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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. 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.

  3. 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.

  4. 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

  5. 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.

  6. Fabrication and characterization of magnetotransport in colossal magnetoresistive manganite thin films and hybrid structures

    NASA Astrophysics Data System (ADS)

    Pietambaram, Srinivas V.

    The continually increasing demand for magnetic information storage and retrieval has driven a significant worldwide effort to improve the performance of relevant hard ware components. As the areal density continues to increase, more sensitive materials and innovative structures will be required to detect the decreasing fringe fields emanating from the media. Doped manganites in thin film form are being examined as a possible next generation magnetoresistance sensor material. The magnetoresistance of these doped manganite thin films is of unprecedented magnitude; however, these large resistance changes are achieved only in a strong field in the Tesla range, thus severely limiting their practical utility. This dissertation addresses some of the critical parameters, which influence the properties and efforts to reduce the field scale necessary to observe high magnetoresistance ratios in these films. The primary deposition technique used in this work is pulsed laser deposition. Initial work was concentrated on the optimization of various process parameters to obtain high quality thin films of manganites. Systematic post deposition heat treatments in oxygen and argon ambient at elevated temperatures revealed that transition temperature is related to the Mn-O fraction and uniform distribution of oxygen across the films rather than just the oxygen content of the films as proposed by others. MR ratio is improved by the improvement in the microstructure (recrystallization and grain growth) of the films after annealing; however vacancies created on the lanthanum site by the high temperature anneal also seem to be an important factor in the determination of the MR ratio. Self-doped, mixed doped and external doped lanthanum manganite thin films, where the external dopant is Ca, have shown different transition temperature and MR ratios. The variation in the insulator-to-metal transition could be explained on the basis of Mn4+ content while the MR property seemed to be related

  7. Anisotropic properties of molecular beam epitaxy-grown colossal magnetoresistance manganite thin films

    SciTech Connect

    ODonnell, J.; Onellion, M.; Rzchowski, M.S.; Eckstein, J.N.; Bozovic, I.

    1997-04-01

    We show that both the magnetoresistance and magnetism in tetragonal MBE-grown films of La{sub 1{minus}x}Ca{sub x}MnO{sub 3} show anisotropic effects that depend on both temperature and magnetic field. We show that the {open_quotes}colossal{close_quotes} magnetoresistance depends on the angle between the magnetization and the transport current and that the size of this effect is temperature-dependent. Below the Curie temperature this results in an unusual upturn in the magnetoresistance for small magnetic fields normal to the plane of the film as the magnetization rotates out of the plane. Low-field hysteresis of the in-plane magnetoresistance is also observed, and also shows an anisotropy with respect to the current and magnetization directions. We also find an in-plane biaxial magnetocrystalline anisotropy with easy axes along the {l_brace}100{r_brace} (Mn{endash}O) crystal directions, and evidence for {ital c}-axis magnetocrystalline anisotropy. {copyright} {ital 1997 American Institute of Physics.}

  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. A positron study of the colossal magnetoresistive material lanthanum(0.7) strontium(0.3) manganite

    NASA Astrophysics Data System (ADS)

    Livesay, Eric Anton

    2000-10-01

    We have performed a spin-dependent 2D-ACAR study of a single crystal sample of La0.7Sr0.3MnO3 (a manganite perovskite that exhibits colossal magnetoresistance). Measurements were made at three well-separated temperatures, two of which were below the ferromagnetic to paramagnetic transition temperature. It is believed that these measurements constitute the first detailed experimental study of the electronic structure of this material. Of the many properties of the electronic structure of a material, the Fermi surface is one of the most important. The most recent self-consistent band structure and momentum density calculations predict La0.7Sr0.3MnO3 to have only two significant Fermi surface features, large R-centered cubic hole pockets and a Gamma-centered electron spheroid. Both of these features result from the Fermi level crossing majority bands. The Fermi level sits only slightly above a gap in the minority bands, that is, those bands behave as in an semi-conductor. As a result, electron transport is largely spin-polarized and the material is referred to as being nearly half-metallic. These theoretical predictions are supported by the results of the experimental measurements. Clear indications of the large cubic Fermi surface are observed in our data and, although some evidence is also seen for the electron spheroid, this is decidedly weaker. The experimental results also qualitatively support the supposed spin-polarized transport in this material. This agreement between experiment and theory indicate that the theoretical description is, to a large degree, valid.

