series of samples.

  11. Lattice Distortion, Polaron Conduction, and Jahn-Teller Effect on teh Magnetoresistance of La(sub 0.7)Ca(sub 0.5)CoO(sub 3) Epitaxial Films

    NASA Technical Reports Server (NTRS)

    Yeh, N. C.; Vasquez, R. P.; Beam, D. A.; Fu, C. C.; Huynh, H.; Beach, G.

    1996-01-01

    In summary, we have investigated the role of lattice distortion, polaron conduction and Jahn-Teller coupling in the occurrence of the colossal negative magnetoresistance in perovskite oxides. We conclude that larger lattice distortion gives rise to larger zero-field resistivity and larger magnitude of negative magnetoresistance.

  12. Effects of dynamic Jahn-Teller distortions by Raman spectroscopy in the layered CMR manganite La{sub 2{minus}2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7}, x = 0.36

    SciTech Connect

    Bordallo, H.N.; Argyriou, D.N.; Mitchell, J.F.; Strouse, G.F.

    1998-12-01

    The close interplay among charge, spin, and lattice degrees of freedom in the colossal magnetoresistive (CMR) manganite oxides is believed to play an important role in the transport mechanism in these itinerant ferromagnets. While the work on CMR materials has concentrated on the 3D perovskite manganites, the discovery of the layered compounds La{sub 2{minus}2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} as another class of CMR oxides provides a rich opportunity to explore the relationship between structure and transport properties on varying length and time scales in reduced dimensions. The crystal structure of the layered CMR compounds La{sub 2{minus}2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} is comprised of perovskite bilayers of corner-linked MnO{sub 6} octahedra forming infinite sheets. Doping of divalent cations such as Sr{sup 2+} gives rise to a mixed valent system were Jahn-Teller (JT) active Mn{sup 3+} and JT-inactive Mn{sup 4+} co-exist on the lattice. Among the current theoretical models of transport in the three-dimensional perovskite materials is the role of JT. This transport mechanism plays a fundamental role above the Curie temperature (T{sub c}). Indeed, localized lattice distortions have been observed experimentally above T{sub c} in the (La,Ca)MnO{sub 3} perovskite system. In this communication, the authors report resonant Raman spectroscopic measurements on a micro-crystalline sample of La{sub 1.28}Sr{sub 1.72}Mn{sub 2}O{sub 7} (x = 0.36). The measurements suggest discrete phonon modes for the Mn{sup 3+} and Mn{sup 4+} lattice sites, which may arise from either dynamic or static localization and the presence of Mn{sup 2+} defects in the lattice.

  13. Manganite films: Tuning phase diagrams

    NASA Astrophysics Data System (ADS)

    Mihailovic, Dragan

    2016-09-01

    Strain engineering can tune a manganite film into an antiferromagnetic insulating state whose extreme photo-susceptibility allows for the ordinary ferromagnetic metal state to then be transiently realized.

  14. Superconducting magnetoresistance in ferromagnet/superconductor/ferromagnet trilayers

    NASA Astrophysics Data System (ADS)

    Stamopoulos, D.; Aristomenopoulou, E.

    2015-08-01

    Magnetoresistance is a multifaceted effect reflecting the diverse transport mechanisms exhibited by different kinds of plain materials and hybrid nanostructures; among other, giant, colossal, and extraordinary magnetoresistance versions exist, with the notation indicative of the intensity. Here we report on the superconducting magnetoresistance observed in ferromagnet/superconductor/ferromagnet trilayers, namely Co/Nb/Co trilayers, subjected to a parallel external magnetic field equal to the coercive field. By manipulating the transverse stray dipolar fields that originate from the out-of-plane magnetic domains of the outer layers that develop at coercivity, we can suppress the supercurrent of the interlayer. We experimentally demonstrate a scaling of the magnetoresistance magnitude that we reproduce with a closed-form phenomenological formula that incorporates relevant macroscopic parameters and microscopic length scales of the superconducting and ferromagnetic structural units. The generic approach introduced here can be used to design novel cryogenic devices that completely switch the supercurrent ‘on’ and ‘off’, thus exhibiting the ultimate magnetoresistance magnitude 100% on a regular basis.

  15. Superconducting magnetoresistance in ferromagnet/superconductor/ferromagnet trilayers.

    PubMed

    Stamopoulos, D; Aristomenopoulou, E

    2015-01-01

    Magnetoresistance is a multifaceted effect reflecting the diverse transport mechanisms exhibited by different kinds of plain materials and hybrid nanostructures; among other, giant, colossal, and extraordinary magnetoresistance versions exist, with the notation indicative of the intensity. Here we report on the superconducting magnetoresistance observed in ferromagnet/superconductor/ferromagnet trilayers, namely Co/Nb/Co trilayers, subjected to a parallel external magnetic field equal to the coercive field. By manipulating the transverse stray dipolar fields that originate from the out-of-plane magnetic domains of the outer layers that develop at coercivity, we can suppress the supercurrent of the interlayer. We experimentally demonstrate a scaling of the magnetoresistance magnitude that we reproduce with a closed-form phenomenological formula that incorporates relevant macroscopic parameters and microscopic length scales of the superconducting and ferromagnetic structural units. The generic approach introduced here can be used to design novel cryogenic devices that completely switch the supercurrent 'on' and 'off', thus exhibiting the ultimate magnetoresistance magnitude 100% on a regular basis.

  16. Superconducting magnetoresistance in ferromagnet/superconductor/ferromagnet trilayers

    PubMed Central

    Stamopoulos, D.; Aristomenopoulou, E.

    2015-01-01

    Magnetoresistance is a multifaceted effect reflecting the diverse transport mechanisms exhibited by different kinds of plain materials and hybrid nanostructures; among other, giant, colossal, and extraordinary magnetoresistance versions exist, with the notation indicative of the intensity. Here we report on the superconducting magnetoresistance observed in ferromagnet/superconductor/ferromagnet trilayers, namely Co/Nb/Co trilayers, subjected to a parallel external magnetic field equal to the coercive field. By manipulating the transverse stray dipolar fields that originate from the out-of-plane magnetic domains of the outer layers that develop at coercivity, we can suppress the supercurrent of the interlayer. We experimentally demonstrate a scaling of the magnetoresistance magnitude that we reproduce with a closed-form phenomenological formula that incorporates relevant macroscopic parameters and microscopic length scales of the superconducting and ferromagnetic structural units. The generic approach introduced here can be used to design novel cryogenic devices that completely switch the supercurrent ‘on’ and ‘off’, thus exhibiting the ultimate magnetoresistance magnitude 100% on a regular basis. PMID:26306543

  17. Magnetoresistance effect in (La, Sr)MnO3 bicrystalline films.

    PubMed

    Alejandro, G; Steren, L B; Pastoriza, H; Vega, D; Granada, M; Sánchez, J C Rojas; Sirena, M; Alascio, B

    2010-09-01

    The angular dependence of the magnetoresistance effect has been measured on bicrystalline La(0.75)Sr(0.25)MnO(3) films. The measurements have been performed on an electronically lithographed Wheatstone bridge. The study of the angular dependence of both the magnetoresistance and the resistance of single-crystalline and grain-boundary regions of the samples allowed us to isolate two contributions of low-field magnetoresistance in manganites. One of them is associated with the spin-orbit effect, i.e. the anisotropic magnetoresistance of ferromagnetic compounds, and the other one is related to spin-disorder regions at the grain boundary. Complementary x-ray diffraction, ferromagnetic resonance and low temperature magnetization experiments contribute to the characterization of the magnetic anisotropy of the samples and the general comprehension of the problem.

  18. Magnetoresistance effect in (La, Sr)MnO3 bicrystalline films.

    PubMed

    Alejandro, G; Steren, L B; Pastoriza, H; Vega, D; Granada, M; Sánchez, J C Rojas; Sirena, M; Alascio, B

    2010-09-01

    The angular dependence of the magnetoresistance effect has been measured on bicrystalline La(0.75)Sr(0.25)MnO(3) films. The measurements have been performed on an electronically lithographed Wheatstone bridge. The study of the angular dependence of both the magnetoresistance and the resistance of single-crystalline and grain-boundary regions of the samples allowed us to isolate two contributions of low-field magnetoresistance in manganites. One of them is associated with the spin-orbit effect, i.e. the anisotropic magnetoresistance of ferromagnetic compounds, and the other one is related to spin-disorder regions at the grain boundary. Complementary x-ray diffraction, ferromagnetic resonance and low temperature magnetization experiments contribute to the characterization of the magnetic anisotropy of the samples and the general comprehension of the problem. PMID:21403272

  19. Charge and magnetic order suppression by Mn site doping in layered and three-dimensional manganites

    NASA Astrophysics Data System (ADS)

    Damay, F.; Martin, C.; Maignan, A.; Raveau, B.

    1998-03-01

    A systematic study of the doping of the Mn sites by various elements (Mg 2+, Fe 3+, Al 3+, Sn 4+, Ti 4+) in three charge ordered manganites - La 0.5Sr 1.5MnO 4, LaSr 2Mn 2O 7 and Pr 0.5Ca 0.5MnO 3 - has been performed. An abrupt disappearance of the charge ordered state is observed, for low level of dopant (˜1-2%) whatever its nature. The change of slope associated to the charge ordering on resistivity curves as well as the coupled antiferromagnetic transition on susceptibility curves indeed tend to disappear. However, whereas magnetoresistance properties are not significantly modified in the case of the layered manganites La 0.5Sr 1.5MnO 4 and LaSr 2Mn 2O 7, huge magnetoresistance is induced in the case of the three-dimensional (3D) manganite Pr 0.5Ca 0.5MnO 3. These strong modifications of the transport properties are discussed in the light of the magnetic properties.

  20. Manganite perovskite ceramics, their precursors and methods for forming

    DOEpatents

    Payne, David Alan; Clothier, Brent Allen

    2015-03-10

    Disclosed are a variety of ceramics having the formula Ln.sub.1-xM.sub.xMnO.sub.3, where 0.Itoreq.x.Itoreq.1 and where Ln is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu or Y; M is Ca, Sr, Ba, Cd, or Pb; manganite precursors for preparing the ceramics; a method for preparing the precursors; and a method for transforming the precursors into uniform, defect-free ceramics having magnetoresistance properties. The manganite precursors contain a sol and are derived from the metal alkoxides: Ln(OR).sub.3, M(OR).sub.2 and Mn(OR).sub.2, where R is C.sub.2 to C.sub.6 alkyl or C.sub.3 to C.sub.9 alkoxyalkyl, or C.sub.6 to C.sub.9 aryl. The preferred ceramics are films prepared by a spin coating method and are particularly suited for incorporation into a device such as an integrated circuit device.

  1. Highly dispersive electron relaxation and colossal thermoelectricity in the correlated semiconductor FeSb2

    NASA Astrophysics Data System (ADS)

    Sun, Peijie; Xu, Wenhu; Tomczak, Jan M.; Kotliar, Gabriel; Søndergaard, Martin; Iversen, Bo B.; Steglich, Frank

    2013-12-01

    We show that the colossal thermoelectric power S (T) observed in the correlated semiconductor FeSb2 below 30 K is accompanied by a huge Nernst coefficient ν (T) and magnetoresistance MR(T). Markedly, the latter two quantities are enhanced in a strikingly similar manner. While in the same temperature range, S (T) of the reference compound FeAs2, which has a seven-times-larger energy gap, amounts to nearly half of that of FeSb2, its ν (T) and MR(T) are intrinsically different to FeSb2: They are smaller by two orders of magnitude and have no common features. Underlying the essentially different thermoelectric properties between FeSb2 and FeAs2, a large mismatch between the electrical and thermal Hall mobilities is found only in the former compound. With the charge transport of FeAs2 successfully captured by the density functional theory, we emphasize a significantly dispersive electron-relaxation time τ (ɛk) related to electron-electron correlations to be at the heart of the peculiar thermoelectricity and magnetoresistance of FeSb2.

  2. Current-voltage characteristics of manganite-titanite perovskite junctions.

    PubMed

    Ifland, Benedikt; Peretzki, Patrick; Kressdorf, Birte; Saring, Philipp; Kelling, Andreas; Seibt, Michael; Jooss, Christian

    2015-01-01

    After a general introduction into the Shockley theory of current voltage (J-V) characteristics of inorganic and organic semiconductor junctions of different bandwidth, we apply the Shockley theory-based, one diode model to a new type of perovskite junctions with polaronic charge carriers. In particular, we studied manganite-titanate p-n heterojunctions made of n-doped SrTi1- y Nb y O3, y = 0.002 and p-doped Pr1- x Ca x MnO3, x = 0.34 having a strongly correlated electron system. The diffusion length of the polaron carriers was analyzed by electron beam-induced current (EBIC) in a thin cross plane lamella of the junction. In the J-V characteristics, the polaronic nature of the charge carriers is exhibited mainly by the temperature dependence of the microscopic parameters, such as the hopping mobility of the series resistance and a colossal electro-resistance (CER) effect in the parallel resistance. We conclude that a modification of the Shockley equation incorporating voltage-dependent microscopic polaron parameters is required. Specifically, the voltage dependence of the reverse saturation current density is analyzed and interpreted as a voltage-dependent electron-polaron hole-polaron pair generation and separation at the interface.

  3. Magnetoelectric and magneto-dielectric effects in multiferroic manganites

    NASA Astrophysics Data System (ADS)

    Hur, Namjung

    2004-12-01

    Ferroelectric and magnetic materials have been a time-honored subject of study and have lead to some of the most important technological advances to date. Magnetic ordering is governed by the exchange interaction of the electron spins, while ferroelectric ordering is governed by the off-center structural distortions in the lattice. These two seemingly unrelated phenomena can actually coexist in certain unusual materials, termed multiferroics. The understanding of this remarkable occurrence remains a scientific challenge. Despite the possible coexistence of ferroelectricity and magnetism, any profound interplay between them has been rarely observed. This fact has largely prevented the realization of devices with a previously unavailable functionality, which these multiferroics could make possible. Herein, I have explored several multiferroic materials, which show astonishing interplays between ferroelectricity and magnetism during the course of my dissertation. A number of new discoveries have been made in the multiferroic manganites. Especially, polarization reversal by magnetic field and colossal magneto-capacitance effect have been observed in ThMn2O5 and DyMn2O5, respectively.

  4. Magnetocaloric effect in manganites

    SciTech Connect

    Koroleva, L. I. Zashchirinskii, D. M.; Morozov, A. S.; Szymczak, R.

    2012-10-15

    The magnetocaloric effect (MCE) in La{sub 1-x}Sr{sub x}MnO{sub 3}, Sm{sub 0.55}Sr{sub 0.45}MnO{sub 3}, and PrBaMn{sub 2}O{sub 6} compounds is studied. The maximum values of MCE ({Delta}T{sub max}) determined by a direct method in the second and third compositions and in La{sub 0.9}Sr{sub 0.1}MnO{sub 3} are found to be much lower than those calculated from the change of the magnetic part of entropy in the Curie temperature (T{sub C}) and the Neel temperature (T{sub N}) range. The negative contribution of the antiferromagnetic (AFM) part of a sample in the La{sub 1-x}Sr{sub x}MnO{sub 3} system at 0.1 {<=} x {<=} 0.3 decreases {Delta}T{sub max} and changes the {Delta}T(T) curve shape, shifting its maximum 20-40 K above T{sub C}. Lower values of {Delta}T{sub max} are detected in the range T{sub C} = 130-142 K in polycrystalline and single-crystal Sm{sub 0.55}Sr{sub 0.45}MnO{sub 3} samples cooled in air. If such samples were cooled in an oxygen atmosphere (which restores broken Mn-O-Mn bonds and, thus, increases the volume of CE-type AFM clusters), the maximum in the temperature dependence of MCE is located at T{sub N} (243 K) for CE-type AFM clusters. A magnetic field applied to a sample during the MCE measurements transforms these clusters into a ferromagnetic (FM) state, and both types of clusters decompose at T = T{sub N}. The PrBaMn{sub 2}O{sub 6} composition undergoes an AFM-FM transition at 231 K, and the temperature dependence of its MCE has a sharp minimum at T = 234 K, where MCE is negative, and a broad maximum covering T{sub C}. The absolute values of MCE at both extrema are several times lower than those calculated from the change in the magnetic entropy. These phenomena are explained by the presence of a magnetically heterogeneous FM-AFM state in these manganites.

  5. Theoretical study of the role of charge ordering in antiferromagnetically ordered manganites

    NASA Astrophysics Data System (ADS)

    Panda, Saswati; Kar, J. K.; Rout, G. C.

    2016-09-01

    We address the interplay of charge and magnetic orderings in colossal magnetoresistive material manganese oxides. We propose here on-site double exchange spin-spin interaction in the presence of Heisenberg-type spin-spin interaction in localized t 2g core electrons. We consider charge-density wave (CDW) interaction in the crystal lattice as an extra mechanism in the itinerant e g band, to take into account of colossal magnetoresistance (CMR) in the system. We calculate electron Green’s functions by Zubarev’s Green’s function technique and hence calculate the charge-ordering gap and magnetic gap in the conduction band as well as core electron states. These orders are solved self-consistently for different model parameters of the system. We observe that the induced magnetic gap in the conduction band exists near the antiferromagnetic Néel temperature, which accounts for the CMR in the system. For all values of temperature, the CDW coupling lies in the range of g = 0.04 to 0.06, where the induced magnetic gap exists. The temperature-dependent specific heat exhibits anomalous jumps near charge-ordering and magnetic-ordering temperatures. The e g electron density of states exhibits a two-gap structure which explains tunneling conductance spectra measurements.

  6. Low-Temperature Electrical Resistivity of Bilayered LaSr2Mn2O_{7 } Manganite

    NASA Astrophysics Data System (ADS)

    Ehsani, M. H.; Mehrabad, M. Jalali; Kameli, P.; Ghazi, M. E.; Razavi, F. S.

    2016-06-01

    Low-temperature transport and magneto-resistance properties were systemically studied for the bilayered polycrystalline LaSr2Mn2O7 manganite under an applied magnetic field from 0 to 9 T. The results obtained from the resistivity measurements between 70 and 130 K were fitted using the electron-electron (e-e) and electron-magnon (e-m) scattering models. The temperature dependence of resistivity showed an upturn behavior at low temperatures (˜ T < 45 K) under various applied magnetic fields. Best fits were obtained by using a variable-range hopping model. The magneto-resistance behavior observed at low temperatures supports the magnetic properties of the sample.

  7. Multiferroicity in Perovskite Manganite Superlattice

    NASA Astrophysics Data System (ADS)

    Tao, Yong-Mei; Jiang, Xue-Fan; Liu, Jun-Ming

    2016-08-01

    Multiferroic properties of short period perovskite type manganite superlattice ((R1MnO3)n/(R2MnO3)n (n=1,2,3)) are considered within the framework of classical Heisenberg model using Monte Carlo simulation. Our result revealed the interesting behaviors in Mn spins structure in superlattice. Apart from simple plane spin cycloid structure which is shown in all manganites including bulk, film, and superlattice here in low temperature, a non-coplanar spiral spin structure is exhibited in a certain temperature range when n equals 1, 2 or 3. Specific heat, spin-helicity vector, spin correlation function, spin-helicity correlation function, and spin configuration are calculated to confirm this non-coplanar spiral spin structure. These results are associated with the competition among exchange interaction, magnetic anisotropy, and Dzyaloshinskii-Moriya interaction. Supported by the National Natural Science Foundation of China (NSFC) under Grant No. 11447136

  8. The conversion of the small magnetic polarons into the large polaron as the cause of the unusual transport properties of layered manganites La1.2Sr1.8Mn2O7

    NASA Astrophysics Data System (ADS)

    Solin, N. I.

    2016-03-01

    The paper is aimed at clarification of nature of unusual transport properties of the layered manganites. Magnetic and magnetotransport properties of the Mn-deficient quasi-two-dimensional manganites La1,2Sr1,8Mn2(1-z)O7 are investigated at 5-400 K in magnetic fields up to 9 T. The studied single crystals show properties typical to layered manganites. Semiconductor-metal-like transition near the Curie temperature (TC), non-metal type of resistance ρ(T) at low temperatures, enormous magnetoresistance near TC, the negative magnetoresistance in the studied temperature range are observed in these single crystals. The obtained results are discussed in the framework of the magnetic polaron conductivity. It is assumed that in quasi-two-dimensional manganites the polarons are preserved in the magnetically ordered state as well, and that small magnetic polarons become big polaron at low temperatures. The increase of size of the magnetic polaron under magnetic ordering or application of a magnetic field explains the basic transport properties of layered manganites La1.2Sr1.8Mn2O7. The temperature and field dependencies of the polaron sizes, defined from the magnetotransport properties, are reasonably described in the model of phase separation.

  9. Emergent long-range magnetic ordering in manganite superlattices

    NASA Astrophysics Data System (ADS)

    Burganov, Bulat; Macke, Sebastian; Monkman, Eric; Adamo, Carolina; Shai, Daniel; Schlom, Darrell; Sawatzky, George; Shen, Kyle

    2015-03-01

    Complex oxides composed into atomically precise heterostructures host a plethora of new phenomena driven by interface effects, dimensionality, correlations and strain. An example is emergent ferromagnetism in the superlattices (SL) of LaMnO3/SrMnO3 and the dimensionality-driven metal insulator transition, still not well understood theoretically. We use soft x-ray scattering combined with SQUID magnetometry to determine the magnetic and orbital ordering in the (LaMnO3)2n /(SrMnO3)n SL for n =1,2,3,4. By composition this system is close to colossal-magnetoresistive La2/3Sr1/3MnO3, an FM metal below 400K. The system undergoes a metal-insulator transition with higher n and is believed to have a complex magnetic ordering. We observe an unexpected long-range order in the n =4 sample where the magnetic period is equal to two chemical periods. The observed half-order Bragg peaks show strong linear and no circular dichroism. The temperature and polarization dependence of reflectometry points towards alignment between A-type AFM orders in the neighboring LaMnO3 layers, which is very unusual and indicates a long range interaction acting across the thick SrMnO3 layers with nominally G-type spin configuration. We simulate the reflectometry data for several model spin configurations to further elucidate the nature of this ordering.

  10. Molecular anisotropic magnetoresistance

    NASA Astrophysics Data System (ADS)

    Otte, Fabian; Heinze, Stefan; Mokrousov, Yuriy

    2015-12-01

    Using density functional theory calculations, we demonstrate that the effect of anisotropic magnetoresistance (AMR) can be enhanced by orders of magnitude with respect to conventional bulk ferromagnets in junctions containing molecules sandwiched between ferromagnetic leads. We study ballistic transport in metal-benzene complexes contacted by 3 d transition-metal wires. We show that a gigantic AMR can arise from spin-orbit coupling effects in the leads, drastically enhanced by orbital-symmetry filtering properties of the molecules. We further discuss how this molecular anisotropic magnetoresistance (MAMR) can be tuned by the proper choice of materials and their electronic properties.

  11. Colossal anisotropic resistivity and oriented magnetic domains in strained La{sub 0.325}Pr{sub 0.3}Ca{sub 0.375}MnO{sub 3} films

    SciTech Connect

    Jiang, Tao; Yang, Shengwei; Liu, Yukuai; Zhao, Wenbo; Feng, Lei; Li, Xiaoguang; Zhou, Haibiao; Lu, Qingyou; Hou, Yubin

    2014-05-19

    Magnetic and resistive anisotropies have been studied for the La{sub 0.325}Pr{sub 0.3}Ca{sub 0.375}MnO{sub 3} films with different thicknesses grown on low symmetric (011)-oriented (LaAlO{sub 3}){sub 0.3}(SrAl{sub 0.5}Ta{sub 0.5}O{sub 3}){sub 0.7} substrates. In the magnetic and electronic phase separation region, a colossal anisotropic resistivity (AR) of ∼10{sup 5}% and an anomalous large anisotropic magnetoresistance can be observed for 30 nm film. However, for 120 nm film, the maximum AR decreases significantly (∼2 × 10{sup 3}%) due to strain relaxation. The colossal AR is strongly associated with the oriented formation of magnetic domains, and the features of the strain effects are believed to be useful for the design of artificial materials and devices.

  12. Geometric tuning of charge and spin correlations in manganite superlattices

    SciTech Connect

    Rogdakis, K. E-mail: christos@ntu.edu.sg; Viskadourakis, Z.; Petrović, A. P.; Choi, E.; Lee, J.; Panagopoulos, C. E-mail: christos@ntu.edu.sg

    2015-01-12

    We report a modulation of the in-plane magnetotransport in artificial manganite superlattice [(NdMnO{sub 3}){sub n}/(SrMnO{sub 3}){sub n}/(LaMnO{sub 3}){sub n}]{sub m} by varying the layer thickness n while keeping the total thickness of the structure constant. Charge transport in these heterostructures is confined to the interfaces and occurs via variable range hopping. Upon increasing n, the interfacial separation rises, leading to a suppression of the electrostatic screening between carriers of neighboring interfaces and the opening of a Coulomb gap at the Fermi level (E{sub F}). The high-field magnetoresistance (MR) is universally negative due to progressive spin alignment. However, at a critical thickness of n = 5 unit cells (u.c.), an exchange field coupling between ferromagnetically ordered interfaces results in positive MR at low magnetic field (H). Our results demonstrate the ability to geometrically tune the electrical transport between regimes dominated by either charge or spin correlations.

  13. Magneto-transport properties in layered manganite crystals

    SciTech Connect

    Kimura, T.; Tomioka, Y.; Okuda, T.; Kuwahara, H.; Asamitsu, A.; Tokura, Y.

    1998-12-31

    Anisotropic charge transport and magnetic properties have been investigated for single crystals of the layered manganite, La{sub 2{minus}2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} (0.3 {le} x {le} 0.5). Remarkable variations in the magnetic structure as well as in the charge-transport properties are observed with changing doping-level x. A crystal with x = 0.3 behaves like a 2-dimensional ferromagnetic metal in the temperature region between {approximately} 90 K and {approximately} 270 K, and shows the interplane tunneling magnetoresistance at lower temperatures. These characteristic charge-transport properties are attributed to the interplane magnetic coupling between the adjacent MnO{sub 2} bilayers, and are strongly affected by the application of pressure as well as low magnetic fields through the change in magnetic structure. With increase of the carrier concentration toward x = 0.5, the charge-ordered phase is stabilized and dominates the charge transport and magnetic properties.

  14. Conductive mechanism in manganite materials

    NASA Astrophysics Data System (ADS)

    Liu, Xianming; Zhu, Hong; Zhang, Yuheng

    2002-01-01

    We describe a model in which f(T)=M(T)/Mmax represents both the fraction of the itinerant electron density in the double-exchange (DE) theory and the magnetization σ in the current carrier density collapse (CCDC) theory. With this model, we have checked the DE and CCDC theories with our experimental results of the transport behavior. The DE theory yields agreement with the experimental resistivity excellently, in which the conductivity is the sum of the polaronic and itinerant electronic conductivity for the insulator-metal transition regime. The fitting curves of the resistivity by the CCDC theory deviate from the experiment seriously. This might be caused by the improper assumption of the temperature-dependent carrier density and the temperature-independent carrier mobility. Therefore, it is concluded that the DE theory is more suitable to explain the conductive mechanism in perovskite manganites.

  15. Chemical ordering suppresses large-scale electronic phase separation in doped manganites

    PubMed Central

    Zhu, Yinyan; Du, Kai; Niu, Jiebin; Lin, Lingfang; Wei, Wengang; Liu, Hao; Lin, Hanxuan; Zhang, Kai; Yang, Tieying; Kou, Yunfang; Shao, Jian; Gao, Xingyu; Xu, Xiaoshan; Wu, Xiaoshan; Dong, Shuai; Yin, Lifeng; Shen, Jian

    2016-01-01

    For strongly correlated oxides, it has been a long-standing issue regarding the role of the chemical ordering of the dopants on the physical properties. Here, using unit cell by unit cell superlattice growth technique, we determine the role of chemical ordering of the Pr dopant in a colossal magnetoresistant (La1−yPry)1−xCaxMnO3 (LPCMO) system, which has been well known for its large length-scale electronic phase separation phenomena. Our experimental results show that the chemical ordering of Pr leads to marked reduction of the length scale of electronic phase separations. Moreover, compared with the conventional Pr-disordered LPCMO system, the Pr-ordered LPCMO system has a metal–insulator transition that is ∼100 K higher because the ferromagnetic metallic phase is more dominant at all temperatures below the Curie temperature. PMID:27053071

  16. Relevance of Cooperative Lattice Effects and Stress Fields in Phase-Separation Theories for CMR Manganites

    NASA Astrophysics Data System (ADS)

    Burgy, Jan; Moreo, Adriana; Dagotto, Elbio

    2004-03-01

    Previous theoretical investigations of colossal magnetoresistance (CMR) materials explain this effect using a “clustered” state with preformed ferromagnetic islands that rapidly align their moments with increasing external magnetic fields. While qualitatively successful, explicit calculations indicate drastically different typical resistivity values in two- and three-dimensional lattices, contrary to experimental observations. This conceptual bottleneck in the phase-separated CMR scenario is resolved here considering the cooperative nature of the Mn-oxide lattice distortions. This effectively induces power-law correlations in the quenched disorder used in toy models with phase competition. When these effects are incorporated, resistor-network calculations reveal very similar results in two and three dimensions, qualitatively modifying previous scenarios and solving the puzzle.

  17. Magnetoresistance of Au films

    DOE PAGESBeta

    Zhang, D. L.; Song, X. H.; Zhang, X.; Zhang, Xiaoguang

    2014-12-10

    Measurement of the magnetoresistance (MR) of Au films as a function of temperature and film thickness reveals a strong dependence on grain size distribution and clear violation of the Kohler s rule. Using a model of random resistor network, we show that this result can be explained if the MR arises entirely from inhomogeneity due to grain boundary scattering and thermal activation of grain boundary atoms.

  18. Giant magnetoresistive sensor

    DOEpatents

    Stearns, Daniel G.; Vernon, Stephen P.; Ceglio, Natale M.; Hawryluk, Andrew M.

    1999-01-01

    A magnetoresistive sensor element with a three-dimensional micro-architecture is capable of significantly improved sensitivity and highly localized measurement of magnetic fields. The sensor is formed of a multilayer film of alternately magnetic and nonmagnetic materials. The sensor is optimally operated in a current perpendicular to plane mode. The sensor is useful in magnetic read/write heads, for high density magnetic information storage and retrieval.

  19. Magnetoresistive emulsion analyzer.

    PubMed

    Lin, Gungun; Baraban, Larysa; Han, Luyang; Karnaushenko, Daniil; Makarov, Denys; Cuniberti, Gianaurelio; Schmidt, Oliver G

    2013-01-01

    We realize a magnetoresistive emulsion analyzer capable of detection, multiparametric analysis and sorting of ferrofluid-containing nanoliter-droplets. The operation of the device in a cytometric mode provides high throughput and quantitative information about the dimensions and magnetic content of the emulsion. Our method offers important complementarity to conventional optical approaches involving ferrofluids, and paves the way to the development of novel compact tools for diagnostics and nanomedicine including drug design and screening. PMID:23989504

  20. Magnetoresistive Emulsion Analyzer

    PubMed Central

    Lin, Gungun; Baraban, Larysa; Han, Luyang; Karnaushenko, Daniil; Makarov, Denys; Cuniberti, Gianaurelio; Schmidt, Oliver G.

    2013-01-01

    We realize a magnetoresistive emulsion analyzer capable of detection, multiparametric analysis and sorting of ferrofluid-containing nanoliter-droplets. The operation of the device in a cytometric mode provides high throughput and quantitative information about the dimensions and magnetic content of the emulsion. Our method offers important complementarity to conventional optical approaches involving ferrofluids, and paves the way to the development of novel compact tools for diagnostics and nanomedicine including drug design and screening. PMID:23989504

  1. Negative magnetoresistivity in holography

    NASA Astrophysics Data System (ADS)

    Sun, Ya-Wen; Yang, Qing

    2016-09-01

    Negative magnetoresistivity is a special magnetotransport property associated with chiral anomaly in four dimensional chiral anomalous systems, which refers to the transport behavior that the DC longitudinal magnetoresistivity decreases with increasing magnetic field. We calculate the longitudinal magnetoconductivity in the presence of back-reactions of the magnetic field to gravity in holographic zero charge and axial charge density systems with and without axial charge dissipation. In the absence of axial charge dissipation, we find that the quantum critical conductivity grows with increasing magnetic field when the backreaction strength is larger than a critical value, in contrast to the monotonically decreasing behavior of quantum critical conductivity in the probe limit. With axial charge dissipation, we find the negative magnetoresistivity behavior. The DC longitudinal magnetoconductivity scales as B in the large magnetic field limit, which deviates from the exact B 2 scaling of the probe limit result. In both cases, the small frequency longitudinal magnetoconductivity still agrees with the formula obtained from the hydrodynamic linear response theory, even in the large magnetic field limit.

  2. Atomic manipulation with Scanning Tunneling Microscopy on the surface of a manganite thin film

    NASA Astrophysics Data System (ADS)

    Vasudevan, Rama; Tselev, Alexander; Baddorf, Arthur; Kalinin, Sergei

    2014-03-01

    Manganites have attracted significant attention in the past two decades, due to an extraordinarily rich spectrum of phenomena stemming from inherent complexity linking spin, charge, lattice and orbital degrees of freedom that result in properties including half-metallicity and giant magnetoresistance. Here, we report atomic manipulation with STM on the surfaces of 25 unit-cell thick La5/8Ca3/8MnO3 (LCMO) SrTiO3 (STO) substrates. We demonstrate that by applying triangular first-order reversal curve (FORC) waveforms of increasing amplitude to STM tips in-situ, it is possible from both A and B terminations to individually extract single units, form vacancies, remove units from layers below, rearrange atoms in the surrounding lattice, and therefore cause reactions to occur at the atomic level. These experiments point to the possibility of STM to manipulate atoms on the surfaces of manganites, opening up further avenues of research into fundamental physical properties defined at atomic scales. This research was sponsored by the Division of Materials Sciences and Engineering (RKV, AT, SVK) and by the Scientific User Facilities Division (APB) of BES, DOE. Research was conducted at the CNMS, which is sponsored at ORNL by the Scientific User Facilities Division, BES, DOE.

  3. Magnetoresistive chip cytometer.

    PubMed

    Loureiro, J; Andrade, P Z; Cardoso, S; da Silva, C L; Cabral, J M; Freitas, P P

    2011-07-01

    Although conventional state-of-the-art flow cytometry systems provide rapid and reliable analytical capacities, they are bulky, expensive and complex. To overcome these drawbacks modern flow cytometers have been developed with enhanced portability for on-site measurements. Unlike external fluorescent/optical detectors, magnetoresistive sensors are micro-fabricated, can be integrated within microfluidic channels, and can detect magnetically labelled cells. This work describes the real-time detection of single magnetically labelled cells with a magnetoresistive based cell cytometer. For Kg1-a cells magnetically labelled with 50 nm CD34 microbeads (Milteny) flowing through a 150 μm wide, 14 μm high microchannel, with speeds around 1 cm s(-1), bipolar signals with an average amplitude of 10-20 μV were observed corresponding to cell events. The number of cells counted by the spin valve cytometer has been compared with that obtained with a hemocytometer. Both methods agree within the respective error bars. PMID:21562656

  4. Polaron absorption for photovoltaic energy conversion in a manganite-titanate pn heterojunction

    NASA Astrophysics Data System (ADS)

    Saucke, Gesine; Norpoth, Jonas; Jooss, Christian; Su, Dong; Zhu, Yimei

    2012-04-01

    The relation among structure, electric transport, and photovoltaic effect is investigated for a pn heterojunction with strong correlation interactions. A perovskite interface is chosen as a model system consisting of the p-doped strongly correlated manganite Pr0.64Ca0.36MnO3 (PCMO) and the n-doped titanate SrTi1-yNbyO3 (y=0.002 and 0.01). High-resolution electron microscopy and spectroscopy reveal a nearly dislocation-free, epitaxial interface and give insight into the local atomic and electronic structure. The presence of a photovoltaic effect under visible light at room temperature suggests the existence of mobile excited polarons within the band-gap-free PCMO absorber. The temperature-dependent rectifying current-voltage characteristics prove to be mainly determined by the presence of an interfacial energy spike in the conduction band and are affected by the colossal electroresistance effect. From the comparison of photocurrents and spatiotemporal distributions of photogenerated carriers (deduced from optical absorption spectroscopy), we discuss the range of the excited polaron diffusion length.

  5. Tunable epitaxial growth of magnetoresistive La2/3Sr1/3MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Fontcuberta, J.; Bibes, M.; Martínez, B.; Trtik, V.; Ferrater, C.; Sánchez, F.; Varela, M.

    1999-04-01

    We report on the growth of epitaxial La2/3Sr1/3MnO3 thin films on buffered Si(001) substrates. We show that a suitable choice of the buffer heterostructure allows one to obtain epitaxial (00h), (0hh), and (hhh) manganite thin films. The magnetotransport properties are investigated and we have found that the low-field magnetoresistance is directly related to the width of the normal-to-plane rocking curves, irrespective of the film orientation. The magnetic anisotropy of these films has also been determined.

  6. Tunnel magnetoresistance of diamondoids

    NASA Astrophysics Data System (ADS)

    Matsuura, Yukihito

    2016-10-01

    Tunnel magnetoresistance (TMR) of diamondoids has been predicted by first principles density functional theory. Diamantane was used as a basic molecular proxy for diamondoids because hydrogen atoms in the apical position are easily substituted for a thiol group. The pristine diamantane exhibited a low TMR ratio of 7%, and boron-substitution considerably decreased the TMR ratio. Conversely, nitrogen-substitution enhanced the TMR ratio by up to 20%. Heteroatom-substitution changes the tunneling probabilities by varying the molecular bond lengths. Furthermore, when the spins of the electrodes are parallel, the heteroatoms resulted in transmittance probabilities at an energy range near the Fermi level. Consequently, heteroatom-substitution can control the TMR ratios of diamondoids very well.

  7. Magnetoresistance of Au films

    SciTech Connect

    Zhang, D. L. Song, X. H.; Zhang, X.; Zhang, X.-G.

    2014-12-14

    Classical magnetoresistance (MR) in nonmagnetic metals are conventionally understood in terms of the Kohler rule, with violation usually viewed as anomalous electron transport, in particular, as evidence of non-Fermi liquid behavior. Measurement of the MR of Au films as a function of temperature and film thickness reveals a strong dependence on grain size distribution and clear violation of the Kohler rule. Using a model of random resistor network, we show that this result can be explained if the MR arises entirely from inhomogeneity due to grain boundary scattering and thermal activation of grain boundary atoms. Consequently, the Kohler rule should not be used to distinguish normal and anomalous electron transport in solids.

  8. Transversal magnetoresistance in Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Klier, J.; Gornyi, I. V.; Mirlin, A. D.

    2015-11-01

    We explore theoretically the magnetoresistivity of three-dimensional Weyl and Dirac semimetals in transversal magnetic fields within two alternative models of disorder: (i) short-range impurities and (ii) charged (Coulomb) impurities. Impurity scattering is treated using the self-consistent Born approximation. We find that an unusual broadening of Landau levels leads to a variety of regimes of the resistivity scaling in the temperature-magnetic field plane. In particular, the magnetoresistance is nonmonotonous for the white-noise disorder model. For H →0 the magnetoresistance for short-range impurities vanishes in a nonanalytic way as H1 /3. In the limits of strongest magnetic fields H , the magnetoresistivity vanishes as 1 /H for pointlike impurities, while it is linear and positive in the model with Coulomb impurities.

  9. Positive magnetoresistance of La0.7Sr0.3MnO3/C composites

    NASA Astrophysics Data System (ADS)

    Kabirov, Yu. V.; Gavrilyachenko, V. G.; Bogatin, A. S.

    2016-07-01

    The perovskite manganite La0.7Sr0.3MnO3 compound is used as a component in ceramic (1‑x)(La0.7Sr0.3MnO3)-xC composites at x = 0.15-0.85. It is found that every studied specimen is characterized by the linear dependence of the positive magnetoresistance (PMR) on the magnetic field strength at room temperature. The 0.6(La0.7Sr0.3MnO3)-0.4C composite has the largest magnetoresistance value (15%) at room temperature and intensity of magnetic field H=15kOe. A possible mechanism for the PMR of (1‑x)(La0.7Sr0.3MnO3)-xC composites is discussed.

  10. Intrinsic interfacial phenomena in manganite heterostructures

    NASA Astrophysics Data System (ADS)

    Vaz, C. A. F.; Walker, F. J.; Ahn, C. H.; Ismail-Beigi, S.

    2015-04-01

    We review recent advances in our understanding of interfacial phenomena that emerge when dissimilar materials are brought together at atomically sharp and coherent interfaces. In particular, we focus on phenomena that are intrinsic to the interface and review recent work carried out on perovskite manganites interfaces, a class of complex oxides whose rich electronic properties have proven to be a useful playground for the discovery and prediction of novel phenomena.

  11. Thermal conductivity analysis of lanthanum doped manganites

    SciTech Connect

    Mansuri, Irfan; Shaikh, M. W.; Khan, E.; Varshney, Dinesh

    2014-04-24

    The temperature-dependent thermal conductivity of the doped manganites La{sub 0.7}Ca{sub 0.3}MnO{sub 3} is theoretically analyzed within the framework of Kubo formulae. The Hamiltonian consists of phonon, electron and magnon thermal conductivity contribution term. In this process we took defects, carrier, grain boundary, scattering process term and then calculate phonon, electron and magnon thermal conductivity.

  12. Colossal Tooling Design: 3D Simulation for Ergonomic Analysis

    NASA Technical Reports Server (NTRS)

    Hunter, Steve L.; Dischinger, Charles; Thomas, Robert E.; Babai, Majid

    2003-01-01

    The application of high-level 3D simulation software to the design phase of colossal mandrel tooling for composite aerospace fuel tanks was accomplished to discover and resolve safety and human engineering problems. The analyses were conducted to determine safety, ergonomic and human engineering aspects of the disassembly process of the fuel tank composite shell mandrel. Three-dimensional graphics high-level software, incorporating various ergonomic analysis algorithms, was utilized to determine if the process was within safety and health boundaries for the workers carrying out these tasks. In addition, the graphical software was extremely helpful in the identification of material handling equipment and devices for the mandrel tooling assembly/disassembly process.

  13. Anomalous Paramagnetic State in Naturally Layered Manganites

    NASA Astrophysics Data System (ADS)

    Berger, Andreas

    2002-03-01

    The nature of the magnetic state near the ferromagnetic phase transition is studied for the layered manganites SrO(La_1-xSr_xMnO_3)2 in the composition range x = 0.32 - 0.40 by means of magnetic field and temperature dependent measurements of the magnetic susceptibility, magnetization and conductivity. In a temperature range T ~ 1.05-1.45 T_C, the paramagnetic phase exhibits a number of very unusual properties, which reflects the fact that the magnetic free energy is distorted due to the existence of a second competing order parameter. In particular, we observe that the field-dependent susceptibility exhibits an anomalous maximum at an intermediate magnetic field value. The size of this field-induced susceptibility enhancement increases dramatically with x from 100.40. The temperature dependence of the effect shows a maximum at T ~ 1.1 TC independent of x. Quantitative analysis of the experimental data reveals that the ferromagnetic exchange coupling is reduced for temperatures above the ferromagnetic phase transition, an effect that is especially pronounced for the x = 0.40 compound. For this material, we also find a strong correlation between the exchange coupling reduction and the measured conductivity, which indicates that the electronic band structure change at the metal-insulator transition also affects the exchange coupling strength in this very compound in contrast to other, mostly perovskite-type manganites. In addition, we observe the appearance of anomalous magnetic losses for temperatures just above TC and applied field values that coincide with the occurrence of the metal-insulator transition. These data suggest that the metal-insulator transition in these layered manganites is associated with a magnetically inhomogeneous state. This work was supported by the U. S. Department of Energy, Basic Energy Sciences - Materials Sciences under Contract W-31-109-ENG-38.

  14. A high pressure neutron study of colossal magnetoresistant NdMnAsO(0.95)F(0.05).

    PubMed

    Wildman, E J; Tucker, M G; Mclaughlin, A C

    2015-03-25

    A high pressure neutron diffraction study of the oxypnictide NdMnAsO0.95F0.05 has been performed at temperatures of 290-383 K and pressures up to 8.59 GPa. The results demonstrate that the antiferromagnetic order of the Mn spins is robust to pressures of up to 8.59 GPa. TN is enhanced from 360 to 383 K upon applying an external pressure of 4.97 GPa, a rate of 4.63 K GPa(-1). NdMnAsO0.95F0.05 is shown to violate Bloch's rule which would suggest that NdMnAsO0.95F0.05 is on the verge of a localized to itinerant transition. There is no evidence of a structural transition but applied pressure tends to result in more regular As-Mn-As and Nd-O-Nd tetrahedra. The unit cell is significantly more compressible along the c-axis than the a-axis, as the interlayer coupling is weaker than the intrinsic bonds contained within NdO and MnAs slabs. PMID:25721358

  15. A high pressure neutron study of colossal magnetoresistant NdMnAsO0.95F0.05

    NASA Astrophysics Data System (ADS)

    Wildman, E. J.; Tucker, M. G.; Mclaughlin, A. C.

    2015-03-01

    A high pressure neutron diffraction study of the oxypnictide NdMnAsO0.95F0.05 has been performed at temperatures of 290-383 K and pressures up to 8.59 GPa. The results demonstrate that the antiferromagnetic order of the Mn spins is robust to pressures of up to 8.59 GPa. TN is enhanced from 360 to 383 K upon applying an external pressure of 4.97 GPa, a rate of 4.63 K GPa-1. NdMnAsO0.95F0.05 is shown to violate Bloch's rule which would suggest that NdMnAsO0.95F0.05 is on the verge of a localized to itinerant transition. There is no evidence of a structural transition but applied pressure tends to result in more regular As-Mn-As and Nd-O-Nd tetrahedra. The unit cell is significantly more compressible along the c-axis than the a-axis, as the interlayer coupling is weaker than the intrinsic bonds contained within NdO and MnAs slabs.

  16. Giant enhancement of magnetocrystalline anisotropy in ultrathin manganite films via nanoscale 1D periodic depth modulation

    NASA Astrophysics Data System (ADS)

    Rajapitamahuni, Anil; Zhang, Le; Singh, Vijay; Burton, John; Koten, Mak; Shield, Jeffrey; Tsymbal, Evgeny; Hong, Xia

    We report a unusual giant enhancement of in-plane magnetocrystalline anisotropy (MCA) in ultrathin colossal magnetoresistive oxide films due to 1D nanoscale periodic depth modulation. High quality epitaxial thin films of La0.67Sr0.33MnO3 (LSMO) of thickness 6 nm were grown on (001) SrTiO3 substrates via off-axis radio frequency magnetron sputtering. The top 2 nm of LSMO films are patterned into periodic nano-stripes using e-beam lithography and reactive ion etching. The resulting structure consists of nano-stripes of 2 nm height and 100-200 nm width on top of a 4 nm thick continuous base layer. We employed planar Hall effect measurements to study the in-plane magnetic anisotropy of the unpatterned and nanopatterned films. The unpatterned films show a biaxial anisotropy with easy axis along [110]. The extracted anisotropy energy density is ~1.1 x 105 erg/cm3, comparable to previously reported values. In the nanopatterned films, a strong uniaxial anisotropy is developed along one of the biaxial easy axes. The corresponding anisotropy energy density is ~5.6 x 106 erg/cm3 within the nano-striped volume, comparable to that of Co. We attribute the observed uniaxial MCA to MnO6 octahedral rotations/tilts and the enhancement in the anisotropy energy density to the strain gradient within the nano-stripes.

  17. Structural studies on the substitution of Ag, Na doped LCSMO CMR manganites

    NASA Astrophysics Data System (ADS)

    Subhashini, P.; Munirathinam, B.; Krishnaiah, M.; Venkatesh, R.; Venkateswarlu, D.; Ganesan, V.

    2016-05-01

    Synthesis and characterization of colossal magnetoresistance (CMR) materials has been a subject of scientific research due to the unique transport, magnetotransport, and magnetic properties. The single phase polycrystalline La0.7Ca0.1Sr0.1M0.1MnO3 (LCSMO) (M=Ag and Na) samples prepared using nitrate route method. The structural properties are studied at different dopants by X-ray diffraction. The surface morphology and elemental analysis of both samples were carried out by scanning electron microscopy (SEM) and energy dispersive X-ray technique (EDAX) respectively. The structural analysis shows that the LCSMO is crystallized in an orthorhombic perovskite structure belonging to Pnma space group. The crystal size of the sample is calculated using Scherrer formula. The SEM images show that the polycrystalline grains are observed to be near spherical shape and uniform in size. EDAX spectra taken from the surface of the synthesized powders show a nominal composition near the desired one for M=Na sample where as some vacancies are present in the A-site in the case of Ag substitution as will be discussed in this paper.

  18. Nonlinear alternating current conduction in polycrystalline manganites

    NASA Astrophysics Data System (ADS)

    Ghosh, T. N.; Nandi, U. N.; Jana, D.; Dey, K.; Giri, S.

    2014-06-01

    The real part of ac conductance Σ(T, f) of yttrium-doped mixed-valent polycrystalline manganite systems La1-x -yYyCaxMnO3 with x = 0.33 and 0.05 and y = 0.07 and iron doped LaMn1-xFexO3 with x = 0.15 is measured as a function of frequency f by varying zero-frequency Ohmic conductance Σ0 by T. The former shows a metal-insulator transition, whereas the latter exhibits insulating character throughout the measured temperature range. At a fixed temperature T, Σ(T, f) remains almost constant to the value Σ0 up to a certain frequency, known as the onset frequency fc and increases from Σ0 as frequency is increased from fc. Scaled appropriately, the data for Σ(T, f) at different T fall on the same universal curve, indicating the existence of a general scaling formalism for the ac conductance. fc scales with Σ0 as fc˜Σ0xf, where xf is the nonlinearity exponent characterising the onset. With the help of data for ac conduction, it is shown that xf is very much phase sensitive and can be used to characterize the different phases in a manganite system originated due to change in temperature or disorder. Scaling theories and existing theoretical models are used to analyze the results of ac conduction and the nonlinearity exponent xf.

  19. Review of the magnetocaloric effect in manganite materials

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong; Yu, Seong-Cho

    2007-01-01

    A thorough understanding of the magnetocaloric properties of existing magnetic refrigerant materials has been an important issue in magnetic refrigeration technology. This paper reviews a new class of magnetocaloric material, that is, the ferromagnetic perovskite manganites (R 1-xM xMnO 3, where R=La, Nd, Pr and M=Ca, Sr, Ba, etc.). The nature of these materials with respect to their magnetocaloric properties has been analyzed and discussed systematically. A comparison of the magnetocaloric effect of the manganites with other materials is given. The potential manganites are nominated for a variety of large- and small-scale magnetic refrigeration applications in the temperature range of 100-375 K. It is believed that the manganite materials with the superior magnetocaloric properties in addition to cheap materials-processing cost will be the option of future magnetic refrigeration technology.

  20. Large linear magnetoresistance in heavily-doped Nb:SrTiO3 epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Jin, Hyunwoo; Lee, Keundong; Baek, Seung-Hyub; Kim, Jin-Sang; Cheong, Byung-Ki; Park, Bae Ho; Yoon, Sungwon; Suh, B. J.; Kim, Changyoung; Seo, S. S. A.; Lee, Suyoun

    2016-10-01

    Interaction between electrons has long been a focused topic in condensed-matter physics since it has led to the discoveries of astonishing phenomena, for example, high-Tc superconductivity and colossal magnetoresistance (CMR) in strongly-correlated materials. In the study of strongly-correlated perovskite oxides, Nb-doped SrTiO3 (Nb:SrTiO3) has been a workhorse not only as a conducting substrate, but also as a host possessing high carrier mobility. In this work, we report the observations of large linear magnetoresistance (LMR) and the metal-to-insulator transition (MIT) induced by magnetic field in heavily-doped Nb:STO (SrNb0.2Ti0.8O3) epitaxial thin films. These phenomena are associated with the interplay between the large classical MR due to high carrier mobility and the electronic localization effect due to strong spin-orbit coupling, implying that heavily Nb-doped Sr(Nb0.2Ti0.8)O3 is promising for the application in spintronic devices.

  1. Large linear magnetoresistance in heavily-doped Nb:SrTiO3 epitaxial thin films

    PubMed Central

    Jin, Hyunwoo; Lee, Keundong; Baek, Seung-Hyub; Kim, Jin-Sang; Cheong, Byung-ki; Park, Bae Ho; Yoon, Sungwon; Suh, B. J.; Kim, Changyoung; Seo, S. S. A.; Lee, Suyoun

    2016-01-01

    Interaction between electrons has long been a focused topic in condensed-matter physics since it has led to the discoveries of astonishing phenomena, for example, high-Tc superconductivity and colossal magnetoresistance (CMR) in strongly-correlated materials. In the study of strongly-correlated perovskite oxides, Nb-doped SrTiO3 (Nb:SrTiO3) has been a workhorse not only as a conducting substrate, but also as a host possessing high carrier mobility. In this work, we report the observations of large linear magnetoresistance (LMR) and the metal-to-insulator transition (MIT) induced by magnetic field in heavily-doped Nb:STO (SrNb0.2Ti0.8O3) epitaxial thin films. These phenomena are associated with the interplay between the large classical MR due to high carrier mobility and the electronic localization effect due to strong spin-orbit coupling, implying that heavily Nb-doped Sr(Nb0.2Ti0.8)O3 is promising for the application in spintronic devices. PMID:27703222

  2. Sign reversal of junction magnetoresistance in p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure: a possibility in spintronics application.

    PubMed

    Giri, S K; Nath, T K

    2012-10-01

    We have fabricated a p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure, consisting of a p-type manganite (La0.7Ca0.3MnO3) and n-type Si with a interfacial layer of SiO2 with typical thickness of about 9 nm using pulsed laser deposition technique. The junction exhibits rectifying behavior over the temperature range of 10-300 K with rectification factor 52 at room temperature. Investigation on the electrical properties of p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure exhibits nonlinear J-V characteristics in a wide temperature range. A crossover from negative to positive junction magnetoresistance (JMR) is observed in p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure in current perpendicular to film plane (CPP) geometry. The temperature dependent sign of junction magnetoresistance of the heterojunction has been investigated carefully in details. It is found that the junction exhibits the positive junction magnetoresistance when the temperature is greater than the ferromagnetic to paramagnetic transition temperature (Tc) of the top highly spin-polarized half-metallic ferromagnetic La0.7Ca0.3MnO3 manganite film layer. The relation between junction magnetoresistance and external magnetic field is found to be of (delta rho/rho approximately equal alphaHbeta) type having both alpha and beta temperature dependent. We attribute the emergence of negative JMR at lower temperature (< Tc) and positive JMR at higher temperature (> Tc) to the quantum mechanical tunneling transport mechanism across the heterojunction. Our results might be very useful to fabricate artificial devices using the manganite-based heterojunction grown on single crystalline n-Si (100) in spintronics device applications.

  3. Spin transport in epitaxial magnetic manganite/ruthenate heterostructures with an LaMnO{sub 3} layer

    SciTech Connect

    Petrzhik, A. M. Ovsyannikov, G. A.; Shadrin, A. V.; Khaidukov, Yu. N.; Mustafa, L.

    2014-12-15

    Epitaxial La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/LaMnO{sub 3}/SrRuO{sub 3} (LSMO/LMO/SRO) heterostructures with an LMO layer 0–35 nm thick are grown by laser ablation on an NdGaO{sub 3} substrate at a high temperature. X-ray diffraction and transmission electron microscopy demonstrate sharp interfaces and epitaxial growth of the LSMO and SRO layers in the heterostructures at an LMO layer thickness of 0–35 nm. SQUID measurements of the magnetic moment of the heterostructures with an LMO layer and the data obtained with reflectometry of polarized neutrons show that the manganite LMO layer is a ferromagnet at a temperature below 150 K and strongly affects the magnetic moment of the heterostructures at low temperatures. The magnetoresistance of the mesostructure created from the heterostructure using lithography and ion etching decreases with increasing LMO layer thickness and weakly depends on the direction of an applied magnetic field. If the LMP layer is absent, a negative magnetoresistance is detected; it is likely to be caused by a negative magnetization of the SRO layer.

  4. Colossal Ultraviolet Photoresponsivity of Few-Layer Black Phosphorus.

    PubMed

    Wu, Jing; Koon, Gavin Kok Wai; Xiang, Du; Han, Cheng; Toh, Chee Tat; Kulkarni, Eeshan S; Verzhbitskiy, Ivan; Carvalho, Alexandra; Rodin, Aleksandr S; Koenig, Steven P; Eda, Goki; Chen, Wei; Neto, A H Castro; Özyilmaz, Barbaros

    2015-08-25

    Black phosphorus has an orthorhombic layered structure with a layer-dependent direct band gap from monolayer to bulk, making this material an emerging material for photodetection. Inspired by this and the recent excitement over this material, we studied the optoelectronics characteristics of high-quality, few-layer black phosphorus-based photodetectors over a wide spectrum ranging from near-ultraviolet (UV) to near-infrared (NIR). It is demonstrated for the first time that black phosphorus can be configured as an excellent UV photodetector with a specific detectivity ∼3 × 10(13) Jones. More critically, we found that the UV photoresponsivity can be significantly enhanced to ∼9 × 10(4) A W(-1) by applying a source-drain bias (VSD) of 3 V, which is the highest ever measured in any 2D material and 10(7) times higher than the previously reported value for black phosphorus. We attribute such a colossal UV photoresponsivity to the resonant-interband transition between two specially nested valence and conduction bands. These nested bands provide an unusually high density of states for highly efficient UV absorption due to the singularity of their nature.

  5. Colossal magnetocaloric effect in magneto-auxetic systems

    NASA Astrophysics Data System (ADS)

    Dudek, M. R.; Wojciechowski, K. W.; Grima, J. N.; Caruana-Gauci, R.; Dudek, K. K.

    2015-08-01

    We show that a mechanically driven magnetocaloric effect (MCE) in magneto-auxetic systems (MASs) in the vicinity of room temperature is possible and the effect can be colossal. Even at zero external magnetic field, the magnetic entropy change in this reversible process can be a few times larger in magnitude than in the case of the giant MCE discovered by Pecharsky and Gschneidner in Gd5(Si2Ge2). MAS represent a novel class of metamaterials having magnetic insertions embedded within a non-magnetic matrix which exhibits a negative Poisson’s ratio. The auxetic behaviour of the non-magnetic matrix may either enhance the magnetic ordering process or it may result in a transition to the disordered phase. In the MAS under consideration, a spin 1/2 system is chosen for the magnetic component and the well-known Onsager solution for the two-dimensional square lattice Ising model at zero external magnetic field is used to show that the isothermal change in magnetic entropy accompanying the auxetic behaviour can take a large value at room temperature. The practical importance of our findings is that MCE materials used in present engineering applications may be further enhanced by changing their geometry such that they exhibit auxetic behaviour.

  6. Enhanced Magnetoresistance at Room Temperature in La_0.8Ba_0.2MnO3 Epitaxial Thin Film.

    NASA Astrophysics Data System (ADS)

    Kanki, Teruo; Tanaka, Hidekazu; Kawai, Tomoji

    2000-03-01

    Mn perovskite oxides ((La_1-xM_x)MnO3 with M=Ba, Sr, Ca) are attracting attention due to their colossal magnetoresistance (CMR) phenomenon. In this study, we have noted the large magnetoresistance of (La_1-xBa_x)MnO3 near room temperature and have fabricated their thin film (x=0.2) on SrTiO3 (001) substrate by pulsed laser deposition technique. As a result, it was found that the MR effect of films exhibited higher MR ratio (33 percent at 320K for 40nm thickness, 43 percent at 307K for 65nm thickness, 48 percent at 267K for 130nm thickness) than that of bulk (21 percent at 270K) under the magnetic field of 0.8T. The metal-insulator transition temperature and magnetoresistance strongly depend on film thickness. The MR ratio of our film is very large in comparison with that of other magnetoresistive oxides at room temperature.

  7. Giant tunneling magnetoresistance in silicene

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Lou, Yiyi

    2013-11-01

    We have theoretically studied ballistic electron transport in silicene under the manipulation of a pair of ferromagnetic gate. Transport properties like transmission and conductance have been calculated by the standard transfer matrix method for parallel and antiparallel magnetization configurations. It is demonstrated here that, due to the stray field-induced wave-vector filtering effect, remarkable difference in configuration-dependent transport gives rise to a giant tunneling magnetoresistance. In combination with the peculiar buckled structure of silicene and its electric tunable energy gap, the receiving magnetoresistance can be efficiently modulated by the externally-tunable stray field, electrostatic potential, and staggered sublattice potential, providing some flexible strategies to construct silicene-based nanoelectronic device.

  8. Giant tunneling magnetoresistance in silicene

    SciTech Connect

    Wang, Yu; Lou, Yiyi

    2013-11-14

    We have theoretically studied ballistic electron transport in silicene under the manipulation of a pair of ferromagnetic gate. Transport properties like transmission and conductance have been calculated by the standard transfer matrix method for parallel and antiparallel magnetization configurations. It is demonstrated here that, due to the stray field-induced wave-vector filtering effect, remarkable difference in configuration-dependent transport gives rise to a giant tunneling magnetoresistance. In combination with the peculiar buckled structure of silicene and its electric tunable energy gap, the receiving magnetoresistance can be efficiently modulated by the externally-tunable stray field, electrostatic potential, and staggered sublattice potential, providing some flexible strategies to construct silicene-based nanoelectronic device.

  9. Magnetoresistance behavior of UNiGe

    SciTech Connect

    Nakotte, H.; Lacerda, A.; Purwanto, A.; Havela, L.; Sechovsky, V.; Prokes, K.; Brueck, E.; Boer, F.R. de; Torikachvili, M.S.

    1995-05-01

    The authors have measured the temperature dependences of the magnetoresistance of single-crystalline UNiGe for both parallel (i//B//c-axis) and perpendicular configurations (i//a-axis, B//c-axis) in magnetic fields up to 18 T. Both configurations yield similar magnetoresistance behavior, which emphasizes the strong magnetic contribution to the resistivity in all directions. Crossing magnetic-phase boundaries causes anomalies in the magnetoresistance, which allowed a completion of the previously proposed magnetic phase diagram.

  10. Extraordinary magnetoresistance: sensing the future

    NASA Astrophysics Data System (ADS)

    Hewett, Thomas H.; Kusmartsev, Feodor V.

    2012-06-01

    Simulations utilising the finite element method (FEM) have been produced in order to investigate aspects of circular extraordinary magnetoresistance (EMR) devices. The effect of three specific features on the resultant magnetoresistance were investigated: the ratio of the metallic to semiconducting conductivities ( σ M / σ S ); the semiconductor mobility; and the introduction of an intermediate region at the semiconductormetal interface in order to simulate a contact resistance. In order to obtain a large EMR effect the conductivity ratio ( σ M / σ S ) is required to be larger than two orders of magnitude; below this critical value the resultant magnetoresistance effect is dramatically reduced. Large mobility semiconductors exhibit larger EMR values for a given field (below saturation) and reduce the magnetic field required to produce saturation of the magnetoresistance. This is due to a larger Hall angle produced at a given magnetic field and is consistent with the mechanism of the EMR effect. Since practical magnetic field sensors are required to operate at low magnetic fields, high mobility semiconductors are required in the production of more sensitive EMR sensors. The formation of a Schottky barrier at the semiconductor-metal interface has been modelled with the introduction of a contact resistance at the semiconductor-metal interface. Increasing values of contact resistance are found to reduce the EMR effect with it disappearing altogether for large values. This has been shown explicitly by looking at the current flow in the system and is consistent with the mechanism of the EMR effect. The interface resistance was used to fit the simulated model to existing experimental data. The best fit occurred with an interface with resistivity of 1.55×10-4 m (overestimate). The EMR effect holds great potential with regard to its future application to magnetic field sensors. The design of any such devices should incorporate high mobility materials (such as graphene

  11. Extraordinary magnetoresistance: sensing the future

    NASA Astrophysics Data System (ADS)

    Hewett, Thomas; Kusmartsev, Feodor

    2012-06-01

    Simulations utilising the finite element method (FEM) have been produced in order to investigate aspects of circular extraordinary magnetoresistance (EMR) devices. The effect of three specific features on the resultant magnetoresistance were investigated: the ratio of the metallic to semiconducting conductivities (σ M/σ S); the semiconductor mobility; and the introduction of an intermediate region at the semiconductormetal interface in order to simulate a contact resistance. In order to obtain a large EMR effect the conductivity ratio (σ M/σ S) is required to be larger than two orders of magnitude; below this critical value the resultant magnetoresistance effect is dramatically reduced. Large mobility semiconductors exhibit larger EMR values for a given field (below saturation) and reduce the magnetic field required to produce saturation of the magnetoresistance. This is due to a larger Hall angle produced at a given magnetic field and is consistent with the mechanism of the EMR effect. Since practical magnetic field sensors are required to operate at low magnetic fields, high mobility semiconductors are required in the production of more sensitive EMR sensors. The formation of a Schottky barrier at the semiconductor-metal interface has been modelled with the introduction of a contact resistance at the semiconductor-metal interface. Increasing values of contact resistance are found to reduce the EMR effect with it disappearing altogether for large values. This has been shown explicitly by looking at the current flow in the system and is consistent with the mechanism of the EMR effect. The interface resistance was used to fit the simulated model to existing experimental data. The best fit occurred with an interface with resistivity of 1.55×10-4 m (overestimate). The EMR effect holds great potential with regard to its future application to magnetic field sensors. The design of any such devices should incorporate high mobility materials (such as graphene) along

  12. Giant magnetoresistance in silicene nanoribbons.

    PubMed

    Xu, Chengyong; Luo, Guangfu; Liu, Qihang; Zheng, Jiaxin; Zhang, Zhimeng; Nagase, Shigeru; Gao, Zhengxiang; Lu, Jing

    2012-05-21

    By performing first-principle quantum transport calculations, we predict a giant magnetoresistance in zigzag silicene nanoribbons (ZSiNRs) connecting two semi-infinite silicene electrodes through switch of the edge spin direction of ZSiNRs. Spin-filter efficiency of both the antiferromagnetic and ferromagnetic ZSiNRs is sign-changeable with the bias voltage. Therefore, potential application of silicene in spintronics devices is suggested.

  13. Ultrafast Control of the electronic phase of a manganite viamode-selective vibrational excitation

    SciTech Connect

    Rini, Matteo; Tobey, Ra'anan I.; Dean, Nicky; Tokura, Yoshinori; Schoenlein, Robert W.; Cavalleri, Andrea

    2007-05-01

    Controlling a phase of matter by coherently manipulatingspecific vibrational modes has long been an attractive (yet elusive) goalfor ultrafast science. Solids with strongly correlated electrons, inwhich even subtle crystallographic distortions can result in colossalchanges of the electronic and magnetic properties, could be directedbetween competing phases by such selective vibrational excitation. Inthis way, the dynamics of the electronic ground state of the systembecome accessible, and new insight into the underlying physics might begained. Here we report the ultrafast switching of the electronic phase ofa magnetoresistive manganite via direct excitation of a phonon mode at 71meV (17 THz). A prompt, five-order-of-magnitude drop in resistivity isobserved, associated with a non-equilibrium transition from the stableinsulating phase to a metastable metallic phase. In contrast withlight-induced, and current-driven phase transitions, the vibrationallydriven bandgap collapse observed here is not related to hot-carrierinjection and is uniquely attributed to a large-amplitude Mn-Odistortion. This corresponds to a perturbation of theperovskite-structure tolerance factor, which in turn controls theelectronic bandwidth via inter-site orbital overlap. Phase control bycoherent manipulation of selected metal--oxygen phonons should findextensive application in other complex solids--notably in copper oxidesuperconductors, in which the role of Cu-O vibrations on the electronicproperties is currently controversial.

  14. Nonlinear alternating current conduction in polycrystalline manganites

    SciTech Connect

    Ghosh, T. N.; Nandi, U. N.; Jana, D.; Dey, K.; Giri, S.

    2014-06-28

    The real part of ac conductance Σ(T, f) of yttrium-doped mixed-valent polycrystalline manganite systems La{sub 1−x−y}Y{sub y}Ca{sub x}MnO{sub 3} with x = 0.33 and 0.05 and y = 0.07 and iron doped LaMn{sub 1−x}Fe{sub x}O{sub 3} with x = 0.15 is measured as a function of frequency f by varying zero-frequency Ohmic conductance Σ{sub 0} by T. The former shows a metal-insulator transition, whereas the latter exhibits insulating character throughout the measured temperature range. At a fixed temperature T, Σ(T, f) remains almost constant to the value Σ{sub 0} up to a certain frequency, known as the onset frequency f{sub c} and increases from Σ{sub 0} as frequency is increased from f{sub c}. Scaled appropriately, the data for Σ(T, f) at different T fall on the same universal curve, indicating the existence of a general scaling formalism for the ac conductance. f{sub c} scales with Σ{sub 0} as f{sub c}∼Σ{sub 0}{sup x{sub f}}, where x{sub f} is the nonlinearity exponent characterising the onset. With the help of data for ac conduction, it is shown that x{sub f} is very much phase sensitive and can be used to characterize the different phases in a manganite system originated due to change in temperature or disorder. Scaling theories and existing theoretical models are used to analyze the results of ac conduction and the nonlinearity exponent x{sub f}.

  15. Structural domain walls in polar hexagonal manganites

    NASA Astrophysics Data System (ADS)

    Kumagai, Yu

    2014-03-01

    The domain structure in the multiferroic hexagonal manganites is currently intensely investigated, motivated by the observation of intriguing sixfold topological defects at their meeting points [Choi, T. et al,. Nature Mater. 9, 253 (2010).] and nanoscale electrical conductivity at the domain walls [Wu, W. et al., Phys. Rev. Lett. 108, 077203 (2012).; Meier, D. et al., Nature Mater. 11, 284 (2012).], as well as reports of coupling between ferroelectricity, magnetism and structural antiphase domains [Geng, Y. et al., Nano Lett. 12, 6055 (2012).]. The detailed structure of the domain walls, as well as the origin of such couplings, however, was previously not fully understood. In the present study, we have used first-principles density functional theory to calculate the structure and properties of the low-energy structural domain walls in the hexagonal manganites [Kumagai, Y. and Spaldin, N. A., Nature Commun. 4, 1540 (2013).]. We find that the lowest energy domain walls are atomically sharp, with {210}orientation, explaining the orientation of recently observed stripe domains and suggesting their topological protection [Chae, S. C. et al., Phys. Rev. Lett. 108, 167603 (2012).]. We also explain why ferroelectric domain walls are always simultaneously antiphase walls, propose a mechanism for ferroelectric switching through domain-wall motion, and suggest an atomistic structure for the cores of the sixfold topological defects. This work was supported by ETH Zurich, the European Research Council FP7 Advanced Grants program me (grant number 291151), the JSPS Postdoctoral Fellowships for Research Abroad, and the MEXT Elements Strategy Initiative to Form Core Research Center TIES.

  16. Origin of colossal permittivity in BaTiO3 via broadband dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Han, Hyuksu; Voisin, Christophe; Guillemet-Fritsch, Sophie; Dufour, Pascal; Tenailleau, Christophe; Turner, Christopher; Nino, Juan C.

    2013-01-01

    Barium titanate (BT) ceramics with Ba/Ti ratios of 0.95 and 1.00 were synthesized using spark plasma sintering (SPS) technique. Dielectric spectroscopy (frequency range from 40 Hz to 1 MHz and temperature range from 300 K to 30 K) was performed on those ceramics (SPS BT). SPS BT showed extremely high permittivity up to ˜105, which can be referred to as colossal permittivity, with relatively low dielectric loss of ˜0.05. Data analyses following Debye relaxation and universal dielectric response models indicate that the origin of colossal permittivity in BT ceramics is the result of a hopping polaron within semiconducting grains in combination with interfacial polarization at the insulating grain boundary. Furthermore, the contributions of each polarization mechanism to the colossal permittivity in SPS BT, such as a hopping polarization, internal barrier layer capacitance effect, and electrode effect, were estimated.

  17. Griffiths phase and temporal effects in phase separated manganites

    NASA Astrophysics Data System (ADS)

    Krivoruchko, V. N.; Marchenko, M. A.

    2016-08-01

    Phenomenological description of relaxation phenomena in magnetic and transport properties of perovskite manganites has been presented. The approach is based on generalization of some hypotheses appropriate to the Preisach picture of magnetization process for half-metallic ferromagnets and on an assumption that in doped manganites the phase separated state exists near the magnetic ordering temperature. For systems with the percolation type of a ferromagnet-paramagnet transition, distinctive features in relaxation of magnetization and resistivity have been found. The relaxation is shown to be most pronounced near the transition temperature, and to be an approximately logarithmic function of time. The theoretical results replicate a broad spectrum of behavior observed experimentally on time dependence of magnetization and resistivity of CMR systems and allow a direct comparison with available experimental data. We propose an additional experimental test to distinguish between the percolation scenario of magnetic and transport transitions in doped manganites, and the ferromagnetic polaron picture. In particular, an anomalously slow relaxation to zero of the order parameter can be considered as a key feature of the Griffiths-like phase transition in doped manganites. It is also shown that a system with the Griffiths-like state will exhibit nonequilibrium aging and rejuvenation phenomena, which in many aspects resemble that of a spin glass. We hope that experimental observation of a set of time decay properties will provide a settlement of apparently conflicting results obtained for different characteristics of phase-separated manganites.

  18. Rashba-Edelstein Magnetoresistance in Metallic Heterostructures

    NASA Astrophysics Data System (ADS)

    Nakayama, Hiroyasu; Kanno, Yusuke; An, Hongyu; Tashiro, Takaharu; Haku, Satoshi; Nomura, Akiyo; Ando, Kazuya

    2016-09-01

    We report the observation of magnetoresistance originating from Rashba spin-orbit coupling (SOC) in a metallic heterostructure: the Rashba-Edelstein (RE) magnetoresistance. We show that the simultaneous action of the direct and inverse RE effects in a Bi /Ag /CoFeB trilayer couples current-induced spin accumulation to the electric resistance. The electric resistance changes with the magnetic-field angle, reminiscent of the spin Hall magnetoresistance, despite the fact that bulk SOC is not responsible for the magnetoresistance. We further found that, even when the magnetization is saturated, the resistance increases with increasing the magnetic-field strength, which is attributed to the Hanle magnetoresistance in this system.

  19. Rashba-Edelstein Magnetoresistance in Metallic Heterostructures.

    PubMed

    Nakayama, Hiroyasu; Kanno, Yusuke; An, Hongyu; Tashiro, Takaharu; Haku, Satoshi; Nomura, Akiyo; Ando, Kazuya

    2016-09-01

    We report the observation of magnetoresistance originating from Rashba spin-orbit coupling (SOC) in a metallic heterostructure: the Rashba-Edelstein (RE) magnetoresistance. We show that the simultaneous action of the direct and inverse RE effects in a Bi/Ag/CoFeB trilayer couples current-induced spin accumulation to the electric resistance. The electric resistance changes with the magnetic-field angle, reminiscent of the spin Hall magnetoresistance, despite the fact that bulk SOC is not responsible for the magnetoresistance. We further found that, even when the magnetization is saturated, the resistance increases with increasing the magnetic-field strength, which is attributed to the Hanle magnetoresistance in this system. PMID:27661708

  20. Giant magnetoresistance in silicene nanoribbons

    NASA Astrophysics Data System (ADS)

    Xu, Chengyong; Luo, Guangfu; Liu, Qihang; Zheng, Jiaxin; Zhang, Zhimeng; Nagase, Shigeru; Gao, Zhengxiang; Lu, Jing

    2012-05-01

    By performing first-principle quantum transport calculations, we predict a giant magnetoresistance in zigzag silicene nanoribbons (ZSiNRs) connecting two semi-infinite silicene electrodes through switch of the edge spin direction of ZSiNRs. Spin-filter efficiency of both the antiferromagnetic and ferromagnetic ZSiNRs is sign-changeable with the bias voltage. Therefore, potential application of silicene in spintronics devices is suggested.By performing first-principle quantum transport calculations, we predict a giant magnetoresistance in zigzag silicene nanoribbons (ZSiNRs) connecting two semi-infinite silicene electrodes through switch of the edge spin direction of ZSiNRs. Spin-filter efficiency of both the antiferromagnetic and ferromagnetic ZSiNRs is sign-changeable with the bias voltage. Therefore, potential application of silicene in spintronics devices is suggested. Electronic supplementary information (ESI) available: The total current contrasts between the AFM and FM configurations and the spin-resolved I-Vbias characteristics in the AFM and FM configurations of all the checked ZSiNRs as a function of bias voltage; the spin-resolved I-Vbias characteristics and SFEs of different-length 5-ZSiNR in the AFM and FM configurations as a function of bias voltage. See DOI: 10.1039/c2nr00037g

  1. Seed layer technique for high quality epitaxial manganite films

    PubMed Central

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O’Shea, K.; MacLaren, D. A.; Bergenti, I.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-01-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

  2. Seed layer technique for high quality epitaxial manganite films

    NASA Astrophysics Data System (ADS)

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O'Shea, K.; MacLaren, D. A.; Riminucci, A.; Bergenti, I.; Fugattini, S.; Prezioso, M.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-08-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

  3. Large magnetic entropy change in Cu-doped manganites

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong; Peng, Hua-Xin; Yu, Seong-Cho; Duc Tho, Nguyen; Chau, Nguyen

    2005-01-01

    Magnetic entropy change above 300 K, which is larger than that of gadolinium (Phys. Rev. B 57 (1998) 3478), has been observed in a Cu-doped manganites of La0.7Sr0.3Mn1-xCuxO3 (x = 0.05 , 0.1). The large magnetic entropy change originated from a sharp magnetization jump is associated with a first-order crystallographic phase transition of the sample near the Curie temperature. These results suggest that the present Cu-doped manganites are suitable candidate materials for magnetic refrigerants in the room temperature magnetic-refrigeration technology.

  4. The role of thermal coupling on avalanches in manganites.

    PubMed

    Macià, F; Abril, G; Hernandez, J M; Tejada, J

    2009-10-01

    We report here a study on the environmental dependence of the occurrence, at low temperature, of ultra-sharp field induced avalanches in phase separated manganites. Despite the high reproducibility of avalanches, it has already been observed that the critical fields shift with the magnetic field sweep rate and that different sample sizes lead to different ignition fields for the avalanches. Critical growing rates have been suggested to describe the avalanche ignition though the role of thermal coupling has hardly been considered. We qualitatively analyze here a set of experimental data on avalanches in manganites and discuss the role of thermal coupling as a key parameter of the instability in a dynamical system.

  5. Seed layer technique for high quality epitaxial manganite films

    PubMed Central

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O’Shea, K.; MacLaren, D. A.; Bergenti, I.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-01-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived. PMID:27648371

  6. Chemical Pressure Effects in Layered Manganites

    NASA Astrophysics Data System (ADS)

    Moritomo, Yutaka; Maruyama, Yousuke; Nakamura, Arao

    1998-03-01

    Lattice effects on the magnetic and transport properties have been investigated for layered-type doped mangaites. The insulator-to-metal transition temperature for La_1.2Sr_1.8Mn_2O7 (T_C=130 K) is significantly suppressed with chemical substitution of the trivalent La^3+ ions to smaller Nd^3+ (or Sm^3+) ions(Y. Moritomo et al), Phys. Rev. B56(1997)R7057. Similarly, the charge-ordering temperature for La_0.5Sr_1.5MnO4 (T_CO=230 K) is suppresses with chemical substitution(Y. Moritomo et al), Phys. Rev. B56, in press. Systematic x-ray as well as neutron diffraction measurements have revealed that above chemical pressure enhances the static Jahn-Teller distortion of the MnO6 octahedra in both the system. We will explain the suppressions of TC and T_CO in terms of the increasing d_3z^2-r^2 character in the occupied eg state. Our observation indicates that the chemical pressure effects are qualitatively different between the cubic and layered manganites systems. The authors are grateful to K. Ohoyama and M. Ohashi for their help in neutron diffraction measurements, and to S. Mori for his help in electron diffraction measurements. This work was supported by a Grant-In-Aid for Scientific Research from the Ministry of Education, Science, Sport and Culture and from PRESTO, Japan Scienece and Technology Corporation (JST), Japan.

  7. Enhanced ordering temperatures in antiferromagnetic manganite superlattices

    SciTech Connect

    May, Stephen J.; Robertson, Lee; Ryan, P J; Kim, J.-W.; Santos, Tiffany S.; Karapetrova, Evgenia; Zarestky, Jerel L.; Zhai, X.; Te velthuis, Suzanne G.; Eckstein, James N.; Bader, S. D.; Bhattacharya, Anand

    2009-01-01

    The disorder inherent to doping by cation substitution in the complex oxides can have profound effects on collective ordered states. Here, we demonstrate that cation-site ordering achieved via digital synthesis techniques can dramatically enhance the antiferromagnetic ordering temperatures of manganite films. Cation-ordered (LaMnO3)m/(SrMnO3)2m superlattices exhibit N el temperatures (TN) that are the highest of any La1-xSrxMnO3 compound, ~70 K greater than compositionally equivalent randomly doped La1/3Sr2/3MnO3. The antiferromagnetic order is A-type, consisting of in-plane double-exchange-mediated ferromagnetic sheets coupled antiferromagnetically along the out-of-plane direction. Via synchrotron x-ray scattering, we have discovered an in-plane structural modulation that reduces the charge itinerancy and hence the ordering temperature within the ferromagnetic sheets, thereby limiting TN. This modulation is mitigated and driven to long wavelengths by cation ordering, enabling the higher TN values of the superlattices. These results provide insight into how cation-site ordering can enhance cooperative behavior in oxides through subtle structural phenomena.

  8. Hall magnetoresistivity response under microwave excitation revisited

    SciTech Connect

    Inarrea, Jesus

    2007-04-23

    The authors theoretically analyzed the microwave-induced modification of the Hall magnetoresistivity in high mobility two-dimensional electron systems. These systems present diagonal magnetoresistivity oscillations and zero-resistance states when subjected to microwave radiation. The most surprising modification of the Hall magnetoresistivity is a periodic reduction which correlates with a periodic increase in the diagonal resistivity. The authors present a model that explains the experimental results considering that radiation affects directly only the diagonal resistivity and that the observed Hall resistivity changes come from the tensor relationship between them.

  9. Spin Hall magnetoresistance in a canted ferrimagnet

    NASA Astrophysics Data System (ADS)

    Ganzhorn, Kathrin; Barker, Joseph; Schlitz, Richard; Piot, Benjamin A.; Ollefs, Katharina; Guillou, Francois; Wilhelm, Fabrice; Rogalev, Andrei; Opel, Matthias; Althammer, Matthias; Geprägs, Stephan; Huebl, Hans; Gross, Rudolf; Bauer, Gerrit E. W.; Goennenwein, Sebastian T. B.

    2016-09-01

    We study the spin Hall magnetoresistance effect in ferrimagnet/normal metal bilayers, comparing the response in collinear and canted magnetic phases. In the collinear magnetic phase, in which the sublattice magnetic moments are all aligned along the same axis, we observe the conventional spin Hall magnetoresistance. In contrast, in the canted phase, the magnetoresistance changes sign. Using atomistic spin simulations and x-ray absorption experiments, we can understand these observations in terms of the magnetic field and temperature dependent orientation of magnetic moments on different magnetic sublattices. This enables a magnetotransport based investigation of noncollinear magnetic textures.

  10. Unconventional proximity effect and inverse spin-switch behavior in a model manganite-cuprate-manganite trilayer system

    SciTech Connect

    Salafranca Laforga, Juan I; Okamoto, Satoshi

    2010-01-01

    The proximity effect in a model manganite-cuprate system is investigated theoretically. We consider a situation in which spin-polarized electrons in manganite layers antiferromagnetically couple with electrons in cuprate layers as observed experimentally. The effect of the interfacial magnetic coupling is found to be much stronger than the injection of spin-polarized electrons into the cuprate region. As a result, the superconducting transition temperature depends on the thickness of the cuprate layer significantly. Since the magnetic coupling creates negative polarization, an applied magnetic field and the negative polarization compete, resulting in the inverse spin-switch behavior where the superconducting transition temperature is increased by applying a magnetic field.

  11. Tunneling magnetoresistance of silicon chains

    NASA Astrophysics Data System (ADS)

    Matsuura, Yukihito

    2016-05-01

    The tunneling magnetoresistance (TMR) of a silicon chain sandwiched between nickel electrodes was examined by using first-principles density functional theory. The relative orientation of the magnetization in a parallel-alignment (PA) configuration of two nickel electrodes enhanced the current with a bias less than 0.4 V compared with that in an antiparallel-alignment configuration. Consequently, the silicon chain-nickel electrodes yielded good TMR characteristics. In addition, there was polarized spin current in the PA configuration. The spin polarization of sulfur atoms functioning as a linking bridge between the chain and nickel electrode played an important role in the magnetic effects of the electric current. Moreover, the hybridization of the sulfur 3p orbital and σ-conjugated silicon 3p orbital contributed to increasing the total current.

  12. Large rectification magnetoresistance in nonmagnetic Al/Ge/Al heterojunctions.

    PubMed

    Zhang, Kun; Li, Huan-Huan; Grünberg, Peter; Li, Qiang; Ye, Sheng-Tao; Tian, Yu-Feng; Yan, Shi-Shen; Lin, Zhao-Jun; Kang, Shi-Shou; Chen, Yan-Xue; Liu, Guo-Lei; Mei, Liang-Mo

    2015-09-21

    Magnetoresistance and rectification are two fundamental physical properties of heterojunctions and respectively have wide applications in spintronics devices. Being different from the well known various magnetoresistance effects, here we report a brand new large magnetoresistance that can be regarded as rectification magnetoresistance: the application of a pure small sinusoidal alternating-current to the nonmagnetic Al/Ge Schottky heterojunctions can generate a significant direct-current voltage, and this rectification voltage strongly varies with the external magnetic field. We find that the rectification magnetoresistance in Al/Ge Schottky heterojunctions is as large as 250% at room temperature, which is greatly enhanced as compared with the conventional magnetoresistance of 70%. The findings of rectification magnetoresistance open the way to the new nonmagnetic Ge-based spintronics devices of large rectification magnetoresistance at ambient temperature under the alternating-current due to the simultaneous implementation of the rectification and magnetoresistance in the same devices.

  13. Large rectification magnetoresistance in nonmagnetic Al/Ge/Al heterojunctions

    NASA Astrophysics Data System (ADS)

    Zhang, Kun; Li, Huan-Huan; Grünberg, Peter; Li, Qiang; Ye, Sheng-Tao; Tian, Yu-Feng; Yan, Shi-Shen; Lin, Zhao-Jun; Kang, Shi-Shou; Chen, Yan-Xue; Liu, Guo-Lei; Mei, Liang-Mo

    2015-09-01

    Magnetoresistance and rectification are two fundamental physical properties of heterojunctions and respectively have wide applications in spintronics devices. Being different from the well known various magnetoresistance effects, here we report a brand new large magnetoresistance that can be regarded as rectification magnetoresistance: the application of a pure small sinusoidal alternating-current to the nonmagnetic Al/Ge Schottky heterojunctions can generate a significant direct-current voltage, and this rectification voltage strongly varies with the external magnetic field. We find that the rectification magnetoresistance in Al/Ge Schottky heterojunctions is as large as 250% at room temperature, which is greatly enhanced as compared with the conventional magnetoresistance of 70%. The findings of rectification magnetoresistance open the way to the new nonmagnetic Ge-based spintronics devices of large rectification magnetoresistance at ambient temperature under the alternating-current due to the simultaneous implementation of the rectification and magnetoresistance in the same devices.

  14. Giant magnetoresistance through a single molecule.

    PubMed

    Schmaus, Stefan; Bagrets, Alexei; Nahas, Yasmine; Yamada, Toyo K; Bork, Annika; Bowen, Martin; Beaurepaire, Eric; Evers, Ferdinand; Wulfhekel, Wulf

    2011-03-01

    Magnetoresistance is a change in the resistance of a material system caused by an applied magnetic field. Giant magnetoresistance occurs in structures containing ferromagnetic contacts separated by a metallic non-magnetic spacer, and is now the basis of read heads for hard drives and for new forms of random access memory. Using an insulator (for example, a molecular thin film) rather than a metal as the spacer gives rise to tunnelling magnetoresistance, which typically produces a larger change in resistance for a given magnetic field strength, but also yields higher resistances, which are a disadvantage for real device operation. Here, we demonstrate giant magnetoresistance across a single, non-magnetic hydrogen phthalocyanine molecule contacted by the ferromagnetic tip of a scanning tunnelling microscope. We measure the magnetoresistance to be 60% and the conductance to be 0.26G(0), where G(0) is the quantum of conductance. Theoretical analysis identifies spin-dependent hybridization of molecular and electrode orbitals as the cause of the large magnetoresistance. PMID:21336269

  15. Science and technology of magnetic oxides

    SciTech Connect

    Hundley, M.F.; Nickel, J.H.; Ramesh, R.; Tokura, Yoshinori

    1998-12-31

    The symposium, Metallic Magnetic Oxides (Symposium V), was held in Boston, Massachusetts, December 1--4, 1997 as part of the 1997 Materials Research Society Fall Meeting. Research into the science and technology of magnetic oxides has undergone a renaissance during the past seven years. In large measure this stems from the rediscovery of the colossal magnetoresistance associated with the ferromagnetic-order-induced, metal-insulator transition exhibited by the doped lanthanum manganites. Research today is focused both on improving the understanding of the phenomena exhibited by these compounds and on developing technological applications that utilize their extremely magnetic-field-dependent conductivity near room temperature. This symposium focused on colossal magnetoresistance (CMR) materials, including manganites and cobalites. Transport and magnetic properties and their dependence on stress, growth conditions, stoichiometry, and elemental composition are now being explored quite extensively. Forty two papers have been processed separately for inclusion on the data base.

  16. Colossal magnetodielectric effect and spin flop in magnetoelectric Co4Nb2O9 crystal

    NASA Astrophysics Data System (ADS)

    Yin, L. H.; Zou, Y. M.; Yang, J.; Dai, J. M.; Song, W. H.; Zhu, X. B.; Sun, Y. P.

    2016-07-01

    We have investigated the detailed magnetic, magnetoelectric (ME), magnetodielectric (MD) and thermal expansion properties in Co4Nb2O9 crystal. A magnetic-field-induced spin flop was observed below antiferromagnetic (AFM) transition temperature TN. Dielectric constant at applied magnetic field nearly diverges around the AFM transition, giving rise to a colossal MD effect as high as ˜138% around TN. Theoretical analysis of the ME and MD data revealed a major contribution of critical spin fluctuation to the colossal MD effect in Co4Nb2O9. These results suggest that linear ME materials with large ME coupling might be potentially used to realize large MD effect for future application.

  17. Colossal magnetodielectric effect in DyMn2O5: Electromagnons or rare earth?

    NASA Astrophysics Data System (ADS)

    Sushkov, Andrei; Drew, Dennis; Kant, Christian; Shuvaev, Alexey; Pimenov, Andrei; Zvyagin, Sergei; Lorenz, Bernd; Cheong, Sang-Wook

    2012-02-01

    We report on the results of spectroscopic studies of the excitations responsible for the colossal magnetodielectric effect in DyMn2O5 [1]. On one hand, many RMn2O5 compounds have electromagnons capable of inducing large steps in the dielectric constant. On the other hand, rare earth ions can posses electric dipole moments and also can produce dielectric anomalies. Both types of excitations are expected in the experimentally difficult low energy range 0.1-1 meV. We use high frequency dielectric, Fourier transform and back-wave oscillator spectroscopies in combination with low temperature and magnetic field up to 9 T to clarify the origin of the dielectric anomaly in DyMn2O5. [1] N. Hur, S. Park, P. A. Sharma, S. Guha, and S-W. Cheong, Colossal Magnetodielectric Effects in DyMn2O5, PRL 93, 107207 (2004).

  18. Tunneling magnetoresistive heads for magnetic data storage.

    PubMed

    Mao, Sining

    2007-01-01

    Spintronics is emerging to be a new form of nanotechnologies, which utilizes not only the charge but also spin degree of freedom of electrons. Spin-dependent tunneling transport is one of the many kinds of physical phenomena involving spintronics, which has already found industrial applications. In this paper, we first provide a brief review on the basic physics and materials for magnetic tunnel junctions, followed more importantly by a detailed coverage on the application of magnetic tunneling devices in magnetic data storage. The use of tunneling magnetoresistive reading heads has helped to maintain a fast growth of areal density, which is one of the key advantages of hard disk drives as compared to solid-state memories. This review is focused on the first commercial tunneling magnetoresistive heads in the industry at an areal density of 80 approximately 100 Gbit/in2 for both laptop and desktop Seagate hard disk drive products using longitudinal media. The first generation tunneling magnetoresistive products utilized a bottom stack of tunnel junctions and an abutted hard bias design. The output signal amplitude of these heads was 3 times larger than that of comparable giant magnetoresistive devices, resulting in a 0.6 decade bit error rate gain over the latter. This has enabled high component and drive yields. Due to the improved thermal dissipation of vertical geometry, the tunneling magnetoresistive head runs cooler with a better lifetime performance, and has demonstrated similar electrical-static-discharge robustness as the giant magnetoresistive devices. It has also demonstrated equivalent or better process and wafer yields compared to the latter. The tunneling magnetoresistive heads are proven to be a mature and capable reader technology. Using the same head design in conjunction with perpendicular recording media, an areal density of 274 Gbit/in2 has been demonstrated, and advanced tunneling magnetoresistive heads can reach 311 Gbit/in2. Today, the

  19. Giant Magneto-Resistance in Epitaxial (La0.7Sr0.3MnO3)0.5: (ZnO)0.5 Nanocomposites

    SciTech Connect

    Pan, Wei; Jiang, Y. X.; Ihlefeld, Jon; Lu, Ping; Lee, Stephen R.

    2015-12-01

    A great deal of research has been carried out in oxide material systems. Among them, ZnO and La0.7Sr0.3MnO3 (LSMO) are of particular interest due to their superb optical properties and colossal magneto-resistive effect. Here, we report our recent results of magneto-transport studies in self-assembled, epitaxial (ZnO)0.5:(La0.7Sr0.3MnO3)0.5 nanocomposite films.

  20. Surface hardening of austenitic stainless steels via low-temperature colossal supersaturation

    NASA Astrophysics Data System (ADS)

    Cao, Yan

    The Swagelok Company has recently developed a low-temperature (470°C) carburization technology for austenitic stainless steels, that increases the surface hardness from 200 to 1200 HV25 without sacrificing corrosion resistance. In order to investigate the microstructural changes responsible for these outstanding properties, bulk specimens, thin foils, and powder specimens of several different low-temperature carburized 316 stainless steels have been studied. XRD studies revealed that the low-temperature carburization of 316 austenitic stainless steels lead to a colossal supersaturation of interstitial carbon in the austenite. While the equilibrium solubility of carbon is 0.03 at% at the carburization temperature of 470°C, high-precision XRD determination of the lattice parameter after carburization indicated a carbon concentration of >10at% in solid solution---a colossal supersaturation! This astonishing result was confirmed by a completely independent experimental method, X-ray photoelectron spectrometry (XPS). Residual stress measurements indicated that low-temperature carburization caused an enormous compressive residual stress of 2 GPa at the surface. The enormous compressive residual stress and a high density of stacking faults caused broadening and shifting of the austenite peaks in X-ray diffraction scans. Analysis of the underlying thermodynamics and kinetics indicate that the key to colossal supersaturation is to kinetically suppress the formation of M23C6. The colossal supersaturation of carbon in the austenite is the dominant feature responsible for the unusual hardness. Only during the extended (>40h) carburization times, M5C 2 carbide (Hagg carbide), instead of M23C6, was observed to form. In addition, TEM studies indicated the presence of a small amount of a second carbide phase, M7C3. The particles of both carbides have the shape of long needles, containing a high density of planar defects normal to the long axis of the needles. The concept of "low

  1. Enhanced magnetoresistance induced by oxygen deficiency in La{sub 0.4}Ca{sub 0.6}MnO{sub 3-δ} oxides

    SciTech Connect

    Triki, M. Dhahri, E.; Hlil, E. K.; Garden, J. L.

    2014-03-14

    We report electrical features and magnetoresistance behavior of the oxygen deficient La{sub 0.4}Ca{sub 0.6}MnO{sub 3-δ} perovskites (δ = 0, 0.15, and 0.2). These samples will be referred to as S0, S15, and S20, respectively. The dependence of electrical transport on temperature and magnetic field is systematically investigated between 2 K and 400 K in magnetic field ranging up to 5 T. The parent compound shows a stable charge ordering/antiferromagnetic state with a semiconductor-like behavior in all considered temperature range. The variable range hopping and thermally activated hopping models are found to fit well with the electrical resistivity data at low and high temperatures, respectively. Oxygen deficiency tends to weaken the charge ordering and induce ferromagnetism and metallicity at low temperature. Metal insulator transition appears at higher fields for lower oxygen deficit (S15 sample) and without field for the S20 sample. The resistivity data for S15 sample are discussed in the framework of the variable-range hopping model. Abnormal transport properties were observed in the S20 sample, characterized by the double metal-insulator transitions and low minimum behavior. These results are discussed in terms of phenomenological percolation model, based on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. While the parent compound shows no magnetoresistance, a large magnetoresistance is observed in the deficient samples at low temperature reaching 90% and 75% at 2 T for S15 and S20 samples, respectively. Noticeably, these values reached 98% and 91% at 5 T. The appearance of colossal magnetoresistance is attributed to the spin dependent hopping between spin clusters and/or ferromagnetic domains.

  2. Nonlocal quartic interactions and universality classes in perovskite manganites.

    PubMed

    Singh, Rohit; Dutta, Kishore; Nandy, Malay K

    2015-07-01

    A modified Ginzburg-Landau model with a screened nonlocal interaction in the quartic term is treated via Wilson's renormalization-group scheme at one-loop order to explore the critical behavior of the paramagnetic-to-ferromagnetic phase transition in perovskite manganites. We find the Fisher exponent η to be O(ε) and the correlation exponent to be ν=1/2+O(ε) through epsilon expansion in the parameter ε=d(c)-d, where d is the space dimension, d(c)=4+2σ is the upper critical dimension, and σ is a parameter coming from the nonlocal interaction in the model Hamiltonian. The ensuing critical exponents in three dimensions for different values of σ compare well with various existing experimental estimates for perovskite manganites with various doping levels. This suggests that the nonlocal model Hamiltonian contains a wide variety of such universality classes. PMID:26274140

  3. Correlation Between Microstructure and Ageing of Iron Manganite Thermistors

    NASA Astrophysics Data System (ADS)

    Battault, T.; Legros, R.; Brieu, M.; Coudere, J. J.; Bernard, L.; Rousset, A.

    1997-05-01

    Negative Temperature Coefficient (NTC) thermistors made of spinel structure transition metal manganites usually display ageing phenomena under thermal stress. Their resistance drift depends on their composition, crystal structure (cubic or tetragonal) and heat treatments. We have previously shown in iron manganite thermistors, Mn{3-x}FexO4 (with 0 leq x leq 1.51), that the ageing is due to the migration of Fe^{3+} and Mn^{2+} ions between tetrahedral and octahedral sites of the spinel structure. Iron manganites were investigated by Transmission Electron Microscopy (TEM) in order to relate microstructure to electrical stability. For iron manganites with iron content x leq 0.78, two dimensional defects result in a domain microstructure (microtwins). As x increases and exceeds 0.78, the domain structure gradually vanishes and transforms into a tweed microstructure (x = 1.05) and, for x > 1.30, no bidimensional defects are observed. Thus it is suggested that the microstructural disturbance plays an important role in the kinetics of the ion migration during the ageing of the studied ceramics. Les thermistances à Coefficient de Température Négatif (CTN) élaborées à partir de manganites de métaux de transition à structure spinelle présentent, sous contrainte thermique, le phénomène de vieillissement. La dérive de leur résistance dépend de la composition chimique, de la structure cristallographique (cubique ou quadratique) et des traitements thermiques. Précédemment, nous avons montré, pour les thermistances à base de manganites de fer de composition Mn{3-x}FexO4 (avec 0 leq x leq 1,51), que le vieillissement est dû à une migration des ions Fe^{3+} et Mn^{2+} entre les sites tétraédriques et octaédriques de la structure spinelle. Une étude des manganites de fer a été réalisée par Microscopie Électronique à Transmission (MET) afin de relier la microstructure à la stabilité électrique. Pour les manganites de fer ayant une teneur en fer x leq

  4. Anisotropic magnetoresistance in an antiferromagnetic semiconductor.

    PubMed

    Fina, I; Marti, X; Yi, D; Liu, J; Chu, J H; Rayan-Serrao, C; Suresha, S; Shick, A B; Zelezný, J; Jungwirth, T; Fontcuberta, J; Ramesh, R

    2014-01-01

    Recent studies in devices comprising metal antiferromagnets have demonstrated the feasibility of a novel spintronic concept in which spin-dependent phenomena are governed by an antiferromagnet instead of a ferromagnet. Here we report experimental observation of the anisotropic magnetoresistance in an antiferromagnetic semiconductor Sr2IrO4. Based on ab initio calculations, we associate the origin of the phenomenon with large anisotropies in the relativistic electronic structure. The antiferromagnet film is exchange coupled to a ferromagnet, which allows us to reorient the antiferromagnet spin-axis in applied magnetic fields via the exchange spring effect. We demonstrate that the semiconducting nature of our AFM electrode allows us to perform anisotropic magnetoresistance measurements in the current-perpendicular-to-plane geometry without introducing a tunnel barrier into the stack. Temperature-dependent measurements of the resistance and anisotropic magnetoresistance highlight the large, entangled tunabilities of the ordinary charge and spin-dependent transport in a spintronic device utilizing the antiferromagnet semiconductor.

  5. Spin Hall magnetoresistance at high temperatures

    SciTech Connect

    Uchida, Ken-ichi; Qiu, Zhiyong; Kikkawa, Takashi; Iguchi, Ryo; Saitoh, Eiji

    2015-02-02

    The temperature dependence of spin Hall magnetoresistance (SMR) in Pt/Y{sub 3}Fe{sub 5}O{sub 12} (YIG) bilayer films has been investigated in a high temperature range from room temperature to near the Curie temperature of YIG. The experimental results show that the magnitude of the magnetoresistance ratio induced by the SMR monotonically decreases with increasing the temperature and almost disappears near the Curie temperature. We found that, near the Curie temperature, the temperature dependence of the SMR in the Pt/YIG film is steeper than that of a magnetization curve of the YIG; the critical exponent of the magnetoresistance ratio is estimated to be 0.9. This critical behavior of the SMR is attributed mainly to the temperature dependence of the spin-mixing conductance at the Pt/YIG interface.

  6. New magnetic structures in novel and conventional manganites

    NASA Astrophysics Data System (ADS)

    Daoud-Aladine, Aziz; Rodríguez-Carvajal, Juan; Perca, Cristian; Pinsard-Gaudart, Loreynne

    2011-03-01

    The determination of the magnetic structures of manganites has always been at the root of their fundamental understanding. We studied the magnetic structures of half-doped charge ordered manganites that are either show the prototype CE-type magnetic structure (Pr 1/2 Ca 1/2 Mn O3), or variants of this order (YBaMn 2 O6 and Pr 0.6 Ca 0.4 Mn O3) with neutron diffraction. The study of Pr 1/2 Ca 1/2 Mn O3 (ILL, France) is the first ever done on a single crystal and it essentially confirms the pioneering picture, whereas the NPD studies of YBaMn 2 O6 (PSI, Switzerland) and Pr 0.6 Ca 0.4 Mn O3 (ISIS, UK), give two unprecedented results. The YBaMn 2 O6 magnetic structure corroborates the hotly debated ordering of Zener Polarons, and high resolution NPD data evidence a new spin reorientation transition around T ~ 20 K far below its TN ~ 170 K in Pr 0.6 Ca 0.4 Mn O3 that has so far only been vaguely observed. We will discuss the consequences that these results have on the still hotly debated understanding of the connection between charge/orbital and spin orderings in the manganites.

  7. Electroresistance and field effect studies on manganite based heterostructure

    SciTech Connect

    Solanki, P. S.; Khachar, Uma; Vagadia, Megha; Ravalia, Ashish; Katba, Savan; Kuberkar, D. G.

    2015-04-14

    Electronic properties of manganites are significantly important for various spintronic applications such as microelectronics, magnetic data storage, communication technologies, and memory devices. Influence of applied electric field on the room temperature charge transport in ZnO/La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrNb{sub 0.002}Ti{sub 0.998}O{sub 3} (SNTO) heterostructure has been investigated using field effect studies. Large negative and positive electroresistance has been observed in heterostructure under various possible circuit geometries. Field effect studies have been carried out using three different circuit geometries, namely: (i) ZnO as a control electrode (E{sub LZ}), (ii) SNTO as a control electrode (E{sub LS}), and (iii) shorted ZnO and SNTO as control electrodes (E{sub LZS}). For this, channel electric field (E{sub CH}) dependent variation in channel resistance (R{sub C}) (of manganite channel) and I-V (across manganite channel) under various control fields (E{sub C}) have been studied. Variation in barrier height (Φ{sub B}) with control field (E{sub C}) for different geometries has been discussed.

  8. Crossed Andreev reflection-induced magnetoresistance.

    PubMed

    Giazotto, Francesco; Taddei, Fabio; Beltram, Fabio; Fazio, Rosario

    2006-08-25

    We show that very large negative magnetoresistance can be obtained in magnetic trilayers in a current-in-plane geometry owing to the existence of crossed Andreev reflection. This spin valve consists of a thin superconducting film sandwiched between two ferromagnetic layers whose magnetization is allowed to be either parallelly or antiparallelly aligned. For a suitable choice of structure parameters and nearly fully spin-polarized ferromagnets, the magnetoresistance can exceed -80%. Our results are relevant for the design and implementation of spintronic devices exploiting ferromagnet-superconductor structures. PMID:17026324

  9. Monte Carlo calculations of the magnetoresistance in magnetic multilayer structures with giant magnetoresistance effects

    NASA Astrophysics Data System (ADS)

    Prudnikov, V. V.; Prudnikov, P. V.; Romanovskiy, D. E.

    2016-06-01

    A Monte Carlo study of trilayer and spin-valve magnetic structures with giant magnetoresistance effects is carried out. The anisotropic Heisenberg model is used for description of magnetic properties of ultrathin ferromagnetic films forming these structures. The temperature and magnetic field dependences of magnetic characteristics are considered for ferromagnetic and antiferromagnetic configurations of these multilayer structures. The methodology for determination of the magnetoresistance by the Monte Carlo method is introduced; this permits us to calculate the magnetoresistance of multilayer structures for different thicknesses of the ferromagnetic films. The calculated temperature dependence of the magnetoresistance agrees very well with the experimental results measured for the Fe(0 0 1)-Cr(0 0 1) multilayer structure and CFAS-Ag-CFAS-IrMn spin-valve structure based on the half-metallic Heusler alloy Co2FeAl0.5Si0.5.

  10. A Self-Emissivity-Controlling Radiator for Spacecrafts by Making Use of a Metal-Insulator Transition in Magnetoresistive Manganites

    NASA Astrophysics Data System (ADS)

    Tanaka, Kohsuke; Tachikawa, Sumitaka; Kuwahara, Hideki; Okawa, Mario; Saitoh, Tomohiko

    A self-emissivity-controlling radiator named SRD (Smart Radiation Device) is one of the next generation thermal control materials for spacecrafts. It is a light ceramic tile that changes its infrared emissivity according to its own Temperature (T). This radiation property keeps the T and decreases the heater power of spacecraft. In order to improve the radiation property of SRD, we have studied various compositions. In this paper, we discuss how we can design an improved SRD and report the results of our compositional survey.

  11. Effect of electronic reconstruction on cuprate-manganite spin switches.

    SciTech Connect

    Liu, Y.; Visani, C.; Nemes, N. M.; Fitzsimmons, M. R.; Zhu, L. Y.; Tornos, J.; Zhernenkov, M.; Hoffmann, A.; Leon, C.; Santamaria, J.; te Velthuis, S. G. E.

    2012-01-01

    We examine the anomalous inverse spin switch behavior in La{sub 0.7}Ca{sub 0.3}MnO{sub 3}(LCMO)/YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO)/LCMO trilayers by combined transport studies and polarized neutron reflectometry. Measuring magnetization profiles and magnetoresistance in an in-plane rotating magnetic field, we prove that, contrary to many accepted theoretical scenarios, the relative orientation between the two LCMO's magnetizations is not sufficient to determine the magnetoresistance. Rather the field dependence of magnetoresistance is explained by the interplay between the applied magnetic field and the (exponential tail of the) induced exchange field in YBCO, the latter originating from the electronic reconstruction at the LCMO/YBCO interfaces.

  12. Spectral origin of the colossal magnetodielectric effect in multiferroic DyMn2O5

    NASA Astrophysics Data System (ADS)

    Sushkov, A. B.; Kant, Ch.; Schiebl, M.; Shuvaev, A. M.; Pimenov, Anna; Pimenov, Andrei; Lorenz, Bernd; Park, S.; Cheong, S.-W.; Mostovoy, Maxim; Drew, H. D.

    2014-08-01

    The origin of the colossal magnetodielectric (CMD) effect in DyMn2O5 [N. Hur et al., Phys. Rev. Lett. 93, 107207 (2004), 10.1103/PhysRevLett.93.107207] has been an outstanding question in multiferroics. Here, we report the activation of the electric dipole mode at 4-5 cm-1 in an applied magnetic field, which fully accounts for the CMD effect. We examine two alternative explanations of this mode: an electromagnon and transitions between f-electron levels of Dy3+ ions. The experimental and theoretical evidence supports an electromagnon origin of the CMD effect.

  13. Origin of Colossal Ionic Conductivity in Oxide Multilayers: Interface Induced Sublattice Disorder

    SciTech Connect

    Pennycook, Timothy J; Beck, Matthew; Varga, Kalman; Varela del Arco, Maria; Pennycook, Stephen J; Pantelides, Sokrates T

    2010-01-01

    Oxide ionic conductors typically operate at high temperatures, which limits their usefulness. Colossal room-temperature ionic conductivity was recently discovered in multilayers of yttria-stabilized zirconia (YSZ) and SrTiO3. Here we report density-functional calculations that trace the origin of the effect to a combination of lattice-mismatch strain and O-sublattice incompatibility. Strain alone in bulk YSZ enhances O mobility at high temperatures by inducing extreme O disorder. In multilayer structures, O-sublattice incompatibility causes the same extreme disorder at room temperature.

  14. Crystal structure and physicochemical properties of doped lanthanum manganites

    NASA Astrophysics Data System (ADS)

    Aksenova, T. V.; Gavrilova, L. Ya.; Cherepanov, V. A.

    2012-12-01

    Substituted lanthanum-strontium manganites La0.7Sr0.3Mn0.9Me0.1O3 ± δ (Me = Ti, Cr, Fe, and Cu) are obtained by standard ceramic and glycerin-nitrate techniques. High-temperature powder X-ray diffraction is employed to study the crystal structure of La0.7Sr0.3Mn0.9Me0.1O3 ± δ oxides. It is shown that in the range 298-1023 K in air, La0.7Sr0.3Mn0.9Me0.103 ± δ manganites crystallized in an orthorhombic cell (space group R-3c). The isobaric temperature dependences of unit cell parameters are determined. Thermal expansion coefficients are calculated for La0.7Sr0.3Mn0.9Me0.103 ± δ oxides. The conductivity of La0.7Sr0.3Mn0.9Me0.103 ± δ is studied as a function of temperature in the range 500 K ≤ T ≤ 1200 K in air. It is shown that substituting 3 d metal for manganese considerably lowers the conductivity of basic La0.7Sr0.3Mn0.9O3 ± δ. The chemical stability of iron-substituted manganite La0.7Sr0.3Mn0.9Fe0.1O3 ± δ is studied with respect to the electrolyte material.