  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. PMID:26683223

  11. Polaron Coherence Condensation As the Mechanism for Colossal Magnetoresistance in Layered Manganites

    SciTech Connect

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

    2007-11-20

    Angle-resolved photoemission spectroscopy data for the bilayer manganite La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} show that, upon lowering the temperature below the Curie point, a coherent polaronic metallic groundstate emerges very rapidly with well defined quasiparticles which track remarkably well the electrical conductivity, consistent with macroscopic transport properties. Our data suggest that the mechanism leading to the insulator-to-metal transition in La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} can be regarded as a polaron coherence condensation process acting in concert with the Double Exchange interaction.

  12. 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.

  13. A-site ordering in colossal magnetoresistance manganite La(1-x)Sr(x)MnO3? Molecular dynamics simulations and quantum mechanics calculations.

    PubMed

    Jang, Yun Hee; Gervais, François; Lansac, Yves

    2009-09-01

    Recent experiments have called into question the assumption of a random A-site distribution in mixed-valence colossal magnetoresistance (CMR) manganites. We explored the possibility of an A-site (La(3+)/Sr(2+)) ordering in a CMR manganite La(3/4)Sr(1/4)MnO(3) using molecular dynamics (MD) simulations with a newly developed force field (FF) and quantum mechanics (QM) (density functional theory with the generalized gradient approximation) calculations of the relative stability of structures obtained from MD. Both methods suggest that the degree of stabilization (enthalpy gain) of A-site ordering is not sufficient to overcome the accompanying entropy loss, supporting the assumption of a random A-site distribution in La(3/4)Sr(1/4)MnO(3). This approach combining MD and QM as well as the versatile FF developed in this study should be useful for investigating the structure and functionality of magnetic tunnel junction devices involving composite materials of mixed-valence manganites. PMID:19739857

  14. 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.

  15. Colossal electroresistance and colossal magnetoresistance in spinel multiferroic CdCr2S4

    NASA Astrophysics Data System (ADS)

    Sun, C. P.; Huang, C. L.; Lin, C. C.; Her, J. L.; Ho, C. J.; Lin, J.-Y.; Berger, H.; Yang, H. D.

    2010-03-01

    Colossal magnetoresistance (CMR) and colossal electroresistance (CER) induced by the electric field in spinel multiferroic CdCr2S4 are reported. It is found that a metal-insulator transition in CdCr2S4 is triggered by the electrical field. In magnetic fields, the resistivity ρ of CdCr2S4 responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr2S4 the unique compound to possess all four properties of the colossal magnetocapacitive, colossal electrocapacitive, CER, and CMR. The present results open a new venue for searching new materials to show CMR by tuning electric and magnetic fields.

  16. 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.

  17. A phenomenological Landauer-type theory on colossal magnetoresistance

    NASA Astrophysics Data System (ADS)

    Ding, M.; Tian, G.-S.; Lin, T.-H.

    1996-12-01

    A two-dimensional interacting magnetic domains model is examined to explain the colossal magnetoresistance (CMR) recently observed in manganese-oxides. Electrons transport properties were studied by using Landauer's multichannel transport theory and recursive Green's function technique. Colossal magnetoresistance shows up in this system. The temperature dependence of system's MR is also studied.

  18. Magnetoresistance of lanthanum manganites with activation-type conductivity

    SciTech Connect

    Kurkin, M. I. Neifeld, E. A.; Korolev, A. V.; Ugryumova, N. A.; Gudin, S. A.; Gapontseva, N. N.

    2013-05-15

    The temperature dependence of the resistivity and magnetic moment of La{sub 0.85}Ba{sub 0.15}MnO{sub 3} and La{sub 0.85}Sr{sub 0.15}MnO{sub 3} manganite single crystals in magnetic fields up to 90 kOe is investigated. Analysis of the experimental results shows that the magnetoresistance of lanthanum manganites far from the Curie temperature T{sub C} can be described quantitatively by the s-d model normally used for ferromagnets and taking into account only the exchange interaction between the spins of charge carriers and magnetic moments. These data also show that the features of lanthanum manganites responsible for colossal magnetoresistance (CMR) are manifested in a narrow temperature interval {delta}T Almost-Equal-To 20 K near T{sub C}. Our results suggest a CMR mechanism analogous to the mechanism of giant magnetoresistance (GMR) observed in Fe/Cr-type multilayers with nanometer layer thickness. The nanostratification observed in lanthanum manganites and required for GMR can be described taking into account the spread in T{sub C} in the CMR range {delta}T.

  19. 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

  20. Colossal magnetoresistance in topological Kondo insulator

    NASA Astrophysics Data System (ADS)

    Slieptsov, Igor O.; Karnaukhov, Igor N.