  15. Colossal enhancement of the Seebeck coefficient in FeSb2 driven by nearly ballistic phonons

    NASA Astrophysics Data System (ADS)

    Takahashi, Hidefumi; Okazaki, Ryuji; Taniguchi, Hiroki; Terasaki, Ichiro

    2015-03-01

    An unusually large S of - 45 mV/K (at 10 K) was discovered in FeSb2 single crystal, which prompted extensive investigations into its physical origin [A. Bentien et al ., EPL 80, 17008 (2007).] This compound has a small energy gap Δ ~ 5 meV, which may be caused by strong correlations of Fe 3d-electrons, as observed with Kondo insulators, and the colossally large S may be attributed to this unique band structure near the Fermi energy. However, the exceptional value of S has not been clearly explained by electron correlations, suggesting an additional contribution such as the non-equilibrium phonon-drag effect [H. Takahashi et al ., JPSJ 80, 054708 (2011)., H. Takahashi et al ., PRB 84, 205215 (2011)., and H. Takahashi et al ., PRB 88, 165205 (2013).]. Here, we report on the direct investigation of this effect by measuring the transport properties of three samples with cross sections ranging from 250 × 245 μm2 to 80 × 160 μm2. S and κ show a significant size effect, indicating that nearly ballistic phonons, which have a long mean free path relative to the sample dimensions, are responsible for the colossal S.

  16. DisClose: Discovering Colossal Closed Itemsets via a Memory Efficient Compact Row-Tree

    SciTech Connect

    Zulkurnain, Nurul F.; Keane, John A.; Haglin, David J.

    2013-02-01

    Itemset mining has recently focused on discovery of frequent itemsets from high-dimensional datasets with relatively few rows and a larger number of items. With exponentially in-creasing running time as average row length increases, mining such datasets renders most conventional algorithms impracti-cal. Unfortunately, large cardinality closed itemsets are likely to be more informative than small cardinality closed itemsets in this type of dataset. This paper proposes an approach, called DisClose, to extract large cardinality (colossal) closed itemsets from high-dimensional datasets. The approach relies on a memory-efficient Compact Row-Tree data structure to represent itemsets during the search process. The search strategy explores the transposed representation of the dataset. Large cardinality itemsets are enumerated first followed by smaller ones. In addition, we utilize a minimum cardinality threshold to further reduce the search space. Experimental result shows that DisClose can complete the extraction of colossal closed itemsets in the considered dataset, even for low support thresholds. The algorithm immediately discovers closed itemsets without needing to check if each new closed itemset has previously been found.

  17. Colossal resistivity with diminished tangent loss in Zn-Ni ferrite nanoparticles

    NASA Astrophysics Data System (ADS)

    Younas, M.; Atif, M.; Nadeem, M.; Siddique, M.; Idrees, M.; Grossinger, R.

    2011-08-01

    We have investigated the electrical and magnetic response of the sol-gel synthesized ZnxNi1-xFe2O4 (x = 0.0, 0.5 and 1) nanoparticles. The ratio of A-site sextet intensity to that of B-site sextet is featured in terms of divergence in coordination of Fe3+ ions from four-fold (A-site) to six-fold (B-site). Canted spin structure and weakening of Fe3+(A)-Fe3+(B) interactions at the surface of the nanoparticles assign the reduced value of room temperature magnetization in these nanoparticles. Shift of the blocking temperature with Zn content is ascribed to the change in the magnetic anisotropy. Colossal resistivity and reduced dielectric constant are discussed on the basis of dangling bond, superparamagnetic character, canted spin structure and polarizability of the cations. Diminished tangent loss is stipulated in terms of decrease in magnetocrystalline anisotropy and collapse of long-range magnetic order. We report colossal resistivity (i.e. 3.15 × 109 Ω cm), reduced dielectric constant (3.97) and diminished tangent loss (0.07) for Ni0.5Zn0.5Fe2O4 nanoparticles.

  18. Driving magnetic order in a manganite by ultrafast lattice excitation.

    SciTech Connect

    Forst, M.; Tobey, R. I.; Wall, S.; Bromberger, H.; Khanna, V.; Cavalieri, A. L.; Chuang, Y.-D.; Lee, W. S.; Moore, R.; Schlotter, W. F.; Turner, J. J.; Krupin, O.; Trigo, M.; Zheng, H.; Mitchell, J. F.; Dhesi, S. S.; Hill, J. P.; Cavalleri, A.

    2011-01-01

    Femtosecond midinfrared pulses are used to directly excite the lattice of the single-layer manganite La{sub 0.5}Sr{sub 1.5}MnO{sub 4}. Magnetic and orbital orders, as measured by femtosecond resonant soft x-ray diffraction with an x-ray free-electron laser, are reduced within a few picoseconds. This effect is interpreted as a displacive exchange quench, a prompt shift in the equilibrium value of the magnetic- and orbital-order parameters after the lattice has been distorted. Control of magnetism through ultrafast lattice excitation may be of use for high-speed optomagnetism.

  19. Low Temperature Resistive Switching Behavior in a Manganite

    NASA Astrophysics Data System (ADS)

    Salvo, Christopher; Lopez, Melinda; Tsui, Stephen

    2012-02-01

    The development of new nonvolatile memory devices remains an important field of consumer electronics. A possible candidate is bipolar resistive switching, a method by which the resistance of a material changes when a voltage is applied. Although there is a great deal of research on this topic, not much has been done at low temperatures. In this work, we compare the room temperature and low temperature behaviors of switching in a manganite thin film. The data indicates that the switching is suppressed upon cooling to cryogenic temperatures, and the presence of crystalline charge traps is tied to the physical mechanism.

  20. Magnetic anisotropy and lattice distortions in the doped perovskite manganites

    SciTech Connect

    Suzuki, Y.; Hwang, H.Y.; Cheong, S.W.; Dover, R.B. van; Asamitsu, A.; Tokura, Y.

    1998-12-31

    The authors have investigated the magnetic anisotropies of doped manganite materials in epitaxial thin film and single crystal form. Structural characterization, including x-ray diffraction, Rutherford backscattering spectroscopy and atomic force microscopy, indicate that the epitaxial films are single crystalline and have excellent crystallinity. Since lattice distortions greatly affect the magnetic and transport properties of this family of materials, it is not surprising to find the profound effect of strain in films due to the lattice mismatch between the substrate and film. Magnetic anisotropy results of single crystals, subject to no external stress, is compared to those of epitaxial films.

  1. Quantized magnetoresistance in atomic-size contacts.

    PubMed

    Sokolov, Andrei; Zhang, Chunjuan; Tsymbal, Evgeny Y; Redepenning, Jody; Doudin, Bernard

    2007-03-01

    When the dimensions of a metallic conductor are reduced so that they become comparable to the de Broglie wavelengths of the conduction electrons, the absence of scattering results in ballistic electron transport and the conductance becomes quantized. In ferromagnetic metals, the spin angular momentum of the electrons results in spin-dependent conductance quantization and various unusual magnetoresistive phenomena. Theorists have predicted a related phenomenon known as ballistic anisotropic magnetoresistance (BAMR). Here we report the first experimental evidence for BAMR by observing a stepwise variation in the ballistic conductance of cobalt nanocontacts as the direction of an applied magnetic field is varied. Our results show that BAMR can be positive and negative, and exhibits symmetric and asymmetric angular dependences, consistent with theoretical predictions. PMID:18654248

  2. Magnetoresistive system with concentric ferromagnetic asymmetric nanorings

    SciTech Connect

    Avila, J. I. Tumelero, M. A.; Pasa, A. A.; Viegas, A. D. C.

    2015-03-14

    A structure consisting of two concentric asymmetric nanorings, each displaying vortex remanent states, is studied with micromagnetic calculations. By orienting in suitable directions, both the asymmetry of the rings and a uniform magnetic field, the vortices chiralities can be switched from parallel to antiparallel, obtaining in this way the analogue of the ferromagnetic and antiferromagnetic configurations found in bar magnets pairs. Conditions on the thickness of single rings to obtain vortex states, as well as formulas for their remanent magnetization are given. The concentric ring structure enables the creation of magnetoresistive systems comprising the qualities of magnetic nanorings, such as low stray fields and high stability. A possible application is as contacts in spin injection in semiconductors, and estimations obtained here of magnetoresistance change for a cylindrical spin injection based device show significant variations comparable to linear geometries.

  3. Anisotropic giant magnetoresistance in NbSb₂

    DOE PAGESBeta

    Wang, Kefeng; Graf, D.; Li, Lijun; Wang, Limin; Petrovic, C.

    2014-12-05

    We report large transverse magnetoreistance (the magnetoresistant ratio ~ 1.3 × 10⁵% in 2 K and 9 T field, and 4.3 × 10⁶% in 0.4 K and 32 T field, without saturation) and field-induced metal semiconductor-like transition in NbSb₂. Magnetoresistance is significantly suppressed but the metal-semiconductor-like transition persists when the current is along the ac-plane. The sign reversal of the Hall resistivity and Seebeck coefficient in the field, plus the electronic structure reveal the coexistence of a small number of holes with very high mobility and a large number of electrons with low mobility. The large MR is attributed tomore » the change of the Fermi surface induced by the magnetic field in addition to the high mobility metal.« less

  4. Dirac State in Giant Magnetoresistive Materials

    NASA Astrophysics Data System (ADS)

    Wu, Y.; Jo, N. H.; Ochi, M.; Huang, L.; Mou, D.; Kong, T.; Mun, E.; Wang, L.; Lee, Y.; Bud'Ko, S. L.; Canfield, P. C.; Trivedi, N.; Arito, R.; Kaminski, A.

    We use ultrahigh resolution, tunable, vacuum ultraviolet laser-based angle-resolved photoemission spectroscopy (ARPES) to study the electronic properties of materials that recently were discovered to display titanic magnetoresistance. We find that that several of these materials have Dirac-like features in their band structure. In some materials those features are ``ordinary'' Dirac cones, while in others the linear Dirac dispersion of two crossing bands forms a linear object in 3D momentum space. Our observation poses an important question about the role of Dirac dispersion in the unusually high, non-saturating magnetoresistance of these materials. Research was supported by the US DOE, Office of Basic Energy Sciences under Contract No. DE-AC02-07CH11358; Gordon and Betty Moore Foundation EPiQS Initiative (Grant No. GBMF4411); CEM, a NSF MRSEC, under Grant No. DMR-1420451.

  5. Magnetoresistance of Rippled Graphene in a Parallel Magnetic Field

    NASA Astrophysics Data System (ADS)

    Wakabayashi, Junichi; Sano, Tomoya

    2011-12-01

    The magnetoresistance of a monolayer graphene in a random magnetic field(RMF) with zero mean has been investigated. The RMF was produced by applying a magnetic field parallel to the graphene plane utilizing ripples. The magnetoresistance has shown the same magnetic field dependence and, unexpectedly, the same carrier density dependence as the conventional two-dimensional electron systems in random magnetic fields. The relation between the characteristic length of ripples and the magnitude of the magnetoresistance is discussed.

  6. Ultra-Sensitive Magnetoresistive Displacement Sensing Device

    NASA Technical Reports Server (NTRS)

    Olivas, John D. (Inventor); Lairson, Bruce M. (Inventor); Ramesham, Rajeshuni (Inventor)

    2003-01-01

    An ultrasensitive displacement sensing device for use in accelerometers, pressure gauges, temperature transducers, and the like, comprises a sputter deposited, multilayer, magnetoresistive field sensor with a variable electrical resistance based on an imposed magnetic field. The device detects displacement by sensing changes in the local magnetic field about the magnetoresistive field sensor caused by the displacement of a hard magnetic film on a movable microstructure. The microstructure, which may be a cantilever, membrane, bridge, or other microelement, moves under the influence of an acceleration a known displacement predicted by the configuration and materials selected, and the resulting change in the electrical resistance of the MR sensor can be used to calculate the displacement. Using a micromachining approach, very thin silicon and silicon nitride membranes are fabricated in one preferred embodiment by means of anisotropic etching of silicon wafers. Other approaches include reactive ion etching of silicon on insulator (SOI), or Low Pressure Chemical Vapor Deposition of silicon nitride films over silicon substrates. The device is found to be improved with the use of giant magnetoresistive elements to detect changes in the local magnetic field.

  7. Giant magnetoresistance in organic spin-valves.

    PubMed

    Xiong, Z H; Wu, Di; Vardeny, Z Valy; Shi, Jing

    2004-02-26

    A spin valve is a layered structure of magnetic and non-magnetic (spacer) materials whose electrical resistance depends on the spin state of electrons passing through the device and so can be controlled by an external magnetic field. The discoveries of giant magnetoresistance and tunnelling magnetoresistance in metallic spin valves have revolutionized applications such as magnetic recording and memory, and launched the new field of spin electronics--'spintronics'. Intense research efforts are now devoted to extending these spin-dependent effects to semiconductor materials. But while there have been noteworthy advances in spin injection and detection using inorganic semiconductors, spin-valve devices with semiconducting spacers have not yet been demonstrated. pi-conjugated organic semiconductors may offer a promising alternative approach to semiconductor spintronics, by virtue of their relatively strong electron-phonon coupling and large spin coherence. Here we report the injection, transport and detection of spin-polarized carriers using an organic semiconductor as the spacer layer in a spin-valve structure, yielding low-temperature giant magnetoresistance effects as large as 40 per cent. PMID:14985756

  8. Emerging single-phase state in small manganite nanodisks.

    PubMed

    Shao, Jian; Liu, Hao; Zhang, Kai; Yu, Yang; Yu, Weichao; Lin, Hanxuan; Niu, Jiebin; Du, Kai; Kou, Yunfang; Wei, Wengang; Lan, Fanli; Zhu, Yinyan; Wang, Wenbin; Xiao, Jiang; Yin, Lifeng; Plummer, E W; Shen, Jian

    2016-08-16

    In complex oxides systems such as manganites, electronic phase separation (EPS), a consequence of strong electronic correlations, dictates the exotic electrical and magnetic properties of these materials. A fundamental yet unresolved issue is how EPS responds to spatial confinement; will EPS just scale with size of an object, or will the one of the phases be pinned? Understanding this behavior is critical for future oxides electronics and spintronics because scaling down of the system is unavoidable for these applications. In this work, we use La0.325Pr0.3Ca0.375MnO3 (LPCMO) single crystalline disks to study the effect of spatial confinement on EPS. The EPS state featuring coexistence of ferromagnetic metallic and charge order insulating phases appears to be the low-temperature ground state in bulk, thin films, and large disks, a previously unidentified ground state (i.e., a single ferromagnetic phase state emerges in smaller disks). The critical size is between 500 nm and 800 nm, which is similar to the characteristic length scale of EPS in the LPCMO system. The ability to create a pure ferromagnetic phase in manganite nanodisks is highly desirable for spintronic applications. PMID:27482108

  9. Chemically induced Jahn-Teller ordering on manganite surfaces.

    PubMed

    Gai, Zheng; Lin, Wenzhi; Burton, J D; Fuchigami, K; Snijders, P C; Ward, T Z; Tsymbal, Evgeny Y; Shen, J; Jesse, Stephen; Kalinin, Sergei V; Baddorf, Arthur P

    2014-01-01

    Physical and electrochemical phenomena at the surfaces of transition metal oxides and their coupling to local functionality remains one of the enigmas of condensed matter physics. Understanding the emergent physical phenomena at surfaces requires the capability to probe the local composition, map order parameter fields and establish their coupling to electronic properties. Here we demonstrate that measuring the sub-30-pm displacements of atoms from high-symmetry positions in the atomically resolved scanning tunnelling microscopy allows the physical order parameter fields to be visualized in real space on the single-atom level. Here, this local crystallographic analysis is applied to the in-situ-grown manganite surfaces. In particular, using direct bond-angle mapping we report direct observation of structural domains on manganite surfaces, and trace their origin to surface-chemistry-induced stabilization of ordered Jahn-Teller displacements. Density functional calculations provide insight into the intriguing interplay between the various degrees of freedom now resolved on the atomic level. PMID:25058540

  10. Emerging single-phase state in small manganite nanodisks

    NASA Astrophysics Data System (ADS)

    Shao, Jian; Liu, Hao; Zhang, Kai; Yu, Yang; Yu, Weichao; Lin, Hanxuan; Niu, Jiebin; Du, Kai; Kou, Yunfang; Wei, Wengang; Lan, Fanli; Zhu, Yinyan; Wang, Wenbin; Xiao, Jiang; Yin, Lifeng; Plummer, E. W.; Shen, Jian

    2016-08-01

    In complex oxides systems such as manganites, electronic phase separation (EPS), a consequence of strong electronic correlations, dictates the exotic electrical and magnetic properties of these materials. A fundamental yet unresolved issue is how EPS responds to spatial confinement; will EPS just scale with size of an object, or will the one of the phases be pinned? Understanding this behavior is critical for future oxides electronics and spintronics because scaling down of the system is unavoidable for these applications. In this work, we use La0.325Pr0.3Ca0.375MnO3 (LPCMO) single crystalline disks to study the effect of spatial confinement on EPS. The EPS state featuring coexistence of ferromagnetic metallic and charge order insulating phases appears to be the low-temperature ground state in bulk, thin films, and large disks, a previously unidentified ground state (i.e., a single ferromagnetic phase state emerges in smaller disks). The critical size is between 500 nm and 800 nm, which is similar to the characteristic length scale of EPS in the LPCMO system. The ability to create a pure ferromagnetic phase in manganite nanodisks is highly desirable for spintronic applications.

  11. Emerging single-phase state in small manganite nanodisks

    PubMed Central

    Shao, Jian; Liu, Hao; Zhang, Kai; Yu, Yang; Yu, Weichao; Lin, Hanxuan; Niu, Jiebin; Du, Kai; Kou, Yunfang; Wei, Wengang; Lan, Fanli; Zhu, Yinyan; Wang, Wenbin; Xiao, Jiang; Yin, Lifeng; Plummer, E. W.; Shen, Jian

    2016-01-01

    In complex oxides systems such as manganites, electronic phase separation (EPS), a consequence of strong electronic correlations, dictates the exotic electrical and magnetic properties of these materials. A fundamental yet unresolved issue is how EPS responds to spatial confinement; will EPS just scale with size of an object, or will the one of the phases be pinned? Understanding this behavior is critical for future oxides electronics and spintronics because scaling down of the system is unavoidable for these applications. In this work, we use La0.325Pr0.3Ca0.375MnO3 (LPCMO) single crystalline disks to study the effect of spatial confinement on EPS. The EPS state featuring coexistence of ferromagnetic metallic and charge order insulating phases appears to be the low-temperature ground state in bulk, thin films, and large disks, a previously unidentified ground state (i.e., a single ferromagnetic phase state emerges in smaller disks). The critical size is between 500 nm and 800 nm, which is similar to the characteristic length scale of EPS in the LPCMO system. The ability to create a pure ferromagnetic phase in manganite nanodisks is highly desirable for spintronic applications. PMID:27482108

  12. Photon-induced phase transitions of individual electronic phase separated domains in manganites strips

    NASA Astrophysics Data System (ADS)

    Lin, Hanxuan; Zhang, Kai; Liu, Hao; Miao, Tian; Yu, Yang; Yin, Lifeng; Shen, Jian

    Effective photosensors should be built on materials whose properties depend sensitively on light. Manganites are one of the candidates, where light can trigger resistivity change by several orders of magnitude. Such dramatic change is often associated with photoinduced phase transitions of electronic phase separated (EPS) domains in manganites. Previous studies of the light effect all use macroscopic manganite samples, which consist of large numbers of EPS domains smearing out the photon-induced phase transitions. Here, we observe the signature of individual domains' photoinduced phase transition by macroscopic transport measurement of spatially confined manganites strips. Pronounced photon-induced resistivity jumps emerge in the warming process, which reveals the dynamics of the phase transitions of individual EPS domains upon interaction with light. Magnetic force microscope (MFM) has been used to investigate the mechanism of those resistivity jumps. Supervisor.

  13. Influence of magnetic field on electric-field-induced local polar states in manganites

    SciTech Connect

    Mamin, R. F.; Strle, J.; Kabanov, V. V.; Kranjec, A.; Borovsak, M.; Mihailovic, D.; Bizyaev, D. A.; Yusupov, R. V.; Bukharaev, A. A.

    2015-11-09

    It is shown that creation of local charged states at the surface of the lanthanum-strontium manganite single crystals by means of bias application via a conducting atomic force microscope tip is strongly affected by magnetic field. Both a charge and a size of created structures increase significantly on application of the magnetic field during the induction. We argue that the observed phenomenon originates from a known tendency of manganites toward charge segregation and its intimate relation to magnetic ordering.

  14. Magnetotransport and thermoelectric power of La 2/3Ba 1/3Mn 1- xSb xO 3 ( x=0-0.05) manganite perovskites

    NASA Astrophysics Data System (ADS)

    Sen, Vikram; Panwar, Neeraj; Rao, Ashok; Hsu, C. K.; Kuo, Y. K.; Agarwal, S. K.

    2008-01-01

    The effect of Sb +5-doping on the magnetotransport and thermoelectric power of La 2/3Ba 1/3Mn 1- xSb xO 3 ( x=0-0.05) perovskite manganites is reported here. Two insulator-metal (I-M) transitions have been observed in the electrical resistivity-temperature ρ(T) behavior of the undoped sample La 2/3Ba 1/3MnO 3. Both the transitions (at T and T) shift to lower temperatures with doping but to a different extent. T decreases faster while T remains almost invariant up to 3% of doping and then decreases. With increasing Sb +5 content, the intrinsic magnetoresistance (MR at T) gets suppressed whereas the extrinsic magnetoresistance at lower temperatures gets enhanced. The thermoelectric behavior S(T) of the pristine sample shows a peak at T while for the doped samples the peak gets suppressed. All the samples exhibit a crossover in their S(T) behavior from positive to negative at a temperature T∗, indicating that the dominant carrier in these compounds changes from hole to electron above T∗. Transport behavior above T (the paramagnetic insulating region) is explained on the basis of the small polaron hopping model while the electron-magnon scattering process has been invoked to explain the thermoelectric power and electrical resistivity behavior in the ferromagnetic regime.

  15. Colossal dielectric constant and relaxation behaviors in Pr:SrTiO{sub 3} ceramics

    SciTech Connect

    Liu Cheng; Liu Peng; Zhou Jianping; Su Lina; Cao Lei; He Ying; Zhang Huaiwu

    2010-05-15

    Sr{sub 1-x}Pr{sub x}TiO{sub 3} ceramics (0.00{<=}x{<=}0.03) were prepared by a traditional solid-state reaction method. Two relaxation processes (marked as A and B) of the Sr{sub 0.09}Pr{sub 0.01}TiO{sub 3} ceramics were investigated by analyzing the E{sub a} values obtained from the Arrhenius law. Colossal dielectric constant (CDC) was first obtained in Sr{sub 0.09}Pr{sub 0.01}TiO{sub 3} ceramics, whose permittivity was up to 3000 (1 kHz, room temperature), greater than that of pure SrTiO{sub 3} ceramics and samples with more Pr addition (x=0.02 and 0.03). This CDC behavior was related to the internal barrier layer capacitance mechanism.

  16. Coexistence of colossal stress and texture gradients in sputter deposited nanocrystalline ultra-thin metal films

    SciTech Connect

    Kuru, Yener; Welzel, Udo; Mittemeijer, Eric J.

    2014-12-01

    This paper demonstrates experimentally that ultra-thin, nanocrystalline films can exhibit coexisting colossal stress and texture depth gradients. Their quantitative determination is possible by X-ray diffraction experiments. Whereas a uniform texture by itself is known to generally cause curvature in so-called sin{sup 2}ψ plots, it is shown that the combined action of texture and stress gradients provides a separate source of curvature in sin{sup 2}ψ plots (i.e., even in cases where a uniform texture does not induce such curvature). On this basis, the texture and stress depth profiles of a nanocrystalline, ultra-thin (50 nm) tungsten film could be determined.

  17. Dramatically decreased magnetoresistance in non-stoichiometric WTe2 crystals

    NASA Astrophysics Data System (ADS)

    Lv, Yang-Yang; Zhang, Bin-Bin; Li, Xiao; Pang, Bin; Zhang, Fan; Lin, Da-Jun; Zhou, Jian; Yao, Shu-Hua; Chen, Y. B.; Zhang, Shan-Tao; Lu, Minghui; Liu, Zhongkai; Chen, Yulin; Chen, Yan-Feng

    2016-05-01

    Recently, the layered semimetal WTe2 has attracted renewed interest owing to the observation of a non-saturating and giant positive magnetoresistance (~105%), which can be useful for magnetic memory and spintronic devices. However, the underlying mechanisms of the giant magnetoresistance are still under hot debate. Herein, we grew the stoichiometric and non-stoichiometric WTe2 crystals to test the robustness of giant magnetoresistance. The stoichiometric WTe2 crystals have magnetoresistance as large as 3100% at 2 K and 9-Tesla magnetic field. However, only 71% and 13% magnetoresistance in the most non-stoichiometry (WTe1.80) and the highest Mo isovalent substitution samples (W0.7Mo0.3Te2) are observed, respectively. Analysis of the magnetic-field dependent magnetoresistance of non-stoichiometric WTe2 crystals substantiates that both the large electron-hole concentration asymmetry and decreased carrier mobility, induced by non-stoichiometry, synergistically lead to the decreased magnetoresistance. This work sheds more light on the origin of giant magnetoresistance observed in WTe2.

  18. Hall effect and magnetoresistivity in the ternary molybdenum sulfides

    NASA Technical Reports Server (NTRS)

    Woollam, J. A.; Haugland, E. J.; Alterovitz, S. A.

    1978-01-01

    The Hall coefficient and magnetoresistance of sputtered films of Cu(x)Mo6S8 and PbMo6S8 have been measured, as well as the magnetoresistance in sintered samples of the same materials. Assuming a single band model, net carrier densities and mean mobilities are determined

  19. Dramatically decreased magnetoresistance in non-stoichiometric WTe2 crystals

    PubMed Central

    Lv, Yang-Yang; Zhang, Bin-Bin; Li, Xiao; Pang, Bin; Zhang, Fan; Lin, Da-Jun; Zhou, Jian; Yao, Shu-Hua; Chen, Y. B.; Zhang, Shan-Tao; Lu, Minghui; Liu, Zhongkai; Chen, Yulin; Chen, Yan-Feng

    2016-01-01

    Recently, the layered semimetal WTe2 has attracted renewed interest owing to the observation of a non-saturating and giant positive magnetoresistance (~105%), which can be useful for magnetic memory and spintronic devices. However, the underlying mechanisms of the giant magnetoresistance are still under hot debate. Herein, we grew the stoichiometric and non-stoichiometric WTe2 crystals to test the robustness of giant magnetoresistance. The stoichiometric WTe2 crystals have magnetoresistance as large as 3100% at 2 K and 9-Tesla magnetic field. However, only 71% and 13% magnetoresistance in the most non-stoichiometry (WTe1.80) and the highest Mo isovalent substitution samples (W0.7Mo0.3Te2) are observed, respectively. Analysis of the magnetic-field dependent magnetoresistance of non-stoichiometric WTe2 crystals substantiates that both the large electron-hole concentration asymmetry and decreased carrier mobility, induced by non-stoichiometry, synergistically lead to the decreased magnetoresistance. This work sheds more light on the origin of giant magnetoresistance observed in WTe2. PMID:27228908

  20. Sign control of magnetoresistance through chemically engineered interfaces.

    PubMed

    Ciudad, David; Gobbi, Marco; Kinane, Christy J; Eich, Marius; Moodera, Jagadeesh S; Hueso, Luis E

    2014-12-01

    Chemically engineered interfaces are shown to produce inversions of the magnetoresistance in spintronic devices including lithium fluoride interlayers. This behavior is explained by the formation of anti-ferromagnetic difluoride layers. By changing the order of deposition of the different materials, the sign of the magnetoresistance can be deterministically controlled both in organic spin valves and in inorganic magnetic tunnel junctions.

  1. Sign control of magnetoresistance through chemically engineered interfaces.

    PubMed

    Ciudad, David; Gobbi, Marco; Kinane, Christy J; Eich, Marius; Moodera, Jagadeesh S; Hueso, Luis E

    2014-12-01

    Chemically engineered interfaces are shown to produce inversions of the magnetoresistance in spintronic devices including lithium fluoride interlayers. This behavior is explained by the formation of anti-ferromagnetic difluoride layers. By changing the order of deposition of the different materials, the sign of the magnetoresistance can be deterministically controlled both in organic spin valves and in inorganic magnetic tunnel junctions. PMID:25339373

  2. Large magnetoresistance in oxide based ferromagnet/superconductor spin switches.

    SciTech Connect

    Pena, V.; Nemes, N.; Visani, C.; Garcia-Barriocanal, J.; Bruno, F.; Arias, D.; Sefrioui, Z.; Leon, C.; te Velthuis, S. G. E.; Hoffmann, A.; Garcia-Hernandez, M.; Santamaria, J.; Materials Science Division; Univ. Complutense de Madrid; Inst. de Ciencia de Materiales de Madrid

    2006-01-01

    We report large magnetoresistance (in excess of 1000%) in ferromagnet / superconductor / ferromagnet structures made of La{sub 0.7}Ca{sub 0.3}MnO{sub 3} and YBa{sub 2}Cu{sub 3}O{sub 7} in the current in plane (CIP) geometry. This magnetoresistance has many of the ingredients of the giant magnetoresistance of metallic superlattices: it is independent on the angle between current and magnetic field, depends on the relative orientation of the magnetization in the ferromagnetic layers, and takes very large values. The origin is enhanced scattering at the F/S interface in the anti parallel configuration of the magnetizations. Furthermore, we examine the dependence of the magnetoresistance effect on the thickness of the superconducting layer, and show that the magnetoresistance dies out for thickness in excess of 30 nm, setting a length scale for the diffusion of spin polarized quasiparticles.

  3. Electrically tuned magnetic order and magnetoresistance in a topological insulator.

    PubMed

    Zhang, Zuocheng; Feng, Xiao; Guo, Minghua; Li, Kang; Zhang, Jinsong; Ou, Yunbo; Feng, Yang; Wang, Lili; Chen, Xi; He, Ke; Ma, Xucun; Xue, Qikun; Wang, Yayu

    2014-09-15

    The interplay between topological protection and broken time reversal symmetry in topological insulators may lead to highly unconventional magnetoresistance behaviour that can find unique applications in magnetic sensing and data storage. However, the magnetoresistance of topological insulators with spontaneously broken time reversal symmetry is still poorly understood. In this work, we investigate the transport properties of a ferromagnetic topological insulator thin film fabricated into a field effect transistor device. We observe a complex evolution of gate-tuned magnetoresistance, which is positive when the Fermi level lies close to the Dirac point but becomes negative at higher energies. This trend is opposite to that expected from the Berry phase picture, but is intimately correlated with the gate-tuned magnetic order. The underlying physics is the competition between the topology-induced weak antilocalization and magnetism-induced negative magnetoresistance. The simultaneous electrical control of magnetic order and magnetoresistance facilitates future topological insulator based spintronic devices.

  4. Comparative Study of Magnetic Ordering and Electrical Transport in Bulk and Nano-Grained Nd0.67Sr0.33MnO3 Manganites

    NASA Astrophysics Data System (ADS)

    Arun, B.; Suneesh, M. V.; Vasundhara, M.

    2016-11-01

    We have prepared bulk and nano-sized Nd0.67Sr0.33MnO3 manganites by solid state and low-temperature mild solgel methods respectively. Both the compounds crystallized into an orthorhombic structure with Pbnm space group confirmed from Rietveld refinement of X-ray powder diffraction patterns. Nano-grained compound shows an average particle size of 22 nm with broad grain size distribution revealed from the Transmission electron micrographs. It appeared that the long range ferromagnetic order becomes unstable upon the reduction of the samples dimension down to nano meter scale. DC magnetization and AC susceptibility results showed frustration of spins in nano-grained compound and thereby it could lead to a cluster glass-like behaviour. Temperature dependence of electrical resistivity under different magnetic fields shows the broad maxima at higher temperatures and a low temperature upturn in both the compounds, however, the latter is more prominent in the nano grained compound. Combination of Kondo effect with electron and phonon interactions govern the low temperature resistivity and a small polaron hopping mechanism dominates at high temperatures for both the compounds. The magnetoresistance is understood by the effect of spin polarized tunneling through the grain boundary. The experimental results revealed that the reduction in particle size influences severely on the magnetic, electrical and magneto transport properties.

  5. Charge, orbital and spin ordering phenomena in the mixed valence manganite (NaMn3+(3))(Mn3+(2)Mn4+(2))O12.

    PubMed

    Prodi, A; Gilioli, E; Gauzzi, A; Licci, F; Marezio, M; Bolzoni, F; Huang, Q; Santoro, A; Lynn, J W

    2004-01-01

    Mixed-valence manganites with the ABO3 perovskite structure display a variety of magnetic and structural transitions, dramatic changes of electrical conductivity and magnetoresistance effects. The physical properties vary with the relative concentration of Mn3+ and Mn4+ in the octahedral corner-sharing network, and the proportion of these two cations is usually changed by doping the trivalent large A cation (for example, La3+) with divalent cations. As the dopant and the original cation have, in general, different sizes, and as they are distributed randomly in the structure, such systems are characterized by local distortions that make it difficult to obtain direct information about their crystallographic and physical properties. On the other hand, the double oxides of formula AA'3Mn4O12 contain a perovskite-like network of oxygen octahedra centred on the Mn cations, coupled with an ordered arrangement of the A and A' cations, whose valences control the proportion of Mn3+ and Mn4+ in the structure. The compound investigated in this work, (NaMn3+(3))(Mn3+(2)Mn4+(2))O12, contains an equal number of Mn3+ and Mn4+ in the octahedral sites. We show that the absence of disorder enables the unambiguous determination of symmetry, the direct observation of full, or nearly full, charge ordering of Mn3+ and Mn4+ in distinct crystallographic sites, and a nearly perfect orbital ordering of the Mn3+ octahedra.

  6. Asymmetric electroresistance of cluster glass state in manganites

    SciTech Connect

    Lourembam, James; Lin, Weinan; Ding, Junfeng; Bera, Ashok; Wu, Tom

    2014-03-31

    We report the electrostatic modulation of transport in strained Pr{sub 0.65}(Ca{sub 0.75}Sr{sub 0.25}){sub 0.35}MnO{sub 3} thin films grown on SrTiO{sub 3} by gating with ionic liquid in electric double layer transistors (EDLT). In such manganite films with strong phase separation, a cluster glass magnetic state emerges at low temperatures with a spin freezing temperature of about 99 K, which is accompanied by the reentrant insulating state with high resistance below 30 K. In the EDLT, we observe bipolar and asymmetric modulation of the channel resistance, as well as an enhanced electroresistance up to 200% at positive gate bias. Our results provide insights on the carrier-density-dependent correlated electron physics of cluster glass systems.

  7. Asymmetric electroresistance of cluster glass state in manganites

    NASA Astrophysics Data System (ADS)

    Lourembam, James; Ding, Junfeng; Bera, Ashok; Lin, Weinan; Wu, Tom

    2014-03-01

    We report the electrostatic modulation of transport in strained Pr0.65(Ca0.75Sr0.25)0.35MnO3 thin films grown on SrTiO3 by gating with ionic liquid in electric double layer transistors (EDLT). In such manganite films with strong phase separation, a cluster glass magnetic state emerges at low temperatures with a spin freezing temperature of about 99 K, which is accompanied by the reentrant insulating state with high resistance below 30 K. In the EDLT, we observe bipolar and asymmetric modulation of the channel resistance, as well as an enhanced electroresistance up to 200% at positive gate bias. Our results provide insights on the carrier-density-dependent correlated electron physics of cluster glass systems.

  8. Magnetoresistive nanosensors: controlling magnetism at the nanoscale.

    PubMed

    Leitao, Diana C; Silva, Ana V; Paz, Elvira; Ferreira, Ricardo; Cardoso, Susana; Freitas, Paulo P

    2016-01-29

    The ability to detect the magnetic fields that surround us has promoted vast technological advances in sensing techniques. Among those, magnetoresistive sensors display an unpaired spatial resolution. Here, we successfully control the linear range of nanometric sensors using an interfacial exchange bias sensing layer coupling. An effective matching of material properties and sensor geometry improves the nanosensor performance, with top sensitivities of 3.7% mT(-1). The experimental results are well supported by 3D micromagnetic and magneto-transport simulations. PMID:26658286

  9. Giant magnetoresistance in organic spin valves

    SciTech Connect

    Sun, Da-Li; Yin, Lifeng; Sun, Chengjun; Guo, Hangwen; Gai, Zheng; Zhang, Xiaoguang; Ward, Thomas Z; Cheng, Zhaohua; Shen, Jian

    2010-01-01

    Interfacial diffusion between magnetic electrodes and organic spacer layers is a serious problem in the organic spintronics which complicates attempts to understand the spin-dependent transport mechanism and hurts the achievement of a desirably high magnetoresistance (MR). We deposit nanodots instead of atoms onto the organic layer using buffer layer assist growth. Spin valves using this method exhibit a sharper interface and a giant MR of up to {approx}300%. Analysis of the current-voltage characteristics indicates that the spin-dependent carrier injection correlates with the observed MR.

  10. Diluted magnetic semiconductor nanowires exhibiting magnetoresistance

    DOEpatents

    Yang, Peidong; Choi, Heonjin; Lee, Sangkwon; He, Rongrui; Zhang, Yanfeng; Kuykendal, Tevye; Pauzauskie, Peter

    2011-08-23

    A method for is disclosed for fabricating diluted magnetic semiconductor (DMS) nanowires by providing a catalyst-coated substrate and subjecting at least a portion of the substrate to a semiconductor, and dopant via chloride-based vapor transport to synthesize the nanowires. Using this novel chloride-based chemical vapor transport process, single crystalline diluted magnetic semiconductor nanowires Ga.sub.1-xMn.sub.xN (x=0.07) were synthesized. The nanowires, which have diameters of .about.10 nm to 100 nm and lengths of up to tens of micrometers, show ferromagnetism with Curie temperature above room temperature, and magnetoresistance up to 250 Kelvin.

  11. Giant magnetoresistance in bilayer graphene nanoflakes

    NASA Astrophysics Data System (ADS)

    Farghadan, Rouhollah; Farekiyan, Marzieh

    2016-09-01

    Coherent spin transport through bilayer graphene (BLG) nanoflakes sandwiched between two electrodes made of single-layer zigzag graphene nanoribbon was investigated by means of Landauer-Buttiker formalism. Application of a magnetic field only on BLG structure as a channel produces a perfect spin polarization in a large energy region. Moreover, the conductance could be strongly modulated by magnetization of the zigzag edge of AB-stacked BLG, and the junction, entirely made of carbon, produces a giant magnetoresistance (GMR) up to 100%. Intestinally, GMR and spin polarization could be tuned by varying BLG width and length. Generally, MR in a AB-stacked BLG strongly increases (decreases) with length (width).

  12. Magnetization and magnetoresistance of a spin valve

    NASA Astrophysics Data System (ADS)

    Bebenin, N. G.; Ustinov, V. V.

    2015-02-01

    Hysteresis of magnetization and magnetoresistance caused by a change in the orientation of the free layer of a spin valve has been investigated theoretically. It has been shown that the width of the hysteresis loop determined from the data on the dependence of the magnetic moment of the valve on the magnetic field can be less than the width of the loop determined from the resistive data. Formulas have been obtained that describe the dependence of the width of the hysteresis loop on the magnetic field at various values of the exchange field acting on the free layer.

  13. Systematic study of doping dependence on linear magnetoresistance in p-PbTe

    SciTech Connect

    Schneider, J. M.; Chitta, V. A.; Oliveira, N. F.; Peres, M. L. Castro, S. de; Soares, D. A. W.; Wiedmann, S.; Zeitler, U.; Abramof, E.; Rappl, P. H. O.; Mengui, U. A.

    2014-10-20

    We report on a large linear magnetoresistance effect observed in doped p-PbTe films. While undoped p-PbTe reveals a sublinear magnetoresistance, p-PbTe films doped with BaF{sub 2} exhibit a transition to a nearly perfect linear magnetoresistance behaviour that is persistent up to 30 T. The linear magnetoresistance slope ΔR/ΔB is to a good approximation, independent of temperature. This is in agreement with the theory of Quantum Linear Magnetoresistance. We also performed magnetoresistance simulations using a classical model of linear magnetoresistance. We found that this model fails to explain the experimental data. A systematic study of the doping dependence reveals that the linear magnetoresistance response has a maximum for small BaF{sub 2} doping levels and diminishes rapidly for increasing doping levels. Exploiting the huge impact of doping on the linear magnetoresistance signal could lead to new classes of devices with giant magnetoresistance behavior.

  14. Extrinsic mechanism for colossal dielectric constant in CaCu3Ti4O12 ceramics evidenced by nanodomain

    NASA Astrophysics Data System (ADS)

    Patel, Piyush Kumar; Yadav, K. L.

    2014-03-01

    We studied the effect of various sintering temperature and dwell time on phase formation, microstructure and dielectric properties of CaCu3Ti4O12 ceramic synthesized by sol-gel method. The dielectric property was greatly influenced by sintering temperature and dwell time. We found colossal dielectric constant (˜153 816) with low dielectric loss (˜0.20) for 1100 °C/4 h sintered sample at room temperature and 1 kHz frequency. Impedance spectroscopy results support the grain boundary barrier layer capacitor model. Observation of nanostripe structure domains inside the grains of CaCu3Ti4O12 confirms the extrinsic mechanism for colossal dielectric response of this material.

  15. Linearization strategies for high sensitivity magnetoresistive sensors

    NASA Astrophysics Data System (ADS)

    Silva, Ana V.; Leitao, Diana C.; Valadeiro, João; Amaral, José; Freitas, Paulo P.; Cardoso, Susana

    2015-10-01

    Ultrasensitive magnetic field sensors envisaged for applications on biomedical imaging require the detection of low-intensity and low-frequency signals. Therefore linear magnetic sensors with enhanced sensitivity low noise levels and improved field detection at low operating frequencies are necessary. Suitable devices can be designed using magnetoresistive sensors, with room temperature operation, adjustable detected field range, CMOS compatibility and cost-effective production. The advent of spintronics set the path to the technological revolution boosted by the storage industry, in particular by the development of read heads using magnetoresistive devices. New multilayered structures were engineered to yield devices with linear output. We present a detailed study of the key factors influencing MR sensor performance (materials, geometries and layout strategies) with focus on different linearization strategies available. Furthermore strategies to improve sensor detection levels are also addressed with best reported values of ˜40 pT/√Hz at 30 Hz, representing a step forward the low field detection at room temperature.

  16. Advanced giant magnetoresistance technology for measurement applications

    NASA Astrophysics Data System (ADS)

    Weiss, Roland; Mattheis, Roland; Reiss, Günter

    2013-08-01

    Giant magnetoresistance (GMR) sensors are considered one of the first real applications of nanotechnology. They consist of nm-thick layered structures where ferromagnetic metals are sandwiched by nonmagnetic metals. Such multilayered films produce a large change in resistance (typically 10 to 20%) when subjected to a magnetic field, compared with a maximum change of a few per cent for other types of magnetic sensors. This technology has been intensively used in read heads for hard disk drives and now increasingly finds applications due to the high sensitivity and signal-to-noise ratio. Additionally these sensors are compatible with miniaturization and thus offer a high spatial resolution combined with a frequency range up to the 100 MHz regime and simple electronic conditioning. In this review, we first discuss the basics of the underlying magnetoresistance effects in layered structures and then present three prominent examples for future applications: in the field of current sensing the new GMR sensors offer high bandwidth and good accuracy in a space-saving open loop measurement configuration. In rotating systems they can be used for multiturn angle measurements, and in biotechnology the detection of magnetic particles enables the quantitative measurement of biomolecule concentrations.

  17. Magnetoresistive Flux Focusing Eddy Current Flaw Detection

    NASA Technical Reports Server (NTRS)

    Wincheski, Russell A. (Inventor); Namkung, Min (Inventor); Simpson, John W. (Inventor)

    2005-01-01

    A giant magnetoresistive flux focusing eddy current device effectively detects deep flaws in thick multilayer conductive materials. The probe uses an excitation coil to induce eddy currents in conducting material perpendicularly oriented to the coil s longitudinal axis. A giant magnetoresistive (GMR) sensor, surrounded by the excitation coil, is used to detect generated fields. Between the excitation coil and GMR sensor is a highly permeable flux focusing lens which magnetically separates the GMR sensor and excitation coil and produces high flux density at the outer edge of the GMR sensor. The use of feedback inside the flux focusing lens enables complete cancellation of the leakage fields at the GMR sensor location and biasing of the GMR sensor to a location of high magnetic field sensitivity. In an alternate embodiment, a permanent magnet is positioned adjacent to the GMR sensor to accomplish the biasing. Experimental results have demonstrated identification of flaws up to 1 cm deep in aluminum alloy structures. To detect deep flaws about circular fasteners or inhomogeneities in thick multi-layer conductive materials, the device is mounted in a hand-held rotating probe assembly that is connected to a computer for system control, data acquisition, processing and storage.

  18. Magnetoresistive flux focusing eddy current flaw detection

    NASA Technical Reports Server (NTRS)

    Wincheski, Russell A. (Inventor); Namkung, Min (Inventor); Simpson, John W. (Inventor)

    2005-01-01

    A giant magnetoresistive flux focusing eddy current device effectively detects deep flaws in thick multilayer conductive materials. The probe uses an excitation coil to induce eddy currents in conducting material perpendicularly oriented to the coil's longitudinal axis. A giant magnetoresistive (GMR) sensor, surrounded by the excitation coil, is used to detect generated fields. Between the excitation coil and GMR sensor is a highly permeable flux focusing lens which magnetically separates the GMR sensor and excitation coil and produces high flux density at the outer edge of the GMR sensor. The use of feedback inside the flux focusing lens enables complete cancellation of the leakage fields at the GMR sensor location and biasing of the GMR sensor to a location of high magnetic field sensitivity. In an alternate embodiment, a permanent magnet is positioned adjacent to the GMR sensor to accomplish the biasing. Experimental results have demonstrated identification of flaws up to 1 cm deep in aluminum alloy structures. To detect deep flaws about circular fasteners or inhomogeneities in thick multilayer conductive materials, the device is mounted in a hand-held rotating probe assembly that is connected to a computer for system control, data acquisition, processing and storage.

  19. Nonlocal Magnetoresistance Mediated by Spin Superfluidity

    NASA Astrophysics Data System (ADS)

    Takei, So; Tserkovnyak, Yaroslav

    2015-10-01

    The electrical response of two diffusive metals is studied when they are linked by a magnetic insulator hosting a topologically stable (superfluid) spin current. We discuss how charge currents in the metals induce a spin supercurrent state, which in turn generates a magnetoresistance that depends on the topology of the electrical circuit. This magnetoresistance relies on phase coherence over the entire magnet and gives direct evidence for spin superfluidity. We show that driving the magnet with an ac current allows coherent spin transport even in the presence of U(1)-breaking magnetic anisotropy that can preclude dc superfluid transport. Spin transmission in the ac regime shows a series of resonance peaks as a function of frequency. The peak locations, heights, and widths can be used to extract static interfacial properties, e.g., the spin-mixing conductance and effective spin Hall angle, and to probe dynamic properties such as the spin-wave dispersion. Thus, ac transport may provide a simpler route to realizing nonequilbrium coherent spin transport and a useful way to characterize the magnetic system, serving as a precursor to the realization of dc superfluid spin transport.

  20. Quantitative current measurements using scanning magnetoresistance microscopy.

    PubMed

    Takezaki, Taiichi; Sueoka, Kazuhisa

    2008-08-01

    We have demonstrated the capability of scanning magnetoresistance microscope (SMRM) to be used for quantitative current measurements. The SMRM is a magnetic microscope that is based on an atomic force microscope (AFM) and simultaneously measures the localized surface magnetic field distribution and surface topography. The proposed SMRM employs an in-house built AFM cantilever equipped with a miniaturized magnetoresistive (MR) sensor as a magnetic field sensor. In this study, a spin-valve type MR sensor with a width of 1 microm was used to measure the magnetic field distribution induced by a current carrying wire with a width of 5 microm and a spacing of 1.6 microm at room temperature and under ambient conditions. Simultaneous imaging of the magnetic field distribution and the topography was successfully performed in the DC current ranging from 500 microA to 8 mA. The characterized SV sensor, which has a linear response to magnetic fields, offers the quantitative analysis of a magnetic field and current. The measured magnetic field strength was in good agreement with the result simulated using Biot-Savart's law. PMID:18599218

  1. Relaxation of magnetoresistance of single-crystalline (La0.5Eu0.5)0.7Pb0.3MnO3 in a pulsed magnetic field

    NASA Astrophysics Data System (ADS)

    Bykov, A. A.; Popkov, S. I.; Shaykhutdinov, K. A.; Sablina, K. A.

    2012-12-01

    The magnetoresistance (MR) of substituted lanthanum manganite (La0.5Eu0.5)0.7Pb0.3MnO3 has been measured in a pulsed magnetic field with amplitude H = 250 kOe at various temperatures. It is established that temperature dependence of the MR relaxation parameter τ( T) is correlated with temperature dependence of the electric resistance R( T). A mechanism of relaxation is proposed that is related to the relaxation of conducting and dielectric phases in the volume of a sample under the conditions of phase separation. It is shown that the behavior of τ is related to the number of phase boundaries in the volume.

  2. Ultra-sharp oscillatory magneto-resistance in spatially confined La{sub 0.3}Pr{sub 0.4}Ca{sub 0.3}MnO{sub 3} epitaxial thin films

    SciTech Connect

    Alagoz, H. S. Jeon, J.; Boos, R.; Ahangharnejhad, R. H.; Chow, K. H. Jung, J.

    2014-10-20

    Our investigations of magneto-transport properties of La{sub 0.3}Pr{sub 0.4}Ca{sub 0.3}MnO{sub 3} manganite thin films of reduced dimensions revealed dramatic changes in R(θ), the dependence of resistivity on the angle between the magnetic field direction and the current direction, and consequently in the anisotropic magneto-resistance. A regular oscillatory  sin{sup 2}θ form of R(θ) is replaced by a very sharp rectangular-shaped ones when the dimensions of the system become comparable to the size of the intrinsic electronic domains. We discuss possible mechanisms that could be responsible for these changes.

  3. Non-local magnetoresistance in YIG/Pt nanostructures

    SciTech Connect

    Goennenwein, Sebastian T. B. Pernpeintner, Matthias; Gross, Rudolf; Huebl, Hans; Schlitz, Richard; Ganzhorn, Kathrin; Althammer, Matthias

    2015-10-26

    We study the local and non-local magnetoresistance of thin Pt strips deposited onto yttrium iron garnet. The local magnetoresistive response, inferred from the voltage drop measured along one given Pt strip upon current-biasing it, shows the characteristic magnetization orientation dependence of the spin Hall magnetoresistance. We simultaneously also record the non-local voltage appearing along a second, electrically isolated, Pt strip, separated from the current carrying one by a gap of a few 100 nm. The corresponding non-local magnetoresistance exhibits the symmetry expected for a magnon spin accumulation-driven process, confirming the results recently put forward by Cornelissen et al. [“Long-distance transport of magnon spin information in a magnetic insulator at room temperature,” Nat. Phys. (published online 14 September 2015)]. Our magnetotransport data, taken at a series of different temperatures as a function of magnetic field orientation, rotating the externally applied field in three mutually orthogonal planes, show that the mechanisms behind the spin Hall and the non-local magnetoresistance are qualitatively different. In particular, the non-local magnetoresistance vanishes at liquid Helium temperatures, while the spin Hall magnetoresistance prevails.

  4. Research progress on electronic phase separation in low-dimensional perovskite manganite nanostructures

    PubMed Central

    2014-01-01

    Perovskite oxide manganites with a general formula of R1-x AxMnO3 (where R is a trivalent rare-earth element such as La, Pr, Sm, and A is a divalent alkaline-earth element such as Ca, Sr, and Ba) have received much attention due to their unusual electron-transport and magnetic properties, which are indispensable for applications in microelectronic, magnetic, and spintronic devices. Recent advances in the science and technology have resulted in the feature sizes of microelectronic devices based on perovskite manganite oxides down-scaling into nanoscale dimensions. At the nanoscale, low-dimensional perovskite manganite oxide nanostructures display novel physical properties that are different from their bulk and film counterparts. Recently, there is strong experimental evidence to indicate that the low-dimensional perovskite manganite oxide nanostructures are electronically inhomogeneous, consisting of different spatial regions with different electronic orders, a phenomenon that is named as electronic phase separation (EPS). As the geometry sizes of the low-dimensional manganite nanostructures are reduced to the characteristic EPS length scale (typically several tens of nanometers in manganites), the EPS is expected to be strongly modulated, leading to quite dramatic changes in functionality and more emergent phenomena. Therefore, reduced dimensionality opens a door to the new functionalities in perovskite manganite oxides and offers a way to gain new insight into the nature of EPS. During the past few years, much progress has been made in understanding the physical nature of the EPS in low-dimensional perovskite manganite nanostructures both from experimentalists and theorists, which have a profound impact on the oxide nanoelectronics. This nanoreview covers the research progresses of the EPS in low-dimensional perovskite manganite nanostructures such as nanoparticles, nanowires/nanotubes, and nanostructured films and/or patterns. The possible physical origins of the

  5. Large magnetoresistance of insulating silicon films with superconducting nanoprecipitates

    NASA Astrophysics Data System (ADS)

    Heera, V.; Fiedler, J.; Skorupa, W.

    2016-10-01

    We report on large negative and positive magnetoresistance in inhomogeneous, insulating Si:Ga films below a critical temperature of about 7 K. The magnetoresistance effect exceeds 300 % at temperatures below 3 K and fields of 8 T. The comparison of the transport properties of superconducting samples with that of insulating ones reveals that the large magnetoresistance is associated with the appearance of local superconductivity. A simple phenomenological model based on localized Cooper pairs and hopping quasiparticles is able to describe the temperature and magnetic field dependence of the sheet resistance of such films.

  6. Magnetoresistance in magnetic and nonmagnetic rare earth compounds

    NASA Astrophysics Data System (ADS)

    Gratz, E.; Maikis, M.; Bauer, E.; Nowotny, H.

    1995-02-01

    The temperature dependence of the magnetoresistance Δρ/ ρ of selected magnetic and nonmagnetic RE compounds in fields up to 10 T has been measured. The discussion of the positive magnetoresistance is based on Kohler's rule. It was found that deviations from Kohler's rule at low temperatures depend on the magnitude of the individual residual resistivity. Ferromagnetic compounds exhibit negative values and a minimum in the vicinity of the Curie temperature in accordance to a model calculation of Yamada and Takada. The positive Δρ/ ρ contribution in the low temperature region, observed in all magnetic compounds, is due to the dominating classical magnetoresistance in this temperature range.

  7. Anisotropic magnetoresistance dominant in a three terminal Hanle measurement

    NASA Astrophysics Data System (ADS)

    Malec, Christopher; Miller, Michael M.; Johnson, Mark

    2016-02-01

    Experiments are performed on mesoscopic nonlocal lateral spin valves with aluminum channels and Permalloy electrodes. Four-terminal magnetoresistance and Hanle measurements characterize the spin accumulation with results that compare well with published work. Three-terminal Hanle measurements of the Permalloy/aluminum (Py/Al) interfaces show bell-shaped curves that can be fit to Lorentzians. These curves are three orders of magnitude larger than the spin accumulation. Using anisotropic magnetoresistance measurements of individual Permalloy electrodes, we demonstrate that the three-terminal measurements are dominated by anisotropic magnetoresistance effects unrelated to spin accumulation.

  8. Nonlocal ordinary magnetoresistance in indium arsenide

    NASA Astrophysics Data System (ADS)

    Liu, Pan.; Yuan, Zhonghui.; Wu, Hao.; Ali, S. S.; Wan, Caihua.; Ban, Shiliang.

    2015-07-01

    Deflection of carriers by Lorentz force results in an ordinary magnetoresistance (OMR) of (μB)2 at low field. Here we demonstrate that the OMR in high mobility semiconductor InAs could be enhanced by measurement geometry where two probes of voltmeter were both placed on one outer side of two probes of current source. The nonlocal OMR was 3.6 times as large as the local one, reaching 1.8×104% at 5 T. The slope of the linear field dependence of the nonlocal OMR was improved from 12.6 T-1 to 45.3 T-1. The improvement was ascribed to polarity-conserved charges accumulating on boundaries in nonlocal region due to Hall effect. This InAs device with nonlocal geometry could be competitive in B-sensors due to its high OMR ratio, linear field dependence and simple structure.

  9. Evaluation of Magnetoresistive RAM for Space Applications

    NASA Technical Reports Server (NTRS)

    Heidecker, Jason

    2014-01-01

    Magnetoresistive random-access memory (MRAM) is a non-volatile memory that exploits electronic spin, rather than charge, to store data. Instead of moving charge on and off a floating gate to alter the threshold voltage of a CMOS transistor (creating different bit states), MRAM uses magnetic fields to flip the polarization of a ferromagnetic material thus switching its resistance and bit state. These polarized states are immune to radiation-induced upset, thus making MRAM very attractive for space application. These magnetic memory elements also have infinite data retention and erase/program endurance. Presented here are results of reliability testing of two space-qualified MRAM products from Aeroflex and Honeywell.

  10. Anomalous magnetoresistance in magnetized topological insulator cylinders

    NASA Astrophysics Data System (ADS)

    Siu, Zhuo Bin; Jalil, Mansoor B. A.

    2015-05-01

    The close coupling between the spin and momentum degrees of freedom in topological insulators (TIs) presents the opportunity for the control of one to manipulate the other. The momentum can, for example, be confined on a curved surface and the spin influenced by applying a magnetic field. In this work, we study the surface states of a cylindrical TI magnetized in the x direction perpendicular to the cylindrical axis lying along the z direction. We show that a large magnetization leads to an upwards bending of the energy bands at small |kz| . The bending leads to an anomalous magnetoresistance where the transmission between two cylinders magnetized in opposite directions is higher than when the cylinders are magnetized at intermediate angles with respect to each other.

  11. Anomalous magnetoresistance in magnetized topological insulator cylinders

    SciTech Connect

    Siu, Zhuo Bin; Jalil, Mansoor B. A.

    2015-05-07

    The close coupling between the spin and momentum degrees of freedom in topological insulators (TIs) presents the opportunity for the control of one to manipulate the other. The momentum can, for example, be confined on a curved surface and the spin influenced by applying a magnetic field. In this work, we study the surface states of a cylindrical TI magnetized in the x direction perpendicular to the cylindrical axis lying along the z direction. We show that a large magnetization leads to an upwards bending of the energy bands at small |k{sub z}|. The bending leads to an anomalous magnetoresistance where the transmission between two cylinders magnetized in opposite directions is higher than when the cylinders are magnetized at intermediate angles with respect to each other.

  12. Robustness of the magnetoresistance of nanoparticle arrays

    NASA Astrophysics Data System (ADS)

    Estévez, V.; Bascones, E.

    2011-08-01

    Recent work has found that the interplay between spin accumulation and Coulomb blockade in nanoparticle arrays results in peaky I-V and tunneling magnetoresistance (TMR) curves and in huge values of the TMR. We analyze how these effects are influenced by a polarization asymmetry of the electrodes, the dimensionality of the array, the temperature, resistance, or charge disorder, and long-range interactions. We show that the magnitude and voltage dependence of the TMR do not change with the dimensionality of the array or the presence of junction resistance disorder. A different polarization in the electrodes modifies the peak shape in the I-V and TMR curves but not their order of magnitude. Increasing the temperature or length of the interaction reduces to some extent the size of the peaks, the reduction being due to long-range interactions that are smaller in longer arrays. Charge disorder should be avoided to observe large TMR values.

  13. Magnetocardiography with sensors based on giant magnetoresistance

    NASA Astrophysics Data System (ADS)

    Pannetier-Lecoeur, M.; Parkkonen, L.; Sergeeva-Chollet, N.; Polovy, H.; Fermon, C.; Fowley, C.

    2011-04-01

    Biomagnetic signals, mostly due to the electrical activity in the body, are very weak and they can only be detected by the most sensitive magnetometers, such as Superconducting Quantum Interference Devices (SQUIDs). We report here biomagnetic recordings with hybrid sensors based on Giant MagnetoResistance (GMR). We recorded magnetic signatures of the electric activity of the human heart (magnetocardiography) in healthy volunteers. The P-wave and QRS complex, known from the corresponding electric recordings, are clearly visible in the recordings after an averaging time of about 1 min. Multiple recordings at different locations over the chest yielded a dipolar magnetic field map and allowed localizing the underlying current sources. The sensitivity of the GMR-based sensors is now approaching that of SQUIDs and paves way for spin electronics devices for functional imaging of the body.

  14. Magnetoresistive sensors for surveillance and remote sensing

    NASA Astrophysics Data System (ADS)

    Dalichaouch, Yacine; Perry, Alexander R.; Whitecotton, Brian W.; Moeller, Charles R.; Czipott, Peter V.

    2001-02-01

    Quantum Magnetics (QM) has developed a sensing array using small and lightweight magnetoresistive (MR) sensors. These sensors, which operate at room temperature with high sensitivity and wide bandwidth, provide new operational performance capabilities. The wide bandwidth makes them ideal for both passive and active detection techniques. Using a DSP-based electronics developed by QM, we have been able to operate these sensors with an unprecedented noise performance at low frequencies. Recent tests using an MR room temperature gradiometer show that its resolution equals that of a fluxgate room-temperature gradiometer we have previously developed. These results represent an important development for both attended and unattended ground sensor applications since MR sensors cost about ten times less than fluxgate sensors.

  15. Low field magnetoresistance of gadolinium nanowire

    SciTech Connect

    Chakravorty, Manotosh Raychaudhuri, A. K.

    2014-02-07

    We report low field (μ{sub 0}H < 0.2 T) magnetoresistance (MR) studies on a single Gd nanowire patterned from a nano-structured film (average grain size ∼ 35 nm) by focused ion beam. For comparison, we did similar MR measurements on a polycrystalline sample with large crystallographic grains (∼4 μm). It is observed that in the low field region where the MR is due to motion of magnetic domains, the MR in the large grained sample shows a close relation to the characteristic temperature dependent magnetocrystalline anisotropy including a sharp rise in MR at the spin reorientation transition at 235 K. In stark contrast, in the nanowire, the MR shows complete suppression of the above behaviours and it shows predominance of the grain boundary and spin disorder controlling the domain response.

  16. Colossal thermomagnetic response in chiral d-wave superconductor URu2Si2

    NASA Astrophysics Data System (ADS)

    Matsuda, Yuji

    The heavy-fermion compound URu2Si2 exhibits unconventional superconductivity at Tc = 1.45 K deep inside the so-called hidden order phase. An intriguing aspect is that this system has been suggested to be a candidate of a chiral d-wave superconductor, and possible Weyl-type topological superconducting states have been discussed recently. Here we report on the observation of a highly unusual Nernst signal due to the superconducting fluctuations above Tc. The Nernst coefficient is anomalously enhanced (by a factor of ~106) as compared with the theoretically expected value of the Gaussian fluctuations. This colossal Nernst effect intimately reflects the highly unusual superconducting state of URu2Si2. The results invoke possible chiral or Berry-phase fluctuations associated with the broken time-reversal symmetry of the superconducting order parameter. In collaboration with T. Yamashita, Y. Shimoyama, H. Sumiyoshi (Kyoto), S. Fujimoto (Osaka), T. Shibauchi (Tokyo), Y. Haga (JAEA), T. D. Matsuda (TMU) , Y. Onuki (Ryukyus), A. Levchenko (Wisconsin-Madison).

  17. Colossal Spincaloritronic Cooling by Adiabatic Spin-Entropy Expansion in Nanospintronics

    NASA Astrophysics Data System (ADS)

    Katayama-Yoshida, Hiroshi; Fukushima, Tetsuya; Dinh, Van An; Sato, Kazunori

    2009-03-01

    The exchange interactions in DMS are short ranged and can not play an important role for realizing high-TC because the solubility of magnetic impurity is too low to achieve magnetic percolation [1]. We show that spinodal nano-decomposition under layer-by-layer crystal growth condition (2D) leads to characteristic quasi-one dimensional nano-structures (Konbu- Phase) with highly anisotropic shape and high TC (> 1000K) even for low concentrations in DMS [2]. We design a spin-currents- controlled 100 Tera bits/icnh^2, Tera Hz switching, and non- volatile MRAM without Si-CMOS based on Konbu-Phase [3]. In addition to the conventional Peltier effect, we propose a colossal spincaloritronic cooling based on the adiabatic spin- entropy expansion in a Konbu-Phase (Zn,Cr)Te with very high blocking temperature (TB > 1000 K) by spinodal nano- decomposition and by nano-column of Half-Heusler NiMnSi (TC = 1050 K) [4]. [1] K. Sato et al., Phys. Rev. B70, 201202 (2004). [2] H. Katayama-Yoshida et al., Phys. stat. sol. (a) 204 (2007) 15. [3] Japanese Patent: JP3571034, US Patent: US 7,164,180 B2, EU Patent: EP 1548832A1, Taiwan Patent:1262593, Korean Patent: 0557387. [4] H. Katayama-Yoshida et al., Jpn. J. Appl. Phys. 46 (2007) L777.

  18. Colossal magnetoelectric effect in Co3TeO6 family of compounds

    NASA Astrophysics Data System (ADS)

    Artyukhin, Sergey; Oh, Yoon Seok; Yang, Jun Jie; Zapf, Vivien; Kim, Jae Wook; Cheong, Sang-Wook; Vanderbilt, David

    2014-03-01

    Multiferroic Co3TeO6 and related materials attracted much attention recently due to their rich phase diagrams, magnetic field - driven electric polarization and incommensurate spin structures. We model the interacting magnetic and ferroelectric degrees of freedom in these compounds with Landau-type theory and calculate the phase diagram. Comparison of our results with experiment reveals that a particular magnetic anisotropy in some of the compounds results in a second-order spin-flop transition, associated with a large change of polarization. In the vicinity of the transition the spin-flopped phase can be stabilized by a small external magnetic field, which gives rise to a colossal magnetoelectric effect, recently demostrated experimentally. Furthermore, we analyze the types of domain walls that can occur in these materials, and study their interactions. The clamping of domain walls of different types enables the cross-control of ferroic orderings, although they may not be coupled in the bulk. We corraborate our results with ab-initio computations of the polarization, piezoelectric response and optical properties. Our results could pave the way to the design of a new generation of magnetoelectric devices. The work at Rutgers University was supported by the NSF under Grant NSF-DMREF-1233349.

  19. High speed magneto-resistive random access memory

    NASA Technical Reports Server (NTRS)

    Wu, Jiin-Chuan (Inventor); Stadler, Henry L. (Inventor); Katti, Romney R. (Inventor)

    1992-01-01

    A high speed read MRAM memory element is configured from a sandwich of magnetizable, ferromagnetic film surrounding a magneto-resistive film which may be ferromagnetic or not. One outer ferromagnetic film has a higher coercive force than the other and therefore remains magnetized in one sense while the other may be switched in sense by a switching magnetic field. The magneto-resistive film is therefore sensitive to the amplitude of the resultant field between the outer ferromagnetic films and may be constructed of a high resistivity, high magneto-resistive material capable of higher sensing currents. This permits higher read voltages and therefore faster read operations. Alternate embodiments with perpendicular anisotropy, and in-plane anisotropy are shown, including an embodiment which uses high permeability guides to direct the closing flux path through the magneto-resistive material. High density, high speed, radiation hard, memory matrices may be constructed from these memory elements.

  20. The suppression of the large magnetoresistance in thin WTe2

    NASA Astrophysics Data System (ADS)

    Shen, Jie; Woods, John; Cha, Judy

    The layered nature of WTe2 suggests the possibility of making a single layer WTe2 memory device that exploits the recently observed large magnetoresistance. Presently, the origin of the magnetoresistance is attributed to the charge balance between the electron and hole carriers, yet the exact underlying physical mechanism is unclear. Here we show a systematic suppression of the large magnetoresistance, as well as turn-on temperature, with decreasing thickness of WTe2. We attribute the thickness-dependent transport properties to undesirable parasitic effects that become dominant in thin films of WTe2. Our results highlight the increasing importance of characterizing the parasitic effects for 2D layered materials in a single- to a few-layer thick limit. Finally, our observations support the hypothesis that the origin of the large magnetoresistance may be due to the charge balance between the electron and the hole carriers.

  1. Recent Developments of Magnetoresistive Sensors for Industrial Applications

    PubMed Central

    Jogschies, Lisa; Klaas, Daniel; Kruppe, Rahel; Rittinger, Johannes; Taptimthong, Piriya; Wienecke, Anja; Rissing, Lutz; Wurz, Marc Christopher

    2015-01-01

    The research and development in the field of magnetoresistive sensors has played an important role in the last few decades. Here, the authors give an introduction to the fundamentals of the anisotropic magnetoresistive (AMR) and the giant magnetoresistive (GMR) effect as well as an overview of various types of sensors in industrial applications. In addition, the authors present their recent work in this field, ranging from sensor systems fabricated on traditional substrate materials like silicon (Si), over new fabrication techniques for magnetoresistive sensors on flexible substrates for special applications, e.g., a flexible write head for component integrated data storage, micro-stamping of sensors on arbitrary surfaces or three dimensional sensing under extreme conditions (restricted mounting space in motor air gap, high temperatures during geothermal drilling). PMID:26569263

  2. Recent Developments of Magnetoresistive Sensors for Industrial Applications.

    PubMed

    Jogschies, Lisa; Klaas, Daniel; Kruppe, Rahel; Rittinger, Johannes; Taptimthong, Piriya; Wienecke, Anja; Rissing, Lutz; Wurz, Marc Christopher

    2015-11-12

    The research and development in the field of magnetoresistive sensors has played an important role in the last few decades. Here, the authors give an introduction to the fundamentals of the anisotropic magnetoresistive (AMR) and the giant magnetoresistive (GMR) effect as well as an overview of various types of sensors in industrial applications. In addition, the authors present their recent work in this field, ranging from sensor systems fabricated on traditional substrate materials like silicon (Si), over new fabrication techniques for magnetoresistive sensors on flexible substrates for special applications, e.g., a flexible write head for component integrated data storage, micro-stamping of sensors on arbitrary surfaces or three dimensional sensing under extreme conditions (restricted mounting space in motor air gap, high temperatures during geothermal drilling).

  3. Evolution and control of the phase competition morphology in a manganite film

    PubMed Central

    Zhou, Haibiao; Wang, Lingfei; Hou, Yubin; Huang, Zhen; Lu, Qingyou; Wu, Wenbin

    2015-01-01

    The competition among different phases in perovskite manganites is pronounced since their energies are very close under the interplay of charge, spin, orbital and lattice degrees of freedom. To reveal the roles of underlying interactions, many efforts have been devoted towards directly imaging phase transitions at microscopic scales. Here we show images of the charge-ordered insulator (COI) phase transition from a pure ferromagnetic metal with reducing field or increasing temperature in a strained phase-separated manganite film, using a home-built magnetic force microscope. Compared with the COI melting transition, this reverse transition is sharp, cooperative and martensitic-like with astonishingly unique yet diverse morphologies. The COI domains show variable-dimensional growth at different temperatures and their distribution can illustrate the delicate balance of the underlying interactions in manganites. Our findings also display how phase domain engineering is possible and how the phase competition can be tuned in a controllable manner. PMID:26603478

  4. On magnetic ordering in heavily sodium substituted hole doped lanthanum manganites

    NASA Astrophysics Data System (ADS)

    Sethulakshmi, N.; Unnimaya, A. N.; Al-Omari, I. A.; Al-Harthi, Salim; Sagar, S.; Thomas, Senoy; Srinivasan, G.; Anantharaman, M. R.

    2015-10-01

    Mixed valence manganite system with monovalent sodium substituted lanthanum manganites form the basis of the present work. Lanthanum manganites belonging to the series La1-xNaxMnO3 with x=0.5-0.9 were synthesized using modified citrate gel method. Variation of lattice parameters and unit cell volume with Na concentration were analyzed and the magnetization measurements indicated ferromagnetic ordering in all samples at room temperature. Low temperature magnetization behavior indicated that all samples exhibit antiferromagnetism along with ferromagnetism and it has also been observed that antiferromagnetic ordering dominates ferromagnetic ordering as concentration is increased. Evidence for such a magnetic inhomogeneity in these samples has been confirmed from the variation in Mn3+/Mn4+ ion ratio from X-ray Photoelectron Spectroscopy and from the absorption peak studies using Ferromagnetic Resonance Spectroscopy.

  5. A Minimal tight-binding model for ferromagnetic canted bilayer manganites

    PubMed Central

    Baublitz, M.; Lane, C.; Lin, Hsin; Hafiz, Hasnain; Markiewicz, R. S.; Barbiellini, B.; Sun, Z.; Dessau, D. S.; Bansil, A.

    2014-01-01

    Half-metallicity in materials has been a subject of extensive research due to its potential for applications in spintronics. Ferromagnetic manganites have been seen as a good candidate, and aside from a small minority-spin pocket observed in La2−2xSr1+2xMn2O7 (x = 0.38), transport measurements show that ferromagnetic manganites essentially behave like half metals. Here we develop robust tight-binding models to describe the electronic band structure of the majority as well as minority spin states of ferromagnetic, spin-canted antiferromagnetic, and fully antiferromagnetic bilayer manganites. Both the bilayer coupling between the MnO2 planes and the mixing of the |x2 − y2 > and |3z2 − r2 > Mn 3d orbitals play an important role in the subtle behavior of the bilayer splitting. Effects of kz dispersion are included. PMID:25522737

  6. Quantum conductance in electrodeposited nanocontacts and magnetoresistance measurements

    NASA Astrophysics Data System (ADS)

    Elhoussine, F.; Encinas, A.; Mátéfi-Tempfli, S.; Piraux, L.

    2003-05-01

    We present conductance and magnetoresistance measurements in magnetic Ni-Ni and Co-Ni nanocontacts prepared by electrodeposition within the pores of a track-etched polymer membrane. At room temperature, Ni-Ni constrictions show broad quantization plateaus of conductance during their dissolution into units of e2/h, as expected for ferromagnetic ballistic nanocontacts. Additionally, positive and negative magnetoresistance has been measured in Co-Ni nanocontacts.

  7. Anomalous magnetoresistance in NiMnGa thin films

    NASA Astrophysics Data System (ADS)

    Golub, Vladimir O.; Vovk, Andriy Ya.; Malkinski, Leszek; O'Connor, Charles J.; Wang, Zhenjun; Tang, Jinke

    2004-10-01

    The origin of anomalous negative magnetoresistance and its temperature dependence in polycrystalline Ni -Mn-Ga films prepared by pulse laser deposition was studied. The investigation of structural, transports, magnetic, and ferromagnetic resonance properties of the films suggests contributions of different mechanisms in magnetotransport. At low magnetic fields the main contribution to magnetoresistance is due to the transport between the areas with different orientation of magnetic moments, while at high fields it is an electron scattering of in spin-disordered areas.

  8. One-Dimensional Perovskite Manganite Oxide Nanostructures: Recent Developments in Synthesis, Characterization, Transport Properties, and Applications

    NASA Astrophysics Data System (ADS)

    Li, Lei; Liang, Lizhi; Wu, Heng; Zhu, Xinhua

    2016-03-01

    One-dimensional nanostructures, including nanowires, nanorods, nanotubes, nanofibers, and nanobelts, have promising applications in mesoscopic physics and nanoscale devices. In contrast to other nanostructures, one-dimensional nanostructures can provide unique advantages in investigating the size and dimensionality dependence of the materials' physical properties, such as electrical, thermal, and mechanical performances, and in constructing nanoscale electronic and optoelectronic devices. Among the one-dimensional nanostructures, one-dimensional perovskite manganite nanostructures have been received much attention due to their unusual electron transport and magnetic properties, which are indispensable for the applications in microelectronic, magnetic, and spintronic devices. In the past two decades, much effort has been made to synthesize and characterize one-dimensional perovskite manganite nanostructures in the forms of nanorods, nanowires, nanotubes, and nanobelts. Various physical and chemical deposition techniques and growth mechanisms are explored and developed to control the morphology, identical shape, uniform size, crystalline structure, defects, and homogenous stoichiometry of the one-dimensional perovskite manganite nanostructures. This article provides a comprehensive review of the state-of-the-art research activities that focus on the rational synthesis, structural characterization, fundamental properties, and unique applications of one-dimensional perovskite manganite nanostructures in nanotechnology. It begins with the rational synthesis of one-dimensional perovskite manganite nanostructures and then summarizes their structural characterizations. Fundamental physical properties of one-dimensional perovskite manganite nanostructures are also highlighted, and a range of unique applications in information storages, field-effect transistors, and spintronic devices are discussed. Finally, we conclude this review with some perspectives/outlook and future

  9. Large, Tunable Magnetoresistance in Nonmagnetic III-V Nanowires.

    PubMed

    Li, Sichao; Luo, Wei; Gu, Jiangjiang; Cheng, Xiang; Ye, Peide D; Wu, Yanqing

    2015-12-01

    Magnetoresistance, the modulation of resistance by magnetic fields, has been adopted and continues to evolve in many device applications including hard-disk, memory, and sensors. Magnetoresistance in nonmagnetic semiconductors has recently raised much attention and shows great potential due to its large magnitude that is comparable or even larger than magnetic materials. However, most of the previous work focus on two terminal devices with large dimensions, typically of micrometer scales, which severely limit their performance potential and more importantly, scalability in commercial applications. Here, we investigate magnetoresistance in the impact ionization region in InGaAs nanowires with 20 nm diameter and 40 nm gate length. The deeply scaled dimensions of these nanowires enable high sensibility with less power consumption. Moreover, in these three terminal devices, the magnitude of magnetoresistance can be tuned by the transverse electric field controlled by gate voltage. Large magnetoresistance between 100% at room temperature and 2000% at 4.3 K can be achieved at 2.5 T. These nanoscale devices with large magnetoresistance offer excellent opportunity for future high-density large-scale magneto-electric devices using top-down fabrication approaches, which are compatible with commercial silicon platform. PMID:26561728

  10. Striped Multiferroic Phase in Double-Exchange Model for Quarter-Doped Manganites

    SciTech Connect

    Dong, Shuai; Yu, Rong; Liu, J.-M.; Dagotto, Elbio R

    2009-01-01

    The phase diagram of quarter-hole-doped perovskite manganites is investigated using the doubleexchange model. An exotic striped type-II multiferroic phase, where 25% of the nearest-neighbor spin couplings are orthogonal to each other, is found in the narrow-bandwidth region. Comparing with the spiral-spin ordering phase of undoped manganites, the multiferroic Curie temperature of the new phase is estimated to be 4 times higher, while the ferroelectric polarization is similar in magnitude. Our study provides a path for noncollinear spin multiferroics based on electronic self-organization, different from the traditional approach based on superexchange frustration.

  11. Spectroscopic Evidence of Formation of Small Polarons in Doped Manganites

    NASA Astrophysics Data System (ADS)

    Moritomo, Yutaka; Machida, Akihiko; Nakamura, Arao

    1998-03-01

    Temperature dependence of absorption spectra for thin films of doped manganites R_0.6Sr_0.4MnO_3, where R is rare-earth atom, has been investigated systematically changing averaged ionic radius < rA > of perovskite A-site. We have observed a specific absorption band at ~1.5eV due to optical excitations from small polarons (SP)(Machida et al.), submitted.. Spectral weight of the SP band increases with decreasing temperature and eventually disappears at the insulator-metal (IM) transition, indicating that SP in the paramagnetic state (T >= T_C) changes into bare electrons (or large polarons) in the ferromagnetic state due to the enhanced one-electron bandwidth W. We further derived important physical quantities, i.e., W, on-site exchange interaction J and binding energy Ep of SP, and discuss material dependence of stability of SP. This work was supported by a Grant-In-Aid for Scientific Research from the Ministry of Education, Science, Sport and Culture and from PRESTO, Japan Scienece and Technology Corporation (JST), Japan.

  12. Altering the equilibrium condition in Sr-doped lanthanum manganite.

    SciTech Connect

    Carter, J. D.; Krumpelt, M.; Vaughey, J.; Wang, X.

    1999-05-28

    The material of choice for a solid oxide fuel cell cathode based on a yttria-stabilized zirconia (YSZ) electrolyte is doped lanthanum manganite, (La, Sr)MnO{sub 3}. It excels at many of the attributes necessary for a system to work at the required operating temperature and is flexible enough to allow for materials optimization. Although strontium-doping increases the electronic conductivity of the material, the ionic conductivity of the material remains negligible under operating conditions. Studies have shown that the internal equilibrium of the material heavily favors oxidation of the manganese and rather than the loss of lattice oxygen as a charge compensation mechanism. This lack of oxygen vacancies in the structure retards the ability of the material to conduct oxygen ions; thus the optimized system requires a large number of engineered triple point boundary locations to work efficiently. We have successfully doped the host LSM lattice to alter the interred equilibrium of the material to increase its ionic conductivity and thus lower the cathodic overpotential of the system. Our presentation will discuss these new materials, the results of cell tests, and a number of characterization experiments performed.

  13. Photocreating supercooled spiral-spin states in a multiferroic manganite

    NASA Astrophysics Data System (ADS)

    Sheu, Y. M.; Ogawa, N.; Kaneko, Y.; Tokura, Y.

    2016-08-01

    We demonstrate that the dynamics of the a b -spiral-spin order in a magnetoelectric multiferroic Eu0.55Y0.45MnO3 can be unambiguously probed through optical second harmonic signals, generated via spin-induced ferroelectric polarization. In the case of weak excitation, the ferroelectric and the spiral-spin order remains interlocked, both relaxing through spin-lattice relaxation in the nonequilibrium state. When the additional optical pulse illuminating the sample is intense enough to induce a local phase transition thermally, the system creates a metastable state of the b c -spiral-spin order (with the electric polarization P ∥c ) via supercooling across the first-order phase transition between the a b and b c spiral. The supercooled state of the b c -spiral spin is formed in the thermodynamical ground state of the a b spiral (P ∥a ), displaying a prolonged lifetime with strong dependence on the magnetic field along the a axis. The observed phenomena provide a different paradigm for photoswitching between the two distinct multiferroic states, motivating further research into a direct observation of the photocreated supercooled b c -spiral spin in multiferroic manganites.

  14. Reinforcement of double-exchange ferromagnetic coupling by Ru in La{sub 1.24}Sr{sub 1.76}Mn{sub 2-y}Ru{sub y}O{sub 7} manganite system

    SciTech Connect

    Kumaresavanji, M.; Fontes, M.B.; Lopes, A.M.L.; Araujo, J.P.

    2014-03-01

    Highlights: • Effect of Mn-site doping by Ru has been studied in La{sub 1.24}Sr{sub 1.76}Mn{sub 2-y}Ru{sub y}O{sub 7}. • Electrical resistance, magnetoresistance and magnetic properties were measured. • Ru substitution enhances the ferromagnetism and metallicity. • Results were interpreted by the ferromagnetically coupled Ru with Mn ions in Mn–O–Ru network. - Abstract: The effect of Mn-site doping on magnetic and transport properties in the bilayer manganites La{sub 1.24}Sr{sub 1.76}Mn{sub 2-y}Ru{sub y}O{sub 7} (y = 0.0, 0.04, 0.08 and 0.15) has been studied. The undoped compound La{sub 1.24}Sr{sub 1.76}Mn{sub 2}O{sub 7} exhibits a ferromagnetic metal to paramagnetic insulator transition at T{sub C} = 130 K and the substitution of Ru shifts the transition temperatures to higher temperature values. The increased metal–insulator transition by Ru substitution, obtained from temperature dependence of resistivity measurements, indicates that the Ru substitution enhances the metallic state at low temperature regime and favours the Mn–Ru pairs in the Ru doped samples. Moreover, the activation energy values calculated from the temperature dependence of resistivity curves suggest that the Ru substitution weakens the formation of polarons. The increased magnetoresistance ratio from 108% to 136% by Ru substitution, measured at 5 K, points out that the Ru substitution also enhances the inter-grain tunneling magnetoresistance. Thus, the ferromagnetic order and metallic state in La{sub 1.24}Sr{sub 1.76}Mn{sub 2}O{sub 7} system have been enhanced by the presence of Ru in the Mn-site. These reinforcements of ferromagnetic metallic state and magnetoresistance have been interpreted by the ferromagnetically coupled high spin states of Ru with Mn ions in the Mn–O–Ru network.

  15. Oxygen Isotope Evidence for Mn(II)-Catalyzed Recrystallization of Manganite (γ-MnOOH).

    PubMed

    Frierdich, Andrew J; Spicuzza, Michael J; Scherer, Michelle M

    2016-06-21

    Manganese is biogeochemically cycled between aqueous Mn(II) and Mn(IV) oxides. Aqueous Mn(II) often coexists with Mn(IV) oxides, and redox reactions between the two (e.g., comproportionation) are well known to result in the formation of Mn(III) minerals. It is unknown, however, whether aqueous Mn(II) exchanges with structural Mn(III) in manganese oxides in the absence of any mineral transformation (similar to what has been reported for aqueous Fe(II) and some Fe(III) minerals). To probe whether atoms exchange between a Mn(III) oxide and water, we use a (17)O tracer to measure oxygen isotope exchange between structural oxygen in manganite (γ-MnOOH) and water. In the absence of aqueous Mn(II), about 18% of the oxygen atoms in manganite exchange with the aqueous phase, which is close to the estimated surface oxygen atoms (∼11%). In the presence of aqueous Mn(II), an additional 10% (for a total of 28%) of the oxygen atoms exchange with water, suggesting that some of the bulk manganite mineral (i.e., beyond surface) is exchanging with the fluid. Exchange of manganite oxygen with water occurs without any observable change in mineral phase and appears to be independent of the rapid Mn(II) sorption kinetics. These experiments suggest that Mn(II) catalyzes manganese oxide recrystallization and illustrate a new pathway by which these ubiquitous minerals interact with their surrounding fluid. PMID:27249316

  16. Local bias induced ferroelectricity in manganites with competing charge and orbital order states.

    PubMed

    Figueiras, Fábio G N; Bdikin, Igor K; Amaral, Vitor B S; Kholkin, Andrei L

    2014-03-14

    Perovskite-type manganites, such as Pr1-xCaxMnO3, La1-xCaxMnO3 and La1-xSrxMnO3 solid solutions, are set forth as a case study of ferroelectricity formation mechanisms associated with the appearance of site- and bond-centered orbital ordering which breaks structural inversion symmetry. Even though the observation of macroscopic ferroelectricity may be hindered by the finite conductivity of manganites, polarization can still exist in nanoscale volumes. We use Piezoresponse Force Microscopy to probe local bias induced modifications of electrical and electromechanical properties at the manganite surface. Clear bias-induced piezocontrast and local hysteresis loops are observed for La0.89Sr0.11MnO3 and Pr0.60Ca0.40MnO3 compounds providing convincing evidence of the existence of locally induced polar states well above the transition temperature of the CO phase, while the reference samples without CO behavior show no ferroelectric-like response. Such coexistence of ferroelectricity and magnetism in manganites due to the charge ordering (CO) under locally applied electric field opens up a new pathway to expand the phase diagrams of such systems and to achieve spatially localized multiferroic effects with a potential to be used in a new generation of memory cells and data processing circuits. PMID:24477353

  17. Oxygen Isotope Evidence for Mn(II)-Catalyzed Recrystallization of Manganite (γ-MnOOH).

    PubMed

    Frierdich, Andrew J; Spicuzza, Michael J; Scherer, Michelle M

    2016-06-21

    Manganese is biogeochemically cycled between aqueous Mn(II) and Mn(IV) oxides. Aqueous Mn(II) often coexists with Mn(IV) oxides, and redox reactions between the two (e.g., comproportionation) are well known to result in the formation of Mn(III) minerals. It is unknown, however, whether aqueous Mn(II) exchanges with structural Mn(III) in manganese oxides in the absence of any mineral transformation (similar to what has been reported for aqueous Fe(II) and some Fe(III) minerals). To probe whether atoms exchange between a Mn(III) oxide and water, we use a (17)O tracer to measure oxygen isotope exchange between structural oxygen in manganite (γ-MnOOH) and water. In the absence of aqueous Mn(II), about 18% of the oxygen atoms in manganite exchange with the aqueous phase, which is close to the estimated surface oxygen atoms (∼11%). In the presence of aqueous Mn(II), an additional 10% (for a total of 28%) of the oxygen atoms exchange with water, suggesting that some of the bulk manganite mineral (i.e., beyond surface) is exchanging with the fluid. Exchange of manganite oxygen with water occurs without any observable change in mineral phase and appears to be independent of the rapid Mn(II) sorption kinetics. These experiments suggest that Mn(II) catalyzes manganese oxide recrystallization and illustrate a new pathway by which these ubiquitous minerals interact with their surrounding fluid.

  18. Giant magnetoresistance materials for magnetic recording technology

    SciTech Connect

    Heffner, R.H.; Adams, C.D.; Brosha, E.L.

    1997-12-01

    This is the final report of a two-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). This work focused on a class of transition-metal-oxide (TMO) materials (LaMnO{sub 3} doped with Ca, Ba, or Sr) that exhibits an insulator-to-metal transition near a ferromagnetic phase transition temperature. This yields a very large magnetoresistance; thus these materials may have important uses as magnetic sensors in a variety of applications, ranging from automobiles to read heads for magnetic storage. In addition, the transport current in the ferromagnetic state is likely to be very highly polarized, which means that additional device applications using the phenomena of spin-polarized tunneling can be envisioned. Use of these materials as magnetic sensors depends upon learning to control the synthesis parameters (principally temperature, pressure and composition) to achieve a specific carrier concentration and/or mobility. A second challenge is the high magnetic fields ({ge}1 Tesla) currently required to achieve a large change in resistance. The authors began an investigation of two novel approaches to this field-sensitivity problem, involving the development of multilayer structures of the TMO materials. Finally, they began to explore the use of epitaxial strain as a means of changing the transport properties in thin-film multilayers.

  19. Noncontact vibration measurements using magnetoresistive sensing elements

    NASA Astrophysics Data System (ADS)

    Tomassini, R.; Rossi, G.

    2016-06-01

    Contactless instrumentations is more and more used in turbomachinery testing thanks to the non-intrusive character and the possibility to monitor all the components of the machine at the same time. Performances of blade tip timing (BTT) measurement systems, used for noncontact turbine blade vibration measurements, in terms of uncertainty and resolution are strongly affected by sensor characteristics and processing methods. The sensors used for BTT generate pulses, used for precise measurements of turbine blades time of arrival. Nowadays proximity sensors used in this application are based on optical, capacitive, eddy current and microwave measuring principle. Pressure sensors has been also tried. This paper summarizes the results achieved using a novel instrumentation based on the magnetoresistive sensing elements. The characterization of the novel probe has been already published. The measurement system was validated in test benches and in a real jet-engine comparing different sensor technologies. The whole instrumentation was improved. The work presented in this paper focuses on the current developments. In particular, attention is given to the data processing software and new sensor configurations.

  20. Positive magnetoresistance in Ca-doped cobaltites

    SciTech Connect

    Zhou, S. M. Li, Y.; Guo, Y. Q.; Zhao, J. Y.; Shi, L.

    2014-12-08

    Transport properties of polycrystalline La{sub 1−x}Ca{sub x}CoO{sub 3} (0.10 ≤ x ≤ 0.25) are systemically studied in this work. Three types of magnetoresistance (MR) effects are found in the Ca-doped cobaltites. Two negative MRs appear around high-temperature ferromagnetic transition and at low temperatures, which correspond to the conventional MR due to the field-induced suppression of spin-disorder scattering and the intergranular giant-MR due to spin-dependent transport between the ferromagnetic clusters, respectively. More interestingly, another exotic positive MR emerges at intermediate temperature region, which had not been previously reported in Sr- and Ba-doped cobaltites. It is found that this positive MR is associated with an abnormally magnetic transition and increases with the increase of x. For x = 0.25, the MR at low temperatures is dominated by the positive one, which is isotropic and nearly linear with the magnetic field. The possible origin of the positive MR in the Ca-doped cobaltites is discussed.

  1. Planar Hall magnetoresistive aptasensor for thrombin detection.

    PubMed

    Sinha, B; Ramulu, T S; Kim, K W; Venu, R; Lee, J J; Kim, C G

    2014-09-15

    The use of aptamer-based assays is an emerging and attractive approach in disease research and clinical diagnostics. A sensitive aptamer-based sandwich-type sensor is presented to detect human thrombin using a planar Hall magnetoresistive (PHR) sensor in cooperation with superparamagnetic labels. A PHR sensor has the great advantages of a high signal-to-noise ratio, a small offset voltage and linear response in the low-field region, allowing it to act as a high-resolution biosensor. In the system presented here, the sensor has an active area of 50 µm × 50 µm with a 10-nm gold layer deposited onto the sensor surface prior to the binding of thiolated DNA primary aptamer. A polydimethylsiloxane well of 600-µm radius and 1-mm height was prepared around the sensor surface to maintain the same specific area and volume for each sensor. The sensor response was traced in real time upon the addition of streptavidin-functionalized magnetic labels on the sensor. A linear response to the thrombin concentration in the range of 86 pM-8.6 µM and a lower detection limit down to 86 pM was achieved by the proposed present method with a sample volume consumption of 2 µl. The proposed aptasensor has a strong potential for application in clinical diagnosis.

  2. Spin Hall Magnetoresistance in Metallic Bilayers.

    PubMed

    Kim, Junyeon; Sheng, Peng; Takahashi, Saburo; Mitani, Seiji; Hayashi, Masamitsu

    2016-03-01

    Spin Hall magnetoresistance (SMR) is studied in metallic bilayers that consist of a heavy metal (HM) layer and a ferromagnetic metal (FM) layer. We find a nearly tenfold increase of SMR in W/CoFeB compared to previously studied HM/ferromagnetic insulator systems. The SMR increases with decreasing temperature despite the negligible change in the W layer resistivity. A model is developed to account for the absorption of the longitudinal spin current to the FM layer, one of the key characteristics of a metallic ferromagnet. We find that the model not only quantitatively describes the HM layer thickness dependence of SMR, allowing accurate estimation of the spin Hall angle and the spin diffusion length of the HM layer, but also can account for the temperature dependence of SMR by assuming a temperature dependent spin polarization of the FM layer. These results illustrate the unique role a metallic ferromagnetic layer plays in defining spin transmission across the HM/FM interface. PMID:26991195

  3. Scanning magnetoresistance microscopy of atom chips.

    PubMed

    Volk, M; Whitlock, S; Wolff, C H; Hall, B V; Sidorov, A I

    2008-02-01

    Surface based geometries of microfabricated wires or patterned magnetic films can be used to magnetically trap and manipulate ultracold neutral atoms or Bose-Einstein condensates. We investigate the magnetic properties of such atom chips using a scanning magnetoresistive (MR) microscope with high spatial resolution and high field sensitivity. By comparing MR scans of a permanent magnetic atom chip to field profiles obtained using ultracold atoms, we show that MR sensors are ideally suited to observe small variations of the magnetic field caused by imperfections in the wires or magnetic materials which ultimately lead to fragmentation of ultracold atom clouds. Measurements are also provided for the magnetic field produced by a thin current-carrying wire with small geometric modulations along the edge. Comparisons of our measurements with a full numeric calculation of the current flow in the wire and the subsequent magnetic field show excellent agreement. Our results highlight the use of scanning MR microscopy as a convenient and powerful technique for precisely characterizing the magnetic fields produced near the surface of atom chips.

  4. Linear unsaturating magnetoresistance in disordered systems

    NASA Astrophysics Data System (ADS)

    Lai, Ying Tong; Lara, Silvia; Love, Cameron; Ramakrishnan, Navneeth; Adam, Shaffique

    Theoretical works have shown that disordered systems exhibit classical magnetoresistance (MR). In this talk, we examine a variety of experimental systems that observe linear MR at high magnetic fields, including silver chalcogenides, graphene, graphite and Weyl semimetals. We show that a careful analysis of the magnitude of the MR, as well as the field strength at which the MR changes from quadratic to linear, reveal important properties of the system, such as the ratio of the root-mean-square fluctuations in the carrier density and the average carrier density. By looking at other properties such as the zero-field mobility, we show that this carrier density inhomogeneity is consistent with what is known about the microscopic impurities in these experiments. The application of this disorder-induced MR to a variety of different experimental scenarios underline the universality of these theoretical models. This work is supported by the Singapore National Research Foundation (NRF-NRFF2012-01) and the Singapore Ministry of Education and Yale-NUS College through Grant Number R-607-265-01312.

  5. Lateral flow immunoassay using magnetoresistive sensors

    NASA Astrophysics Data System (ADS)

    Taton, Kristin; Johnson, Diane; Guire, Patrick; Lange, Erik; Tondra, Mark

    2009-05-01

    Magnetic particles have been adapted for use as labels in biochemical lateral flow strip tests. Standard gold particle lateral flow assays are generally qualitative; however, with magnetic particles, quantitative results can be obtained by using electronic detection systems with giant magnetoresistive (GMR) sensors. As described here, these small integrated sensor chips can detect the presence of magnetic labels in capture spots whose volume is approximately 150 μm×150 μm×150 μm. The range of linear detection is better than two orders of magnitude; the total range is up to four orders of magnitude. The system was demonstrated with both indirect and sandwich enzyme-linked immunosorbent assays (ELISAs) for protein detection of rabbit IgG and interferon-γ, respectively, achieving detection of 12 pg/ml protein. Ultimately, the goal is for the detector to be fully integrated into the lateral flow strip backing to form a single consumable item that is interrogated by a handheld electronic reader.

  6. Tunneling magnetoresistance phenomenon utilizing graphene magnet electrode

    NASA Astrophysics Data System (ADS)

    Hashimoto, T.; Kamikawa, S.; Soriano, D.; Pedersen, J. G.; Roche, S.; Haruyama, J.

    2014-11-01

    Using magnetic rare-metals for spintronic devices is facing serious problems for the environmental contamination and the limited material-resource. In contrast, by fabricating ferromagnetic graphene nanopore arrays (FGNPAs) consisting of honeycomb-like array of hexagonal nanopores with hydrogen-terminated zigzag-type atomic structure edges, we reported observation of polarized electron spins spontaneously driven from the pore edge states, resulting in rare-metal-free flat-energy-band ferromagnetism. Here, we demonstrate observation of tunneling magnetoresistance (TMR) behaviors on the junction of cobalt/SiO2/FGNPA electrode, serving as a prototype structure for future rare-metal free TMR devices using magnetic graphene electrodes. Gradual change in TMR ratios is observed across zero-magnetic field, arising from specified alignment between pore-edge- and cobalt-spins. The TMR ratios can be controlled by applying back-gate voltage and by modulating interpore distance. Annealing the SiO2/FGNPA junction also drastically enhances TMR ratios up to ˜100%.

  7. Tunneling magnetoresistance phenomenon utilizing graphene magnet electrode

    SciTech Connect

    Hashimoto, T.; Kamikawa, S.; Haruyama, J.; Soriano, D.; Pedersen, J. G.; Roche, S.

    2014-11-03

    Using magnetic rare-metals for spintronic devices is facing serious problems for the environmental contamination and the limited material-resource. In contrast, by fabricating ferromagnetic graphene nanopore arrays (FGNPAs) consisting of honeycomb-like array of hexagonal nanopores with hydrogen-terminated zigzag-type atomic structure edges, we reported observation of polarized electron spins spontaneously driven from the pore edge states, resulting in rare-metal-free flat-energy-band ferromagnetism. Here, we demonstrate observation of tunneling magnetoresistance (TMR) behaviors on the junction of cobalt/SiO{sub 2}/FGNPA electrode, serving as a prototype structure for future rare-metal free TMR devices using magnetic graphene electrodes. Gradual change in TMR ratios is observed across zero-magnetic field, arising from specified alignment between pore-edge- and cobalt-spins. The TMR ratios can be controlled by applying back-gate voltage and by modulating interpore distance. Annealing the SiO{sub 2}/FGNPA junction also drastically enhances TMR ratios up to ∼100%.

  8. Magnetoresistance of heavy and light metal/ferromagnet bilayers

    SciTech Connect

    Avci, Can Onur; Garello, Kevin; Mendil, Johannes; Ghosh, Abhijit; Blasakis, Nicolas; Gabureac, Mihai; Trassin, Morgan; Fiebig, Manfred; Gambardella, Pietro

    2015-11-09

    We studied the magnetoresistance of normal metal (NM)/ferromagnet (FM) bilayers in the linear and nonlinear (current-dependent) regimes and compared it with the amplitude of the spin-orbit torques and thermally induced electric fields. Our experiments reveal that the magnetoresistance of the heavy NM/Co bilayers (NM = Ta, W, and Pt) is phenomenologically similar to the spin Hall magnetoresistance (SMR) of YIG/Pt, but has a much larger anisotropy of the order of 0.5%, which increases with the atomic number of the NM. This SMR-like behavior is absent in light NM/Co bilayers (NM = Ti and Cu), which present the standard anisotropic magnetoresistance expected from polycrystalline FM layers. In the Ta, W, and Pt/Co bilayers, we find an additional magnetoresistance directly proportional to the current and to the transverse component of the magnetization. This so-called unidirectional SMR, of the order of 0.005%, is largest in W and correlates with the amplitude of the antidamping spin-orbit torque. The unidirectional SMR is below the accuracy of our measurements in YIG/Pt.

  9. Experimental evidence for the formation of CoFe2C phase with colossal magnetocrystalline-anisotropy

    SciTech Connect

    El-Gendy, AA; Bertino, M; Clifford, D; Qian, MC; Khanna, SN; Carpenter, EE

    2015-05-25

    Attainment of magnetic order in nanoparticles at room temperature is an issue of critical importance for many different technologies. For ordinary ferromagnetic materials, a reduction in size leads to decreased magnetic anisotropy and results in superparamagnetic relaxations. If, instead, anisotropy could be enhanced at reduced particle sizes, then it would be possible to attain stable magnetic order at room temperature. Herein, we provide experimental evidence substantiating the synthesis of a cobalt iron carbide phase (CoFe2C) of nanoparticles. Structural characterization of the CoFe2C carbide phase was performed by transmission electron microscopy, electron diffraction and energy electron spectroscopy. X-ray diffraction was also performed as a complimentary analysis. Magnetic characterization of the carbide phase revealed a blocking temperature, TB, of 790K for particles with a domain size as small as 5 +/- 1 nm. The particles have magnetocrystalline anisotropy of 4.662 +/- 10 6 J/m(3), which is ten times larger than that of Co nanoparticles. Such colossal anisotropy leads to thermally stable long range magnetic order. Moreover, the thermal stability constant is much larger than that of the commonly used FePt nanoparticles. With thermal stability and colossal anisotropy, the CoFe2C nanoparticles have huge potential for enhanced magnetic data storage devices. (C) 2015 AIP Publishing LLC.

  10. Tuning of colossal dielectric constant in gold-polypyrrole composite nanotubes using in-situ x-ray diffraction techniques

    SciTech Connect

    Sarma, Abhisakh; Sanyal, Milan K.

    2014-09-15

    In-situ x-ray diffraction technique has been used to study the growth process of gold incorporated polypyrrole nanotubes that exhibit colossal dielectric constant due to existence of quasi-one-dimensional charge density wave state. These composite nanotubes were formed within nanopores of a polycarbonate membrane by flowing pyrrole monomer from one side and mixture of ferric chloride and chloroauric acid from other side in a sample cell that allows collection of x-ray data during the reaction. The size of the gold nanoparticle embedded in the walls of the nanotubes was found to be dependent on chloroauric acid concentration for nanowires having diameter more than 100 nm. For lower diameter nanotubes the nanoparticle size become independent of chloroauric acid concentration and depends on the diameter of nanotubes only. The result of this study also shows that for 50 nm gold-polypyrrole composite nanotubes obtained with 5.3 mM chloroauric acid gives colossal dielectric constant of about 10{sup 7}. This value remain almost constant over a frequency range from 1Hz to 10{sup 6} Hz even at 80 K temperature.

  11. Experimental evidence for the formation of CoFe{sub 2}C phase with colossal magnetocrystalline-anisotropy

    SciTech Connect

    El-Gendy, Ahmed A. E-mail: ecarpenter2@vcu.edu; Bertino, Massimo; Qian, Meichun; Khanna, Shiv N. E-mail: ecarpenter2@vcu.edu; Clifford, Dustin; Carpenter, Everett E. E-mail: ecarpenter2@vcu.edu

    2015-05-25

    Attainment of magnetic order in nanoparticles at room temperature is an issue of critical importance for many different technologies. For ordinary ferromagnetic materials, a reduction in size leads to decreased magnetic anisotropy and results in superparamagnetic relaxations. If, instead, anisotropy could be enhanced at reduced particle sizes, then it would be possible to attain stable magnetic order at room temperature. Herein, we provide experimental evidence substantiating the synthesis of a cobalt iron carbide phase (CoFe{sub 2}C) of nanoparticles. Structural characterization of the CoFe{sub 2}C carbide phase was performed by transmission electron microscopy, electron diffraction and energy electron spectroscopy. X-ray diffraction was also performed as a complimentary analysis. Magnetic characterization of the carbide phase revealed a blocking temperature, T{sub B}, of 790 K for particles with a domain size as small as 5 ± 1 nm. The particles have magnetocrystalline anisotropy of 4.6 ± 2 × 10{sup 6 }J/m{sup 3}, which is ten times larger than that of Co nanoparticles. Such colossal anisotropy leads to thermally stable long range magnetic order. Moreover, the thermal stability constant is much larger than that of the commonly used FePt nanoparticles. With thermal stability and colossal anisotropy, the CoFe{sub 2}C nanoparticles have huge potential for enhanced magnetic data storage devices.

  12. Effect of a-site cation deficiency and YSZ additions on sintering and properties of doped lanthanum manganite

    SciTech Connect

    Stevenson, J.W.; Armstrong, T.R.; Weber, W.J.

    1995-06-01

    The sintering behavior of Ca- and Sr-doped lanthanum manganite (the preferred SOFC cathode material) is highly dependent on the relative proportion of A and B site cations in the material. In general, A-site cation deficiency increases sintered density. The effect of additions of YSZ to lanthanum manganite (to expand the reactive region at the cathode/electrolyte interface and improve thermal expansion and sintering shrinkage matches) on sintering and other properties will also be reported.

  13. Anomalous electronic structure and magnetoresistance in TaAs2

    PubMed Central

    Luo, Yongkang; McDonald, R. D.; Rosa, P. F. S.; Scott, B.; Wakeham, N.; Ghimire, N. J.; Bauer, E. D.; Thompson, J. D.; Ronning, F.

    2016-01-01

    The change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs2 possesses a very large negative magnetoresistance, with an unknown scattering mechanism. Density functional calculations find that TaAs2 is a new topological semimetal [ℤ2 invariant (0;111)] without Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions. PMID:27271852

  14. Anomalous electronic structure and magnetoresistance in TaAs2.

    PubMed

    Luo, Yongkang; McDonald, R D; Rosa, P F S; Scott, B; Wakeham, N; Ghimire, N J; Bauer, E D; Thompson, J D; Ronning, F

    2016-01-01

    The change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs2 possesses a very large negative magnetoresistance, with an unknown scattering mechanism. Density functional calculations find that TaAs2 is a new topological semimetal [ℤ2 invariant (0;111)] without Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions. PMID:27271852

  15. Anomalous electronic structure and magnetoresistance in TaAs2

    DOE PAGESBeta

    Luo, Yongkang; McDonald, R. D.; Rosa, P. F. S.; Scott, B.; Wakeham, N.; Ghimire, N. J.; Bauer, E. D.; Thompson, J. D.; Ronning, F.

    2016-01-01

    We report that the change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs2 possesses a very large negative magnetoresistance, with an unknown scattering mechanism. In conclusion, density functional calculations find that TaAs2 is a new topological semimetal [Z2 invariant (0;111)] withoutmore » Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions.« less

  16. Electronic structure basis for the extraordinary magnetoresistance in WTe2

    DOE PAGESBeta

    Pletikosić, I.; Ali, Mazhar N.; Fedorov, A. V.; Cava, R. J.; Valla, T.

    2014-11-19

    The electronic structure basis of the extremely large magnetoresistance in layered non-magnetic tungsten ditelluride has been investigated by angle-resolved photoelectron spectroscopy. Hole and electron pockets of approximately the same size were found at the Fermi level, suggesting that carrier compensation should be considered the primary source of the effect. The material exhibits a highly anisotropic, quasi one-dimensional Fermi surface from which the pronounced anisotropy of the magnetoresistance follows. As a result, a change in the Fermi surface with temperature was found and a high-density-of-states band that may take over conduction at higher temperatures and cause the observed turn-on behavior ofmore » the magnetoresistance in WTe₂ was identified.« less

  17. Active control of magnetoresistance of organic spin valves using ferroelectricity

    PubMed Central

    Sun, Dali; Fang, Mei; Xu, Xiaoshan; Jiang, Lu; Guo, Hangwen; Wang, Yanmei; Yang, Wenting; Yin, Lifeng; Snijders, Paul C.; Ward, T. Z.; Gai, Zheng; Zhang, X.-G.; Lee, Ho Nyung; Shen, Jian

    2014-01-01

    Organic spintronic devices have been appealing because of the long spin lifetime of the charge carriers in the organic materials and their low cost, flexibility and chemical diversity. In previous studies, the control of resistance of organic spin valves is generally achieved by the alignment of the magnetization directions of the two ferromagnetic electrodes, generating magnetoresistance. Here we employ a new knob to tune the resistance of organic spin valves by adding a thin ferroelectric interfacial layer between the ferromagnetic electrode and the organic spacer: the magnetoresistance of the spin valve depends strongly on the history of the bias voltage, which is correlated with the polarization of the ferroelectric layer; the magnetoresistance even changes sign when the electric polarization of the ferroelectric layer is reversed. These findings enable active control of resistance using both electric and magnetic fields, opening up possibility for multi-state organic spin valves. PMID:25008155

  18. Active control of magnetoresistance of organic spin valves using ferroelectricity.

    PubMed

    Sun, Dali; Fang, Mei; Xu, Xiaoshan; Jiang, Lu; Guo, Hangwen; Wang, Yanmei; Yang, Wenting; Yin, Lifeng; Snijders, Paul C; Ward, T Z; Gai, Zheng; Zhang, X-G; Lee, Ho Nyung; Shen, Jian

    2014-01-01

    Organic spintronic devices have been appealing because of the long spin lifetime of the charge carriers in the organic materials and their low cost, flexibility and chemical diversity. In previous studies, the control of resistance of organic spin valves is generally achieved by the alignment of the magnetization directions of the two ferromagnetic electrodes, generating magnetoresistance. Here we employ a new knob to tune the resistance of organic spin valves by adding a thin ferroelectric interfacial layer between the ferromagnetic electrode and the organic spacer: the magnetoresistance of the spin valve depends strongly on the history of the bias voltage, which is correlated with the polarization of the ferroelectric layer; the magnetoresistance even changes sign when the electric polarization of the ferroelectric layer is reversed. These findings enable active control of resistance using both electric and magnetic fields, opening up possibility for multi-state organic spin valves. PMID:25008155

  19. Active control of magnetoresistance of organic spin valves using ferroelectricity

    NASA Astrophysics Data System (ADS)

    Shen, Jian

    Organic spintronic devices have been appealing because of the long spin lifetime of the charge carriers in the organic materials and their low cost, flexibility and chemical diversity. In previous studies, the control of resistance of organic spin valves is generally achieved by the alignment of the magnetization directions of the two ferromagnetic electrodes, generating magnetoresistance. Here we employ a new knob to tune the resistance of organic spin valves by adding a thin ferroelectric interfacial layer between the ferromagnetic electrode and the organic spacer: the magnetoresistance of the spin valve depends strongly on the history of the bias voltage, which is correlated with the polarization of the ferroelectric layer; the magnetoresistance even changes sign when the electric polarization of the ferroelectric layer is reversed. These findings enable active control of resistance using both electric and magnetic fields, opening up possibility for multi-state organic spin valves.

  20. Colossal Permittivity in Advanced Functional Heterogeneous Materials: The Relevance of the Local Measurements at Submicron Scale

    NASA Astrophysics Data System (ADS)

    Fiorenza, Patrick; Nigro, Raffaella Lo; Raineri, Vito

    Recently, giant dielectric permittivities (ɛ ' ˜ 104) have been found in several nonferroelectric materials such as CaCu3Ti4O12 (CCTO) (Subramanian et al., J. Solid State Chem. 151:323, 2000; Homes et al., Science 293:673, 2001), doped-NiO (Wu et al., Phys. Rev. Lett. 89:217601, 2002) systems (Li x Ti y Ni1 - x - y O, Li x Si y Ni1 - x - y O, Ki x Ti y Ni1 - x - y O), CuO, (Lin et al., Phys. Rev. B 72:014103, 2005; Sarkar et al., App. Phys. Lett. 92:142901, 2008) etc., and most important, the high ɛ ' values of these materials are almost independent over a wide range of temperature. This is one of the most intriguing features for their implementations in microelectronics devices, and as a consequence, these materials have been subjected to extensive research. Here, an introduction to such materials and to the methods for their dielectric characterization is given. So far, the crucial question is whether the large dielectric response is an intrinsic property of new class of crystals or an extrinsic property originated by a combination of the structural properties and other features such as defects and inhomogeneities. Preliminary, this peculiar dielectric behavior has been explained in powder ceramics by the internal barrier layer capacitor (IBLC) model, that is the presence of semiconducting domains surrounded by thin insulating regions within the crystal microstructure. It has been considered the most appropriate model and it has been generally accepted to explain the giant response of these materials. However, it could not be transferred to single crystals and thin films. In this scenario, scanning probe-based methods (like STM, KPFM, C-AFM, SIM etc) represent the most powerful instrument to understand the colossal permittivity-related physical phenomena, by investigations at nanoscale, clarifying the local effects responsible of the rising of macroscopic giant dielectric responses. Scanning probe microscopy investigations showed the relevance of inhomogeneity

  1. Mechanism of sign crossover of the anisotropic magneto-resistance in La0.7-xPrxCa0.3MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Alagoz, H. S.; Desomberg, J.; Taheri, M.; Razavi, F. S.; Chow, K. H.; Jung, J.

    2015-02-01

    Magneto-resistive anisotropy (AMR) has been studied in 45 nm thick La0.7-xPrxCa0.3MnO3 (LPCMO) manganite films (with Pr doping x between 0 and 0.40) deposited on LaAlO3 (LAO) and SrTiO3 (STO) substrates. The AMR in compressively strained films undergoes a sign change from positive to negative at low temperatures, whereas its sign does not change in films subjected to tensile strain. Temperature dependence of magnetization in a magnetic field applied parallel and perpendicular to the (100)-plane of the films shows that at low temperatures strain-induced rotation of the easy-axis magnetization determines the sign of the AMR. At higher temperatures near the TMI the sign of the AMR is the same in both LPCMO/LAO and LPCMO/STO films, suggesting the dominating influence of percolative transport in the plane of these films at these temperatures.

  2. Detection of magnetic resonance signals using a magnetoresistive sensor

    SciTech Connect

    Budker, Dmitry; Pines, Alexander; Xu, Shoujun; Hilty, Christian; Ledbetter, Micah P; Bouchard, Louis S

    2013-10-01

    A method and apparatus are described wherein a micro sample of a fluidic material may be assayed without sample contamination using NMR techniques, in combination with magnetoresistive sensors. The fluidic material to be assayed is first subject to pre-polarization, in one embodiment, by passage through a magnetic field. The magnetization of the fluidic material is then subject to an encoding process, in one embodiment an rf-induced inversion by passage through an adiabatic fast-passage module. Thereafter, the changes in magnetization are detected by a pair of solid-state magnetoresistive sensors arranged in gradiometer mode. Miniaturization is afforded by the close spacing of the various modules.

  3. Magnetoresistance of nanosized magnetic configurations in single nanowires

    NASA Astrophysics Data System (ADS)

    Wegrowe, J.-E.; Gilbert, S.; Doudin, B.; Ansermet, J.-Ph.

    1998-03-01

    The problem of studying spin configurations at nanoscopic level is that magnetic measurements at this scale cannot be performed using usual magnetometers. We have shown that anisotropic magnetoresistance (AMR) measured with micro-contacts allows spin configurations of a single nanowire to be studied in details. The nanowires are diameter 50 nm and length 6000 nm and are produced by a combination of electrodeposition in track-etched membrane templates and sputtering technics. Magnetoresistance of well-defined spin configurations in single nanowires, like Curling magnetization reversal modes or domain wall, are measured.

  4. Magnetoresistance and magnetic ordering in praseodymium and neodymium hexaborides

    SciTech Connect

    Anisimov, M. A.; Bogach, A. V.; Glushkov, V. V.; Demishev, S. V.; Samarin, N. A.; Filipov, V. B.; Shitsevalova, N. Yu.; Kuznetsov, A. V.; Sluchanko, N. E.

    2009-11-15

    The magnetoresistance {Delta}{rho}/{rho} of single-crystal samples of praseodymium and neodymium hexaborides (PrB{sub 6} and NdB{sub 6}) has been measured at temperatures ranging from 2 to 20 K in a magnetic field of up to 80 kOe. The results obtained have revealed a crossover of the regime from a small negative magnetoresistance in the paramagnetic state to a large positive magnetoresistive effect in magnetically ordered phases of the PrB{sub 6} and NdB{sub 6} compounds. An analysis of the dependences {Delta}{rho}(H)/{rho} has made it possible to separate three contributions to the magnetoresistance for the compounds under investigation. In addition to the main negative contribution, which is quadratic in the magnetic field (-{Delta}{rho}/{rho} {proportional_to} H{sup 2}), a linear positive contribution ({Delta}{rho}/{rho} {proportional_to} H) and a nonlinear ferromagnetic contribution have been found. Upon transition to a magnetically ordered state, the linear positive component in the magnetoresistance of the PrB{sub 6} and NdB{sub 6} compounds becomes dominant, whereas the quadratic contribution to the negative magnetoresistance is completely suppressed in the commensurate magnetic phase of these compounds. The presence of several components in the magnetoresistance has been explained by assuming that, in the antiferromagnetic phases of PrB{sub 6} and NdB{sub 6}, ferromagnetic nanoregions (ferrons) are formed in the 5d band in the vicinity of the rareearth ions. The origin of the quadratic contribution to the negative magnetoresistance is interpreted in terms of the Yosida model, which takes into account scattering of conduction electrons by localized magnetic moments of rare-earth ions. Within the approach used, the local magnetic susceptibility {chi}{sub loc} has been estimated. It has been demonstrated that, in the temperature range T{sub N} < T < 20 K, the behavior of the local magnetic susceptibility {chi}{sub loc} for the compounds under investigation can

  5. Anomalous rf magnetoresistance in copper at 4/degree/K

    SciTech Connect

    Halama, H.J.; Prodell, A.G.; Rogers, J.T.; De Panfilis, S.; Melissinos, A.C.; Moskowitz, B.E.; Semertzidis, Y.K.; Wuensch, W.U.; Fowler, W.B.; Nezrick, F.A.

    1988-03-01

    We have measured the effect of a magnetic field on the surface resistance of polycrystalline Cu at f = 1.2 GHz and at 4.4/degree/K; under these conditions the surface resistance is well into the anomalous skin effect regime but has not reached its limiting value. We find that the transverse and longitudinal magnetoresistance are an order of magnitude smaller than the DC magnetoresistance and depend quadratically on the field. At low fields we observe a decrease in surface resistance with increasing field which can be interpreted as a size effect of the TF surface current. 17 refs., 4 figs., 1 tab.

  6. Structural and giant magnetoresistance characterization of Ag sbnd Co multilayers

    NASA Astrophysics Data System (ADS)

    Angelakeris, M.; Poulopoulos, P.; Valassiades, O.; Stoemenos, J.; Kalogirou, O.; Niarchos, D.; Flevaris, N. K.

    1997-01-01

    Ag sbnd Co multilayers were prepared on various substrates (Si, polyimide and glass) by e-beam evaporation under ultra high vacuum. X-ray diffraction and high resolution electron microscopy studies showed a deterioration of multilayer structure upon reducing the individual Co-layer thickness to 0.5 nm. Furthermore, the saturation field in the parallel field geometry increases, as SQUID magnetometry revealed, while magnetoresistance reaches 16% at room temperature and exceeds 30% at 30 K. Magnetoresistance values were found to depend strongly on individual layer thicknesses as well as on the total film thickness.

  7. Local magnetoresistance in Fe/MgO/Si lateral spin valve at room temperature

    SciTech Connect

    Sasaki, Tomoyuki Koike, Hayato; Oikawa, Tohru; Suzuki, Toshio; Ando, Yuichiro; Suzuki, Yoshishige; Shiraishi, Masashi

    2014-02-03

    Room temperature local magnetoresistance in two-terminal scheme is reported. By employing 1.6 nm-thick MgO tunnel barrier, spin injection efficiency is increased, resulting in large non-local magnetoresistance. The magnitude of the non-local magnetoresistance is estimated to be 0.0057 Ω at room temperature. As a result, a clear rectangle signal is observed in local magnetoresistance measurement even at room temperature. We also investigate the origin of local magnetoresistance by measuring the spin accumulation voltage of each contact separately.

  8. Structural and magnetotransport properties of the Y doped A-site deficient double layered manganites La1.2-x□0.2YxCa1.6Mn2O7

    NASA Astrophysics Data System (ADS)

    Mahamdioua, N.; Amira, A.; Altintas, S. P.; Varilci, A.; Terzioglu, C.

    2016-08-01

    We present structural, magnetic and electrical properties of the polycrystalline A-site-deficient yttrium doped double layered manganites La1.2-x□0.2YxCa1.6Mn2O7 (x=0.2, 0.3 and 0.4) prepared by a solid state reaction method. The samples crystallize in the tetragonal structure with the space group I4/mmm. Doping with Y decreases the cell parameters and causes a decrease of the metal-insulator transition temperature. The same evolution with doping is also seen for the deduced Curie temperature from susceptibility curves which present a clear paramagnetic-ferromagnetic transition. The significant positive intrinsic magnetoresistance, shown in all samples, reaches 85% at 122 K under 7 T for 0.3 doped sample and can be attributed to the suppression of spin fluctuations via aligning the spins under external magnetic field, while the extrinsic one is attributed to the inter-grain spin-polarized tunneling across the grain boundaries. The simulation of the resistivity curves in the entire temperature range show that the percolation model is suitable to fit our results. The applied magnetic field increases the density of states near the Fermi level, which is in accordance with the observed decrease of resistivity.

  9. Low temperature magnetoresistance studies in MBE grown topological insulator thin films

    NASA Astrophysics Data System (ADS)

    Dey, Rik; Roy, Anupam; Pramanik, Tanmoy; Guchhait, Samaresh; Sonde, Sushant; Rai, Amritesh; Majumder, Sarmita; Ghosh, Bahniman; Register, Leonard; Banerjee, Sanjay

    2015-03-01

    We studied low temperature magnetoresistance in molecular beam epitaxy grown topological insulator Bi2Se3andBi2Te3 thin films. The surface and structural characterization of the grown films showed smooth epitaxial growth on Si(111). The magnetoresistance has been measured at low temperatures (2 - 20 K) with magnetic fields upto 9 T. The full range perpendicular field magnetoresistance has been explained with the original Hikami-Larkin-Nagaoka theory. Altshuler-Aronov theory of localization has been used to understand the full range parallel field magnetoresistance. Various scattering times have been estimated by fitting the magnetoresistance data with the theory. It is shown that the Zeeman effect is not needed to explain the magnetoresistance and has not been considered in the theory either. The angle dependent anisotropic magnetoresistance has also been observed and explained using the above theories. This work is funded by NRI-SWAN.

  10. Giant Magnetoresistance: Basic Concepts, Microstructure, Magnetic Interactions and Applications

    PubMed Central

    Ennen, Inga; Kappe, Daniel; Rempel, Thomas; Glenske, Claudia; Hütten, Andreas

    2016-01-01

    The giant magnetoresistance (GMR) effect is a very basic phenomenon that occurs in magnetic materials ranging from nanoparticles over multilayered thin films to permanent magnets. In this contribution, we first focus on the links between effect characteristic and underlying microstructure. Thereafter, we discuss design criteria for GMR-sensor applications covering automotive, biosensors as well as nanoparticular sensors. PMID:27322277

  11. Giant Magnetoresistive (GMR) Sensor Microelectromechanical System (MEMS) Device

    NASA Technical Reports Server (NTRS)

    Ramesham, R.

    1999-01-01

    The measurement of acceleration has been accomplished using several technologies in high-reliability applications such as guidance control, detonation, and shock/vibration measurement. Electromechanical, piezoelectric, piezoresistive, and capacitive acceleration sensors are available and the literature pertinent to giant magnetoresistive sensors (GMR) for the above applications are scanty.

  12. Giant Magnetoresistance: Basic Concepts, Microstructure, Magnetic Interactions and Applications.

    PubMed

    Ennen, Inga; Kappe, Daniel; Rempel, Thomas; Glenske, Claudia; Hütten, Andreas

    2016-01-01

    The giant magnetoresistance (GMR) effect is a very basic phenomenon that occurs in magnetic materials ranging from nanoparticles over multilayered thin films to permanent magnets. In this contribution, we first focus on the links between effect characteristic and underlying microstructure. Thereafter, we discuss design criteria for GMR-sensor applications covering automotive, biosensors as well as nanoparticular sensors. PMID:27322277

  13. Tuning spin transport properties and molecular magnetoresistance through contact geometry

    SciTech Connect

    Ulman, Kanchan; Narasimhan, Shobhana; Delin, Anna

    2014-01-28

    Molecular spintronics seeks to unite the advantages of using organic molecules as nanoelectronic components, with the benefits of using spin as an additional degree of freedom. For technological applications, an important quantity is the molecular magnetoresistance. In this work, we show that this parameter is very sensitive to the contact geometry. To demonstrate this, we perform ab initio calculations, combining the non-equilibrium Green's function method with density functional theory, on a dithienylethene molecule placed between spin-polarized nickel leads of varying geometries. We find that, in general, the magnetoresistance is significantly higher when the contact is made to sharp tips than to flat surfaces. Interestingly, this holds true for both resonant and tunneling conduction regimes, i.e., when the molecule is in its “closed” and “open” conformations, respectively. We find that changing the lead geometry can increase the magnetoresistance by up to a factor of ∼5. We also introduce a simple model that, despite requiring minimal computational time, can recapture our ab initio results for the behavior of magnetoresistance as a function of bias voltage. This model requires as its input only the density of states on the anchoring atoms, at zero bias voltage. We also find that the non-resonant conductance in the open conformation of the molecule is significantly impacted by the lead geometry. As a result, the ratio of the current in the closed and open conformations can also be tuned by varying the geometry of the leads, and increased by ∼400%.

  14. Magnetoresistance, electrical conductivity, and Hall effect of glassy carbon

    SciTech Connect

    Baker, D.F.

    1983-02-01

    These properties of glassy carbon heat treated for three hours between 1200 and 2700/sup 0/C were measured from 3 to 300/sup 0/K in magnetic fields up to 5 tesla. The magnetoresistance was generally negative and saturated with reciprocal temperature, but still increased as a function of magnetic field. The maximum negative magnetoresistance measured was 2.2% for 2700/sup 0/C material. Several models based on the negative magnetoresistance being proportional to the square of the magnetic moment were attempted; the best fit was obtained for the simplest model combining Curie and Pauli paramagnetism for heat treatments above 1600/sup 0/C. Positive magnetoresistance was found only in less than 1600/sup 0/C treated glassy carbon. The electrical conductivity, of the order of 200 (ohm-cm)/sup -1/ at room temperature, can be empirically written as sigma = A + Bexp(-CT/sup -1/4) - DT/sup -1/2. The Hall coefficient was independent of magnetic field, insensitive to temperature, but was a strong function of heat treatment temperature, crossing over from negative to positive at about 1700/sup 0/C and ranging from -0.048 to 0.126 cm/sup 3//coul. The idea of one-dimensional filaments in glassy carbon suggested by the electrical conductivity is compatible with the present consensus view of the microstructure.

  15. Giant Magnetoresistance: Basic Concepts, Microstructure, Magnetic Interactions and Applications.

    PubMed

    Ennen, Inga; Kappe, Daniel; Rempel, Thomas; Glenske, Claudia; Hütten, Andreas

    2016-01-01

    The giant magnetoresistance (GMR) effect is a very basic phenomenon that occurs in magnetic materials ranging from nanoparticles over multilayered thin films to permanent magnets. In this contribution, we first focus on the links between effect characteristic and underlying microstructure. Thereafter, we discuss design criteria for GMR-sensor applications covering automotive, biosensors as well as nanoparticular sensors.

  16. Low temperature magnetoresistance measurements on bismuth nanowire arrays

    NASA Astrophysics Data System (ADS)

    Kaiser, Ch; Weiss, G.; Cornelius, T. W.; Toimil-Molares, M. E.; Neumann, R.

    2009-05-01

    We present low temperature resistance R(T) and magnetoresistance measurements for Bi nanowires with diameters between 100 and 500 nm, which are close to being single-crystalline. The nanowires were fabricated by electrochemical deposition in pores of polycarbonate membranes. R(T) varies as T2 in the low temperature range 1.5 Kmagnetoresistance. The transverse magnetoresistance of all samples shows a clear B1.5 variation. Its size depends strongly on the diameter of the wires but only weakly on temperature. Finally, a steplike increase in the magnetoresistance of our sample with a wire diameter of 100 nm was found and this might be attributed to a transition from one-dimensional to three-dimensional localization.

  17. Direct Imaging of Dynamic Glassy Behavior in a Strained Manganite Film.

    PubMed

    Kundhikanjana, Worasom; Sheng, Zhigao; Yang, Yongliang; Lai, Keji; Ma, Eric Yue; Cui, Yong-Tao; Kelly, Michael A; Nakamura, Masao; Kawasaki, Masashi; Tokura, Yoshinori; Tang, Qiaochu; Zhang, Kun; Li, Xinxin; Shen, Zhi-Xun

    2015-12-31

    Complex many-body interaction in perovskite manganites gives rise to a strong competition between ferromagnetic metallic and charge-ordered phases with nanoscale electronic inhomogeneity and glassy behaviors. Investigating this glassy state requires high-resolution imaging techniques with sufficient sensitivity and stability. Here, we present the results of a near-field microwave microscope imaging on the strain-driven glassy state in a manganite film. The high contrast between the two electrically distinct phases allows direct visualization of the phase separation. The low-temperature microscopic configurations differ upon cooling with different thermal histories. At sufficiently high temperatures, we observe switching between the two phases in either direction. The dynamic switching, however, stops below the glass transition temperature. Compared with the magnetization data, the phase separation was microscopically frozen, while spin relaxation was found in a short period of time. PMID:26765006

  18. Reversible modulation of orbital occupations via an interface-induced polar state in metallic manganites.

    PubMed

    Chen, Hanghui; Qiao, Qiao; Marshall, Matthew S J; Georgescu, Alexandru B; Gulec, Ahmet; Phillips, Patrick J; Klie, Robert F; Walker, Frederick J; Ahn, Charles H; Ismail-Beigi, Sohrab

    2014-09-10

    The breaking of orbital degeneracy on a transition metal cation and the resulting unequal electronic occupations of these orbitals provide a powerful lever over electron density and spin ordering in metal oxides. Here, we use ab initio calculations to show that reversibly modulating the orbital populations on Mn atoms can be achieved at ferroelectric/manganite interfaces by the presence of ferroelectric polarization on the nanoscale. The change in orbital occupation can be as large as 10%, greatly exceeding that of bulk manganites. This reversible orbital splitting is in large part controlled by the propagation of ferroelectric polar displacements into the interfacial region, a structural motif absent in the bulk and unique to the interface. We use epitaxial thin film growth and scanning transmission electron microscopy to verify this key interfacial polar distortion and discuss the potential of reversible control of orbital polarization via nanoscale ferroelectrics.

  19. Direct Imaging of Dynamic Glassy Behavior in a Strained Manganite Film

    NASA Astrophysics Data System (ADS)

    Kundhikanjana, Worasom; Sheng, Zhigao; Yang, Yongliang; Lai, Keji; Ma, Eric Yue; Cui, Yong-Tao; Kelly, Michael A.; Nakamura, Masao; Kawasaki, Masashi; Tokura, Yoshinori; Tang, Qiaochu; Zhang, Kun; Li, Xinxin; Shen, Zhi-Xun

    2015-12-01

    Complex many-body interaction in perovskite manganites gives rise to a strong competition between ferromagnetic metallic and charge-ordered phases with nanoscale electronic inhomogeneity and glassy behaviors. Investigating this glassy state requires high-resolution imaging techniques with sufficient sensitivity and stability. Here, we present the results of a near-field microwave microscope imaging on the strain-driven glassy state in a manganite film. The high contrast between the two electrically distinct phases allows direct visualization of the phase separation. The low-temperature microscopic configurations differ upon cooling with different thermal histories. At sufficiently high temperatures, we observe switching between the two phases in either direction. The dynamic switching, however, stops below the glass transition temperature. Compared with the magnetization data, the phase separation was microscopically frozen, while spin relaxation was found in a short period of time.

  20. Direct view at colossal permittivity in donor-acceptor (Nb, In) co-doped rutile TiO2

    NASA Astrophysics Data System (ADS)

    Mandal, Suman; Pal, Somnath; Kundu, Asish K.; Menon, Krishnakumar S. R.; Hazarika, Abhijit; Rioult, Maxime; Belkhou, Rachid

    2016-08-01

    Topical observations of colossal permittivity (CP) with low dielectric loss in donor-acceptor cations co-doped rutile TiO2 have opened up several possibilities in microelectronics and energy-storage devices. Yet, the precise origin of the CP behavior, knowledge of which is essential to empower the device integration suitably, is highly disputed in the literature. From spectromicroscopic approach besides dielectric measurements, we explore that microscopic electronic inhomogeneities along with the nano-scale phase boundaries and the low temperature polaronic relaxation are mostly responsible for such a dielectric behavior, rather than electron-pinned defect-dipoles/grain-boundary effects as usually proposed. Donor-acceptor co-doping results in a controlled carrier-hopping inevitably influencing the dielectric loss while invariably upholding the CP value.

  1. [Oxidation Process of Dissolvable Sulfide by Manganite and Its Influencing Factors].

    PubMed

    Luo, Yao; Li, Shan; Tan, Wen-feng; Liu, Fan; Cai, Chong-fa; Qiu, Guo-hong

    2016-04-15

    As one of the manganese oxides, which are easily generated and widely distributed in supergene environment, manganite participates in the oxidation of dissolvable sulfide (S²⁻), and affects the migration, transformation, and the fate of sulfides. In the present work, the redox mechanism was studied by determining the intermediates, and the influence of initial pH and oxygen atmosphere on the processes were studied. The chemical composition, crystal structures and micromorphologies were characterized by XRD, FTIR and TEM. The concentration of S²⁻ and its oxidation products were analyzed using spectrophotometer, high performance liquid chromatograph and ion chromatograph. The results indicated that elemental sulfur was formed as the major oxidation product of S²⁻ oxidation, and decreased pH could accelerate the oxidation rate of S²⁻ in the initial stage, however, there was no significant influence on final products. Elemental S could be further oxidized to S₂O₃²⁻ when the reaction system was bubbled with oxygen, and manganite exhibited excellent catalytic performance and chemical stability during the oxidation of dissolvable sulfide by oxygen. After reaction of more than 10 h, the crystal structure of manganite remained stable. PMID:27548980

  2. Temperature-Dependent Asymmetry of Anisotropic Magnetoresistance in Silicon p-n Junctions

    PubMed Central

    Yang, D. Z.; Wang, T.; Sui, W. B.; Si, M. S.; Guo, D. W.; Shi, Z.; Wang, F. C.; Xue, D. S.

    2015-01-01

    We report a large but asymmetric magnetoresistance in silicon p-n junctions, which contrasts with the fact of magnetoresistance being symmetric in magnetic metals and semiconductors. With temperature decreasing from 293 K to 100 K, the magnetoresistance sharply increases from 50% to 150% under a magnetic field of 2 T. At the same time, an asymmetric magnetoresistance, which manifests itself as a magnetoresistance voltage offset with respect to the sign of magnetic field, occurs and linearly increases with magnetoresistance. More interestingly, in contrast with other materials, the lineshape of anisotropic magnetoresistance in silicon p-n junctions significantly depends on temperature. As temperature decreases from 293 K to 100 K, the width of peak shrinks from 90° to 70°. We ascribe these novel magnetoresistance to the asymmetric geometry of the space charge region in p-n junction induced by the magnetic field. In the vicinity of the space charge region the current paths are deflected, contributing the Hall field to the asymmetric magnetoresistance. Therefore, the observed temperature-dependent asymmetry of magnetoresistance is proved to be a direct consequence of the spatial configuration evolution of space charge region with temperature. PMID:26323495

  3. Spin rectification induced by spin Hall magnetoresistance at room temperature

    NASA Astrophysics Data System (ADS)

    Wang, P.; Jiang, S. W.; Luan, Z. Z.; Zhou, L. F.; Ding, H. F.; Zhou, Y.; Tao, X. D.; Wu, D.

    2016-09-01

    We have experimentally and theoretically investigated the dc voltage generation in the heterostructure of Pt and yttrium iron garnet under the ferromagnetic resonance. Besides a symmetric Lorenz line shape dc voltage, an antisymmetric Lorenz line shape dc voltage is observed in field scan, which can solely originate from the spin rectification effect due to the spin Hall magnetoresistance. The angular dependence of the dc voltage is theoretically analyzed by taking into account both the spin pumping and the spin rectification effects. We find that the experimental results are in excellent agreement with the theoretical model, further identifying the spin Hall magnetoresistance origin of the spin rectification effect. Moreover, the spin pumping and the spin rectification effects are quantitatively separated by their different angular dependence at particular experimental geometry.

  4. Enhancing magnetoresistance in tetrathiafulvalene carboxylate modified iron oxide nanoparticle assemblies

    NASA Astrophysics Data System (ADS)

    Lv, Zhong-Peng; Luan, Zhong-Zhi; Cai, Pei-Yu; Wang, Tao; Li, Cheng-Hui; Wu, Di; Zuo, Jing-Lin; Sun, Shouheng

    2016-06-01

    We report a facile approach to stabilize Fe3O4 nanoparticles (NPs) by using tetrathiafulvalene carboxylate (TTF-COO-) and to control electron transport with an enhanced magnetoresistance (MR) effect in TTF-COO-Fe3O4 NP assemblies. This TTF-COO-coating is advantageous over other conventional organic coatings, making it possible to develop stable Fe3O4 NP arrays for sensitive spintronics applications.We report a facile approach to stabilize Fe3O4 nanoparticles (NPs) by using tetrathiafulvalene carboxylate (TTF-COO-) and to control electron transport with an enhanced magnetoresistance (MR) effect in TTF-COO-Fe3O4 NP assemblies. This TTF-COO-coating is advantageous over other conventional organic coatings, making it possible to develop stable Fe3O4 NP arrays for sensitive spintronics applications. Electronic supplementary information (ESI) available: Experimental details; supplementary figures and tables. See DOI: 10.1039/c6nr03311c

  5. Maximum non-saturating magnetoresistance in MoTe2

    NASA Astrophysics Data System (ADS)

    Abdel-Hafiez, Mahmoud; Gu, Zhehao; Chen, Xiao-Jia; Center for High Pressure Science; Technology Advanced Research, Shanghai, 201203, China Team

    The search for exotic materials with a linear magnetoresistance (MR) is one of the most challenging tasks of the condensed matter community and materials science. Here, we investigated the magnetoresistance behavior of high-quality single crystals MoTe2. A large linear non-staturated MR in a magnetic field of 60 T, was observed with a maximum at a temperature of T = 45 K. The detailed field and temperature dependencies will be presented. Our results not only provide a general scaling approach for the anisotropic MR but also are crucial for correctly understanding the mechanism of the linear MR, including the origin of the remarkable ``turn-on'' behavior in the resistance versus temperature curve.

  6. Co/Cu multilayers with reduced magnetoresistive hysteresis

    NASA Astrophysics Data System (ADS)

    Kubinski, D. J.; Holloway, H.

    1997-01-01

    Practical applications of Co/Cu multilayers (MLs) require copper thicknesses either ≈ 9 Å or ≈ 20 Å corresponding to the first or second antiferromagnetic maximum (AFM). The first AFM has much smaller magnetoresistive hysteresis than the second, but also has lower sensitivity. We discuss application of these MLs when low hysteresis is required. For the first AFM we may improve the sensitivity while retaining low hysteresis by increasing the cobalt thickness to 30-40 Å. At the second AFM we can reduce the magnetoresistive hysteresis by reducing the cobalt thickness to ˜ 3 Å. A particularly attractive combination of high sensitivity and low hysteresis is obtained at the second AFM by alternating such very thin Co layers with 15 Å thick Co layers.

  7. A Magnetoresistive Tactile Sensor for Harsh Environment Applications

    PubMed Central

    Alfadhel, Ahmed; Khan, Mohammed Asadullah; Cardoso, Susana; Leitao, Diana; Kosel, Jürgen

    2016-01-01

    A magnetoresistive tactile sensor is reported, which is capable of working in high temperatures up to 140 °C. Hair-like bioinspired structures, known as cilia, made out of permanent magnetic nanocomposite material on top of spin-valve giant magnetoresistive (GMR) sensors are used for tactile sensing at high temperatures. The magnetic nanocomposite, consisting of iron nanowires incorporated into the polymer polydimethylsiloxane (PDMS), is very flexible, biocompatible, has high remanence, and is also resilient to antagonistic sensing ambient. When the cilia come in contact with a surface, they deflect in compliance with the surface topology. This yields a change of the GMR sensor signal, enabling the detection of extremely fine features. The spin-valve is covered with a passivation layer, which enables adequate performance in spite of harsh environmental conditions, as demonstrated in this paper for high temperature. PMID:27164113

  8. Negative Magnetoresistance in Viscous Flow of Two-Dimensional Electrons

    NASA Astrophysics Data System (ADS)

    Alekseev, P. S.

    2016-10-01

    At low temperatures, in very clean two-dimensional (2D) samples, the electron mean free path for collisions with static defects and phonons becomes greater than the sample width. Under this condition, the electron transport occurs by formation of a viscous flow of an electron fluid. We study the viscous flow of 2D electrons in a magnetic field perpendicular to the 2D layer. We calculate the viscosity coefficients as the functions of magnetic field and temperature. The off-diagonal viscosity coefficient determines the dispersion of the 2D hydrodynamic waves. The decrease of the diagonal viscosity in magnetic field leads to negative magnetoresistance which is temperature and size dependent. Our analysis demonstrates that this viscous mechanism is responsible for the giant negative magnetoresistance recently observed in the ultrahigh-mobility GaAs quantum wells. We conclude that 2D electrons in those structures in moderate magnetic fields should be treated as a viscous fluid.

  9. Insensitivity of tunneling anisotropic magnetoresistance to non-magnetic electrodes

    SciTech Connect

    Wang, Y. Y.; Song, C. Wang, G. Y.; Zeng, F.; Pan, F.

    2013-11-11

    Ferromagnetic electrodes play a crucial role in magnetoresistance effect and spin injection, whereas the essential features of non-magnetic metal electrodes in spintronics are commonly ignored except for their electrical conductivity. Here, we verify that the room-temperature tunneling anisotropic magnetoresistance (TAMR) behavior in antiferromagnet-based [Pt/Co]/IrMn/AlO{sub x}/metal (metal = Pt, Au, Cu, Al) junctions is insensitive to the top metal electrodes. Similar out-of-plane signals are detected for different electrodes, in contrast to the varied shapes of in-plane TAMR curves which are most likely attributed to the differences in the multidomain structure of the magnetic electrode. This would add a different dimension to spintronics.

  10. Theoretical study of disorder induced magnetoresistance in graphene

    NASA Astrophysics Data System (ADS)

    Adam, Shaffique; Ping, Jinglei; Yudhistira, Indra; Ramakrishnan, Navneeth; Cho, Sungjae; Fuhrer, Michael S.

    2014-03-01

    In this work we predict theoretically that carrier density inhomogeneity provides a new mechanism for classical magnetoresistance. For concreteness, we study the case of graphene where density inhomogeneity and carrier scattering is dominated by charged impurities, although the mechanism itself is quite general and applies to other systems in which there are large spatial fluctuations of the carrier density. Calculations using an effective medium approximation show that low-field magnetoresistance becomes a universal function of the ratio between the average carrier density and the fluctuations of the carrier density, and scales as a power-law when this ratio is large. Our finding is in excellent agreement with recent experimental results. This work is supported by the Singapore National Research Foundation NRF-NRFF2012-01.

  11. Development of eddy current probes based on magnetoresistive sensors arrays

    NASA Astrophysics Data System (ADS)

    Sergeeva-Chollet, N.; Decitre, J.-M.; Fermon, C.; Pelkner, M.; Reimund, V.; Kreutzbruck, M.

    2014-02-01

    Eddy Current Technique is a powerful method for detection of surface notches and of buried flaws during inspection of metallic parts. Recent EC array probes have demonstrated a fast and efficient control of large surfaces. Nevertheless, when the size of flaws decreases or the defect is rather deep, traditional winding coil probes turn out to be useless. Magnetoresistive sensors present the advantages of flat frequency response and micron size. These sensors are hence very attractive for the detection of buried defects that require low frequencies because of skin depth effect. An optimization of the probe with magnetoresistive sensors as receivers has been made by simulations using CIVA software and finite elements methods with OPERA. EC probes for buried flaw detection have been designed. Experimental results have been compared with simulations.

  12. Giant magnetoresistance in the variable-range hopping regime

    SciTech Connect

    Ioffe, L. B.; Spivak, B. Z.

    2013-09-15

    We predict the universal power-law dependence of the localization length on the magnetic field in the strongly localized regime. This effect is due to the orbital quantum interference. Physically, this dependence shows up in an anomalously large negative magnetoresistance in the hopping regime. The reason for the universality is that the problem of the electron tunneling in a random media belongs to the same universality class as the directed polymer problem even in the case of wave functions of random sign. We present numerical simulations that prove this conjecture. We discuss the existing experiments that show anomalously large magnetoresistance. We also discuss the role of localized spins in real materials and the spin polarizing effect of the magnetic field.

  13. A Magnetoresistive Tactile Sensor for Harsh Environment Applications.

    PubMed

    Alfadhel, Ahmed; Khan, Mohammed Asadullah; Cardoso, Susana; Leitao, Diana; Kosel, Jürgen

    2016-01-01

    A magnetoresistive tactile sensor is reported, which is capable of working in high temperatures up to 140 °C. Hair-like bioinspired structures, known as cilia, made out of permanent magnetic nanocomposite material on top of spin-valve giant magnetoresistive (GMR) sensors are used for tactile sensing at high temperatures. The magnetic nanocomposite, consisting of iron nanowires incorporated into the polymer polydimethylsiloxane (PDMS), is very flexible, biocompatible, has high remanence, and is also resilient to antagonistic sensing ambient. When the cilia come in contact with a surface, they deflect in compliance with the surface topology. This yields a change of the GMR sensor signal, enabling the detection of extremely fine features. The spin-valve is covered with a passivation layer, which enables adequate performance in spite of harsh environmental conditions, as demonstrated in this paper for high temperature. PMID:27164113

  14. Wheatstone bridge giant-magnetoresistance based cell counter.

    PubMed

    Lee, Chiun-Peng; Lai, Mei-Feng; Huang, Hao-Ting; Lin, Chi-Wen; Wei, Zung-Hang

    2014-07-15

    A Wheatstone bridge giant magnetoresistance (GMR) biosensor was proposed here for the detection and counting of magnetic cells. The biosensor was made of a top-pinned spin-valve layer structure, and it was integrated with a microchannel possessing the function of hydrodynamic focusing that allowed the cells to flow in series one by one and ensured the accuracy of detection. Through measuring the magnetoresistance variation caused by the stray field of the magnetic cells that flowed through the microchannel above the GMR biosensor, we can not only detect and count the cells but we can also recognize cells with different magnetic moments. In addition, a magnetic field gradient was applied for the separation of different cells into different channels. PMID:24534580

  15. Zener double exchange polynomial law for metallic region of La1-xKxMnO3 manganites

    NASA Astrophysics Data System (ADS)

    Gadani, Keval; Dhruv, Davit; Joshi, Zalak; Boricha, Hetal; Vaghela, Eash; Pandya, D. D.; Shah, N. A.; Solanki, P. S.

    2016-05-01

    In this communication, we present the results of the studied on the charge transport mechanism of well reported La1-xKxMnO3 manganites using various theoretical models and laws. Structural properties and phase quality of the samples have been studied using XRD measurements and analyzed by performing Rietveld refinements. Single phasic nature with doping level dependent structural phase transition has been observed for the presently studied manganite system. Metallic region of the reported resistivity data has been explained using two different theoretical models, namely, small polaron conduction (SPC) mechanism and zener double exchange (ZDE) polynomial law. ZDE polynomial law is found to be an appropriate mechanism to understand the charge transport in metallic region of presently studied manganites and has been discussed in the context of one magnon scattering law.

  16. Competition between covalent bonding and charge transfer at complex-oxide interfaces.

    PubMed

    Salafranca, Juan; Rincón, Julián; Tornos, Javier; León, Carlos; Santamaria, Jacobo; Dagotto, Elbio; Pennycook, Stephen J; Varela, Maria

    2014-05-16

    Here we study the electronic properties of cuprate-manganite interfaces. By means of atomic resolution electron microscopy and spectroscopy, we produce a subnanometer scale map of the transition metal oxidation state profile across the interface between the high Tc superconductor YBa2Cu3O7-δ and the colossal magnetoresistance compound (La,Ca)MnO3. A net transfer of electrons from manganite to cuprate with a peculiar nonmonotonic charge profile is observed. Model calculations rationalize the profile in terms of the competition between standard charge transfer tendencies (due to band mismatch), strong chemical bonding effects across the interface, and Cu substitution into the Mn lattice, with different characteristic length scales.

  17. Enhancing magnetoresistance in tetrathiafulvalene carboxylate modified iron oxide nanoparticle assemblies.

    PubMed

    Lv, Zhong-Peng; Luan, Zhong-Zhi; Cai, Pei-Yu; Wang, Tao; Li, Cheng-Hui; Wu, Di; Zuo, Jing-Lin; Sun, Shouheng

    2016-06-16

    We report a facile approach to stabilize Fe3O4 nanoparticles (NPs) by using tetrathiafulvalene carboxylate (TTF-COO(-)) and to control electron transport with an enhanced magnetoresistance (MR) effect in TTF-COO-Fe3O4 NP assemblies. This TTF-COO-coating is advantageous over other conventional organic coatings, making it possible to develop stable Fe3O4 NP arrays for sensitive spintronics applications. PMID:27271347

  18. Large linear magnetoresistance in topological crystalline insulator Pb0.6Sn0.4Te

    NASA Astrophysics Data System (ADS)

    Roychowdhury, Subhajit; Ghara, Somnath; Guin, Satya N.; Sundaresan, A.; Biswas, Kanishka

    2016-01-01

    Classical magnetoresistance generally follows the quadratic dependence of the magnetic field at lower field and finally saturates when field is larger. Here, we report the large positive non-saturating linear magnetoresistance in topological crystalline insulator, Pb0.6Sn0.4Te, at different temperatures between 3 K and 300 K in magnetic field up to 9 T. Magnetoresistance value as high as ∼200% was achieved at 3 K at magnetic field of 9 T. Linear magnetoresistance observed in Pb0.6Sn0.4Te is mainly governed by the spatial fluctuation carrier mobility due to distortions in the current paths in inhomogeneous conductor.

  19. Negative magnetoresistance in Dirac semimetal Cd3As2

    PubMed Central

    Li, Hui; He, Hongtao; Lu, Hai-Zhou; Zhang, Huachen; Liu, Hongchao; Ma, Rong; Fan, Zhiyong; Shen, Shun-Qing; Wang, Jiannong

    2016-01-01

    A large negative magnetoresistance (NMR) is anticipated in topological semimetals in parallel magnetic fields, demonstrating the chiral anomaly, a long-sought high-energy-physics effect, in solid-state systems. Recent experiments reveal that the Dirac semimetal Cd3As2 has the record-high mobility and positive linear magnetoresistance in perpendicular magnetic fields. However, the NMR has not yet been unveiled. Here we report the observation of NMR in Cd3As2 microribbons in parallel magnetic fields up to 66% at 50 K and visible at room temperatures. The NMR is sensitive to the angle between magnetic and electrical fields, robust against temperature and dependent on the carrier density. The large NMR results from low carrier densities in our Cd3As2 samples, ranging from 3.0 × 1017 cm−3 at 300 K to 2.2 × 1016 cm−3 below 50 K. We therefore attribute the observed NMR to the chiral anomaly. In perpendicular magnetic fields, a positive linear magnetoresistance up to 1,670% at 14 T and 2 K is also observed. PMID:26744088

  20. Isothermal anisotropic magnetoresistance in antiferromagnetic metallic IrMn

    PubMed Central

    Galceran, R.; Fina, I.; Cisneros-Fernández, J.; Bozzo, B.; Frontera, C.; López-Mir, L.; Deniz, H.; Park, K.-W.; Park, B.-G.; Balcells, Ll.; Martí, X.; Jungwirth, T.; Martínez, B.

    2016-01-01

    Antiferromagnetic spintronics is an emerging field; antiferromagnets can improve the functionalities of ferromagnets with higher response times, and having the information shielded against external magnetic field. Moreover, a large list of aniferromagnetic semiconductors and metals with Néel temperatures above room temperature exists. In the present manuscript, we persevere in the quest for the limits of how large can anisotropic magnetoresistance be in antiferromagnetic materials with very large spin-orbit coupling. We selected IrMn as a prime example of first-class moment (Mn) and spin-orbit (Ir) combination. Isothermal magnetotransport measurements in an antiferromagnetic-metal(IrMn)/ferromagnetic-insulator thin film bilayer have been performed. The metal/insulator structure with magnetic coupling between both layers allows the measurement of the modulation of the transport properties exclusively in the antiferromagnetic layer. Anisotropic magnetoresistance as large as 0.15% has been found, which is much larger than that for a bare IrMn layer. Interestingly, it has been observed that anisotropic magnetoresistance is strongly influenced by the field cooling conditions, signaling the dependence of the found response on the formation of domains at the magnetic ordering temperature. PMID:27762278

  1. Anisotropic magnetoresistivity in structured elastomer composites: modelling and experiments.

    PubMed

    Mietta, José Luis; Tamborenea, Pablo I; Martin Negri, R

    2016-08-14

    A constitutive model for the anisotropic magnetoresistivity in structured elastomer composites (SECs) is proposed. The SECs considered here are oriented pseudo-chains of conductive-magnetic inorganic materials inside an elastomer organic matrix. The pseudo-chains are formed by fillers which are simultaneously conductive and magnetic dispersed in the polymer before curing or solvent evaporation. The SEC is then prepared in the presence of a uniform magnetic field, referred to as Hcuring. This procedure generates the pseudo-chains, which are preferentially aligned in the direction of Hcuring. Electrical conduction is present in that direction only. The constitutive model for the magnetoresistance considers the magnetic pressure, Pmag, induced on the pseudo-chains by an external magnetic field, H, applied in the direction of the pseudo-chains. The relative changes in conductivity as a function of H are calculated by evaluating the relative increase of the electron tunnelling probability with Pmag, a magneto-elastic coupling which produces an increase of conductivity with magnetization. The model is used to adjust experimental results of magnetoresistance in a specific SEC where the polymer is polydimethylsiloxane, PDMS, and fillers are microparticles of magnetite-silver (referred to as Fe3O4[Ag]). Simulations of the expected response for other materials in both superparamagnetic and blocked magnetic states are presented, showing the influence of the Young's modulus of the matrix and filler's saturation magnetization. PMID:27418417

  2. Anisotropic giant magnetoresistance in NbSb2

    PubMed Central

    Wang, Kefeng; Graf, D.; Li, Lijun; Wang, Limin; Petrovic, C.

    2014-01-01

    The magnetic field response of the transport properties of novel materials and then the large magnetoresistance effects are of broad importance in both science and application. We report large transverse magnetoreistance (the magnetoresistant ratio ~ 1.3 × 105% in 2 K and 9 T field, and 4.3 × 106% in 0.4 K and 32 T field, without saturation) and field-induced metal-semiconductor-like transition, in NbSb2 single crystal. Magnetoresistance is significantly suppressed but the metal-semiconductor-like transition persists when the current is along the ac-plane. The sign reversal of the Hall resistivity and Seebeck coefficient in the field, plus the electronic structure reveal the coexistence of a small number of holes with very high mobility and a large number of electrons with low mobility. The large MR is attributed to the change of the Fermi surface induced by the magnetic field which is related to the Dirac-like point, in addition to orbital MR expected for high mobility metals. PMID:25476239

  3. Magnetoresistance in organic spintronic devices: the role of nonlinear effects

    NASA Astrophysics Data System (ADS)

    Shumilin, A. V.; Kabanov, V. V.; Dediu, V. A.

    2015-02-01

    We derive kinetic equations describing injection and transport of spin-polarized carriers in organic semiconductors with hopping conductivity via an impurity level. The model predicts a strongly voltage dependent magnetoresistance, defined as resistance variation between devices with parallel and antiparallel electrode magnetizations (spin-valve effect). The voltage dependence of the magnetoresistance splits into three distinct regimes. The first regime matches well-known inorganic spintronic regimes, corresponding to barrier-controlled spin injection or the well-known conductivity mismatch case. The second regime at intermediate voltages corresponds to strongly suppressed magnetoresistance. The third regime develops at higher voltages and accounts for a novel paradigm. It is promoted by the strong nonlinearity in the charge transport whose strength is characterized by the dimensionless parameter eU/kBT. This nonlinearity, depending on device conditions, can lead to both significant enhancement or to exponential suppression of the spin-valve effect in organic devices. We believe that these predictions are valid beyond the case of organic semiconductors and should be considered for any material characterized by strongly nonlinear charge transport.

  4. Enhancement of Low-field Magnetoresistance in Self-Assembled Epitaxial La0.67Ca0.33MnO3:NiO and La0.67Ca0.33MnO3:Co3O4 Composite Films via Polymer-Assisted Deposition

    PubMed Central

    Zhou, Meng; Li, Yuling; Jeon, Il; Yi, Qinghua; Zhu, Xuebin; Tang, Xianwu; Wang, Haiyan; Fei, Ling; Sun, Yuping; Deng, Shuguang; Matsuo, Yutaka; Luo, Hongmei; Zou, Guifu

    2016-01-01

    Polymer-assisted deposition method has been used to fabricate self-assembled epitaxial La0.67Ca0.33MnO3:NiO and La0.67Ca0.33MnO3:Co3O4 films on LaAlO3 substrates. Compared to pulsed-laser deposition method, polymer-assisted deposition provides a simpler and lower-cost approach to self-assembled composite films with enhanced low-field magnetoresistance effect. After the addition of NiO or Co3O4, triangular NiO and tetrahedral Co3O4 nanoparticles remain on the surface of La0.67Ca0.33MnO3 films. This results in a dramatic increase in resistivity of the films from 0.0061 Ω•cm to 0.59 Ω•cm and 1.07 Ω•cm, and a decrease in metal-insulator transition temperature from 270 K to 180 K and 172 K by the addition of 10%-NiO and 10%-Co3O4, respectively. Accordingly, the maximum absolute magnetoresistance value is improved from −44.6% to −59.1% and −52.7% by the addition of 10%-NiO and 10%-Co3O4, respectively. The enhanced low-field magnetoresistance property is ascribed to the introduced insulating phase at the grain boundaries. The magnetism is found to be more suppressed for the La0.67Ca0.33MnO3:Co3O4 composite films than the La0.67Ca0.33MnO3:NiO films, which can be attributed to the antiferromagnetic properties of the Co3O4 phase. The solution-processed composite films show enhanced low-field magnetoresistance effect which are crucial in practical applications. We expect our polymer-assisted deposited films paving the pathway in the field of hole-doped perovskites with their intrinsic colossal magnetoresistance. PMID:27381661

  5. Enhancement of Low-field Magnetoresistance in Self-Assembled Epitaxial La0.67Ca0.33MnO3:NiO and La0.67Ca0.33MnO3:Co3O4 Composite Films via Polymer-Assisted Deposition.

    PubMed

    Zhou, Meng; Li, Yuling; Jeon, Il; Yi, Qinghua; Zhu, Xuebin; Tang, Xianwu; Wang, Haiyan; Fei, Ling; Sun, Yuping; Deng, Shuguang; Matsuo, Yutaka; Luo, Hongmei; Zou, Guifu

    2016-01-01

    Polymer-assisted deposition method has been used to fabricate self-assembled epitaxial La0.67Ca0.33MnO3:NiO and La0.67Ca0.33MnO3:Co3O4 films on LaAlO3 substrates. Compared to pulsed-laser deposition method, polymer-assisted deposition provides a simpler and lower-cost approach to self-assembled composite films with enhanced low-field magnetoresistance effect. After the addition of NiO or Co3O4, triangular NiO and tetrahedral Co3O4 nanoparticles remain on the surface of La0.67Ca0.33MnO3 films. This results in a dramatic increase in resistivity of the films from 0.0061 Ω•cm to 0.59 Ω•cm and 1.07 Ω•cm, and a decrease in metal-insulator transition temperature from 270 K to 180 K and 172 K by the addition of 10%-NiO and 10%-Co3O4, respectively. Accordingly, the maximum absolute magnetoresistance value is improved from -44.6% to -59.1% and -52.7% by the addition of 10%-NiO and 10%-Co3O4, respectively. The enhanced low-field magnetoresistance property is ascribed to the introduced insulating phase at the grain boundaries. The magnetism is found to be more suppressed for the La0.67Ca0.33MnO3:Co3O4 composite films than the La0.67Ca0.33MnO3:NiO films, which can be attributed to the antiferromagnetic properties of the Co3O4 phase. The solution-processed composite films show enhanced low-field magnetoresistance effect which are crucial in practical applications. We expect our polymer-assisted deposited films paving the pathway in the field of hole-doped perovskites with their intrinsic colossal magnetoresistance. PMID:27381661

  6. Microstructural and electrical changes in nickel manganite powder induced by mechanical activation

    SciTech Connect

    Savic, S.M.; Mancic, L.; Stojanovic, G.; Brankovic, Z.; Aleksic, O.S.; Brankovic, G.

    2011-07-15

    Highlights: {yields} The influence of mechanical activation on microstructure evolution in the nickel manganite powder was investigated as well as electrical properties of the sintered samples. {yields} Structural refinement obtained by Topas-Academic software based on Rietveld analysis showed that the milling process remarkably changed the powder morphology and microstructure. {yields} SEM studies of sintered samples also revealed the strong influence of milling time on ceramics density (increases with milling time). {yields} The electrical properties of ceramic samples are clearly conditioned by terms of synthesis, in our case the time of mechanical activation. {yields} The highest density and higher values of dielectric constant were achieved at the sample activated for 45 min. -- Abstract: Nickel manganite powder synthesized by calcination of a stoichiometric mixture of manganese and nickel oxide was additionally mechanically activated in a high energy planetary ball mill for 5-60 min in order to obtain a pure NiMn{sub 2}O{sub 4} phase. The as-prepared powders were uniaxially pressed into disc shape pellets and then sintered for 60 min at 1200 {sup o}C. Changes in the particle morphology induced by mechanical activation were monitored using scanning electron microscopy, while changes in powder structural characteristics were followed using X-ray powder diffraction. The ac impedance spectroscopy was performed on sintered nickel manganite samples at 25 {sup o}C, 50 {sup o}C and 80 {sup o}C. It was shown that mechanical activation intensifies transport processes causing a decrease in the average crystallites size, while longer activation times can lead to the formation of aggregates, defects and increase of lattice microstrains. The observed changes in microstructures were correlated with measured electrical properties in order to define optimal processing conditions.

  7. Dynamic and structural properties of orthorhombic rare-earth manganites under high pressure

    NASA Astrophysics Data System (ADS)

    Mota, D. A.; Almeida, A.; Rodrigues, V. H.; Costa, M. M. R.; Tavares, P.; Bouvier, P.; Guennou, M.; Kreisel, J.; Moreira, J. Agostinho

    2014-08-01

    We report a high-pressure study of orthorhombic rare-earth manganites AMnO3 using Raman scattering (for A=Pr, Nd, Sm, Eu, Tb, and Dy) and synchrotron x-ray diffraction (XRD), for A = Pr, Sm, Eu, and Dy. In all cases, a phase transition was evidenced by the disappearance of the Raman signal at a critical pressure that depends on the A cation. For the compounds with A=Pr, Sm, and Dy, XRD confirms the presence of a corresponding structural transition to a noncubic phase, so that the disappearance of the Raman spectrum can be interpreted as an insulator-to-metal transition. We analyze the compression mechanisms at work in the different manganites via the pressure dependence of the lattice parameters, the shear strain in the ac plane, and the Raman bands associated with out-of-phase MnO6 rotations and in-plane O2 symmetric stretching modes. Our data show a crossover across the rare-earth series between two different kinds of behavior. For the smaller A cations considered in this study (Dy and Tb), the compression is nearly isotropic in the ac plane, with only small evolutions of the tilt angles and cooperative Jahn-Teller distortion. As the radius of the A cation increases, the pressure-induced reduction of Jahn-Teller distortion becomes more pronounced and increasingly significant as a compression mechanism, while the pressure-induced tilting of octahedra chains becomes conversely less pronounced. We finally discuss our results in light of the notion of chemical pressure and show that the analogy with hydrostatic pressure works quite well for manganites with the smaller A cations considered in this paper but can be misleading with large A cations.

  8. Magnetic exchange interaction between rare-earth and Mn ions in multiferroic hexagonal manganites

    SciTech Connect

    Talbayev, Diyar; Trugman, Stuart A; Taylor, Antoinette J; Averitt, Richard D; Namjung, Hur; Andrew, Laforge D; Dimitri, Basov N

    2008-01-01

    The authors report a study of magnetic dynamics in multiferroic hexagonal manganite HoMnO{sub 3} by far-infrared spectroscopy. Low-temperature magnetic excitation spectrum of HoMnO{sub 3} consists of magnetic-dipole transitions of Ho ions within the crystal-field split J = 8 manifold and of the triangular antiferromagnetic resonance of Mn ions. They determine the effective spin Hamiltonian for the Ho ion ground state. The magnetic-field splitting of the Mn antiferromagnetic resonance allows us to measure the magnetic exchange coupling between the rare-earth and Mn ions.

  9. Homotopy-Theoretic Study &Atomic-Scale Observation of Vortex Domains in Hexagonal Manganites.

    PubMed

    Li, Jun; Chiang, Fu-Kuo; Chen, Zhen; Ma, Chao; Chu, Ming-Wen; Chen, Cheng-Hsuan; Tian, Huanfang; Yang, Huaixin; Li, Jianqi

    2016-01-01

    Essential structural properties of the non-trivial "string-wall-bounded" topological defects in hexagonal manganites are studied through homotopy group theory and spherical aberration-corrected scanning transmission electron microscopy. The appearance of a "string-wall-bounded" configuration in RMnO3 is shown to be strongly linked with the transformation of the degeneracy space. The defect core regions (~50 Å) mainly adopt the continuous U(1) symmetry of the high-temperature phase, which is essential for the formation and proliferation of vortices. Direct visualization of vortex strings at atomic scale provides insight into the mechanisms and macro-behavior of topological defects in crystalline materials.

  10. X-ray effects in charge-ordered manganites: A magnetic mechanism of persistent photoconductivity

    SciTech Connect

    Keimer, B.; Casa, D.; Kiryukhin, V.; Saleh, O.A.; Hill, J.P.; Tomioka, Y.; Tokura, Y. |

    1998-12-31

    Charge-ordered manganites of composite Pr{sub 1{minus}x}(Ca{sub 1{minus}y}Sr{sub y}){sub x}MnO{sub 3} exhibit persistent photoconductivity when illuminated by x-rays. The authors review transport and x-ray diffraction data as functions of x-ray exposure, magnetic field, and temperature which shed light on the origin of this unusual behavior. The experimental evidence suggests that the mechanism primarily involves a ferromagnetic polarization of local spins by hot electrons generated by the x-rays.

  11. Successive Magnetic-Field-Induced Transitions and Colossal Magnetoelectric Effect in Ni3TeO6

    DOE PAGESBeta

    Kim, Jae Wook; Artyukhin, Sergei; Mun, Eun Deok; Jaime, Marcelo; Harrison, Neil; Hansen, Anders; Yang, J. J.; Oh, Yoon Seok; Vanderbilt, David; Zapf, Vivien S.; et al

    2015-09-24

    In this paper, we report the discovery of a metamagnetic phase transition in a polar antiferromagnet Ni3TeO6 that occurs at 52 T. The new phase transition accompanies a colossal magnetoelectric effect, with a magnetic-field-induced polarization change of 0.3 μC/cm2, a value that is 4 times larger than for the spin-flop transition at 9 T in the same material, and also comparable to the largest magnetically induced polarization changes observed to date. Via density-functional calculations we construct a full microscopic model that describes the data. We model the spin structures in all fields and clarify the physics behind the 52 Tmore » transition. The high-field transition involves a competition between multiple different exchange interactions which drives the polarization change through the exchange-striction mechanism. Finally, the resultant spin structure is rather counterintuitive and complex, thus providing new insights on design principles for materials with strong magnetoelectric coupling.« less

  12. Colossal Piezoresistance in strained La0.67Sr0.33MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Viitaniemi, Maria; Kwak, In Hae; Biswas, Amlan

    2015-03-01

    Piezoresistance is the change in electrical resistance as a function of strain. A known mechanism leading to piezoresistance is thermodynamic phase separation. It has been shown that the compound (La1-yPry)1-xCaxMnO3 (LPCMO) exhibits colossal piezoresistance (CPR) at low temperatures due to electronic phase separation. For use in many applications, such as sensors, materials must exhibit CPR near room temperature. A possible candidate compound is La0.67Sr0.33MnO3 (LSMO) which has a Curie temperature of approximately 350 K. However, bulk LSMO single crystals do not show CPR since such samples are uniformly ferromagnetic and metallic with no phase separation. In this study, we examine the piezoresistance of ultrathin LSMO films grown on SrTiO3 (STO) substrates using a three-point beam bending method to control the compressive and tensile strain. It has been suggested that the lattice mismatch strain due to the substrate induces phase separation in these thin films. We have observed CPR in such strained LSMO thin films even at room temperature. NSF DMR-1410237.

  13. Fermi surfaces, spin-mixing parameter, and colossal anisotropy of spin relaxation in transition metals from ab initio theory

    NASA Astrophysics Data System (ADS)

    Zimmermann, Bernd; Mavropoulos, Phivos; Long, Nguyen H.; Gerhorst, Christian-Roman; Blügel, Stefan; Mokrousov, Yuriy

    2016-04-01

    The Fermi surfaces and Elliott-Yafet spin-mixing parameter (EYP) of several elemental metals are studied by ab initio calculations. We focus first on the anisotropy of the EYP as a function of the direction of the spin-quantization axis [B. Zimmermann et al., Phys. Rev. Lett. 109, 236603 (2012), 10.1103/PhysRevLett.109.236603]. We analyze in detail the origin of the gigantic anisotropy in 5 d hcp metals as compared to 5 d cubic metals by band structure calculations and discuss the stability of our results against an applied magnetic field. We further present calculations of light (4 d and 3 d ) hcp crystals, where we find a huge increase of the EYP anisotropy, reaching colossal values as large as 6000 % in hcp Ti. We attribute these findings to the reduced strength of spin-orbit coupling, which promotes the anisotropic spin-flip hot loops at the Fermi surface. In order to conduct these investigations, we developed an adapted tetrahedron-based method for the precise calculation of Fermi surfaces of complicated shape and accurate Fermi-surface integrals within the full-potential relativistic Korringa-Kohn-Rostoker Green function method.

  14. Phase separation and size effects in Pr0.70Ba0.30MnO3+δ perovskite manganites

    NASA Astrophysics Data System (ADS)

    Trukhanov, S. V.; Trukhanov, A. V.; Botez, C. E.; Adair, A. H.; Szymczak, H.; Szymczak, R.

    2007-07-01

    The crystal structure and magnetotransport properties of the A-site ionic ordered state in Pr0.70Ba0.30MnO3+δ (δ = 0, 0.025) have been investigated. It is shown that such a state can be formed in complex manganites with cation ratios \\mathrm {Pr^{3+}/Ba^{2+}}\\gg 1 by using a 'two-step' reduction-reoxidization method. The parent A-site ionic disordered Pr0.70Ba0.30MnO3+δ (δ = 0) compound is an orthorhombic (SG = Imma, Z = 4) ferromagnet with Curie temperature TCap173 K and ground-state spontaneous magnetic moment σS~3.70 µB/f.u. It exhibits two metal-insulator transitions, at TI~128 K and TII~173 K, as well as two peaks of magnetoresistance ~74% and ~79% in a field of 50 kOe. The parent A-site ionic disordered Pr0.70Ba0.30MnO3+δ (δ = 0) sample used in our studies has an average grain size \\langle D\\rangle \\approx 10.213~\\micmu \\mathrm { m} . Successive annealing of this sample in vacuum P[O2]ap10-4 Pa and then in air at T = 800 °C leads to the destruction of its initial grain structure and to its chemical separation into two phases: (i) oxygen stoichiometric A-site ordered PrBaMn2O6 with a tetragonal (SG = P4/mmm, Z = 2) perovskite-like unit cell and Curie temperature TCap313 K and (ii) oxygen superstoichiometric A-site disordered Pr0.90Ba0.10MnO3.05 with an orthorhombic (SG = Pnma, Z = 4) perovskite-like unit cell and Curie temperature TCap133 K. This processed sample has a spontaneous magnetic moment σS~2.82 µB/f.u. in its ground state, and σS~0.59 μB/f.u. at T~300 K. It also exhibits a magnetoresistance of ~14% at ~313 K in a field of 50 kOe. This processed sample has a reduced average grain size \\langle D\\rangle \\approx 491 nm. The two magnetic phases, Pr0.90Ba0.10MnO3.05 and PrBaMn2O6, are exchange-coupled. For Pr0.90Ba0.10MnO3.05 the temperature hysteresis is ~22 K in a field of 10 Oe and ~5 K in a field of 1 kOe. The observed magnetic properties are interpreted in terms of chemical phase separation, grain size, and A-site ionic ordering

  15. Superconductivity emerging from a suppressed large magnetoresistant state in tungsten ditelluride

    PubMed Central

    Kang, Defen; Zhou, Yazhou; Yi, Wei; Yang, Chongli; Guo, Jing; Shi, Youguo; Zhang, Shan; Wang, Zhe; Zhang, Chao; Jiang, Sheng; Li, Aiguo; Yang, Ke; Wu, Qi; Zhang, Guangming; Sun, Liling; Zhao, Zhongxian

    2015-01-01

    The recent discovery of large magnetoresistance in tungsten ditelluride provides a unique playground to find new phenomena and significant perspective for potential applications. The large magnetoresistance effect originates from a perfect balance of hole and electron carriers, which is sensitive to external pressure. Here we report the suppression of the large magnetoresistance and emergence of superconductivity in pressurized tungsten ditelluride via high-pressure synchrotron X-ray diffraction, electrical resistance, magnetoresistance and alternating current magnetic susceptibility measurements. Upon increasing pressure, the positive large magnetoresistance effect is gradually suppressed and turned off at a critical pressure of 10.5 GPa, where superconductivity accordingly emerges. No structural phase transition is observed under the pressure investigated. In situ high-pressure Hall coefficient measurements at low temperatures demonstrate that elevating pressure decreases the population of hole carriers but increases that of the electron ones. Significantly, at the critical pressure, a sign change of the Hall coefficient is observed. PMID:26203807

  16. Superconductivity emerging from a suppressed large magnetoresistant state in tungsten ditelluride

    NASA Astrophysics Data System (ADS)

    Kang, Defen; Zhou, Yazhou; Yi, Wei; Yang, Chongli; Guo, Jing; Shi, Youguo; Zhang, Shan; Wang, Zhe; Zhang, Chao; Jiang, Sheng; Li, Aiguo; Yang, Ke; Wu, Qi; Zhang, Guangming; Sun, Liling; Zhao, Zhongxian

    2015-07-01

    The recent discovery of large magnetoresistance in tungsten ditelluride provides a unique playground to find new phenomena and significant perspective for potential applications. The large magnetoresistance effect originates from a perfect balance of hole and electron carriers, which is sensitive to external pressure. Here we report the suppression of the large magnetoresistance and emergence of superconductivity in pressurized tungsten ditelluride via high-pressure synchrotron X-ray diffraction, electrical resistance, magnetoresistance and alternating current magnetic susceptibility measurements. Upon increasing pressure, the positive large magnetoresistance effect is gradually suppressed and turned off at a critical pressure of 10.5 GPa, where superconductivity accordingly emerges. No structural phase transition is observed under the pressure investigated. In situ high-pressure Hall coefficient measurements at low temperatures demonstrate that elevating pressure decreases the population of hole carriers but increases that of the electron ones. Significantly, at the critical pressure, a sign change of the Hall coefficient is observed.

  17. Magnetoresistance in nanostructured Tb/Ti and Tb/Si multilayers

    SciTech Connect

    Svalov, A. V.; Kurlyandskaya, G. V.; Vas'kovskiy, V. O.; Sorokin, A. N.; Diercks, D.

    2011-01-15

    Magnetic, magnetoresistive and structural properties were studied for [Tb/Ti]{sub n} and [Tb/Si]{sub n} multilayers which were prepared by rf-sputtering. The thickness of the Tb layers varied from 1.5 to 12 nm. The thickness of 2 nm nonmagnetic spacers of Ti or Si was kept constant. Both anisotropic and isotropic magnetoresistance was observed in [Tb/Ti]{sub n} and [Tb/Si]{sub n} multilayers. A decrease in the thickness of the terbium layers led to a decrease in the anisotropic contribution to the total magnetoresistance. The negative isotropic magnetoresistanse in [Tb/Ti]{sub n} and [Tb/Si]{sub n} multilayers can be attributed to the giant magnetoresistance (GMR) and/or high field isotropic magnetoresistance. The structure of the samples of both types enabled the existence of the GMR effect.

  18. Large anisotropic normal-state magnetoresistance in clean MgB2 thin films.

    PubMed

    Li, Qi; Liu, B T; Hu, Y F; Chen, J; Gao, H; Shan, L; Wen, H H; Pogrebnyakov, A V; Redwing, J M; Xi, X X

    2006-04-28

    We report a large normal-state magnetoresistance with temperature-dependent anisotropy in very clean epitaxial MgB2 thin films (residual resistivity much smaller than 1 microOmega cm) grown by hybrid physical-chemical vapor deposition. The magnetoresistance shows a complex dependence on the orientation of the applied magnetic field, with a large magnetoresistance (Delta(rho)/(rho)0=136%) observed for the field H perpendicular ab plane. The angular dependence changes dramatically as the temperature is increased, and at high temperatures the magnetoresistance maximum changes to H||ab. We attribute the large magnetoresistance and the evolution of its angular dependence with temperature to the multiple bands with different Fermi surface topology in MgB2 and the relative scattering rates of the sigma and pi bands, which vary with temperature due to stronger electron-phonon coupling for the sigma bands.

  19. Systematic Angular Study of Magnetoresistance in Permalloy Connected Kagome Artificial Spin Ice

    NASA Astrophysics Data System (ADS)

    Park, Jungsik; Le, Brian; Watts, Justin; Leighton, Chris; Samarth, Nitin; Schiffer, Peter

    Artificial spin ices are nanostructured two-dimensional arrays of ferromagnetic elements, where frustrated interactions lead to unusual collective magnetic behavior. Here we report a room-temperature magnetoresistance study of connected permalloy (Ni81Fe19) kagome artificial spin ice networks, wherein the direction of the applied in-plane magnetic field is systematically varied. We measure both the longitudinal and transverse magnetoresistance in these structures, and we find certain transport geometries of the network show strong angular sensitivity - even small variations in the applied field angle lead to dramatic changes of the magnetoresistance response. We also investigate the magnetization reversal of the networks using magnetic force microscopy (MFM), demonstrating avalanche behavior in the magnetization reversal. The magnetoresistance features are analyzed using an anisotropic magnetoresistance (AMR) model. Supported by the US Department of Energy. Work at the University of Minnesota was supported by Seagate Technology, NSF MRSEC, and a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme.

  20. Giant magnetoresistance effects in 5f-materials

    SciTech Connect

    Havela, L.; Sechovsky, V.; Prokes, K. |

    1995-09-01

    Very large magnetoresistance effects related to reorientation of magnetic moments were observed in a number of U-intermetallics. The resemblance to magnetic multilayers is a basis of discussion of possible mechanisms of these phenomena, in background of which is probably the strong hybridization of 5f- and conduction-electron states. A clear cut evidence of relative contributions of varied scattering rate on one side and carrier concentration on the other side can be presumably obtained from experiments on samples with controlled disorder.

  1. Angular dependence of anisotropic magnetoresistance in magnetic systems

    SciTech Connect

    Zhang, Steven S.-L. Zhang, Shufeng

    2014-05-07

    Anisotropic magnetoresistance (AMR), whose physical origin is attributed to the combination of spin dependent scattering and spin orbital coupling (SOC), usually displays simple angular dependence for polycrystalline ferromagnetic metals. By including generic spin dependent scattering and spin Hall (SH) terms in the Ohm's law, we explicitly show that various magneto-transport phenomena such as anomalous Hall (AH), SH, planar Hall (PH) and AMR could be quantitatively related for bulk polycrystalline ferromagnetic metals. We also discuss how AMR angular dependence is affected by the presence of interfacial SOC in magnetic layered structure.

  2. Negative magnetoresistance in a low-k dielectric

    NASA Astrophysics Data System (ADS)

    McGowan, B. T.; Lloyd, J. R.

    2014-12-01

    We observed negative magnetoresistance in amorphous SiCOH, a low-k dielectric, applying modest magnetic fields (<150 Gauss) at room temperature. The conductivity increases with increasing magnetic field. The change in conductivity due to the applied magnetic field increases with electric field and has little or no temperature dependence over the range studied. The magnitude of the effect is independent of the orientation of magnetic field relative to the direction of current flow. The effect is attributed to spin constraints associated with double occupancy of a trap site under the assumption that trap sites which have double occupancy have lower hopping frequencies than traps that have single occupancy.

  3. Negative magnetoresistance in a low-k dielectric

    SciTech Connect

    McGowan, B. T.; Lloyd, J. R.

    2014-12-22

    We observed negative magnetoresistance in amorphous SiCOH, a low-k dielectric, applying modest magnetic fields (<150 Gauss) at room temperature. The conductivity increases with increasing magnetic field. The change in conductivity due to the applied magnetic field increases with electric field and has little or no temperature dependence over the range studied. The magnitude of the effect is independent of the orientation of magnetic field relative to the direction of current flow. The effect is attributed to spin constraints associated with double occupancy of a trap site under the assumption that trap sites which have double occupancy have lower hopping frequencies than traps that have single occupancy.

  4. Percolation Blocking as the Origin of Organic Magneto-resistance

    NASA Astrophysics Data System (ADS)

    Zhao, Jun-Qing; Sun, Ling-Ling; Wang, Ting

    2016-05-01

    In order to identify the elementary mechanisms governing the organic magneto-resistance (OMAR) phenomenon, we demonstrated how the applied magnetic field acts on the variable hopping mobility. Based on a percolation model of hopping between localized states, we introduced an analytic expression for magneto-mobility and thus the OMAR, and discussed the influence of inter-site electronic interaction, operating bias, film thickness, temperature, and material parameters on the OMAR. The double occupied states and the spin selection rules play a major role in the mechanism.

  5. Magnetoresistance of galfenol-based magnetic tunnel junction

    NASA Astrophysics Data System (ADS)

    Gobaut, B.; Vinai, G.; Castán-Guerrero, C.; Krizmancic, D.; Rafaqat, H.; Roddaro, S.; Rossi, G.; Panaccione, G.; Eddrief, M.; Marangolo, M.; Torelli, P.

    2015-12-01

    The manipulation of ferromagnetic layer magnetization via electrical pulse is driving an intense research due to the important applications that this result will have on memory devices and sensors. In this study we realized a magnetotunnel junction in which one layer is made of Galfenol (Fe1-xGax) which possesses one of the highest magnetostrictive coefficient known. The multilayer stack has been grown by molecular beam epitaxy and e-beam evaporation. Optical lithography and physical etching have been combined to obtain 20x20 micron sized pillars. The obtained structures show tunneling conductivity across the junction and a tunnel magnetoresistance (TMR) effect of up to 11.5% in amplitude.

  6. Angular dependence of the magnetoresistance in nanoparticle arrays

    NASA Astrophysics Data System (ADS)

    Estévez, V.; Guslienko, K. Y.

    2013-10-01

    The interplay between the ferromagnetism and the charging effects strongly affects the electron transport through nanoparticle arrays when they are placed between two ferromagnetic electrodes with collinear magnetizations. There are oscillations in the current for the parallel orientation of magnetizations, and large values of the tunneling magnetoresistance (TMR). We analyze the transport properties in nanoparticle arrays for the case of noncollinear magnetizations. We show that the I-V and TMR curves strongly depend on the angle θ between the magnetization orientations of both electrodes. Large values of TMR are obtained for several values of θ.

  7. Magnetoresistance of polycrystalline gadolinium with varying grain size

    SciTech Connect

    Chakravorty, Manotosh Raychaudhuri, A. K.

    2015-01-21

    In this paper, we report a study of evolution of low field magnetoresistance (MR) of Gadolinium as the grain size in the sample is changed from few microns (∼4 μm) to the nanoscopic regime (∼35 nm). The low field MR has a clear effect on varying grain size. In large grain sample (few μm), the magnetic domains are controlled by local anisotropy field determined mainly by the magnetocrystalline anisotropy. The low field MR clearly reflects the temperature dependence of the magnetocrystalline anisotropy. For decreasing gain size, the contribution of spin disorder at the grain boundary increases and enhances the local anisotropy field.

  8. Controlled lateral anisotropy in correlated manganite heterostructures by interface-engineered oxygen octahedral coupling

    NASA Astrophysics Data System (ADS)

    Liao, Z.; Huijben, M.; Zhong, Z.; Gauquelin, N.; Macke, S.; Green, R. J.; van Aert, S.; Verbeeck, J.; van Tendeloo, G.; Held, K.; Sawatzky, G. A.; Koster, G.; Rijnders, G.

    2016-04-01

    Controlled in-plane rotation of the magnetic easy axis in manganite heterostructures by tailoring the interface oxygen network could allow the development of correlated oxide-based magnetic tunnelling junctions with non-collinear magnetization, with possible practical applications as miniaturized high-switching-speed magnetic random access memory (MRAM) devices. Here, we demonstrate how to manipulate magnetic and electronic anisotropic properties in manganite heterostructures by engineering the oxygen network on the unit-cell level. The strong oxygen octahedral coupling is found to transfer the octahedral rotation, present in the NdGaO3 (NGO) substrate, to the La2/3Sr1/3MnO3 (LSMO) film in the interface region. This causes an unexpected realignment of the magnetic easy axis along the short axis of the LSMO unit cell as well as the presence of a giant anisotropic transport in these ultrathin LSMO films. As a result we possess control of the lateral magnetic and electronic anisotropies by atomic-scale design of the oxygen octahedral rotation.

  9. Tailoring transport properties of phase-separated manganite films with ordered magnetic nanostructures

    NASA Astrophysics Data System (ADS)

    Vlaminck, V.; Yánez, W.; Hoffman, J.; Hoffmann, A.; Niebieskikwiat, D.

    2016-08-01

    The magnetotransport properties of thin manganite films (La0.7Ca0.3MnO3 ) coupled with arrays of permalloy (Py) nanodots deposited on the surface of the film are studied as a function of temperature, magnetic field, and the size of the dots. In the presence of the magnetic dots, a reduction of the electrical resistivity is observed, especially at the insulator-to-metal transition, as well as a shift of the transition peak towards higher temperatures. This indicates that, due to local interface exchange coupling, highly conductive ferromagnetic domains are nucleated in the manganite film underneath the Py nanodots. The use of a simplified resistor network model allows us to estimate the size of the metallic regions induced by exchange coupling. At low temperatures, these regions extend ˜70 nm beyond the edge of the nanodots, a length scale comparable to the correlation length of the ferromagnetic clusters in the phase-separated state of La0.7Ca0.3MnO3 .

  10. Emergent ferroelectricity in disordered tri-color multilayer structure comprised of ferromagnetic manganites

    NASA Astrophysics Data System (ADS)

    Niu, Li-Wei; Chen, Chang-Le; Dong, Xiang-Lei; Xing, Hui; Luo, Bing-Cheng; Jin, Ke-Xin

    2016-10-01

    Multiferroic materials, showing the coexistence and coupling of ferroelectric and magnetic orders, are of great technological and fundamental importance. However, the limitation of single phase multiferroics with robust magnetization and polarization hinders the magnetoelectric effect from being applied practically. Magnetic frustration, which can induce ferroelectricity, gives rise to multiferroic behavior. In this paper, we attempt to construct an artificial magnetically frustrated structure comprised of manganites to induce ferroelectricity. A disordered stacking of manganites is expected to result in frustration at interfaces. We report here that a tri-color multilayer structure comprised of non-ferroelectric La0.9Ca0.1MnO3(A)/Pr0.85Ca0.15MnO3(B)/Pr0.85Sr0.15MnO3(C) layers with the disordered arrangement of ABC-ACB-CAB-CBA-BAC-BCA is prepared to form magnetoelectric multiferroics. The multilayer film exhibits evidence of ferroelectricity at room temperature, thus presenting a candidate for multiferroics. Project supported by the National Natural Science Foundation of China (Grant Nos. 61471301, 61078057, 51172183, 51402240, and 51471134), the Specialized Research Fund for the Doctoral Program of Higher Education, China (Grant No. 20126102110045), the Natural Science Foundation of Shaanxi Province, China (Grant No. 2015JQ5125), and the Fundamental Research Funds for the Central Universities, China (Grant No. 3102015ZY078).

  11. Controlled lateral anisotropy in correlated manganite heterostructures by interface-engineered oxygen octahedral coupling.

    PubMed

    Liao, Z; Huijben, M; Zhong, Z; Gauquelin, N; Macke, S; Green, R J; Van Aert, S; Verbeeck, J; Van Tendeloo, G; Held, K; Sawatzky, G A; Koster, G; Rijnders, G

    2016-04-01

    Controlled in-plane rotation of the magnetic easy axis in manganite heterostructures by tailoring the interface oxygen network could allow the development of correlated oxide-based magnetic tunnelling junctions with non-collinear magnetization, with possible practical applications as miniaturized high-switching-speed magnetic random access memory (MRAM) devices. Here, we demonstrate how to manipulate magnetic and electronic anisotropic properties in manganite heterostructures by engineering the oxygen network on the unit-cell level. The strong oxygen octahedral coupling is found to transfer the octahedral rotation, present in the NdGaO3 (NGO) substrate, to the La2/3Sr1/3MnO3 (LSMO) film in the interface region. This causes an unexpected realignment of the magnetic easy axis along the short axis of the LSMO unit cell as well as the presence of a giant anisotropic transport in these ultrathin LSMO films. As a result we possess control of the lateral magnetic and electronic anisotropies by atomic-scale design of the oxygen octahedral rotation. PMID:26950593

  12. Manganite-based three level memristive devices with self-healing capability

    NASA Astrophysics Data System (ADS)

    Acevedo, W. Román; Rubi, D.; Lecourt, J.; Lüders, U.; Gomez-Marlasca, F.; Granell, P.; Golmar, F.; Levy, P.

    2016-08-01

    We report on non-volatile memory devices based on multifunctional manganites. The electric field induced resistive switching of Ti/La1/3Ca2/3MnO3/n-Si devices is explored using different measurement protocols. We show that using current as the electrical stimulus (instead of standard voltage-controlled protocols) improves the electrical performance of our devices and unveils an intermediate resistance state. We observe three discrete resistance levels (low, intermediate and high), which can be set either by the application of current-voltage ramps or by means of single pulses. These states exhibit retention and endurance capabilities exceeding 104 s and 70 cycles, respectively. We rationalize our experimental observations by proposing a mixed scenario were a metallic filament and a SiOx layer coexist, accounting for the observed resistive switching. Overall electrode area dependence and temperature dependent resistance measurements support our scenario. After device failure takes place, the system can be turned functional again by heating up to low temperature (120 °C), a feature that could be exploited for the design of memristive devices with self-healing functionality. These results give insight into the existence of multiple resistive switching mechanisms in manganite-based memristive systems and provide strategies for controlling them.

  13. High-K MISFET channel mobility from magnetoresistance

    NASA Astrophysics Data System (ADS)

    Bate, R. T.

    2005-03-01

    Carrier trapping in the gate insulator or at the interface with the silicon can depress the effective channel mobility of high-K MISFETs below the drift mobility. This reduction in effective mobility can be distinguished from true mobility reduction due to carrier scattering by using the Hall effect to measure the channel carrier density [1]. However, channel Hall measurements have traditionally required nonstandard multidrain devices, which must be included in the test chip design. We propose measuring the reduction in drain current of conventional transistors by a magnetic field to determine the Hall coefficient. This method, which requires no multidrain devices, could become a routine diagnostic procedure. It is based on a theorem concerning the magnetoresistance of a rectangular plate with perfectly conducting end contacts [2], which has apparently not been tested experimentally, at least on MOSFET's. The validity of the method can be determined by comparison with channel carrier density determined in other ways, including split capacitance on MOSFETS, conventional Hall effect, and Corbino magnetoresistance on MISFETs. Progress toward these goals is described. [1] N.S Saks and A.K Agarwal, Appl. Phys. Letters 77 (20), 3281 -- 3283 (2000); R. T. Bate and W. P. Kirk, Bull. Am. Phys, Soc. March, 2004, Abstract S6.011 [2] H. H. Jenson and H. Smith, J. Phys. C: Solid State, 5, 2867-2880, (1972)

  14. Tunable magnetoresistance in an asymmetrically coupled single-molecule junction.

    PubMed

    Warner, Ben; El Hallak, Fadi; Prüser, Henning; Sharp, John; Persson, Mats; Fisher, Andrew J; Hirjibehedin, Cyrus F

    2015-03-01

    Phenomena that are highly sensitive to magnetic fields can be exploited in sensors and non-volatile memories. The scaling of such phenomena down to the single-molecule level may enable novel spintronic devices. Here, we report magnetoresistance in a single-molecule junction arising from negative differential resistance that shifts in a magnetic field at a rate two orders of magnitude larger than Zeeman shifts. This sensitivity to the magnetic field produces two voltage-tunable forms of magnetoresistance, which can be selected via the applied bias. The negative differential resistance is caused by transient charging of an iron phthalocyanine (FePc) molecule on a single layer of copper nitride (Cu2N) on a Cu(001) surface, and occurs at voltages corresponding to the alignment of sharp resonances in the filled and empty molecular states with the Cu(001) Fermi energy. An asymmetric voltage-divider effect enhances the apparent voltage shift of the negative differential resistance with magnetic field, which inherently is on the scale of the Zeeman energy. These results illustrate the impact that asymmetric coupling to metallic electrodes can have on transport through molecules, and highlight how this coupling can be used to develop molecular spintronic applications. PMID:25622229

  15. Tunable magnetoresistance in an asymmetrically coupled single-molecule junction

    NASA Astrophysics Data System (ADS)

    Warner, Ben; El Hallak, Fadi; Prüser, Henning; Sharp, John; Persson, Mats; Fisher, Andrew J.; Hirjibehedin, Cyrus F.

    2015-03-01

    Phenomena that are highly sensitive to magnetic fields can be exploited in sensors and non-volatile memories. The scaling of such phenomena down to the single-molecule level may enable novel spintronic devices. Here, we report magnetoresistance in a single-molecule junction arising from negative differential resistance that shifts in a magnetic field at a rate two orders of magnitude larger than Zeeman shifts. This sensitivity to the magnetic field produces two voltage-tunable forms of magnetoresistance, which can be selected via the applied bias. The negative differential resistance is caused by transient charging of an iron phthalocyanine (FePc) molecule on a single layer of copper nitride (Cu2N) on a Cu(001) surface, and occurs at voltages corresponding to the alignment of sharp resonances in the filled and empty molecular states with the Cu(001) Fermi energy. An asymmetric voltage-divider effect enhances the apparent voltage shift of the negative differential resistance with magnetic field, which inherently is on the scale of the Zeeman energy. These results illustrate the impact that asymmetric coupling to metallic electrodes can have on transport through molecules, and highlight how this coupling can be used to develop molecular spintronic applications.

  16. Large Magnetoresistance in Nanostructured Armchair Graphene Nanoribbon Junctions

    NASA Astrophysics Data System (ADS)

    Li, Suchun; Son, Young-Woo; Quek, Su Ying

    2014-03-01

    The prospect of all-carbon nanoelectronics has motivated significant interest in the transport of electrons through graphene and graphene nanoribbon (GNR) based junctions.... The weak intrinsic spin-orbit coupling in graphene also makes graphene an attractive candidate for replacing conventional materials in spintronics applications. Several interesting spin transport properties, such as giant magnetoresistance and half-metallicity, have been predicted. Most of these predictions have centered on GNRs with zigzag atomic edges (ZGNRs). On the other hand, significant progress has been made in the controlled atomic-scale synthesis of GNRs with armchair edges (AGNRs), all with specific widths.... Yet, to date, little is known about the potential of such well-defined AGNRs in electronics or spintronics. In this work, we use first principles transport calculations to predict the electron and spin transport properties of nanostructured AGNR junctions. We predict a large magnetoresistance of ~ 900%, related to resonant transmission channels close to the Fermi energy. We gratefully acknowledge helpful discussions with YP Feng and CK Gan, funding from Singapore NRF and A*STAR, Korea MEST NRF, and HJ Choi for use of the SCARLET code (PRB 76, 155420, 2007).

  17. Landau levels and longitudinal magnetoresistance in generalized Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Li, Xiao; Roy, Bitan

    The notion of axial anomaly is a venerable concept in quantum field theory that has received ample attention in condensed matter physics due to the discovery of Weyl materials (WSMs). In such systems Kramers non-degenerate bands touch at isolated points in the Brillouin zone that act as (anti)monopoles of Berry flux, and the monopole number (m) defines the topological invariant of the system. Although so far only simple WSMs (with m = 1) has been found in various inversion and/or time-reversal asymmetric systems, generalized Weyl semimetals with m > 1 can also be found in nature, for example double-Weyl semimetals in HgCr2Se4 and SrSi2 and triple-Weyl semimetals. In this work, we demonstrate the Landau level spectrum in generalized Weyl systems and its ramification on longitudinal magnetotransport measurements. We show that in the quantum limit generalized Weyl semimetals display negative longitudinal magnetoresistance due to the chiral anomaly. Moreover, the magnetoresistance has nontrivial dependence on the relative orientation of the external fields with the crystallographic axis, stemming from underlying anisotropic quasiparticle dispersion in the pristine system. Our theory can thus provide diagnostic tools to pin the quasiparticle properties in Weyl systems.

  18. Linear magnetoresistance in Ag2+δSe thin films

    NASA Astrophysics Data System (ADS)

    von Kreutzbruck, M.; Lembke, G.; Mogwitz, B.; Korte, C.; Janek, J.

    2009-01-01

    In the nonstoichiometric low-temperature phase of silver selenide a very small silver excess within the semiconducting silver selenide matrix in the order of 0.01% is sufficient to generate a linear magnetoresistance (LMR) of more than 300% at 5 T, which does not saturate at fields up to 60 T. Different theoretical models have been proposed to explain this unusual magnetoresistance (MR) behavior, among them a random resistor network consisting of four-terminal resistor units. According to this model the LMR and the crossover field from linear to quadratic behavior are primarily controlled by both the spatial distribution of the charge-carrier mobility and its average value, being essentially functions of the local and average compositions. Here we report measurements on silver-rich thin AgxSe films with a thickness between 20 nm and 2μm , which show an increasing average mobility in conjunction with an enhanced MR for increasing film thickness. We found a linear scaling between the size of the transverse LMR and the crossover field, as predicted by the theory. For films thinner than about 100 nm the MR with field directed in the sample plane shows a breakdown of the LMR, revealing the physical length scale of the inhomegeneities in thin AgxSe devices.

  19. Scanning magnetoresistive microscopy: An advanced characterization tool for magnetic nanosystems

    NASA Astrophysics Data System (ADS)

    Mitin, D.; Grobis, M.; Albrecht, M.

    2016-02-01

    An advanced scanning magnetoresistive microscopy (SMRM) — a robust magnetic imaging and probing technique — will be presented, which utilizes state-of-the-art recording heads of a hard disk drive as sensors. The spatial resolution of modern tunneling magnetoresistive sensors is nowadays comparable to the more commonly used magnetic force microscopes. Important advantages of SMRM are the ability to detect pure magnetic signals directly proportional to the out-of-plane magnetic stray field, negligible sensor stray fields, and the ability to apply local bipolar magnetic field pulses up to 10 kOe with bandwidths from DC up to 1 GHz. Moreover, the SMRM can be further equipped with a heating stage and external magnetic field units. The performance of this method and corresponding best practices are demonstrated by presenting various examples, including a temperature dependent recording study on hard magnetic L10 FeCuPt thin films, imaging of magnetic vortex states in an in-plane magnetic field, and their controlled manipulation by applying local field pulses.

  20. Large magnetoresistance in the antiferromagnetic semimetal NdSb

    NASA Astrophysics Data System (ADS)

    Wakeham, N.; Bauer, E. D.; Neupane, M.; Ronning, F.

    2016-05-01

    There has been considerable interest in topological semimetals that exhibit extreme magnetoresistance (XMR). These have included materials lacking inversion symmetry such as TaAs, as well Dirac semimetals such as Cd3As2 . However, it was reported recently that LaSb and LaBi also exhibit XMR, even though the rocksalt structure of these materials has inversion symmetry, and the band-structure calculations do not show a Dirac dispersion in the bulk. Here, we present magnetoresistance and specific-heat measurements on NdSb, which is isostructural with LaSb. NdSb has an antiferromagnetic ground state and, in analogy with the lanthanum monopnictides, is expected to be a topologically nontrivial semimetal. We show that NdSb has an XMR of ˜104% , even within the antiferromagnetic state, illustrating that XMR can occur independently of the absence of time-reversal symmetry breaking in zero magnetic field. The persistence of XMR in a magnetic system offers the promise of new functionality when combining topological matter with electronic correlations. We also find that in an applied magnetic field below the Néel temperature there is a first-order transition, consistent with evidence from previous neutron scattering work.

  1. Negative longitudinal magnetoresistance in Dirac and Weyl metals

    NASA Astrophysics Data System (ADS)

    Burkov, A. A.

    2015-06-01

    It has recently been found that Dirac and Weyl metals are characterized by an unusual weak-field longitudinal magnetoresistance: large, negative, and quadratic in the magnetic field. This has been shown to arise from the chiral anomaly, i.e., nonconservation of the chiral charge in the presence of external electric and magnetic fields, oriented collinearly. In this paper we report on a theory of this effect in both Dirac and Weyl metals. We demonstrate that this phenomenon contains two important ingredients. One is the magnetic-field-induced coupling between the chiral and the total (or vector, in relativistic field theory terminology) charge densities. This arises from the Berry curvature and is present in principle whenever the Berry curvature is nonzero, i.e., is nonspecific to Dirac and Weyl metals. This coupling, however, leads to a large negative quadratic magnetoresistance only when the second ingredient is present, namely when the chiral charge density is a nearly conserved quantity with a long relaxation time. This property is specific to Dirac and Weyl metals and is realized only when the Fermi energy is close to Dirac or Weyl nodes, expressing an important low-energy property of these materials, emergent chiral symmetry.

  2. Scanning magnetoresistive microscopy: An advanced characterization tool for magnetic nanosystems.

    PubMed

    Mitin, D; Grobis, M; Albrecht, M

    2016-02-01

    An advanced scanning magnetoresistive microscopy (SMRM) - a robust magnetic imaging and probing technique - will be presented, which utilizes state-of-the-art recording heads of a hard disk drive as sensors. The spatial resolution of modern tunneling magnetoresistive sensors is nowadays comparable to the more commonly used magnetic force microscopes. Important advantages of SMRM are the ability to detect pure magnetic signals directly proportional to the out-of-plane magnetic stray field, negligible sensor stray fields, and the ability to apply local bipolar magnetic field pulses up to 10 kOe with bandwidths from DC up to 1 GHz. Moreover, the SMRM can be further equipped with a heating stage and external magnetic field units. The performance of this method and corresponding best practices are demonstrated by presenting various examples, including a temperature dependent recording study on hard magnetic L1(0) FeCuPt thin films, imaging of magnetic vortex states in an in-plane magnetic field, and their controlled manipulation by applying local field pulses. PMID:26931856

  3. Evidence of weak localization in quantum interference effects observed in epitaxial La0.7Sr0.3MnO3 ultrathin films

    PubMed Central

    Niu, Wei; Gao, Ming; Wang, Xuefeng; Song, Fengqi; Du, Jun; Wang, Xinran; Xu, Yongbing; Zhang, Rong

    2016-01-01

    Quantum interference effects (QIEs) dominate the appearance of low-temperature resistivity minimum in colossal magnetoresistance manganites. The T1/2 dependent resistivity under high magnetic field has been evidenced as electron-electron (e-e) interaction. However, the evidence of the other source of QIEs, weak localization (WL), still remains insufficient in manganites. Here we report on the direct experimental evidence of WL in QIEs observed in the single-crystal La0.7Sr0.3MnO3 (LSMO) ultrathin films deposited by laser molecular beam epitaxy. The sharp cusps around zero magnetic field in magnetoresistance measurements is unambiguously observed, which corresponds to the WL effect. This convincingly leads to the solid conclusion that the resistivity minima at low temperatures in single-crystal manganites are attributed to both the e-e interaction and the WL effect. Moreover, the temperature-dependent phase-coherence length corroborates the WL effect of LSMO ultrathin films is within a two-dimensional localization theory. PMID:27181882

  4. Double-exchange theory of ferroelectric polarization in orthorhombic manganites with twofold periodic magnetic texture

    NASA Astrophysics Data System (ADS)

    Solovyev, I. V.; Nikolaev, S. A.

    2013-04-01

    We argue that many aspects of improper ferroelectric (FE) activity in orthorhombic manganites can be rationalized by considering the limit of infinite intra-atomic splitting between majority- and minority-spin states (or the double-exchange limit), which reduces the problem to the analysis of a spinless double-exchange (DE) Hamiltonian. We apply this strategy to the low-energy model, derived from the first-principles electronic-structure calculations, and combine it with the Berry-phase theory of electric polarization. We start with the analysis of the simplest two-orbital model, describing the behavior of the eg bands, and apply it to the E-type antiferromagnetic (AFM) phase, which in the DE limit effectively breaks up into one-dimensional zigzag chains. We derive an analytical expression for the electronic polarization (Pel) and explain how it depends on the orbital ordering and the energy splitting Δ between eg states. Then, we evaluate parameters of this model for the series of manganites. For these purposes, we start from a more general five-orbital model for all Mn 3d bands and construct a new downfolded model for the eg bands. From the analysis of these parameters, we conclude that the behavior of Pel in realistic manganites always corresponds to the limit of large Δ. This property holds for all considered compounds even in the local-density approximation, which typically underestimates Δ. We further utilize this property in order to derive an analytical expression for Pel in a general twofold periodic magnetic texture, based on the five-orbital model and the perturbation-theory expansion for the Wannier functions in the first order of 1/Δ. This expression explains the functional dependence of Pel on the relative directions of spins. Furthermore, it suggests that Pel is related to the asymmetry of transfer integrals, which should have simultaneously symmetric and antisymmetric components in the crystal-field representation. The main contribution to this

  5. Enhancement of tunnel magnetoresistance in magnetic tunnel junction by a superlattice barrier

    SciTech Connect

    Chen, C. H.; Hsueh, W. J.

    2014-01-27

    Tunnel magnetoresistance of magnetic tunnel junction improved by a superlattice barrier composed of alternate layers of a nonmagnetic metal and an insulator is proposed. The forbidden band of the superlattice is used to predict the low transmission range in the superlattice barrier. By forbidding electron transport in the anti-parallel configuration, the tunnel magnetoresistance is enhanced in the superlattice junction. The results show that the tunnel magnetoresistance ratio for a superlattice magnetic tunnel junction is greater than that for traditional single or double barrier junctions.

  6. Large Magnetoresistance at Room Temperature in Ferromagnet/Topological Insulator Contacts

    NASA Astrophysics Data System (ADS)

    Majumder, Sarmita; Guchhait, Samaresh; Dey, Rik; Register, Leonard Franklin; Banerjee, Sanjay K.

    2016-07-01

    We report magnetoresistance for current flow through iron/topological insulator (Fe/TI) and Fe/evaporated-oxide/TI contacts when a magnetic field is used to initially orient the magnetic alignment of the incorporated ferromagnetic Fe bar, at temperatures ranging from 100 K to room temperature. This magnetoresistance is associated with the relative orientation of the Fe bar magnetization and spin-polarization of electrons moving on the surface of the TI with helical spin-momentum locking. The magnitude of the observed magnetoresistance is relatively large compared to that observed in prior work.

  7. Magnetoresistance and magnetodynamics in thin-film magnetic heterostructures

    NASA Astrophysics Data System (ADS)

    Parks, Sarah Cunegunda

    Current information technology relies heavily on magnetism. Gaining a deeper understanding of magnetism, and in particular spin dynamics, is important to today's quickly evolving technology. In this thesis, two separate studies have been conducted to help aid in the study of spin dynamics. The first project explores giant magnetoresistive (GMR) devices. These devices are presumed to be made of materials that are radiation hard with respect to both photons and particles, potentially increasing their utility for nuclear energy and space based applications. However, to date there are few detailed studies of magnetism and GMR devices in hard radiation environments. This project utilizes the facilities at The Ohio State University Nuclear Reactor Laboratory to study the effects of gamma ray and neutron irradiation on GMR samples. The structure used in this experiment is a standard GMR trilayer consisting of a thin, non-magnetic layer placed between thin ferromagnetic layers, with one of the two magnetic layers in contact with an exchange biased antiferromagnet (Py/Cu/Py/FeMn/Ge). To study the effects of radiation three types of magnetic measurements, vibrating sample magnetometery (VSM), magnetoresistance (MR), and magneto-optical Kerr effect (MOKE), are taken and correlated pre and post gamma radiation. We present characterization of the devices pre and post gamma irradiation for multiple device geometries and radiation doses up to 50 Mrad for gamma rays and a minimum fast flux (En>0.5MeV) of 4.2E12 nv for neutrons, both of which are well above the failure threshold for semiconducting devices. The second study that was done in this thesis uses current-induced magnetodynamics in giant magnetoresistive (GMR) trilayers. These devices promise a novel platform for microwave electronics. One of the keys to developing this potential has been the development of nanoscale fabrication techniques, typically resulting in either nanopillar or point-contact geometries. As a result

  8. Homotopy-Theoretic Study &Atomic-Scale Observation of Vortex Domains in Hexagonal Manganites.

    PubMed

    Li, Jun; Chiang, Fu-Kuo; Chen, Zhen; Ma, Chao; Chu, Ming-Wen; Chen, Cheng-Hsuan; Tian, Huanfang; Yang, Huaixin; Li, Jianqi

    2016-01-01

    Essential structural properties of the non-trivial "string-wall-bounded" topological defects in hexagonal manganites are studied through homotopy group theory and spherical aberration-corrected scanning transmission electron microscopy. The appearance of a "string-wall-bounded" configuration in RMnO3 is shown to be strongly linked with the transformation of the degeneracy space. The defect core regions (~50 Å) mainly adopt the continuous U(1) symmetry of the high-temperature phase, which is essential for the formation and proliferation of vortices. Direct visualization of vortex strings at atomic scale provides insight into the mechanisms and macro-behavior of topological defects in crystalline materials. PMID:27324701

  9. Evidence of photo-induced dynamic competition of metallic and insulating phase in a layered manganite

    SciTech Connect

    Li, Yuelin; Walko, Daonld A.; Li, Qing'an; Liu, Yaohua; Rosenkranz, Stephen; Zheng, Hong; Mitchell, J. F.

    2015-11-17

    We show evidence that the competition between the antiferromagetic metallic phase and the charge- and orbital-ordered insulating phase at the reentrant phase boundary of a layered manganite, LaSr2Mn2O7, can be manipulated using ultrafast optical excitation. The time-dependent evolution of the Jahn-Teller superlattice reflection, which indicates the formation of the charge and orbital order, was measured at different laser fluences. The laser-induced enhancement and reduction the Jahn-Teller reflection intensity shows a reversal of sign between earlier (~10 ns) and later (~150 ns) time delays during the relaxation after photo excitation. This effect is consistent with a scenario whereby the laser excitation modulates the local competition between the metallic and the insulating phases.

  10. Evidence of photo-induced dynamic competition of metallic and insulating phase in a layered manganite

    DOE PAGESBeta

    Li, Yuelin; Walko, Daonld A.; Li, Qing'an; Liu, Yaohua; Rosenkranz, Stephen; Zheng, Hong; Mitchell, J. F.

    2015-11-17

    We show evidence that the competition between the antiferromagetic metallic phase and the charge- and orbital-ordered insulating phase at the reentrant phase boundary of a layered manganite, LaSr2Mn2O7, can be manipulated using ultrafast optical excitation. The time-dependent evolution of the Jahn-Teller superlattice reflection, which indicates the formation of the charge and orbital order, was measured at different laser fluences. The laser-induced enhancement and reduction the Jahn-Teller reflection intensity shows a reversal of sign between earlier (~10 ns) and later (~150 ns) time delays during the relaxation after photo excitation. This effect is consistent with a scenario whereby the laser excitationmore » modulates the local competition between the metallic and the insulating phases.« less

  11. Evidence of Photo-induced Dynamic Competition of Metallic and Insulating Phase in a Layered Manganite.

    SciTech Connect

    Li, Yuelin; Walko, Donald A.; Li, Qing'an; Liu, Yaohua; Rosenkranz, Stephan; Zheng, Hong; Mitchell, J. F.

    2015-12-16

    We show evidence that the competition between the antiferromagetic metallic phase and the charge- and orbital-ordered insulating phase at the reentrant phase boundary of a layered manganite, LaSr2Mn2O7, can be manipulated using ultrafast optical excitation. The time- dependent evolution of the Jahn-Teller superlattice reflection, which indicates the formation of the charge and orbital order, was measured at different laser fluences. The laser-induced enhancement and reduction the Jahn-Teller reflection intensity shows a reversal of sign between earlier (~10 ns) and later (~150 ns) time delays during the relaxation after photo excitation. This effect is consistent with a scenario whereby the laser excitation modulates the local competition between the metallic and the insulating phases.

  12. Proximity-Induced Spin Polarization of Graphene in Contact with Half-Metallic Manganite.

    PubMed

    Sakai, Seiji; Majumdar, Sayani; Popov, Zakhar I; Avramov, Pavel V; Entani, Shiro; Hasegawa, Yuri; Yamada, Yoichi; Huhtinen, Hannu; Naramoto, Hiroshi; Sorokin, Pavel B; Yamauchi, Yasushi

    2016-08-23

    The role of proximity contact with magnetic oxides is of particular interest from the expectations of the induced spin polarization and weak interactions at the graphene/magnetic oxide interfaces, which would allow us to achieve efficient spin-polarized injection in graphene-based spintronic devices. A combined approach of topmost-surface-sensitive spectroscopy utilizing spin-polarized metastable He atoms and ab initio calculations provides us direct evidence for the magnetic proximity effect in the junctions of single-layer graphene and half-metallic manganite La0.7Sr0.3MnO3 (LSMO). It is successfully demonstrated that in the graphene/LSMO junctions a sizable spin polarization is induced at the Fermi level of graphene in parallel to the spin polarization direction of LSMO without giving rise to a significant modification in the π band structure. PMID:27438899

  13. Small polaron effect on carrier recombination in perovskite manganite thin films

    NASA Astrophysics Data System (ADS)

    Wu, G.-R.; Sasaki, M.; Isa, T.; Negishi, H.; Inoue, M.; Gao, W.-X.; Xiong, G.-C.

    2001-05-01

    Photoinduced 'transient thermoelectric effect (TTE)' in perovskite manganite La 0.6Ca 0.4MnO 3 thin film has been measured under magnetic fields. The fast decay process of TTE signals is due to a recombination of photogenerated electron-hole pairs through Mn 4+ ions as capture centers, whose evaluated cross section σ obeys the power law σ∝ T- n ( n=0.75) in the ferromagnetic phase far below Tc and in the paramagnetic phase. From the observed relaxation time τ1, we evaluated the parameter α characterizing a small polaron effect and the effective mass m∗; both are enhanced appreciably near Tc. Such anomaly is attributed to the change in the thermal velocity of diffusing holes with downspin due to a small polaron effect.

  14. Carrier generation/recombination processes and polaron effect in perovskite manganite thin films

    NASA Astrophysics Data System (ADS)

    Wu, Guang-Ri; Inoue, Masasi; Sasaki, Minoru; Negishi, Hiroshi; Xiong, Guang-Cheng

    2000-07-01

    Pulsed-laser-induced transient thermoelectric effect (TTE) for perovskite manganite films, La 0.6Ca 0.4MnO 3 (LCMO), Pr 0.67Sr 0.33MnO 3 (PSMO), La 0.7Sr 0.3MnO 3 (LSMO), has been measured under DC electric and magnetic fields. The photoinduced TTE voltage and its sign are strongly dependent on both temperature and magnetic field, which is due to the formation of a bipolar state of photogenerated electrons and holes. It is found that Jahn-Teller and polaron effects are appreciable near the Curie temperature for the carrier recombination, in particular, for LCMO with small ionic radius of Ca 2+ ions.

  15. The effect of external magnetic field on the Raman peaks in manganites

    SciTech Connect

    Sahu, A. K.; Rout, G. C.

    2014-04-24

    We report here a microscopic theoretical model study exhibiting the effect of external magnetic field on the Raman excitation peaks in the CMR manganite system. The Hamiltonian consists of Jahn-Teller (J-T) distortion in e{sub g} band, the double exchange interaction and the Heisenberg spin-spin interaction. Further the phonons are coupled to e{sub g} band electrons, J-T distorted e{sub g} band and the double exchange interaction. The Raman spectral intensity is calculated from the imaginary part of the phonon Green function. The spectra exhibits three peaks besides a very weak high energy peak. The magnetic field effect on these peaks are reported.

  16. Charge-order domain walls with enhanced conductivity in a layered manganite

    NASA Astrophysics Data System (ADS)

    Ma, Eric Yue; Bryant, Benjamin; Tokunaga, Yusuke; Aeppli, Gabriel; Tokura, Yoshinori; Shen, Zhi-Xun

    2015-07-01

    Interfaces and boundaries in condensed-matter systems often have electronic properties distinct from the bulk material and thus have become a topic of both fundamental scientific interest and technological importance. Here we identify, using microwave impedance microscopy, enhanced conductivity of charge-order domain walls in the layered manganite Pr(Sr0.1Ca0.9)2Mn2O7. We obtain a complete mesoscopic map of surface topography, crystalline orientation and electronic phase, and visualize the thermal phase transition between two charge-ordered phases. In both phases, charge-order domains occur with domain walls showing enhanced conductivity likely due to local lifting of the charge order. Finite element analysis shows that the resolved domain walls can be as narrow as few nanometres. The domain walls are stabilized by structural twins and have a strong history dependence, suggesting that they may be manipulated to create novel devices.

  17. Homotopy-Theoretic Study & Atomic-Scale Observation of Vortex Domains in Hexagonal Manganites

    NASA Astrophysics Data System (ADS)

    Li, Jun; Chiang, Fu-Kuo; Chen, Zhen; Ma, Chao; Chu, Ming-Wen; Chen, Cheng-Hsuan; Tian, Huanfang; Yang, Huaixin; Li, Jianqi

    2016-06-01

    Essential structural properties of the non-trivial “string-wall-bounded” topological defects in hexagonal manganites are studied through homotopy group theory and spherical aberration-corrected scanning transmission electron microscopy. The appearance of a “string-wall-bounded” configuration in RMnO3 is shown to be strongly linked with the transformation of the degeneracy space. The defect core regions (~50 Å) mainly adopt the continuous U(1) symmetry of the high-temperature phase, which is essential for the formation and proliferation of vortices. Direct visualization of vortex strings at atomic scale provides insight into the mechanisms and macro-behavior of topological defects in crystalline materials.

  18. Finite-size effect on evolution of Griffiths phase in manganite nanoparticles

    NASA Astrophysics Data System (ADS)

    Pramanik, A. K.; Banerjee, A.

    2016-09-01

    The finite-size effect on the evolution of the Griffiths phase (GP) is studied using nanoparticles of half-doped manganite Pr0.5Sr0.5MnO3 with different average particle sizes but with similar structural parameters. All the samples exhibit pronounced GP behavior. With reducing the particle size, the Griffiths temperature remains almost unchanged but the characteristic critical temperature T\\text{c}R decreases and the GP properties are strengthened. It is noteworthy that the shift of T\\text{c}R follows finite-size scaling with the particle size revealing an exotic interplay between the GP properties and the sample dimension. This reinforces an earlier proposal of length-scale related evolution of GP.

  19. Coupled magnetic and elastic properties in LaPr(CaSr)MnO manganites

    NASA Astrophysics Data System (ADS)

    Eslava, G. G.; Parisi, F.; Bernardo, P. L.; Quintero, M.; Leyva, G.; Cohen, L. F.; Ghivelder, L.

    2016-09-01

    We investigate a series of manganese oxides, the La0.225Pr0.4(Ca1-xSrx)0.375MnO3 system. The x = 0 sample is a prototype compound for the study of phase separation in manganites, where ferromagnetic and charge ordered antiferromagnetic phases coexist. Replacing Ca2+ by Sr2+ gradually turns the system into a homogeneous ferromagnet. Our results show that the material structure plays a major role in the observed magnetic properties. On cooling, at temperatures below ∼ 100 K, a strong contraction of the lattice is followed by an increase in the magnetization. This is observed both through thermal expansion and magnetostriction measurements, providing distinct evidence of magneto-elastic coupling in these phase separated compounds.

  20. Emergent dimensional reduction of the spin sector in a model for narrow-band manganites

    SciTech Connect

    Liang, Shuhua; Daghofer, Maria; Dong, Shuai; Sen, Cengiz; Dagotto, Elbio R

    2011-01-01

    The widely used double-exchange model for manganites is shown to support various striped phases at filling fractions 1/n (n = 3, 4, 5, . . .), in the previously unexplored regime of narrow bandwidth and small Jahn-Teller coupling. Working in two dimensions, our main result is that these stripes can be individually spin flipped without a physically relevant change in the energy, i.e., we find a large ground-state manifold with nearly degenerate energies. The two-dimensional spin system thus displays an unexpected dynamically generated dimensional reduction into decoupled one-dimensional stripes, even though the electronic states remain two dimensional. Relations of our results with recent literature addressing compass models in quantum computing are discussed.

  1. Electron-lattice coupling and partial nesting as the origin of Fermi-Arcs in manganites

    SciTech Connect

    Salafranca Laforga, Juan I; Alvarez, Gonzalo; Dagotto, Elbio R

    2009-01-01

    A tight-binding model for e{sub g} electrons coupled to Jahn-Teller lattice distortions is studied via Monte Carlo simulations. By focusing on the periodicity of the cooperative Jahn-Teller distortions, and the one-particle spectral function, our results clarify the physical origin of the Fermi-arcs phase observed in layered manganites. In a range of parameters where no broken symmetry phase exists, the nearly nested Fermi surface favors certain correlations between Jahn-Teller distortions. The spectral weight near the Brillouin zone edge is suppressed, leading to the pseudogap in the density of states. We discuss the stability of this phase as a function of temperature and coupling strength for different hole dopings.

  2. Homotopy-Theoretic Study & Atomic-Scale Observation of Vortex Domains in Hexagonal Manganites

    PubMed Central

    Li, Jun; Chiang, Fu-Kuo; Chen, Zhen; Ma, Chao; Chu, Ming-Wen; Chen, Cheng-Hsuan; Tian, Huanfang; Yang, Huaixin; Li, Jianqi

    2016-01-01

    Essential structural properties of the non-trivial “string-wall-bounded” topological defects in hexagonal manganites are studied through homotopy group theory and spherical aberration-corrected scanning transmission electron microscopy. The appearance of a “string-wall-bounded” configuration in RMnO3 is shown to be strongly linked with the transformation of the degeneracy space. The defect core regions (~50 Å) mainly adopt the continuous U(1) symmetry of the high-temperature phase, which is essential for the formation and proliferation of vortices. Direct visualization of vortex strings at atomic scale provides insight into the mechanisms and macro-behavior of topological defects in crystalline materials. PMID:27324701

  3. Magnetic Order and Spin Dynamics in a Hexagonal Rare Earth Manganite

    NASA Astrophysics Data System (ADS)

    Helton, J. S.; Singh, D. K.; Elizabeth, S.; Harikrishnan, S.; Lynn, J. W.

    2011-03-01

    Hexagonal rare earth manganites, RMn O3 R = Dy, Ho, Er, Tm, Yb, Lu, Y, or Sc), have attracted a great deal of recent attention as magnetoelectric multiferroics as most of these systems are ferroelectric at room temperature and display magnetic order below TN ~ 100 K. This magnetic order can be quite complex, as both the R and Mn ions lie on geometrically frustrated triangular lattices. DyMn O3 is typically orthorhombic, but can also be grown in the hexagonal phase; Dy 0.5 Y0.5 Mn O3 displays the hexagonal phase and is magnetically diluted at the rare earth site. We have used neutron scattering experiments to explore the magnetic structure and spin dynamics of Dy 0.5 Y0.5 Mn O3 .

  4. Effect of bismuth doping on the physical properties of La-Li-Mn-O manganite

    NASA Astrophysics Data System (ADS)

    Yanapu, Kalyana Lakshmi; Samatham, S. Shanmukharao; Kumar, Devendra; Ganesan, V.; Reddy, P. Venugopal

    2016-03-01

    The effects of bismuth doping at La site on magnetic, electrical and thermopower properties of LaLiMnO3 manganites have been investigated. The substitution of Bi ion leads to the weakening of ferromagnetic ordering at low temperature, and Curie temperature ( T C) decreases with increase in Bi content. Interestingly, a dramatic increase in the magnitude of Seebeck coefficient at low temperature is observed in Bi-doped samples which might find potential application as thermoelectric. The results are attributed to the combined effect of the disorder and antiferromagnetic interaction induced by Bi doping. Both ρ( T) and S( T) data in the high-temperature region are discussed using small polaron hopping model.

  5. Nonuniversal scaling of the magnetocaloric effect as an insight into spin-lattice interactions in manganites

    NASA Astrophysics Data System (ADS)

    Smith, Anders; Nielsen, Kaspar K.; Bez, Henrique N.; Bahl, Christian R. H.

    2016-08-01

    We measure the magnetocaloric effect of the manganite series La0.67Ca0.33 -xSrxMnO3 by determining the isothermal entropy change upon magnetization, using variable-field calorimetry. The results demonstrate that the field dependence of the magnetocaloric effect close to the critical temperature is not given uniquely by the critical exponents of the ferromagnetic-paramagnetic phase transition, i.e., the scaling is nonuniversal. A theoretical description based on the Bean-Rodbell model and taking into account compositional inhomogeneities is shown to be able to account for the observed field dependence. In this way the determination of the nonuniversal field dependence of the magnetocaloric effect close to a phase transition can be used as a method to gain insight into the strength of the spin-lattice interactions of magnetic materials. The approach is shown also to be applicable to first-order transitions.

  6. Nonuniform paramagnetic state in nonstoichiometric lanthanum manganites La1- x Mn1- y O3

    NASA Astrophysics Data System (ADS)

    Arbuzova, T. I.; Naumov, S. V.

    2016-06-01

    The magnetic properties of nonstoichiometric lanthanum manganites La1- x Mn1- y O3 have been studied in the temperature range 80 K < T < 650 K. The Curie temperature T C changes nonmonotonically as the number of Mn4+ ions increases. In the paramagnetic region, there exist isolated Mn ions and magnetic polarons which can be conserved to T ⩽ 4 T C, independent of the lattice symmetry. In the T C < T < T pol region, the temperature dependences of the magnetic susceptibility are nonlinear and can be described by the Curie law with a temperature-dependent Curie constant C. The sample has been prepared having a composition near the O' → O structural transition; the spontaneous magnetization of the sample at T ⩽ 1.6 T C is associated to correlated polarons forming due to the double exchange in chains of the E-type antiferromagnetic phase.

  7. Mn K-edge XANES spectra of manganites measured by Kbeta emission.

    PubMed

    García, J; Sánchez, M C; Subías, G; Blasco, J; Proietti, M G

    2001-03-01

    The electronic state of Mn atoms in mixed valence manganites has been studied by means of X-ray absorption spectroscopy at the Mn K-edge. Higher resolution than in conventional measurements has been achieved by measuring the Mn Kbeta fluorescence line. We have found a unique resonance at the edge in the XANES spectra of intermediate composition RE1-xCa(x)MnO3 samples. The features of these XANES spectra do not depend on small changes in the local structure around the Mn atom. However, the spectra of the intermediate composition samples can not be reproduced by a linear combination of REMnO3 and CaMnO3 spectra. Accordingly, the electronic state of Mn atoms in these compounds can not be considered as a mixture of Mn3+ and Mn4+ pure states.

  8. Effect of copper on the magnetism of half doped bilayer manganite

    NASA Astrophysics Data System (ADS)

    Bhatia, S. N.; Mohapatra, Niharika

    2016-08-01

    We have studied the effect of substituting copper at the manganese site on the structure, resistivity and magnetism of the bilayer manganite LaSr2Mn2-xCuxO7 (0≤x≤0.3). All samples form in tetragonal structure with I4/mmm space group. Copper was established to be present in the +2 state by the ESCA spectra. Although no structural transition was observed with this substitution, the electrical transport and magnetic properties change significantly. The parent composition consists of an antiferromagnetic phase ordering at 210 K (=TN(x)) and a ferromagnetic phase with its spins ordering at 135 K (=TC(x)). Charge ordering is not observed. These transition temperatures agree with those of the majority La0.96Sr2.04Mn2O7 and minority La1.2Sr1.8Mn2O7 phases observed by Battle et al. The transport data is also more consistent with two manganites conducting in parallel. A freezing transition appears just above the TN(x) of each composition x≤0.15. The transition temperatures of both phases decrease with increasing copper concentration due to the replacement of the strong intersheet antiferromagnetic (AFM) superexchange Mnn+-Mnn+(n=3,4) with a much weaker Cu2+-Mn3+interaction. But in the ferromagnetic (FM) composition this substitution replaces the FM intersheet interaction with an AFM interaction and thereby produces heterogeneity in the intersheet interactions leading to a canonical spin glass transition in the minority phase of the x=0.2 composition.

  9. Spatial anisotropy and character of the exchange interaction in single and double layer manganites^*.

    NASA Astrophysics Data System (ADS)

    Mryasov, O. N.; Sabiryanov, R. F.; Jaswal, S. S.; Freeman, A. J.

    1998-03-01

    The influence of the doping and number of layers (double vs. single layer) on spatial anisotropy (in-plane J_in vs. inter-plane J_out) in single LaMnO3 and double layer LaSr_2Mn_2O7 manganites studied on the basis of the ab-initio calculations using the linear muffin-tin orbital method generalized to treat non-collinear magnetic configurations^1. We find that contribution of the DE is not effected significantly by the doping (Ca,Sr,Ba) and is substantially smaller than predicted by the Anderson-Hasegawa model. On the other hand, both global and internal lattice distortions dramatically influence the character and strength of the exchange interactions. Spatial anisotropy of the exchange interaction in pure LaMnO3 is found to be slightly underestimated (J_in = 2.0 mRy but J_out = -1.2 mRy) if compared with extracted from newtron scattering experiments (J_in = 1.6 mRy but J_out = -0.8 mRy). We find that exchange interactions in double layer manganites have pronounced two dimensional character with layers effectivaly decoupled (J=0.05 mRy) due to the effect of buffer Sr/La atoms, however within layers J_in = 1 mRy but J_out = 0.3 mRy. ^* Work at NU supported by U.S. DOE (Grant No. DE-FG02-ER45372) and at UNL by NSF [Grant No. OSR9255225], DOE [Grant No. DE-FG2-86ER45262]. ^1 O.N.Mryasov et al., J. of Phys: Condensed Matter 3, 7683 (1991).

  10. Space magnetometer based on an anisotropic magnetoresistive hybrid sensor

    NASA Astrophysics Data System (ADS)

    Brown, P.; Whiteside, B. J.; Beek, T. J.; Fox, P.; Horbury, T. S.; Oddy, T. M.; Archer, M. O.; Eastwood, J. P.; Sanz-Hernández, D.; Sample, J. G.; Cupido, E.; O'Brien, H.; Carr, C. M.

    2014-12-01

    We report on the design and development of a low resource, dual sensor vector magnetometer for space science applications on very small spacecraft. It is based on a hybrid device combining an orthogonal triad of commercial anisotropic magnetoresistive (AMR) sensors with a totem pole H-Bridge drive on a ceramic substrate. The drive enables AMR operation in the more sensitive flipped mode and this is achieved without the need for current spike transmission down a sensor harness. The magnetometer has sensitivity of better than 3 nT in a 0-10 Hz band and a total mass of 104 g. Three instruments have been launched as part of the TRIO-CINEMA space weather mission, inter-calibration against the International Geomagnetic Reference Field model makes it possible to extract physical signals such as field-aligned current deflections of 20-60 nT within an approximately 45 000 nT ambient field.

  11. A Magnetoresistive Heat Switch for the Continuous ADR

    NASA Technical Reports Server (NTRS)

    Canavan, E. R.; Dipirro, M. J.; Jackson, M.; Panek, J.; Shirron, P. J.; Tuttle, J. G.; Krebs, C. (Technical Monitor)

    2001-01-01

    In compensated elemental metals at low temperature, a several Tesla field can suppress electronic heat conduction so thoroughly that heat is effectively carried by phonons alone. In approximately one mm diameter single crystal samples with impurity concentrations low enough that electron conduction is limited by surface scattering, the ratio of zerofield to high-field thermal conductivity can exceed ten thousand. We have used this phenomenon to build a compact, solid-state heat switch with no moving parts and no enclosed fluids. The time scale for switching states is limited by time scale for charging the magnet that supplies the controlling field. Our design and fabrication techniques overcome the difficulties associated with manufacturing and assembling parts from single crystal tungsten. A clear disadvantage of the magnetoresistive switch is the mass and complexity of the magnet system for the controlling field. We have discovered a technique of minimizing this mass and complexity, applicable to the continuous adiabatic demagnetization refrigerator.

  12. Giant magnetoresistive heterogeneous alloys and method of making same

    DOEpatents

    Bernardi, J.J.; Thomas, G.; Huetten, A.R.

    1999-03-16

    The inventive material exhibits giant magnetoresistance upon application of an external magnetic field at room temperature. The hysteresis is minimal. The inventive material has a magnetic phase formed by eutectic decomposition. The bulk material comprises a plurality of regions characterized by (a) the presence of magnetic lamellae wherein the lamellae are separated by a distance smaller than the mean free path of the conduction electrons, and (b) a matrix composition having nonmagnetic properties that is interposed between the lamellae within the regions. The inventive, rapidly quenched, eutectic alloys form microstructure lamellae having antiparallel antiferromagnetic coupling and give rise to GMR properties. The inventive materials made according to the inventive process yielded commercially acceptable quantities and timeframes. Annealing destroyed the microstructure lamellae and the GMR effect. Noneutectic alloys did not exhibit the antiparallel microstructure lamellae and did not possess GMR properties. 7 figs.

  13. Giant magnetoresistive heterogeneous alloys and method of making same

    DOEpatents

    Bernardi, J.J.; Thomas, G.; Huetten, A.R.

    1998-10-20

    The inventive material exhibits giant magnetoresistance upon application of an external magnetic field at room temperature. The hysteresis is minimal. The inventive material has a magnetic phase formed by eutectic decomposition. The bulk material comprises a plurality of regions characterized by (a) the presence of magnetic lamellae wherein the lamellae are separated by a distance smaller than the mean free path of the conduction electrons, and (b) a matrix composition having nonmagnetic properties that is interposed between the lamellae within the regions. The inventive, rapidly quenched, eutectic alloys form microstructure lamellae having antiparallel antiferromagnetic coupling and give rise to GMR properties. The inventive materials made according to the inventive process yielded commercially acceptable quantities and timeframes. Annealing destroyed the microstructure lamellae and the GMR effect. Noneutectic alloys did not exhibit the antiparallel microstructure lamellae and did not possess GMR properties. 7 figs.

  14. Giant magnetoresistive heterogeneous alloys and method of making same

    DOEpatents

    Bernardi, Johannes J.; Thomas, Gareth; Huetten, Andreas R.

    1998-01-01

    The inventive material exhibits giant magnetoresistance upon application of an external magnetic field at room temperature. The hysteresis is minimal. The inventive material has a magnetic phase formed by eutectic decomposition. The bulk material comprises a plurality of regions characterized by a) the presence of magnetic lamellae wherein the lamellae are separated by a distance smaller than the mean free path of the conduction electrons, and b) a matrix composition having nonmagnetic properties that is interposed between the lamellae within the regions. The inventive, rapidly quenched, eutectic alloys form microstructure lamellae having antiparallel antiferromagnetic coupling and give rise to GMR properties. The inventive materials made according to the inventive process yielded commercially acceptable quantities and timeframes. Annealing destroyed the microstructure lamellae and the GMR effect. Noneutectic alloys did not exhibit the antiparallel microstructure lamellae and did not possess GMR properties.

  15. Giant magnetoresistive heterogeneous alloys and method of making same

    DOEpatents

    Bernardi, Johannes J.; Thomas, Gareth; Huetten, Andreas R.

    1999-01-01

    The inventive material exhibits giant magnetoresistance upon application of an external magnetic field at room temperature. The hysteresis is minimal. The inventive material has a magnetic phase formed by eutectic decomposition. The bulk material comprises a plurality of regions characterized by a) the presence of magnetic lamellae wherein the lamellae are separated by a distance smaller than the mean free path of the conduction electrons, and b) a matrix composition having nonmagnetic properties that is interposed between the lamellae within the regions. The inventive, rapidly quenched, eutectic alloys form microstructure lamellae having antiparallel antiferromagnetic coupling and give rise to GMR properties. The inventive materials made according to the inventive process yielded commercially acceptable quantities and timeframes. Annealing destroyed the microstructure lamellae and the GMR effect. Noneutectic alloys did not exhibit the antiparallel microstructure lamellae and did not possess GMR properties.

  16. Micromagnetic modeling of overlaid exchange-biased giant magnetoresistance head

    NASA Astrophysics Data System (ADS)

    Zheng, Yuankai; You, Dan; Wu, Yihong

    2002-05-01

    Overlaid exchange-biased structures for giant magnetoresistance head have been proposed and investigated. A home-developed three-dimensional micromagnetic modeling tool has been used to simulate synthetic antiferromagnetic spin valves of this type of biased structure with dimensions of 100 nm in width and 80 nm in height. Simulation results showed that, with a properly chosen antiferromagnetic material and structure, the exchange-biasing field could be made sufficient to suppress the noise without severely reducing the sensitivity. The sensitivity of overlaid exchange-biased spin valves is 1.73 times that of the abutted hard biased ones. Microtrack profiles showed that side reading effect could be suppressed effectively with an effective exchange-biasing field over 600 Oe.

  17. Interlayer transverse magnetoresistance in the presence of an anisotropic pseudogap

    NASA Astrophysics Data System (ADS)

    Smith, M. F.; McKenzie, Ross H.

    2009-12-01

    The interlayer magnetoresistance of a quasi-two-dimensional layered metal with a d -wave pseudogap is calculated semiclassically. An expression for the interlayer resistivity as a function of the strength and direction of the magnetic field, the magnitude of the pseudogap, temperature, and scattering rate is obtained. We find that the pseudogap, by introducing low-energy nodal quasiparticle contours, smooths the dependence on field direction in a manner characteristic of its anisotropy. We thus propose that interlayer resistance measurements under a strong field of variable orientation can be used to fully characterize an anisotropic pseudogap. The general result is applied to the case of a magnetic field parallel to the conducting layers using a model band structure appropriate for overdoped Tℓ2201 .

  18. Theory of spin Hall magnetoresistance (SMR) and related phenomena.

    PubMed

    Chen, Yan-Ting; Takahashi, Saburo; Nakayama, Hiroyasu; Althammer, Matthias; Goennenwein, Sebastian T B; Saitoh, Eiji; Bauer, Gerrit E W

    2016-03-16

    We review the so-called spin Hall magnetoresistance (SMR) in bilayers of a magnetic insulator and a metal, in which spin currents are generated in the normal metal by the spin Hall effect. The associated angular momentum transfer to the ferromagnetic layer and thereby the electrical resistance is modulated by the angle between the applied current and the magnetization direction. The SMR provides a convenient tool to non-invasively measure the magnetization direction and spin-transfer torque to an insulator. We introduce the minimal theoretical instruments to calculate the SMR, i.e. spin diffusion theory and quantum mechanical boundary conditions. This leads to a small set of parameters that can be fitted to experiments. We discuss the limitations of the theory as well as alternative mechanisms such as the ferromagnetic proximity effect and Rashba spin-orbit torques, and point out new developments.

  19. Gamma Irradiation of Magnetoresistive Sensors for Planetary Exploration

    PubMed Central

    Sanz, Ruy; Fernández, Ana B.; Dominguez, Jose A.; Martín, Boris; Michelena, Marina D.

    2012-01-01

    A limited number of Anisotropic Magnetoresistive (AMR) commercial-off-the-shelf (COTS) magnetic sensors of the HMC series by Honeywell, with and without integrated front-end electronics, were irradiated with gamma rays up to a total irradiation dose of 200 krad (Si), following the ESCC Basic Specification No. 22900. Due to the magnetic cleanliness required for these tests a special set-up was designed and successfully employed. Several parameters of the sensors were monitored during testing and the results are reported in this paper. The authors conclude that AMR sensors without front-end electronics seem to be robust against radiation doses of up to 200 krad (Si) with a dose rate of 5 krad (Si)/hour and up to a resolution of tens of nT, but sensors with an integrated front-end seem to be more vulnerable to radiation. PMID:22666039

  20. Magnetoresistance in permalloy/GaMnAs circular microstructures

    NASA Astrophysics Data System (ADS)

    Guenther, Justin Michael

    When two ferromagnetic materials are deposited directly on top of one another, their magnetic moments lock together and will no longer switch independently. This effect is known as exchange spring coupling. Reports in literature indicate that a bilayer composed of GaMnAs and permalloy may be a rare exception. Such a bilayer would allow for independent switching and, as a result, giant magnetoresistance. For this thesis, we verified the independent switching of continuous films of GaMnAs and expanded on existing literature. We also investigated GMR in bilayers. Samples were fabricated and measured using novel techniques and software developed specifically for this project. Transport measurements of GaMnAs/Py bilayers revealed a minimal to non-existent GMR effect; instead, the main discernible effect was due to AMR of the bulk substrate of the samples. This thesis also details the construction process of an inexpensive, temporary cleanroom environment.

  1. Large anisotropic magnetoresistance of ruthenium-based Heusler alloys

    NASA Astrophysics Data System (ADS)

    Mizusaki, S.; Ohnishi, T.; Douzono, A.; Nagata, Y.; Ozawa, T. C.; Samata, H.; Noro, Y.

    2009-04-01

    Anomalous magnetic behavior was found in the polycrystalline Heusler alloy system Ru2Mn1-xFexGe. Samples of x =0 and 1.0 show no magnetoresistance (MR); however, the anisotropic MR effect is observed for x =0.5 (MR ratios of -4% and +2% are observed under parallel and perpendicular configurations of applied field and applied current, respectively). Moreover, magnetic measurement revealed that the sample of x =0 is antiferromagnetic, whereas the samples of x =0.5 and 1.0 are ferromagnetic with Curie temperatures of 270 and 490 K, respectively. The saturation magnetization and coercivity at 5 K are 3.1μB/f.u. and negligibly small for x =1.0 and 1.8μB/f.u. and 0.1 T for x =0.5, respectively. The MR effect is explained by a model in which antiferromagnetic and ferromagnetic domains coexist.

  2. Theory of spin Hall magnetoresistance (SMR) and related phenomena.

    PubMed

    Chen, Yan-Ting; Takahashi, Saburo; Nakayama, Hiroyasu; Althammer, Matthias; Goennenwein, Sebastian T B; Saitoh, Eiji; Bauer, Gerrit E W

    2016-03-16

    We review the so-called spin Hall magnetoresistance (SMR) in bilayers of a magnetic insulator and a metal, in which spin currents are generated in the normal metal by the spin Hall effect. The associated angular momentum transfer to the ferromagnetic layer and thereby the electrical resistance is modulated by the angle between the applied current and the magnetization direction. The SMR provides a convenient tool to non-invasively measure the magnetization direction and spin-transfer torque to an insulator. We introduce the minimal theoretical instruments to calculate the SMR, i.e. spin diffusion theory and quantum mechanical boundary conditions. This leads to a small set of parameters that can be fitted to experiments. We discuss the limitations of the theory as well as alternative mechanisms such as the ferromagnetic proximity effect and Rashba spin-orbit torques, and point out new developments. PMID:26881498

  3. Theory of spin Hall magnetoresistance (SMR) and related phenomena

    NASA Astrophysics Data System (ADS)

    Chen, Yan-Ting; Takahashi, Saburo; Nakayama, Hiroyasu; Althammer, Matthias; Goennenwein, Sebastian T. B.; Saitoh, Eiji; Bauer, Gerrit E. W.

    2016-03-01

    We review the so-called spin Hall magnetoresistance (SMR) in bilayers of a magnetic insulator and a metal, in which spin currents are generated in the normal metal by the spin Hall effect. The associated angular momentum transfer to the ferromagnetic layer and thereby the electrical resistance is modulated by the angle between the applied current and the magnetization direction. The SMR provides a convenient tool to non-invasively measure the magnetization direction and spin-transfer torque to an insulator. We introduce the minimal theoretical instruments to calculate the SMR, i.e. spin diffusion theory and quantum mechanical boundary conditions. This leads to a small set of parameters that can be fitted to experiments. We discuss the limitations of the theory as well as alternative mechanisms such as the ferromagnetic proximity effect and Rashba spin-orbit torques, and point out new developments.

  4. Space magnetometer based on an anisotropic magnetoresistive hybrid sensor.

    PubMed

    Brown, P; Whiteside, B J; Beek, T J; Fox, P; Horbury, T S; Oddy, T M; Archer, M O; Eastwood, J P; Sanz-Hernández, D; Sample, J G; Cupido, E; O'Brien, H; Carr, C M

    2014-12-01

    We report on the design and development of a low resource, dual sensor vector magnetometer for space science applications on very small spacecraft. It is based on a hybrid device combining an orthogonal triad of commercial anisotropic magnetoresistive (AMR) sensors with a totem pole H-Bridge drive on a ceramic substrate. The drive enables AMR operation in the more sensitive flipped mode and this is achieved without the need for current spike transmission down a sensor harness. The magnetometer has sensitivity of better than 3 nT in a 0-10 Hz band and a total mass of 104 g. Three instruments have been launched as part of the TRIO-CINEMA space weather mission, inter-calibration against the International Geomagnetic Reference Field model makes it possible to extract physical signals such as field-aligned current deflections of 20-60 nT within an approximately 45,000 nT ambient field.

  5. Characteristics of the dual-bridge giant magnetoresistance magnetometer.

    PubMed

    Jeng, Jen-Tzong; Hsu, Ting-Yu

    2011-03-01

    The responsivity and the field noise characteristics of the giant magnetoresistance (GMR) magnetometer driven by an alternating magnetic field are investigated. The harmonic spectrum of the sensor voltage shows that only the odd harmonics of excitation frequency are sensitive to the external dc field. To cancel out the even harmonics, the dual-bridge GMR magnetometer with the balanced output is proposed. With the dual-bridge configuration, the field-to-voltage transfer coefficient is doubled and the field noise is reduced by a factor of 1.4. The minimum field noise is 7 nT∕√Hz at 1 Hz with the ac excitation power of 5.5 mW. The proposed sensor is suitable for the electronic compass application.

  6. Impurity-assisted tunneling magnetoresistance under a weak magnetic field.

    PubMed

    Txoperena, Oihana; Song, Yang; Qing, Lan; Gobbi, Marco; Hueso, Luis E; Dery, Hanan; Casanova, Fèlix

    2014-10-01

    Injection of spins into semiconductors is essential for the integration of the spin functionality into conventional electronics. Insulating layers are often inserted between ferromagnetic metals and semiconductors for obtaining an efficient spin injection, and it is therefore crucial to distinguish between signatures of electrical spin injection and impurity-driven effects in the tunnel barrier. Here we demonstrate an impurity-assisted tunneling magnetoresistance effect in nonmagnetic-insulator-nonmagnetic and ferromagnetic-insulator-nonmagnetic tunnel barriers. In both cases, the effect reflects on-off switching of the tunneling current through impurity channels by the external magnetic field. The reported effect is universal for any impurity-assisted tunneling process and provides an alternative interpretation to a widely used technique that employs the same ferromagnetic electrode to inject and detect spin accumulation. PMID:25325651

  7. Magnetoresistance of galfenol-based magnetic tunnel junction

    SciTech Connect

    Gobaut, B.; Vinai, G.; Castán-Guerrero, C.; Krizmancic, D.; Panaccione, G.; Torelli, P.; Rafaqat, H.; Roddaro, S.; Rossi, G.; Eddrief, M.; Marangolo, M.

    2015-12-15

    The manipulation of ferromagnetic layer magnetization via electrical pulse is driving an intense research due to the important applications that this result will have on memory devices and sensors. In this study we realized a magnetotunnel junction in which one layer is made of Galfenol (Fe{sub 1-x}Ga{sub x}) which possesses one of the highest magnetostrictive coefficient known. The multilayer stack has been grown by molecular beam epitaxy and e-beam evaporation. Optical lithography and physical etching have been combined to obtain 20x20 micron sized pillars. The obtained structures show tunneling conductivity across the junction and a tunnel magnetoresistance (TMR) effect of up to 11.5% in amplitude.

  8. Impurity scattering from {delta}-layers in giant magnetoresistance systems

    SciTech Connect

    Marrows, C. H.; Hickey, B. J.

    2001-06-01

    The properties of the archetypal Co/Cu giant magnetoresistance (GMR) spin-valve structure have been modified by the insertion of very thin (submonolayer) {delta}-layers of various elements at different points within the Co layers, and at the Co/Cu interface. Different effects are observed depending on the nature of the impurity, its position within the periodic table, and its location within the spin valve. The GMR can be strongly enhanced or suppressed for various specific combinations of these parameters, giving insight into the microscopic mechanisms giving rise to the GMR. In particular, the doping of Fe and Ni into the spin valve close to, but not at the interface, leads to an increase in GMR, as does the introduction of Cu, a nonmagnetic impurity, into the Co layers.

  9. Finite-size effects in giant magnetoresistance multilayers

    SciTech Connect

    Perez, M.; Marrows, C. H.; Hickey, B. J.

    2001-06-01

    It is of interest to determine the characteristic length scale that determines giant magnetoresistance (GMR). In order to understand this behavior, GMR multilayers of Co/Ru and Co/Cu have been studied at a temperature of 4.2 K. The total thickness of Co/Ru multilayers has been varied from 96 to 1654 Aa and Co/Cu from 77 to 2712 Aa by increasing the number of bilayers (N). It has been observed that GMR increases with the number of bilayers and more than 20 bilayers for Co/Ru and 50 for Co/Cu are needed to reach the saturation value. {copyright} 2001 American Institute of Physics.

  10. Magnetoresistance measurement of permalloy thin film rings with triangular fins

    NASA Astrophysics Data System (ADS)

    Lai, Mei-Feng; Hsu, Chia-Jung; Liao, Chun-Neng; Chen, Ying-Jiun; Wei, Zung-Hang

    2010-01-01

    Magnetization reversals in permalloy rings controlled by nucleation sites using triangular fins at the same side and diagonal with respect to the field direction are demonstrated by magnetoresistance measurement and micromagnetic simulation. In the ring with triangular fins at the same side, there exists two-step reversal from onion to flux-closure state (or vortex state) and then from flux-closure (or vortex state) to reverse onion state; in the ring with diagonal triangular fins, one-step reversal occurs directly from onion to reverse onion state. The reversal processes are repeatable and controllable in contrast to an ideal ring without triangular fins where one-step and two-step reversals occur randomly in sweep-up and sweep-down processes.

  11. Colossal negative thermal expansion induced by magnetic phase competition on frustrated lattices in Laves phase compound (Hf,Ta)Fe2

    NASA Astrophysics Data System (ADS)

    Li, B.; Luo, X. H.; Wang, H.; Ren, W. J.; Yano, S.; Wang, C.-W.; Gardner, J. S.; Liss, K.-D.; Miao, P.; Lee, S.-H.; Kamiyama, T.; Wu, R. Q.; Kawakita, Y.; Zhang, Z. D.

    2016-06-01

    Competition between ferromagnetic and antiferromagnetic phases on frustrated lattices in hexagonal Laves phase compound Hf0.86Ta0.14Fe2 is investigated by using neutron diffraction as a function of temperature and magnetic fields and density-functional-theory calculations. At 325 K, the compound orders into the 120° frustrated antiferromagnetic state with a well-reduced magnetic moment, and an in-plane lattice contraction simultaneously sets in. With further cooling down, however, the accumulated distortion in turn destabilizes this susceptible frustrated structure. The frustration is completely relieved at 255 K when the first-order transition to the ferromagnetic state takes place, where a colossal negative volumetric thermal expansion, -123 ×10-6 /K, is obtained. Meanwhile, the antiferromagnetic state can be suppressed by few-tesla magnetic fields, which results in a colossal positive magnetostriction. Such delicate competition is attributed to the giant magnetic fluctuation inherent in the frustrated antiferromagnetic state. Therefore, the magnetoelastic instability is approached even under a small perturbation.

  12. Resistance transition assisted geometry enhanced magnetoresistance in semiconductors

    SciTech Connect

    Luo, Zhaochu; Zhang, Xiaozhong

    2015-05-07

    Magnetoresistance (MR) reported in some non-magnetic semiconductors (particularly silicon) has triggered considerable interest owing to the large magnitude of the effect. Here, we showed that MR in lightly doped n-Si can be significantly enhanced by introducing two diodes and proper design of the carrier path [Wan, Nature 477, 304 (2011)]. We designed a geometrical enhanced magnetoresistance (GEMR) device whose room-temperature MR ratio reaching 30% at 0.065 T and 20 000% at 1.2 T, respectively, approaching the performance of commercial MR devices. The mechanism of this GEMR is: the diodes help to define a high resistive state (HRS) and a low resistive state (LRS) in device by their openness and closeness, respectively. The ratio of apparent resistance between HRS and LRS is determined by geometry of silicon wafer and electrodes. Magnetic field could induce a transition from LRS to HRS by reshaping potential and current distribution among silicon wafer, resulting in a giant enhancement of intrinsic MR. We expect that this GEMR could be also realized in other semiconductors. The combination of high sensitivity to low magnetic fields and large high-field response should make this device concept attractive to the magnetic field sensing industry. Moreover, because this MR device is based on a conventional silicon/semiconductor platform, it should be possible to integrate this MR device with existing silicon/semiconductor devices and so aid the development of silicon/semiconductor-based magnetoelectronics. Also combining MR devices and semiconducting devices in a single Si/semiconductor chip may lead to some novel devices with hybrid function, such as electric-magnetic-photonic properties. Our work demonstrates that the charge property of semiconductor can be used in the magnetic sensing industry, where the spin properties of magnetic materials play a role traditionally.

  13. Extraordinary magnetoresistance in two and three dimensions: Geometrical optimization

    NASA Astrophysics Data System (ADS)

    Pugsley, Lisa M.; Ram-Mohan, L. R.; Solin, S. A.

    2013-02-01

    The extraordinary magnetoresistance (EMR) in metal-semiconductor hybrid structures was first demonstrated using a van der Pauw configuration for a circular semiconductor wafer with a concentric metallic inclusion in it. This effect depends on the orbital motion of carriers in an external magnetic field, and the remarkably high magnetoresistance response observed suggests that the geometry of the metallic inclusion can be optimized to further significantly enhance the EMR. Here, we consider the theory and simulations to achieve this goal by comparing both two-dimensional (2D) and three-dimensional (3D) structures in an external magnetic field to evaluate the EMR in them. New results for 3D structures are presented to show the feasibility of such modeling. Examples of structures that are compatible with present day technological capabilities are given together with their expected responses in terms of EMR. For a 10 μm 2D square structure with a square metallic inclusion, we find an MR up to 107 percent for an applied magnetic field of 1 T. In 3D, for a 10 μm cube with a 5 μm centered metallic inclusion, we obtain an MR of ˜104 percent, which is comparable with the 2D structure of equivalent dimensions. The results presented here for specific geometries are scalable to smaller dimensions down to the onset of ballistic effects in the transport. The present calculations open up the possibility of 3D magnetic field sensors capable of determining the magnitude and also direction of the magnetic field once a full characterization of the sensor response is performed.

  14. Modeling of Nanoparticular Magnetoresistive Systems and the Impact on Molecular Recognition

    PubMed Central

    Teich, Lisa; Kappe, Daniel; Rempel, Thomas; Meyer, Judith; Schröder, Christian; Hütten, Andreas

    2015-01-01

    The formation of magnetic bead or nanoparticle superstructures due to magnetic dipole dipole interactions can be used as configurable matter in order to realize low-cost magnetoresistive sensors with very high GMR-effect amplitudes. Experimentally, this can be realized by immersing magnetic beads or nanoparticles in conductive liquid gels and rearranging them by applying suitable external magnetic fields. After gelatinization of the gel matrix the bead or nanoparticle positions are fixed and the resulting system can be used as a magnetoresistive sensor. In order to optimize such sensor structures we have developed a simulation tool chain that allows us not only to study the structuring process in the liquid state but also to rigorously calculate the magnetoresistive characteristic curves for arbitrary nanoparticle arrangements. As an application, we discuss the role of magnetoresistive sensors in finding answers to molecular recognition. PMID:25903554

  15. Magnetoresistance manipulation and sign reversal in Mn-doped ZnO nanowires

    PubMed Central

    Sapkota, Keshab R.; Chen, Weimin; Maloney, F. Scott; Poudyal, Uma; Wang, Wenyong

    2016-01-01

    We report magnetoresistance (MR) manipulation and sign reversal induced by carrier concentration modulation in Mn-doped ZnO nanowires. At low temperatures positive magnetoresistance was initially observed. When the carrier concentration was increased through the application of a gate voltage, the magnetoresistance also increased and reached a maximum value. However, further increasing the carrier concentration caused the MR to decrease, and eventually an MR sign reversal from positive to negative was observed. An MR change from a maximum positive value of 25% to a minimum negative value of 7% was observed at 5 K and 50 KOe. The observed MR behavior was modeled by considering combined effects of quantum correction to carrier conductivity and bound magnetic polarons. This work could provide important insights into the mechanisms that govern magnetotransport in dilute magnetic oxides, and it also demonstrated an effective approach to manipulating magnetoresistance in these materials that have important spintronic applications. PMID:27739442

  16. Oliver E. Buckley Prize Talk: Birth of tunnel magnetoresistance and its development

    NASA Astrophysics Data System (ADS)

    Miyazaki, Terunobu

    2009-03-01

    Nowadays usually we use the word, tunnel magnetoresistance, but it required a long time to combine both words tunnel and magnetoresistance. The study of tunnel junction may originate p-n junction studied first around 1950. On the other hand, magnetoresistance effect was reported first in 1857 which was about 100 years earlier than the start of tunnel junction study. The research of tunnel magnetoresoistance has been mainly developed first for Al-oxide tunnel barrier junctions and made a big progress by the appearance of MgO barrier junctions for both basic research and applications. More recently Heusler electrode tunnel junctions exhibits a large TMR ratio up to about 750 %. In my talk I will explain first the history of the study of tunnel junction and magnetoresistance effect. Then, I will focus on the Heusler electrode junctions and also application of tunnel magnetoresoistance junctions.

  17. A simple formulation for magnetoresistance in metal-insulator granular films with increased current

    NASA Astrophysics Data System (ADS)

    Boff, M. A. S.; Canto, B.; Baibich, M. N.; Pereira, L. G.

    2013-02-01

    We studied the tunnel magnetoresistance in metal/insulator granular films when the applied current is varied. The tunnel magnetoresistance shows a strong modification related to a non-Ohmic behaviour of theses materials. It was verified that spin-dependent tunnelling is the main mechanism for magnetoresistance at low applied current. However, when the current is high, another mechanism gets to be important: it is independent of the magnetization and is associated to variable range hopping between metallic grains. In this work, we propose a simple modification of Inoue and Maekawa's model for tunnelling magnetoresistance in granulars, rewriting the expression for resistance as a function of magnetic field and temperature, also taking into account the two different contributions.

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

    SciTech Connect

    Zhang, Z. H. Bai, Lihui; Hu, C.-M.; Hemour, S.; Wu, K.; Fan, X. L.; Xue, D. S.; Houssameddine, D.

    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, its 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.

  19. Hanle Magnetoresistance in Thin Metal Films with Strong Spin-Orbit Coupling.

    PubMed

    Vélez, Saül; Golovach, Vitaly N; Bedoya-Pinto, Amilcar; Isasa, Miren; Sagasta, Edurne; Abadia, Mikel; Rogero, Celia; Hueso, Luis E; Bergeret, F Sebastian; Casanova, Fèlix

    2016-01-01

    We report measurements of a new type of magnetoresistance in Pt and Ta thin films. The spin accumulation created at the surfaces of the film by the spin Hall effect decreases in a magnetic field because of the Hanle effect, resulting in an increase of the electrical resistance as predicted by Dyakonov [Phys. Rev. Lett. 99, 126601 (2007)]. The angular dependence of this magnetoresistance resembles the recently discovered spin Hall magnetoresistance in Pt/Y(3)Fe(5)O(12) bilayers, although the presence of a ferromagnetic insulator is not required. We show that this Hanle magnetoresistance is an alternative simple way to quantitatively study the coupling between charge and spin currents in metals with strong spin-orbit coupling. PMID:26799036

  20. GMR sensors: magnetoresistive behaviour optimization for biological detection by means of superparamagnetic nanoparticles.

    PubMed

    Manteca, A; Mujika, M; Arana, S

    2011-04-15

    An immunomagnetic method for the selective and quantitative detection of biological species by means of a magnetoresistive biosensor and superparamagnetic particles has been optimized. In order to achieve this, a giant magnetoresistive [Co (5.10nm)/Cu (2.47 nm)](20) multilayer structure has been chosen as the sensitive material, showing a magnetoresistance of 3.60% at 215 Oe and a sensitivity up to 0.19 Ω/Oe between 145 Oe and 350 Oe. The outward gold surface of the sensor is biofunctionalized with a Self-Assembled Monolayer (SAM). In addition, three different types of magnetic labels have been tested. 2 μm diameter magnetic carriers (7.68 pg ferrite/particle) have shown the best response and they have induced a shift in the magnetoresistive hysteresis loops up to 9% at 175 Oe. PMID:21382706

  1. Magnetoresistance manipulation and sign reversal in Mn-doped ZnO nanowires

    NASA Astrophysics Data System (ADS)

    Sapkota, Keshab R.; Chen, Weimin; Maloney, F. Scott; Poudyal, Uma; Wang, Wenyong

    2016-10-01

    We report magnetoresistance (MR) manipulation and sign reversal induced by carrier concentration modulation in Mn-doped ZnO nanowires. At low temperatures positive magnetoresistance was initially observed. When the carrier concentration was increased through the application of a gate voltage, the magnetoresistance also increased and reached a maximum value. However, further increasing the carrier concentration caused the MR to decrease, and eventually an MR sign reversal from positive to negative was observed. An MR change from a maximum positive value of 25% to a minimum negative value of 7% was observed at 5 K and 50 KOe. The observed MR behavior was modeled by considering combined effects of quantum correction to carrier conductivity and bound magnetic polarons. This work could provide important insights into the mechanisms that govern magnetotransport in dilute magnetic oxides, and it also demonstrated an effective approach to manipulating magnetoresistance in these materials that have important spintronic applications.

  2. Electric field control of magnetoresistance in InP nanowires with ferromagnetic contacts.

    PubMed

    Zwanenburg, F A; van der Mast, D W; Heersche, H B; Kouwenhoven, L P; Bakkers, E P A M

    2009-07-01

    We demonstrate electric field control of sign and magnitude of the magnetoresistance in InP nanowires with ferromagnetic contacts. The sign change in the magnetoresistance is directly correlated with a sign change in the transconductance. Additionally, the magnetoresistance is shown to persist at such a high bias that Coulomb blockade has been lifted. We also observe the magnetoresistance when one of the ferromagnets is replaced by a nonmagnetic metal. We conclude that it must be induced by a single ferromagnetic contact, and that spin transport can be ruled out as the origin. Our results emphasize the importance of a systematic investigation of spin-valve devices in order to discriminate between ambiguous interpretations. PMID:19537736

  3. Monte Carlo simulation of multilayer magnetic structures and calculation of the magnetoresistance coefficient

    NASA Astrophysics Data System (ADS)

    Prudnikov, V. V.; Prudnikov, P. V.; Romanovskii, D. E.

    2015-11-01

    The Monte Carlo study of three-layer and spin-valve magnetic structures with giant magnetoresistance effects has been performed with the application of the Heisenberg anisotropic model to the description of the magnetic properties of thin ferromagnetic films. The dependences of the magnetic characteristics on the temperature and external magnetic field have been obtained for the ferromagnetic and antiferromagnetic configurations of these structures. A Monte Carlo method for determining the magnetoresistance coefficient has been developed. The magnetoresistance coefficient has been calculated for three-layer and spin-valve magnetic structures at various thicknesses of ferromagnetic films. It has been shown that the calculated temperature dependence of the magnetoresistance coefficient is in good agreement with experimental data obtained for the Fe(001)/Cr(001) multilayer structure and the CFAS/Ag/CFAS/IrMn spin valve based on the Co2FeAl0.5Si0.5 (CFAS) Heusler alloy.

  4. Immunohistochemistry Successfully Uncovers Intratumoral Heterogeneity and Widespread Co-Losses of Chromatin Regulators in Clear Cell Renal Cell Carcinoma

    PubMed Central

    Devarajan, Karthik; Parsons, Theodore; Wang, Qiong; Liao, Lili; Cho, Eun-Ah; O'Neill, Raymond; Solomides, Charalambos; Peiper, Stephen C.; Testa, Joseph R.; Uzzo, Robert; Yang, Haifeng

    2016-01-01

    Recent studies have shown that intratumoral heterogeneity (ITH) is prevalent in clear cell renal cell carcinoma (ccRCC), based on DNA sequencing and chromosome aberration analysis of multiple regions from the same tumor. VHL mutations were found to be universal throughout individual tumors when it occurred (ubiquitous), while the mutations in other tumor suppressor genes tended to be detected only in parts of the tumors (subclonal). ITH has been studied mostly by DNA sequencing in limited numbers of samples, either by whole genome sequencing or by targeted sequencing. It is not known whether immunohistochemistry (IHC) can be used as a tool to study ITH. To address this question, we examined the protein expression of PBRM1, and PBRM1-related proteins such as ARID1A, SETD2, BRG1, and BRM. Altogether, 160 ccRCC (40 per stage) were used to generate a tissue microarray (TMA), with four foci from each tumor included. Loss of expression was defined as 0–5% of tumor cells with positive nuclear staining in an individual focus. We found that 49/160 (31%), 81/160 (51%), 23/160 (14%), 24/160 (15%), and 61/160 (38%) of ccRCC showed loss of expression of PBRM1, ARID1A, SETD2, BRG1, and BRM, respectively, and that IHC could successfully detect a high prevalence of ITH. Phylogenetic trees were constructed that reflected the ITH. Striking co-losses among proteins were also observed. For instance, ARID1A loss almost always accompanied PBRM1 loss, whereas BRM loss accompanied loss of BRG1, PBRM1 or ARID1A. SETD2 loss frequently occurred with loss of one or more of the other four proteins. Finally, in order to learn the impact of combined losses, we compared the tumor growth after cells acquired losses of ARID1A, PBRM1, or both in a xenograft model. The results suggest that ARID1A loss has a greater tumor-promoting effect than PBRM1 loss, indicating that xenograft analysis is a useful tool to investigate how these losses impact on tumor behavior, either alone or in combination. PMID

  5. Electric field modulation of tunneling anisotropic magnetoresistance in tunnel junctions with antiferromagnetic electrodes

    NASA Astrophysics Data System (ADS)

    Goto, Minori; Nawaoka, Kohei; Miwa, Shinji; Hatanaka, Shohei; Mizuochi, Norikazu; Suzuki, Yoshishige

    2016-08-01

    We present electric field modulation of tunneling anisotropic magnetoresistance (TAMR) in MnIr|MgO|Ta tunnel junctions. TAMR enables direct observation of the antiferromagnetic spin direction at the MnIr|MgO interface. We found that the shape of magnetoresistance (MR) curve can be modulated by an electric field, which can be explained by electric field modulation of the interfacial magnetic anisotropy at MnIr|MgO.

  6. Large magnetoresistance induced by crystallographic defects in FexTaS2 single crystals

    NASA Astrophysics Data System (ADS)

    Chen, Chih-Wei; Morosan, Emilia; Morosan's Group Team

    The search for the materials that show large magnetoresistance and the mechanisms that induce it remains challenging in both experimental and theoretical aspects. The giant magnetoresistance in one class of materials, ferromagnetic conductors, is generally attributed to the misalignments of magnetic moments, which cause spin disorder scattering. Recently, very large magnetoresistance (>60 %) was discovered in the ferromagnetic Fe-intercalated transition metal dichalcogenide, Fe0.28TaS2 [Phys. Rev. B 91, 054426(2015)]. The mechanism that led to this large magnetoresistance was suggested to be due to the deviation of Fe concentration from commensurate values (1/4 or 1/3), which caused magnetic moments' misalignments. Here we report a study of FexTaS2 crystals with x close to the commensurate values. Our results qualitatively demonstrate that crystallographic defects significantly affect magnetoresistance in FexTaS2. This provides a way to search for large magnetoresistance in more intercalated transition metal dichalcogenides. This work is supported by the Department of Defense PECASE.

  7. Quantum and classical contributions to linear magnetoresistance in topological insulator thin films

    NASA Astrophysics Data System (ADS)

    Singh, Sourabh; Gopal, R. K.; Sarkar, Jit; Mitra, Chiranjib

    2016-05-01

    Three dimensional topological insulators possess backscattering immune relativistic Dirac fermions on their surface due to nontrivial topology of the bulk band structure. Both metallic and bulk insulating topological insulators exhibit weak-antilocalization in the low magnetic field and linear like magnetoresistance in higher fields. We explore the linear magnetoresistance in bulk insulating topological insulator Bi2-xSbxTe3-ySey thin films grown by pulsed laser deposition technique. Thin films of Bi2-xSbxTe3-ySey were found to be insulating in nature, which conclusively establishes the origin of linear magnetoresistance from surface Dirac states. The films were thoroughly characterized for their crystallinity and composition and then subjected to transport measurements. We present a careful analysis taking into considerations all the existing models of linear magnetoresistance. We comprehend that the competition between classical and quantum contributions to magnetoresistance results in linear magnetoresistance in high fields. We observe that the cross-over field decreases with increasing temperature and the physical argument for this behavior is explained.

  8. Invariant exchange perturbation theory for multicenter systems and its application to the calculation of magnetic chains in manganites

    SciTech Connect

    Orlenko, E. V. Ershova, E. V.; Orlenko, F. E.

    2013-10-15

    The formalism of exchange perturbation theory is presented with regard to the general principles of constructing an antisymmetric vector with the use of the Young diagrams and tableaux in which the coordinate and spin parts are not separated. The form of the energy and wave function corrections coincides with earlier obtained expressions, which are reduced in the present paper to a simpler form of a symmetry-adapted perturbation operator, which preserves all intercenter exchange contributions. The exchange perturbation theory (EPT) formalism itself is presented in the standard form of invariant perturbation theory that takes into account intercenter electron permutations between overlapping nonorthogonal states. As an example of application of the formalism of invariant perturbation theory, we consider the magnetic properties of perovskite manganites La{sub 1/3}Ca{sub 2/3}MnO{sub 3} that are associated with the charge and spin ordering in magnetic chains of manganese. We try to interpret the experimental results obtained from the study of the effect of doping the above alloys by the model of superexchange interaction in manganite chains that is constructed on the basis of the exchange perturbation theory (EPT) formalism. The model proposed makes it possible to carry out a quantitative analysis of the effect of substitution of manganese atoms by doping elements with different electron configurations on the electronic structure and short-range order in a magnetic chain of manganites.

  9. Magnetoresistance in the magnetic and superconducting phases of RuSr 2GdCu 2O 8

    NASA Astrophysics Data System (ADS)

    Pimentel, J. L.; Jurelo, A. R.; Pureur, P.

    The transverse magnetoresistance of RuSr 2GdCu 2O 8 is studied as a function of the applied field in several fixed temperatures spanning the superconducting and purely magnetic phases. In low applied fields, the magnetoresistance is positive and results from suppression of superconducting fluctuations. In the high field-high temperature regimes, a spin-disorder contribution to the magnetoresistance is identified. This fact indicates that the magnetic Ru-O 2 atomic layers have a conducting character.

  10. Competing Magnetic Ground States in A-Site Layer Ordered Manganites

    NASA Astrophysics Data System (ADS)

    Dabrowski, B.; Chmaissem, O.; Ren, Y.; Brown, D. E.; Kolesnik, S.; Mais, J.

    2010-03-01

    We report the discovery of competing ground states near a multicritical point in A-site layer ordered La1-xBa1+xMn2O6 materials. We demonstrate the dual effects of deliberately introduced disorder on the system's stability, the freezing of the competing states, and the drastic reduction in magnetic fields required for the suppression of charge and orbital ordered phases. Our work suggests that quenched disorder is not the primary reason for phase separation and magnetoresistance, and that increased doping leads to electronic phase separation.

  11. Comparative study of microwave radiation-induced magnetoresistive oscillations induced by circularly- and linearly- polarized photo-excitation

    SciTech Connect

    Ye, Tianyu; Liu, Han -Chun; Wang, Zhuo; Wegscheider, W.; Mani, Ramesh G.

    2015-10-09

    A comparative study of the radiation-induced magnetoresistance oscillations in the high mobility GaAs/AlGaAs heterostructure two dimensional electron system (2DES) under linearly- and circularly- polarized microwave excitation indicates a profound difference in the response observed upon rotating the microwave launcher for the two cases, although circularly polarized microwave radiation induced magnetoresistance oscillations observed at low magnetic fields are similar to the oscillations observed with linearly polarized radiation. For the linearly polarized radiation, the magnetoresistive response is a strong sinusoidal function of the launcher rotation (or linear polarization) angle, θ. As a result, for circularly polarized radiation, the oscillatory magnetoresistive response is hardly sensitive to θ.

  12. The Colossal Cosmic Eye

    NASA Astrophysics Data System (ADS)

    2005-09-01

    Eighty-five million years ago on small planet Earth, dinosaurs ruled, ignorant of their soon-to-come demise in the great Jurassic extinction, while mammals were still small and shy creatures. The southern Andes of Bolivia, Chile, and Argentina were not yet formed and South America was still an island continent. Eighty-five million years ago, our Sun and its solar system was 60,000 light years away from where it now stands [1]. Eighty-five million years ago, in another corner of the Universe, light left the beautiful spiral galaxy NGC 1350, for a journey across the universe. Part of this light was recorded at the beginning of the year 2000 AD by ESO's Very Large Telescope, located on the 2,600m high Cerro Paranal in the Chilean Andes on planet Earth. Astronomers classify NGC 1350 as an Sa(r) type galaxy, meaning it is a spiral with large central regions. In fact, NGC 1350 lies at the border between the broken-ring spiral type and a grand design spiral with two major outer arms. It is about 130,000 light-years across and, hence, is slightly larger than our Milky Way. The rather faint and graceful outer arms originate at the inner main ring and can be traced for almost half a circle when they each meet the opposite arm, giving the impression of completing a second outer ring, the "eye". The arms are given a blue tint as a result of the presence of very young and massive stars. The amount of dust, seen as small fragmented dust spirals in the central part of the galaxy and producing a fine tapestry that bear resemblance with blood vessels in the eye, is also a signature of the formation of stars.

  13. Manganite-based memristive heterojunction with tunable non-linear I-V characteristics

    NASA Astrophysics Data System (ADS)

    Lee, Hong-Sub; Park, Hyung-Ho; Rozenberg, M. J.

    2015-04-01

    A resistive random access memory (ReRAM) based on the memristive effect allows high-density integration through a cross-point array (CPA) structure. However, a significant common drawback of the CPA configuration is the crosstalk between cells. Here, we introduce a solution based on a novel heterojunction stack solely made of members of the perovskite manganite family Pr1-xCaxMnO3 (PCMO) and CaMnO3-δ (CMO) which show electroforming-free bipolar resistive switching. The heterojunction consists of rectifying interfaces and shows a symmetrical and tunable non-linear current-voltage curve. The spectromicroscopic measurements support the scenario of specialized roles, with the memristive effect taking place at the active Al-PCMO interface via a redox mechanism, while non-linearity was achieved by adopting a rectifying double interface PCMO-CMO-PCMO.A resistive random access memory (ReRAM) based on the memristive effect allows high-density integration through a cross-point array (CPA) structure. However, a significant common drawback of the CPA configuration is the crosstalk between cells. Here, we introduce a solution based on a novel heterojunction stack solely made of members of the perovskite manganite family Pr1-xCaxMnO3 (PCMO) and CaMnO3-δ (CMO) which show electroforming-free bipolar resistive switching. The heterojunction consists of rectifying interfaces and shows a symmetrical and tunable non-linear current-voltage curve. The spectromicroscopic measurements support the scenario of specialized roles, with the memristive effect taking place at the active Al-PCMO interface via a redox mechanism, while non-linearity was achieved by adopting a rectifying double interface PCMO-CMO-PCMO. Electronic supplementary information (ESI) available: Experimental method of spectromicroscopy; a scheme of the resistive switching mechanism, work function measurement of the CaMnO3-δ film; linear scale current-voltage characteristics; simulation method of the readout margin of a

  14. Dielectric properties of doping-free NaMn{sub 7}O{sub 12}: Origin of the observed colossal dielectric constant

    SciTech Connect

    Cabassi, R.; Bolzoni, F.; Gauzzi, A.; Gilioli, E.; Prodi, A.; Licci, F.

    2006-07-15

    The semiconducting NaMn{sub 7}O{sub 12} is a doping-free compound with several coexistent properties such as orbital ordering, charge ordering, and magnetic orderings of different types. We investigated its dielectric response by means of frequency impedance measurements in the range from 20 Hz to 1 MHz. Standard measurements on metallized samples exhibit an apparent colossal dielectric constant (CDC) with an {epsilon}{sub R} value of several thousands at low frequencies, but a careful equivalent circuit analysis allows one to ascribe the observed CDC to the effect of a depletion layer on the metal-semiconductor junctions. We bypass this effect by means of a nonstandard technique employing mica linings: the resulting dielectric behavior exhibits the presence of the charge ordering transition at T{sub CO}=176 K and shows a net bulk dielectric constant value {epsilon}{sub R}{approx_equal}68 at room temperature.

  15. Pressure-induced symmetry-lowering transition in dense nitrogen to layered polymeric nitrogen (LP-N) with colossal Raman intensity.

    PubMed

    Tomasino, Dane; Kim, Minseob; Smith, Jesse; Yoo, Choong-Shik

    2014-11-14

    We present the discovery of a novel nitrogen phase synthesized using laser-heated diamond anvil cells at pressures between 120-180 GPa well above the stability field of cubic gauche (cg)-N. This new phase is characterized by its singly bonded, layered polymeric (LP) structure similar to the predicted Pba2 and two colossal Raman bands (at ∼1000 and 1300  cm^{-1} at 150 GPa), arising from two groups of highly polarized nitrogen atoms in the bulk and surface of the layer, respectively. The present result also provides a new constraint for the nitrogen phase diagram, highlighting an unusual symmetry-lowering 3D cg-N to 2D LP-N transition and thereby the enhanced electrostatic contribution to the stabilization of this densely packed LP-N (ρ=4.85  g/cm^{3} at 120 GPa).

  16. Colossal ionic conductivity at interfaces of epitaxial ZrO2:Y2O3/SrTiO3 heterostructures.

    PubMed

    Garcia-Barriocanal, J; Rivera-Calzada, A; Varela, M; Sefrioui, Z; Iborra, E; Leon, C; Pennycook, S J; Santamaria, J

    2008-08-01

    The search for electrolyte materials with high oxygen conductivities is a key step toward reducing the operation temperature of fuel cells, which is currently above 700 degrees C. We report a high lateral ionic conductivity, showing up to eight orders of magnitude enhancement near room temperature, in yttria-stabilized zirconia (YSZ)/strontium titanate epitaxial heterostructures. The enhancement of the conductivity is observed, along with a YSZ layer thickness-independent conductance, showing that it is an interface process. We propose that the atomic reconstruction at the interface between highly dissimilar structures (such as fluorite and perovskite) provides both a large number of carriers and a high-mobility plane, yielding colossal values of the ionic conductivity. PMID:18669859

  17. Colossal Ionic Conductivity at Interfaces of Epitaxial ZrO2:Y2O3/SrTiO3 Heterostructures

    NASA Astrophysics Data System (ADS)

    Garcia-Barriocanal, J.; Rivera-Calzada, A.; Varela, M.; Sefrioui, Z.; Iborra, E.; Leon, C.; Pennycook, S. J.; Santamaria, J.

    2008-08-01

    The search for electrolyte materials with high oxygen conductivities is a key step toward reducing the operation temperature of fuel cells, which is currently above 700°C. We report a high lateral ionic conductivity, showing up to eight orders of magnitude enhancement near room temperature, in yttria-stabilized zirconia (YSZ)/strontium titanate epitaxial heterostructures. The enhancement of the conductivity is observed, along with a YSZ layer thickness independent conductance, showing that it is an interface process. We propose that the atomic reconstruction at the interface between highly dissimilar structures (such as fluorite and perovskite) provides both a large number of carriers and a high-mobility plane, yielding colossal values of the ionic conductivity.

  18. Simultaneous observation of up/down conversion photoluminescence and colossal permittivity properties in (Er+Nb) co-doped TiO2 materials

    NASA Astrophysics Data System (ADS)

    Tse, Mei-Yan; Tsang, Ming-Kiu; Wong, Yuen-Ting; Chan, Yi-Lok; Hao, Jianhua

    2016-07-01

    We have investigated the optical and dielectric properties of rutile TiO2 doped with Nb and Er, i.e., (Er0.5Nb0.5)xTi1-xO2. The up/downconversion photoluminescence was observed in the visible and near-infrared region from the materials under 980 nm laser diode excitation. The upconversion emissions are attributed to the energy transfer between Er ions in the excited states. Moreover, the dielectric measurements indicate that the fabricated materials simultaneously present colossal permittivity properties with relatively low dielectric loss. Our work demonstrates the coexistence of both interesting luminescence and attractive dielectric characteristics in (Er+Nb) co-doped TiO2, showing the potential for multifunctional applications.

  19. Colossal Electroresistive Properties Of CSD Grown Pr{sub 0.7}Ca{sub 0.3}MnO{sub 3} Films For Nonvolatile Memory Applications

    SciTech Connect

    Bhavsar, K. H.; Joshi, U. S.

    2010-12-01

    Colossal electroresistance effects upon application of electric field in perovskite oxide Pr{sub 0.7}Ca{sub 0.3}MnO{sub 3}(PCMO) thin films, which is a promising candidate for resistance random access memory (RRAM) device have been investigated. Nanocrystalline PCMO films were grown on SiO{sub 2} substrates by chemical solution deposition and crystallized at 700 deg. C under different gas atmospheres. Four terminal current voltage characteristics of Ag/PCMO/Ag planar geometry exhibited a sharp transition from a low resistance state (LRS) to a high resistance state (HRS) with a resistance switching ratio of as high as 1100% at room temperature. Nonvolatility and high retention was confirmed by electric pulse induced resistive switching measurements. The resistance switching ratios were found to depend on the annealing conditions, suggesting an interaction between the nonlattice oxygen and oxygen vacancies and/or the cationic vacancy.

  20. The demonstration of colossal magneto-capacitance effect with the promising gate stack characteristics on Ge (100) by the magnetic gate stack design

    NASA Astrophysics Data System (ADS)

    Liao, M.-H.; Huang, S.-C.

    2014-06-01

    The tetragonal-phase BaTiO3 as the high dielectric (HK) layer and the magnetic FePt film as the metal gate (MG) are proposed to be the gate stack scheme on the Ge (100) substrate. The ˜75% dielectric constant (κ-value) improvement, ˜100X gate leakage (Jg) reduction, and the promising Jg-equivalent-oxide-thickness (EOT) gate stack characteristics are achieved in this work with the colossal magneto-capacitance effect. The perpendicular magnetic field from the magnetic FePt MG film couples and triggers the more dipoles in the BaTiO3 HK layer and then results in the super gate capacitance (Cgate) and κ-value. Super Jg-EOT gate stack characteristics with the magnetic gate stack design on the high mobility (Ge) substrate demonstrated in this work provides the useful solution for the future low power mobile device design.

  1. Magnetoresistance in p-type cadmium telluride doped with sodium

    SciTech Connect

    Ahmad, Faisal R.

    2015-01-05

    This paper gives an account of the observations that were made during experiments in which temperature dependent van der Pauw (vdP) measurements were conducted on sodium doped single crystalline CdTe. With the aid of the vdP technique, the resistivity of the sample was measured in the presence of an external transverse magnetic field. The measurements were conducted at temperatures that ranged from 24 K all the way up to 300 K. The measurements indicated that at low temperatures, the resistivity of the sample increased significantly as the magnitude of the magnetic field perpendicular to the sample was raised from 0 T to 1.5 T. It was observed that the magnetoresistance (MR) decreased with increasing temperature. At 24 K, for an applied field of 1.5 T, the maximum MR was over 30%. Furthermore, it was also observed that the MR below 75 K exhibited a more or less linear dependence on the magnetic field. At higher temperatures, the MR as a function of the applied magnetic field exhibited a quadratic dependence. The results seem to indicate that the linear MR is most likely due to inhomogeneity in the semiconductor.

  2. Large Magnetoresistance in Single-Radical Molecular Junctions.

    PubMed

    Hayakawa, Ryoma; Karimi, Mohammad Amin; Wolf, Jannic; Huhn, Thomas; Zöllner, Martin Sebastian; Herrmann, Carmen; Scheer, Elke

    2016-08-10

    Organic radicals are promising building blocks for molecular spintronics. Little is known about the role of unpaired electrons for electron transport at the single-molecule level. Here, we examine the impact of magnetic fields on electron transport in single oligo(p-phenyleneethynylene) (OPE)-based radical molecular junctions, which are formed with a mechanically controllable break-junction technique at a low temperature of 4.2 K. Surprisingly huge positive magnetoresistances (MRs) of 16 to 287% are visible for a magnetic field of 4 T, and the values are at least 1 order of magnitude larger than those of the analogous pristine OPE (2-4%). Rigorous analysis of the MR and of current-voltage and inelastic electron-tunneling spectroscopy measurements reveal an effective reduction of the electronic coupling between the current-carrying molecular orbital and the electrodes with increasing magnetic field. We suggest that the large MR for the single-radical molecular junctions might be ascribed to a loss of phase coherence of the charge carriers induced by the magnetic field. Although further investigations are required to reveal the mechanism underlying the strong MR, our findings provide a potential approach for tuning charge transport in metal-molecule junctions with organic radicals. PMID:27458666

  3. Energy scales and magnetoresistance at a quantum critical point

    NASA Astrophysics Data System (ADS)

    Shaginyan, V. R.; Amusia, M. Ya.; Msezane, A. Z.; Popov, K. G.; Stephanovich, V. A.

    2009-03-01

    The magnetoresistance (MR) of CeCoIn 5 is notably different from that in many conventional metals. We show that a pronounced crossover from negative to positive MR at elevated temperatures and fixed magnetic fields is determined by the scaling behavior of quasiparticle effective mass. At a quantum critical point (QCP) this dependence generates kinks (crossover points from fast to slow growth) in thermodynamic characteristics (like specific heat, magnetization, etc.) at some temperatures when a strongly correlated electron system transits from the magnetic field induced Landau-Fermi liquid (LFL) regime to the non-Fermi liquid (NFL) one taking place at rising temperatures. We show that the above kink-like peculiarity separates two distinct energy scales in QCP vicinity - low temperature LFL scale and high temperature one related to NFL regime. Our comprehensive theoretical analysis of experimental data permits to reveal for the first time new MR and kinks scaling behavior as well as to identify the physical reasons for above energy scales.

  4. Energy scales and magnetoresistance at a quantum critical point

    NASA Astrophysics Data System (ADS)

    Amusia, Miron; Shaginyan, Vasiliy

    2009-05-01

    The magnetoresistance (MR) of CeCoIn55 is notably different from that in many conventional metals. We show that a pronounced crossover from negative to positive MR at elevated temperatures and fixed magnetic fields is determined by the scaling behavior of quasiparticle effective mass. At a quantum critical point (QCP) this dependence generates kinks (crossover points from fast to slow growth) in thermodynamic characteristics (like specific heat, magnetization etc) at some temperatures when a strongly correlated electron system transits from the magnetic field induced Landau Fermi liquid (LFL) regime to the non-Fermi liquid (NFL) one taking place at rising temperatures. We show that the above kink-like peculiarity separates two distinct energy scales in QCP vicinity - low temperature LFL scale and high temperature one related to NFL regime. We show that the same behavior is observed under the application of elevated magnetic field at fixed temperature. These observations are in accord with recent facts (P. Gegenwart, et. al., Science 315, 969 (2007)). Our comprehensive theoretical analysis of experimental data permits to reveal for the first time new MR and kinks scaling behavior as well as to identify the physical reasons for above energy scales.

  5. Magnetoresistance Phenomena in a Variety of Amorphous Semiconductors and Insulators

    NASA Astrophysics Data System (ADS)

    Mutch, Michael; Westley, David; Lenahan, Patrick; Semiconductor Spectroscopy Lab at Penn State University Team

    We report on near zero-field magnetoresistance (MR) phenomena in a variety of amorphous semiconductors and insulators. We utilize electrically detected magnetic resonance (EDMR) measurements at multiple fields and frequencies to complement MR measurements. EDMR, the electrically detected analog of electron paramagnetic resonance (EPR), provides both information about the chemical nature and energy levels of point defects involved. Semiconductors in this study include a-BC:H, a-C:H, diamond-like carbon (DLC), and a-Si:H. Insulators include a-SiN:H, a-SiOC:H, a-SiCN:H. In hydrogenated amorphous systems, near featureless EPR and EDMR spectra are often difficult to analyze. We utilize multiple field and frequency EDMR results including ultra-low field/frequency (ν = 85 MHz, B = 3 mT) EDMR measurements to provide insight into defect chemistry in these systems. We have also made EDMR and MR conditions over a wide range of metal/semiconductor heterojunction and metal/insulator/semiconductor biasing conditions. By comparing variable bias measurements with band diagrams, we gain an elementary understanding of defect energy levels. We believe our results will be of significant importance for understanding defect mediated spin-dependent transport in these systems. The authors would like to thanks Dr. Sean King of Intel Corporation for the provision of samples.

  6. Magnetoresistive-superconducting mixed sensors for biomagnetic applications

    NASA Astrophysics Data System (ADS)

    Pannetier-Lecoeur, M.; Fermon, C.; Dyvorne, H.; Jacquinot, J. F.; Polovy, H.; Walliang, A. L.

    2010-05-01

    When coupled to a giant magnetoresistive (GMR) sensor, a superconducting loop containing a constriction can be a very sensitive magnetometer. It has thermal noise levels of few fT/sqrt(Hz), comparable to low- Tc SQUID noise, with a flat frequency response. These mixed sensors are good candidates for detection of weak biomagnetic signals, like a cardiac or neuronal signature. Furthermore, being sensitive to the flux, mixed sensors can be used for nuclear magnetic resonance (NMR) detection and Magnetic Resonance Imaging (MRI) especially at low fields. They are very robust and accept strong RF pulses with a very short recovery time compared to tuned RF coils, which allow measurements of broad signals (short relaxation time or multiple resonances). We will first present the last generation sensors having a noise level of 3 fT/sqrt(Hz) and we will show signals measured at low frequency (magnetocardiography-magnetoencephalography range) and at higher frequency (NMR signals). The use of additional flux transformers for improving the signal-to-noise will be discussed. Finally, we will present perspectives for low-field MRI, which can be combined with neural signal detection (MEG), especially for brain anatomy and temporal response on the same experimental setup.

  7. Tunnel magnetoresistance in Self-Assembled Monolayers Based Tunnel Junctions

    NASA Astrophysics Data System (ADS)

    Mattana, Richard; Barraud, Clément; Tatay, Sergio; Galbiati, Marta; Seneor, Pierre; Bouzehouane, Karim; Jacquet, Eric; Deranlot, Cyrile; Fert, Albert; Petroff, Frédéric

    2012-02-01

    Organic/molecular spintronics is a rising research field at the frontier between spintronics and organic chemistry. Organic molecule and semiconductors were first seen as promising for spintronics devices due to their expected long spin lifetime. But an exciting challenge has also been to find opportunities arising from chemistry to develop new spintronics functionalities. It was shown that the molecular structure and the ferromagnetic metal/molecule hybridization can strongly influence interfacial spin properties going from spin polarization enhancement to its sign control in spintronics devices. In this scenario, while scarcely studied, self-assembled monolayers (SAMs) are expected to become perfect toy barriers to further test these tailoring properties in molecular magnetic tunnel junctions (MTJs). Due to its very high spin polarization and air stability LSMO has positioned itself as the electrode of choice in most of the organic spintronics devices. We will present a missing building block for molecular spintronics tailoring: the grafting and film characterization of organic monofunctionalized long alkane chains over LSMO. We have obtained 35% of magnetoresistance in LSMO/SAMs/Co MTJs. We will discuss the unusual behaviour of the bias voltage dependence of the TMR.

  8. Theoretical Study on Twofold and Fourfold Symmetric Anisotropic Magnetoresistance Effect

    NASA Astrophysics Data System (ADS)

    Kokado, Satoshi; Tsunoda, Masakiyo

    We theoretically study the twofold and fourfold symmetric anisotropic magnetoresistance (AMR) effect [ 1 ] . We first extend our previous model [ 2 ] to a model including the crystal field effect [ 1 ] . Using the model, we next obtain an analytical expression of the AMR ratio, i.e., AMR (ϕ) =C0 +C2 cos (2 ϕ) +C4 cos (4 ϕ) , with C0=C2 -C4 [ 1 ] . Here, ϕ is the relative angle between the magnetization direction and the electric current direction and C2 (C4) is a coefficient of the twofold (fourfold) symmetric term. The coefficients C2 and C4 are expressed by a spin-orbit coupling constant, an exchange field, a crystal field, and s-s and s-d scattering resistivities. Using this expression, we analyze the experimental results for Fe4N [ 3 ] , in which | C2 | and | C4 | increase with decreasing temperature. The experimental results can be reproduced by assuming that the tetragonal distortion increases with decreasing temperature. [ 1 ] S. Kokado et al., J. Phys. Soc. Jpn. 84 (2015) 094710. [ 2 ] S. Kokado et al., J. Phys. Soc. Jpn. 81 (2012) 024705. [ 3 ] M. Tsunoda et al., Appl. Phys. Express 3 (2010) 113003.

  9. The spin-Dicke effect in OLED magnetoresistance

    NASA Astrophysics Data System (ADS)

    Waters, D. P.; Joshi, G.; Kavand, M.; Limes, M. E.; Malissa, H.; Burn, P. L.; Lupton, J. M.; Boehme, C.

    2015-11-01

    Pairs of charge-carrier spins in organic semiconductors constitute four-level systems that can be driven electromagnetically. Given appropriate conditions for ultrastrong coupling--weak local hyperfine fields Bhyp, large magnetic resonant driving fields B1 and low static fields B0 that define Zeeman splitting--the spin-Dicke effect, a collective transition of spin states, has been predicted. This parameter range is challenging to probe by electron paramagnetic resonance spectroscopy because thermal magnetic polarization is negligible. It is accessed through spin-dependent conductivity that is controlled by electron-hole pairs of singlet and triplet spin-permutation symmetry without the need of thermal spin polarization. Signatures of collective behaviour of carrier spins are revealed in the steady-state magnetoresistance of organic light-emitting diodes (OLEDs), rather than through radiative transitions. For intermediate B1, the a.c.-Zeeman effect appears. For large B1, a collective spin-ensemble state arises, inverting the current change under resonance and removing power broadening, thereby offering a unique window to ambient macroscopic quantum coherence.

  10. Viable chemical approach for patterning nanoscale magnetoresistive random access memory

    SciTech Connect

    Kim, Taeseung; Kim, Younghee; Chen, Jack Kun-Chieh; Chang, Jane P.

    2015-03-15

    A reactive ion etching process with alternating Cl{sub 2} and H{sub 2} exposures has been shown to chemically etch CoFe film that is an integral component in magnetoresistive random access memory (MRAM). Starting with systematic thermodynamic calculations assessing various chemistries and reaction pathways leading to the highest possible vapor pressure of the etch products reactions, the potential chemical combinations were verified by etch rate investigation and surface chemistry analysis in plasma treated CoFe films. An ∼20% enhancement in etch rate was observed with the alternating use of Cl{sub 2} and H{sub 2} plasmas, in comparison with the use of only Cl{sub 2} plasma. This chemical combination was effective in removing metal chloride layers, thus maintaining the desired magnetic properties of the CoFe films. Scanning electron microscopy equipped with energy-dispersive x-ray spectroscopy showed visually and spectroscopically that the metal chloride layers generated by Cl{sub 2} plasma were eliminated with H{sub 2} plasma to yield a clean etch profile. This work suggests that the selected chemistries can be used to etch magnetic metal alloys with a smooth etch profile and this general strategy can be applied to design chemically based etch processes to enable the fabrication of highly integrated nanoscale MRAM devices.

  11. Gilbert damping and anisotropic magnetoresistance in iron-based alloys

    NASA Astrophysics Data System (ADS)

    Berger, L.

    2016-07-01

    We use the two-current model of Campbell and Fert to understand the compositional dependence of the Gilbert damping parameter in certain iron alloys. In that model, spin-up and spin-down carriers have different resistivities ρ↑ and ρ↓. We emphasize the part of the Gilbert parameter, called Gsf, generated by spin-flip interband processes. Both Gsf and the anisotropic magnetoresistance Δρ are proportional to the square of the spin-orbit parameter, and also proportional to ρ↑. In bcc alloys of iron with V, Cr, Mo, etc. solutes on the left of iron in the periodic table, ρ↑ is increased by a scattering resonance (Gomes and Campbell, 1966, 1968). Then ρ↑, Δρ, and Gsf all exhibit a peak at the same moderate concentration of the solute. We find the best fit between this theory and existing experimental data of Gilbert damping for Fe-V epitaxial films at room temperature (Cheng, 2006; Scheck et al., 2007). At room temperature, the predicted Gsf peak is masked by a background arising from non-flip intraband processes. At elevated temperatures, the peak is expected to become more prominent, and less hidden in the background.

  12. Shield-related signal instability in magnetoresistive heads

    NASA Astrophysics Data System (ADS)

    Nakamoto, K.; Narumi, S.; Kawabe, T.; Kobayashi, T.; Fukui, H.

    1999-04-01

    Magnetoresistive (MR) heads with various upper shield materials were fabricated and their read-write performance was tested to clarify the shield-related effect on the signal instability in MR heads. Comparison of a head with an upper shield layer of higher magnetostriction and one with lower magnetostriction showed that the latter had better stability in the output signal of a repeated read-write test. The output amplitude of a head with an upper shield layer of Co52Ni27Fe21 film, which had a high magnetostriction of about +3×10-6, was varied by applying a low external longitudinal field, which affected just the shield layers. This change in the output corresponded well to the output variation in the repeated read-write test. The spin scanning electron micrograph image of this head revealed a distinct domain wall in the air bearing surface near the MR sensor. These results indicated that instability of the domain structure in a shield layer was one of the causes of the signal instability in MR heads; an unusual bias field from a domain wall of the shield layer, which could be moved easily by a repeated writing operation, caused a variation in the biased state of the MR layer which resulted in the signal variation, and that low magnetostriction was required for a shield material to achieve a stable head.

  13. Unexploded ordnance detection using imaging giant magnetoresistive (GMR) sensor arrays

    SciTech Connect

    Chaiken, A., LLNL

    1997-05-06

    False positive detections account for a great part of the expense associated with unexploded ordnance (UXO) remediation. Presently fielded systems like pulsed electromagnetic induction systems and cesium-vapor magnetometers are able to distinguish between UXO and other metallic ground clutter only with difficulty. The discovery of giant magnetoresistance (GMR) has led to the development of a new generation of integrated-circuit magnetic sensors that are far more sensitive than previously available room-temperature-operation electronic devices. The small size of GMR sensors makes possible the construction of array detectors that can be used to image the flux emanating from a ferrous object or from a non-ferrous object with eddy currents imposed by an external coil. The purpose of a GMR-based imaging detector would be to allow the operator to easily distinguish between UXO and benign objects (like shrapnel or spent bullets) that litter formerly used defense sites (FUDS). In order to demonstrate the potential of a GMR-based imaging technology, a crude magnetic imaging system has been constructed using commercially available sensors. The ability to roughly determine the outline and disposition of magnetic objects has been demonstrated. Improvements to the system which are necessary to make it into a high-performance UXO detector are outlined.

  14. Alkanethiol capping-induced changes in the magnetoresistance of Co

    NASA Astrophysics Data System (ADS)

    Knaus, Brad; Garzon, Samir; Crawford, Thomas M.

    2008-03-01

    We demonstrate that chemisorption of a ˜ 1 nm thick dodecanethiol (C12H25SH) self-assembled monolayer on the surface of an Au film alters the magnetotransport of an underlying Co film. Giant paramagnetism has been previously detected in Au thin films and nanoparticles capped with alkanethiols via SQUID magnetometry. By observing the impact of Au-thiol magnetism on a ferromagnetic thin film we avoid background subtraction and the influence of impurities. After thiolation, significant changes are observed in the anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) from Co/Au bilayers (30 nm/5-60 nm) patterned into 1 x 5 mm^2 bars. Driven with nearly perpendicular external fields, we observed domain nucleation shifts of ˜0.65 T and changes in the FWHM of the AMR. We have also measured differences in the MR as a function of ambient exposure time presumably due to oxidation effects known to occur in alkanethiols. Effects of surface scattering were eliminated with the introduction of a 12nm Al2O3 insulation barrier between Co and Au. We have calculated that the effects of magnetostriction are too small by more than two orders of magnitude to explain our observations. We therefore hypothesize that Au-thiol magnetization acts as a source of magnetic field which biases the underlying Co film.

  15. Quantum Fluctuations of Local Magnetoresistance in Organic Spin Valves

    NASA Astrophysics Data System (ADS)

    Raikh, Mikhail; Roundy, Robert; Nemirovsky, Demitry; Kagalovsky, Victor

    2014-03-01

    Aside from interfacial effects, the performance of organic spin valves is limited by the spin memory loss in course of electron transport between the magnetized electrodes. One of the most prominent mechanisms of this loss is the spin precession in the random hyperfine fields of nuclei. We assume that the electron transport is due to incoherent multi-step tunneling. Then the precession takes place while electron ``waits'' for the subsequent tunneling step. While the spatial coherence of electron is lost after a single step, the spin evolution remains absolutely coherent all the way between the electrodes. As a result, the amplitudes of subsequent spin rotation interfere with each other. We demonstrate that this interference leads to a wide spread in the local values of tunnel magnetoresistance (TMR). Moreover, if on average the TMR is positive, the portion of the surface area where the TMR is negative is appreciable. We calculate analytically and numerically the distribution of local TMR as a function of the spin-valve thickness. Supported by the NSF through MRSEC DMR-112125 and by the US-Israel Binational Science Foundation

  16. Temperature‑field phase diagram of extreme magnetoresistance

    NASA Astrophysics Data System (ADS)

    Fallah Tafti, Fazel; Gibson, Quinn; Kushwaha, Satya; Krizan, Jason W.; Haldolaarachchige, Neel; Cava, Robert Joseph

    2016-06-01

    The recent discovery of extreme magnetoresistance (XMR) in LaSb introduced lanthanum monopnictides as a new platform to study this effect in the absence of broken inversion symmetry or protected linear band crossing. In this work, we report XMR in LaBi. Through a comparative study of magnetotransport effects in LaBi and LaSb, we construct a temperature‑field phase diagram with triangular shape that illustrates how a magnetic field tunes the electronic behavior in these materials. We show that the triangular phase diagram can be generalized to other topological semimetals with different crystal structures and different chemical compositions. By comparing our experimental results to band structure calculations, we suggest that XMR in LaBi and LaSb originates from a combination of compensated electron‑hole pockets and a particular orbital texture on the electron pocket. Such orbital texture is likely to be a generic feature of various topological semimetals, giving rise to their small residual resistivity at zero field and subject to strong scattering induced by a magnetic field.

  17. Magnetoresistance detected spin collectivity in organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Malissa, Hans; Waters, David P.; Joshi, Gajadhar; Kavand, Marzieh; Limes, Mark E.; Burn, Paul L.; Lupton, John M.; Boehme, Christoph

    Organic magnetoresistance (OMAR) typically refers to the significant change in the conductivity of thin layers of organic semiconductors at low static magnetic fields (< 10 mT). When radio frequency (rf) radiation is applied to an organic semiconductor under bipolar injection, and in the presence of small magnetic fields B, magnetic resonance can occur, which is observed as a change of the OMAR effect [Baker et al., Nat. Commun. 3, 898 (2012)]. When B and the resonant driving field are stronger than local hyperfine fields, an ultrastrong coupling regime emerges, which is marked by collective spin effects analogous to the optical Dicke effect [Roundy and Raikh, Phys. Rev. B 88, 125206 (2013)]. Experimentally, this collective behavior of spins can be probed in the steady state OMAR of organic light-emitting diodes (OLEDs) at room temperature by observation of a sign reversal of the OMAR change under rf irradiation. Furthermore, in the presence of strong driving fields, an ac Zeeman effect can be observed through OMAR [Waters et al., Nat. Phys. 11, 910 (2015)], a unique window to observe room temperature macroscopic spin quantum coherence.

  18. Femtomolar limit of detection with a magnetoresistive biochip.

    PubMed

    Martins, V C; Cardoso, F A; Germano, J; Cardoso, S; Sousa, L; Piedade, M; Freitas, P P; Fonseca, L P

    2009-04-15

    In this paper the biological limit of detection of a spin-valve-based magnetoresistive biochip applied to the detection of 20 mer ssDNA hybridization events is presented. Two reactional variables and their impact on the biomolecular recognition efficiency are discussed. Both the influence of a 250 nm diameter magnetic particle attached to the target molecule during the hybridization event and the effect of a magnetic focusing system in the hybridization of pre-labeled target DNA (assisted hybridization) are addressed. The particles carrying the target molecules are attracted to the probe active sensor sites by applying a 40 mA DC current on U-shaped aluminium current lines. Experiments comparing pre-hybridization versus post-hybridization magnetic labeling and passive versus magnetically assisted hybridization were conducted. The efficiency of a passive hybridization is reduced by about 50% when constrained to the operational conditions (sample volume, reaction time, temperature and magnetic label) of an on-chip real-time hybridization assay. This reduction has shown to be constant and independent from the initial target concentration. Conversely, the presence of the magnetic label improved the limit of detection when a magnetically assisted hybridization was performed. The use of a labeled target focusing system has permitted a gain of three orders of magnitude (from 1 pM down to 1 fM) in the sensitivity of the device, as compared with passive, diffusion-controlled hybridization. PMID:19261460

  19. Giant single-molecule anisotropic magnetoresistance at room temperature.

    PubMed

    Li, Ji-Jun; Bai, Mei-Lin; Chen, Zhao-Bin; Zhou, Xiao-Shun; Shi, Zhan; Zhang, Meng; Ding, Song-Yuan; Hou, Shi-Min; Schwarzacher, Walther; Nichols, Richard J; Mao, Bing-Wei

    2015-05-13

    We report an electrochemically assisted jump-to-contact scanning tunneling microscopy (STM) break junction approach to create reproducible and well-defined single-molecule spintronic junctions. The STM break junction is equipped with an external magnetic field either parallel or perpendicular to the electron transport direction. The conductance of Fe-terephthalic acid (TPA)-Fe single-molecule junctions is measured and a giant single-molecule tunneling anisotropic magnetoresistance (T-AMR) up to 53% is observed at room temperature. Theoretical calculations based on first-principles quantum simulations show that the observed AMR of Fe-TPA-Fe junctions originates from electronic coupling at the TPA-Fe interfaces modified by the magnetic orientation of the Fe electrodes with respect to the direction of current flow. The present study highlights new opportunities for obtaining detailed understanding of mechanisms of charge and spin transport in molecular junctions and the role of interfaces in determining the MR of single-molecule junctions. PMID:25894840

  20. Decomposition of the magnetoresistance of multilayers into ferromagneticand superparamagnetic contributions

    NASA Astrophysics Data System (ADS)

    Bakonyi, I.; Péter, L.; Rolik, Z.; Kiss-Szabó, K.; Kupay, Z.; Tóth, J.; Kiss, L. F.; Pádár, J.

    2004-08-01

    An analysis of both magnetic and magnetotransport properties is presented for electrodeposited multilayers prepared intentionally under conditions to make the superparamagnetic (SPM) magnetization contribution comparable to or larger than the ferromagnetic term. Based on a model elaborated for the giant magnetoresistance (GMR) of granular metals [N. Wiser, J. Magn. Magn. Mater. 159, 119 (1996); B. Hickey , Phys. Rev. B. 51, 667 (1995)], it is shown that in such multilayers both the magnetization and the GMR can be decomposed into ferromagnetric and superparamagnetic contributions where the latter term is described by a Langevin function. The size of the SPM regions estimated from the experimental data is in the nanoscale regime. It is believed that the method applied here gives a quantitative answer to the problem of the often observed nonsaturating behavior of GMR in multilayers. Electrodeposited multilayers are particularly prone to this feature although the occurrence of SPM regions is quite common in multilayers prepared by any technique. Therefore, this type of analysis should help better understanding of the factors influencing the GMR of multilayer films.

  1. Temperature-field phase diagram of extreme magnetoresistance.

    PubMed

    Fallah Tafti, Fazel; Gibson, Quinn; Kushwaha, Satya; Krizan, Jason W; Haldolaarachchige, Neel; Cava, Robert Joseph

    2016-06-21

    The recent discovery of extreme magnetoresistance (XMR) in LaSb introduced lanthanum monopnictides as a new platform to study this effect in the absence of broken inversion symmetry or protected linear band crossing. In this work, we report XMR in LaBi. Through a comparative study of magnetotransport effects in LaBi and LaSb, we construct a temperature-field phase diagram with triangular shape that illustrates how a magnetic field tunes the electronic behavior in these materials. We show that the triangular phase diagram can be generalized to other topological semimetals with different crystal structures and different chemical compositions. By comparing our experimental results to band structure calculations, we suggest that XMR in LaBi and LaSb originates from a combination of compensated electron-hole pockets and a particular orbital texture on the electron pocket. Such orbital texture is likely to be a generic feature of various topological semimetals, giving rise to their small residual resistivity at zero field and subject to strong scattering induced by a magnetic field. PMID:27274081

  2. Amplification effect of low-field magnetoresistance in silicon dual p - n junctions

    NASA Astrophysics Data System (ADS)

    Yang, Dezheng; Wang, Tao; Si, Mingsu; Wang, Fangcong; Zhou, Shiming; Xue, Desheng

    Nonmagnetic semiconductors with large magnetoresistance are identified as promising feature for the development of magnetoelectronics. However, to manipulate the magnetoresistance require the magnetic field of several Tesla. In this work, we realized an amplification effect of low-field magnetoresistance based on an elementary electronic building block: dual p - n junction. Analogous to the electrical amplification effect of transistor p - n -p junction, where the coupling current between p - n and n - p junctions is tuned by base current, in a silicon p + - n - n + device we demonstrate that the coupling strength of p + - n and n - n + junctions can be tuned by magnetic field. Owing to the amplification effect of magnetic-field-manipulated coupling, at a small magnetic field from 0 to 0.1 T the device is directly switched from conducting state ''on'' (10000 ohms) to blocking state ''off'' (5 megohm), yielding an magnetoresistance of 50,000 per cent and magnetic field sensitivity as high as 50 per cent Oe-1. Such a combination of magnetoresistance and high sensitivity not only makes the semiconductor device available in the magnetic field sensing industry, but also permits a new kind of magnetic-field-manipulated semiconductor electronics.

  3. Tunneling magnetoresistance in junctions composed of ferromagnets and time-reversal invariant topological superconductors

    NASA Astrophysics Data System (ADS)

    Yan, Zhongbo; Wan, Shaolong

    2016-02-01

    Tunneling magnetoresistance between two ferrromagnets is an issue of fundamental importance in spintronics. In this work, we show that tunneling magnetoresistance can also emerge in junctions composed of ferromagnets and time-reversal invariant topological superconductors without spin-rotation symmetry. Here the physical origin is that when the spin-polarization direction of an injected electron from the ferromagnet lies in the same plane of the spin-polarization direction of Majorana zero modes, the electron will undergo a perfect spin-equal Andreev reflection, while injected electrons with other spin-polarization directions will be partially Andreev reflected and partially normal reflected, which consequently has a lower conductance, and therefore, the magnetoresistance effect emerges. Compared to conventional magnetic tunnel junctions, an unprecedented advantage of the junctions studied here is that arbitrary high tunneling magnetoresistance can be obtained even when the magnetization of the ferromagnets are weak and the insulating tunneling barriers are featureless. Our findings provide a new fascinating mechanism to obtain high tunneling magnetoresistance.

  4. c -axis longitudinal magnetoresistance of the electron-doped superconductor Pr1.85Ce0.15CuO4

    NASA Astrophysics Data System (ADS)

    Yu, W.; Liang, B.; Greene, R. L.

    2006-12-01

    We report c -axis resistivity and longitudinal magnetoresistance measurements of superconducting Pr1.85Ce0.15CuO4 single crystals. In the temperature range 13⩽T⩽32K , a negative magnetoresistance is observed at fields just above HC2 . Our studies suggest that this negative magnetoresistance is caused by superconducting fluctuations. At lower temperatures (T⩽13K) , a different magnetoresistance behavior and a resistivity upturn are observed, whose origin is still unknown.

  5. Synthesis and characteristic of nanocrystalline La0.7Sr0.3MnO3 manganites by solid state reaction route

    NASA Astrophysics Data System (ADS)

    Astik, Nidhi; Patil, Swapnilkumar; Bhargava, Parag; Jha, Prafulla K.

    2016-05-01

    Nanocrystalline stoichiometric La0.7Sr0.3MnO3 (x=0.3) manganites have been synthesized through solid-state reaction by ball milling mechanical method at two different sintering temperatures 1250°C and 1350°C. The synthesized samples were characterized using X-ray diffraction (XRD) and found to have rhombohedral crystal structure (R-3c). The calcined samples exhibited a pure single phase perovskite, had a crystallite size of about 47-51 nm. The morphology of the prepared nanocrystalline manganites were recorded by the field emission gun-scanning electron microscope (FEG-SEM) and EDAX.

  6. Delocalized and localized states of eg electrons in half-doped manganites.

    PubMed

    Winkler, E L; Tovar, M; Causa, M T

    2013-07-24

    We have studied the magnetic behaviour of half-doped manganite Y0.5Ca0.5MnO3 in an extended range of temperatures by means of magnetic susceptibility, χ(T), and electron spin resonance (ESR) experiments. At high temperature the system crystallizes in an orthorhombic structure. The resistivity value, ρ ≃ 0.05 Ω cm at 500 K, indicates a metallic behaviour, while the Curie-Weiss dependence of χ(T) and the thermal evolution of the ESR parameters are very well described by a model that considers a system conformed by localized Mn(4+) cores, [Formula: see text], and itinerant, eg, electrons. The strong coupling between t2g and eg electrons results in an enhanced Curie constant and an FM Curie-Weiss temperature that overcomes the AFM interactions between the [Formula: see text] cores. A transition to a more distorted phase is observed at T ≈ 500 K and signatures of localization of the eg electrons appear in the χ(T) behaviour below 300 K. A new Curie-Weiss regime is observed, where the Curie-constant value is consistent with dimer formation. Based on mean-field calculations, the dimer formation is predicted as a function of the interaction strength between the t2g and eg electrons.

  7. Impedance spectroscopy of manganite films prepared by metalorganic chemical vapor deposition.

    PubMed

    Nakamura, Toshihiro; Homma, Kohei; Tachibana, Kunihide

    2011-09-01

    Polycrystalline Pr(1-x)CaxMnO3 (PCMO) films were prepared by liquid source metalorganic chemical vapor deposition using in situ infrared spectroscopic monitoring. The electric properties of the PCMO-based devices with Ni and Al electrodes (Ni-PCMO-Ni and Al-PCMO-Al devices) were studied by dc current-voltage (I-V) measurements and ac impedance spectroscopy. The current varied linearly with the applied voltage in Ni-PCMO-Ni devices, while nonlinear behavior was observed in I-V curves for Al-PCMO-Al devices. Impedance spectra were also different between Ni-PCMO-Ni and Al-PCMO-Al devices. The Cole-Cole plots for the Ni-PCMO-Ni devices showed only a single semicircular arc, which was assigned to the PCMO bulk impedance. Impedance spectra for the Al-PCMO-Al devices had two distinct components, which could be attributed to the PCMO bulk and to the interface between the PCMO film and the Al electrode, respectively. The bias dependence of the impedance spectra suggested that the resistance switching in the Al-PCMO-Al devices was mainly due to the resistance change in the interface between the film and the electrode. The metal electrode plays an important role in the resistance switching in the PCMO-based devices. The choice of the optimum metal electrodes is essential to the ReRAM application of the manganite-based devices.

  8. Interplay between intrinsic and stacking-fault magnetic domains in bi-layered manganites

    SciTech Connect

    Hossain, M.A; Burkhardt, Mark H.; Sarkar, S.; Ohldag, H.; Chuang, Y.-D.; Scholl, A.; Young, A.T.; Doran, A.; Dessau, D.S.; Zheng, H.; Mitchell, J.F.; Durr, H.A.; Stohr, J.

    2012-09-11

    We present a low temperature X-ray photoemission electron microscopy study of the bi-layered manganite compound La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} (BL-LSMO) to investigate the influence of stacking faults, which are structurally and magnetically different from the bi-layered host. In BL-LSMO small magnetic moment persists to T* = 300K, well above the Curie temperature of 120K (T{sub C}). Our magnetic images show that 3D stacking faults are responsible for the T* transition. Furthermore, close to the T{sub C}, stacking faults are well coupled to the bi-layered host with latter magnetic domains controlling the spin direction of the stacking faults. Contrary to recent reports, we find that stacking faults do not seed magnetic domains in the host via an exchange spring mechanism and the intrinsic T{sub C} of the BL-LSMO is not lower than 120K.

  9. High On/Off Ratio Memristive Switching of Manganite/Cuprate Bilayer by Interfacial Magnetoelectricity

    DOE PAGESBeta

    Shen, Xiao; Pennycook, Timothy J.; Hernandez-Martin, David; Pérez, Ana; Puzyrev, Yevgeniy S.; Liu, Yaohua; te Velthuis, Suzanne G. E.; Freeland, John W.; Shafer, Padraic; Zhu, Chenhui; et al

    2016-05-27

    Memristive switching serves as the basis for a new generation of electronic devices. Conventional memristors are two-terminal devices in which the current is turned on and off by redistributing point defects, e.g., vacancies. Memristors based on alternative mechanisms have been explored, but achieving both high on/off ratio and low switching energy, as needed in applications, remains a challenge. This paper reports memristive switching in La0.7Ca0.3MnO3/PrBa2Cu3O7 bilayers with an on/off ratio greater than 103 and results of density functional theory calculations in terms of which it is concluded that the phenomenon is likely the result of a new type of interfacialmore » magnetoelectricity. More specifically, this study shows that an external electric field induces subtle displacements of the interfacial Mn ions, which switches on/off an interfacial magnetic “dead layer”, resulting in memristive behavior for spin-polarized electron transport across the bilayer. The interfacial nature of the switching entails low energy cost, about of a tenth of atto Joule for writing/erasing a “bit”. To conclude, the results indicate new opportunities for manganite/cuprate systems and other transition metal oxide junctions in memristive applications.« less

  10. Manipulation of the ferromagnetic domains of a manganite using an electric field.

    NASA Astrophysics Data System (ADS)

    Dhakal, Tara; Selcuk, Sinan; Hebard, Arthur F.; Biswas, Amlan

    2007-03-01

    We have measured the response of the fluid like phases^1 of ferromagnetic metal (FMM) and charge ordered insulator (COI) in thin films of the manganite (La0.4Pr0.6)0.67Ca0.33MnO3 (LPCMO) to an external electric field. The electric field (set by applying a voltage difference across the material) alters the fluid phases and increases the conductivity of the material by about 2 orders of magnitude above a threshold voltage^2. To check if the enhanced conductivity is associated with an increase in the size of the FMM domains, we measured the magnetization of the thin films using a SQUID magnetometer with and without an applied electric field. The saturation magnetization remained the same in either case showing that the FMM domains do not increase in size, which led us to hypothesize that the domains are just reoriented by the electric field. This hypothesis was verified by measuring the transverse resistance while a voltage difference was applied longitudinally across the material. At a threshold voltage when the longitudinal resistance decreased by about 2 orders of magnitude, the transverse resistance showed a small increase. This increase in resistance was attributed to the FMM domains being stretched in the direction of the electric field. [1] P. A. Sharma et al., Phys. Rev. B 71, 224416 (2005), [2] Tara Dhakal, et. al, Cond-mat/0607502.

  11. Bandlike electrical transport in P r1 -xC axMn O3 manganites

    NASA Astrophysics Data System (ADS)

    Kadyrov, L. S.; Zhang, T.; Zhukova, E. S.; Anzin, V. B.; Trotsenko, V. G.; Torgashev, V. I.; Dressel, M.; Gorshunov, B. P.

    2016-05-01

    The conductivity and dielectric permittivity spectra of polycrystalline manganites P r1 -xC axMn O3 with x =0.3 , 0.4, and 0.5 have been measured in a broad frequency range (5 -3000 c m-1 ) down to low temperatures. From the dispersion analysis the existence of a Drude component can be established that is associated with small polarons coherently moving within a band several meV wide. The temperature-dependent conductivity shows an activated behavior with an activation energy of approximately 165 meV above 170 K and 4.8 meV below 120 K. The change in the activation energy is assigned to the onset of magnetic order at 120 K. In all three samples an absorption band is discovered at 40 -60 c m-1 that is associated with the transition between Stark-split P r3 + electron states which gain optical activity due to coupling to acoustical phonons.

  12. Lanthanum manganite-based air electrode for solid oxide fuel cells

    DOEpatents

    Ruka, Roswell J.; Kuo, Lewis; Li, Baozhen

    1999-01-01

    An air electrode material for a solid oxide fuel cell is disclosed. The electrode material is based on lanthanum manganite having a perovskite-like crystal structure ABO.sub.3. The A-site of the air electrode material preferably comprises La, Ca, Ce and at least one lanthanide selected from Sm, Gd, Dy, Er, Y and Nd. The B-site of the electrode material comprises Mn with substantially no dopants. The ratio of A:B is preferably slightly above 1. A preferred air electrode composition is of the formula La.sub.w Ca.sub.x Ln.sub.y Ce.sub.z MnO.sub.3, wherein Ln comprises at least one lanthanide selected from Sm, Gd, Dy, Er, Y and Nd, w is from about 0.55 to about 0.56, x is from about 0.255 to about 0.265, y is from about 0.175 to about 0.185, and z is from about 0.005 to about 0.02. The air electrode material possesses advantageous chemical and electrical properties as well as favorable thermal expansion and thermal cycle shrinkage characteristics.

  13. Lanthanum manganite-based air electrode for solid oxide fuel cells

    DOEpatents

    Ruka, R.J.; Kuo, L.; Li, B.

    1999-06-29

    An air electrode material for a solid oxide fuel cell is disclosed. The electrode material is based on lanthanum manganite having a perovskite-like crystal structure ABO[sub 3]. The A-site of the air electrode material preferably comprises La, Ca, Ce and at least one lanthanide selected from Sm, Gd, Dy, Er, Y and Nd. The B-site of the electrode material comprises Mn with substantially no dopants. The ratio of A:B is preferably slightly above 1. A preferred air electrode composition is of the formula La[sub w]Ca[sub x]Ln[sub y]Ce[sub z]MnO[sub 3], wherein Ln comprises at least one lanthanide selected from Sm, Gd, Dy, Er, Y and Nd, w is from about 0.55 to about 0.56, x is from about 0.255 to about 0.265, y is from about 0.175 to about 0.185, and z is from about 0.005 to about 0.02. The air electrode material possesses advantageous chemical and electrical properties as well as favorable thermal expansion and thermal cycle shrinkage characteristics. 10 figs.

  14. Chemical compatibility between strontium-doped lanthanum manganite and yttria-stabilized zirconia

    SciTech Connect

    Stochniol, G.; Syskakis, E.; Naoumidis, A.

    1995-04-01

    Equimolar powder mixtures and multilayer pellets of single-phase Sr-doped lanthanum manganite perovskite materials La{sub y{minus}x}Sr{sub x}MnO{sub 3} with La content y = 1 and 0.95 and Sr content 0 {<=} x {<=} 0.5 were annealed in air with 8 mol% Y{sub 2}O{sub 3}ZrO{sub 2} at 1470 K up to 400 h and at 1670 K up to 200 h. X-ray diffraction and electron probe microanalysis confirmed the formation of La{sub 2}Zr{sub 2}O{sub 7} or SrZrO{sub 3} depending on the composition of the perovskites. No reaction products could be detected for La{sub 0.95 {minus}x}Sr{sub x}MnO{sub 3} with 0.2 {<=} x {<=} 0.4 after annealing for 400 h at 1470 K, and for the perovskite La{sub 0.65}Sr{sub 0.3}MnO{sub 3} even after annealing for 200 h at 1,670 K. The results demonstrate the improved chemical compatibility of La-deficient perovskites against reaction with zirconia and can provide a basis for the selection of a sufficiently chemically stable material for the air electrode of solid oxide fuel cells.

  15. Magnetic and Transport Properties of Heterostructured Films of Prussian Blue Analogues and Manganites

    NASA Astrophysics Data System (ADS)

    Quintero, P. A.; Jeen, H.; Knowles, E. S.; Biswas, A.; Meisel, M. W.; Andrus, M. J.; Talham, D. R.

    2011-03-01

    The magnetic and transport properties of heterostructured films consisting of Prussian blue analogues, Aj M' k [M(CN)6 ]l . n H2 O (M' M-PBA), where A is an alkali ion and M' ,M are transition metals, and manganites have been studied. Specifically, NiCr-PBA and CoFe-PBA films of ~ 100 ~nm thickness have been deposited on perovskite (La 1-y Pr y)0.67 Ca 0.33 Mn O3 (LPCMO) manganese films of ~ 30 ~nm thickness. The effect of the ferromagnetic NiCr-PBA, Tc ~ 70 ~K, and the photo-controllable ferrimagnetic CoFe-PBA, Tc ~ 20 ~K, on the I-V properties of the LPCMO will be reported, where special attention will be given to the changes of the transition temperatures of the ferromagnetic metallic (FMM) and the charge-ordered insulating (COI) phases in the LPCMO substrate. ** Supported by NSF DMR-0701400 (MWM), DMR-0804452 (AB), DMR-1005581 (DRT), DMR-0654118 (NHMFL), and by scholarship from the Organization of American States (PAQ). D.M.~Pajerowski et al., J.~Am.~Chem. Soc. 132 (2010) 4058.

  16. Giant Enhancement of Magnetic Anisotropy in Ultrathin Manganite Films via Nanoscale 1D Periodic Depth Modulation.

    PubMed

    Rajapitamahuni, A; Zhang, L; Koten, M A; Singh, V R; Burton, J D; Tsymbal, E Y; Shield, J E; Hong, X

    2016-05-01

    The relatively low magnetocrystalline anisotropy (MCA) in strongly correlated manganites (La,Sr)MnO_{3} has been a major hurdle for implementing them in spintronic applications. Here we report an unusual, giant enhancement of in-plane MCA in 6 nm La_{0.67}Sr_{0.33}MnO_{3} (LSMO) films grown on (001) SrTiO_{3} substrates when the top 2 nm is patterned into periodic stripes of 100 or 200 nm width. Planar Hall effect measurements reveal an emergent uniaxial anisotropy superimposed on one of the original biaxial easy axes for unpatterned LSMO along ⟨110⟩ directions, with a 50-fold enhanced anisotropy energy density of 5.6×10^{6}  erg/cm^{3} within the nanostripes, comparable to the value for cobalt. The magnitude and direction of the uniaxial anisotropy exclude shape anisotropy and the step edge effect as its origin. High resolution transmission electron microscopy studies reveal a nonequilibrium strain distribution and drastic suppression in the c-axis lattice constant within the nanostructures, which is the driving mechanism for the enhanced uniaxial MCA, as suggested by first-principles density functional calculations. PMID:27203341

  17. A Combined Density Functional Theory and Monte Carlo Study of Manganites for Magnetic Refrigeration

    NASA Astrophysics Data System (ADS)

    Korotana, Romi; Mallia, Giuseppe; Gercsi, Zsolt; Harrison, Nicholas

    2015-03-01

    Perovskite oxides are considered to be strong candidates for applications in magnetic refrigeration technology, due to their remarkable properties, in addition to low processing costs. Manganites with the general formula R1-xAxMnO3, particularly for A=Ca and 0 . 2 < x < 0 . 5 , undergo a field driven transition from a paramagnetic to ferromagnetic state, which is accompanied by changes in the lattice and electronic structure. Therefore, one may anticipate a large entropy change across the phase transition due to the first order nature. The present work aims to achieve an understanding of the relevant structural, magnetic, and electronic entropy contributions in the doped compound La0.75Ca0.25MnO3. A combination of thermodynamics and first principles theory is applied to determine individual contributions to the total entropy change of the system. Hybrid-exchange density functional (B3LYP) calculations for La0.75Ca0.25MnO3 predict an anti-Jahn-Teller polaron in the localised hole state, which is influenced by long-range cooperative Jahn-Teller distortions. Through the analysis of individual entropy contributions, it is identified that the electronic and vibrational terms have a deleterious effect on the total entropy change.

  18. Electrical performance of nanostructured strontium-doped lanthanum manganite impregnated onto yttria-stabilized zirconia backbone

    NASA Astrophysics Data System (ADS)

    Ju, Jiangwei; Lin, Jie; Wang, Yusu; Zhang, Yanxiang; Xia, Changrong

    2016-01-01

    Strontium-doped lanthanum manganite (LSM) nanoparticles are deposited onto porous yttria-stabilized zirconia frameworks via an ion impregnation/infiltration process. The apparent conductivity of the impregnated LSM nanostructure is investigated regarding the fabricating parameters including LSM loading, heat treatment temperature, heating rate, and annealing at 750 °C for 400 h. Besides, the conductivity, the intrinsic conductivity as well as Bruggeman factor of the impregnated LSM is estimated from the apparent conductivity using the analytical model for the three-dimensional impregnate network. The conductivity increases with LSM loading while the interfacial polarization resistance exhibits the lowest value at an optimal loading of about 5 vol.%, which corresponds to the largest three-phase boundary as predicted using the numerical infiltration methodology. At the optimal loading, the area specific ohmic resistance of the impregnated LSM is about 0.032 Ω cm2 at 700 °C for a typical impregnated cathode of 30 μm thick. It is only 5.5% of the cathode interfacial polarization resistance and 3.3% of the total resistance for a single cell consisting of a Ni-YSZ support, a 10 μm thick electrolyte and a 30 μm thick cathode, demonstrating that the ohmic resistance is negligible in the LSM impregnated cathode for SOFCs.

  19. Self-assembled monolayer-functionalized half-metallic manganite for molecular spintronics.

    PubMed

    Tatay, Sergio; Barraud, Clément; Galbiati, Marta; Seneor, Pierre; Mattana, Richard; Bouzehouane, Karim; Deranlot, Cyrile; Jacquet, Eric; Forment-Aliaga, Alicia; Jegou, Pascale; Fert, Albert; Petroff, Frédéric

    2012-10-23

    (La,Sr)MnO(3) manganite (LSMO) has emerged as the standard ferromagnetic electrode in organic spintronic devices due to its highly spin-polarized character and air stability. Whereas organic semiconductors and polymers have been mainly envisaged to propagate spin information, self-assembled monolayers (SAMs) have been overlooked and should be considered as promising materials for molecular engineering of spintronic devices. Surprisingly, up to now the first key step of SAM grafting protocols over LSMO surface thin films is still missing. We report the grafting of dodecyl (C12P) and octadecyl (C18P) phosphonic acids over the LSMO half-metallic oxide. Alkylphosphonic acids form ordered self-assembled monolayers, with the phosphonic group coordinated to the surface and alkyl chains tilted from the surface vertical by 43° (C12P) and 27° (C18P). We have electrically characterized these SAMs in nanodevices and found that they act as tunnel barriers, opening the door toward the integration of alkylphosphonic acid//LSMO SAMs into future molecular/organic spintronic devices such as spin OLEDs.

  20. Structure, stoichiometry, and phase purity of calcium substituted lanthanum manganite powders

    SciTech Connect

    Faaland, S.; Einarsrud, M.A.; Roermark, L.; Hoeier, R.; Grande, T.; Knudsen, K.D.

    1998-11-01

    Calcium-doped lanthanum manganite La{sub 1{minus}x}Ca{sub x}MnO{sub 3}, synthesized by the glycine/nitrate method, was characterized by high resolution synchrotron X-ray powder diffraction, electron diffraction, and infrared spectroscopy. A strong correlation was observed between the cooling rate from the calcination temperature and the powder quality, indicating the importance of a homogeneous oxygen stoichiometry. The structure refinement reveals that La{sub 1{minus}x}Ca{sub x}MnO{sub 3} with x = 0.2, 0.3, 0.4, and 0.6 has orthorhombic symmetry with space group Pnma. The MnO{sub 6} octahedra are fairly symmetrical, but the octahedra are tilted about 20{degree} relative to the ideal perovskite structure. Infrared spectroscopy revealed that only the O-Mn-O bending mode is significantly influenced by the substitution of La with Ca. In La{sub 0.8}Ca{sub 0.2}MnO{sub 3} the authors found diffraction evidence of a superstructure in domains in some of the grains. They propose that the superstructure in La{sub 0.8}Ca{sub 0.2}MnO{sub 3} is due to ordering of Ca{sup 2+} ions on A (La{sup 3+}) sites in the perovskite ABO{sub 3} structure.