    2016-04-01

    Abnormal electronic properties of complex systems require new ideas concerning explanation of their behavior and possibility of realization. In this acticle we show that a colossal magnetoresistance is realized in the state of the topological Kondo insulator, that is similar to the Kondo insulator state in the Kondo lattice. The mechanism of the phenomenon is the following: in the spin gapless phase an external magnetic field induces the gap in the spectrum of spin excitations, the gap in the spectrum of fermions is opened due to a hybridization between spin and fermion subsystems at half-filling, as the result the magnetic field leads to metal–insulator (or bad metal–insulator) phase transition. A model of the topological Kondo lattice defined on a honeycomb lattice is studied for the case when spinless fermion bands are half-filled. It is shown that the hybridization between local moments and itinerant fermions should be understood as the hybridization between corresponding Majorana fermions of the spin and charge sectors. The system is a topological insulator, single fermion and spin excitations at low energies are massive. We will show that a spin gap induces a gap in the charge channel, it leads to an appearance of a topological insulator state with chiral gapless edge modes and the Chern number one or two depending on the exchange integrals’ values. The relevance of this to the traditional Kondo insulator state is discussed.

  1. Colossal piezoresistance in phase separated manganites.

    PubMed

    Tosado, Jacob; Dhakal, Tara; Biswas, Amlan

    2009-05-13

    We have measured the strain dependent transport properties of phase separated manganite thin films. We subjected (La(1-y)Pr(y))(1-x)Ca(x)MnO(3) thin films grown on NdGaO(3)(110) substrates to direct external mechanical stress using a three-point beam bending method. The resultant change in resistance reveals a colossal piezoresistance (CPR) in manganites. Our experiments reveal that phase separation is a necessary but not sufficient condition for CPR. The maximum CPR is observed only when the phase boundaries are free to move in the fluid-like phase separated state. Our results show that both long-range strain interactions and quenched disorder play an important role in micrometer scale phase separation in manganites, albeit in different temperature ranges. PMID:21825473

  2. Colossal positive magnetoresistance in a doped nearly magnetic semiconductor

    SciTech Connect

    Hu, R.; Thomas, K.; Lee, Y.; Vogt, T.; Choi, E.; Mitrovic, V.; Hermann, R.; Grandjean, F.; Canfield, P.; Kim, J.; Goldman, A.; Petrovic, C.

    2008-02-27

    We report on a positive colossal magnetoresistance (MR) induced by metallization of FeSb{sub 2}, a nearly magnetic or 'Kondo' semiconductor with 3d ions. We discuss the contribution of orbital MR and quantum interference to the enhanced magnetic field response of electrical resistivity.

  3. Colossal Magnetoresistance in a Mott Insulator via Magnetic Field-Driven Insulator-Metal Transition

    NASA Astrophysics Data System (ADS)

    Zhu, M.; Peng, J.; Zou, T.; Prokes, K.; Mahanti, S. D.; Hong, T.; Mao, Z. Q.; Liu, G. Q.; Ke, X.

    2016-05-01

    We present a new type of colossal magnetoresistance (CMR) arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti-doped Ca3Ru2O7 . Such an insulator-metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott-Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin-lattice-charge coupling. This study further provides a model approach to search for CMR systems other than manganites, such as Mott insulators in the vicinity of the boundary between competing phases.

  4. Colossal Magnetoresistance in a Mott Insulator via Magnetic Field-Driven Insulator-Metal Transition.

    PubMed

    Zhu, M; Peng, J; Zou, T; Prokes, K; Mahanti, S D; Hong, T; Mao, Z Q; Liu, G Q; Ke, X

    2016-05-27

    We present a new type of colossal magnetoresistance (CMR) arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti-doped Ca_{3}Ru_{2}O_{7}. Such an insulator-metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott-Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin-lattice-charge coupling. This study further provides a model approach to search for CMR systems other than manganites, such as Mott insulators in the vicinity of the boundary between competing phases. PMID:27284665

  5. Strong-coupling theory of high-temperature superconductivity and colossal magnetoresistance

    NASA Astrophysics Data System (ADS)

    Alexandrov, A. S.

    2005-08-01

    We argue that the extension of the BCS theory to the strong-coupling regime describes the high-temperature superconductivity of cuprates and the colossal magnetoresistance (CMR) of ferromagnetic oxides if the phonon dressing of carriers and strong attractive correlations are taken into account. The attraction between carriers, which is prerequisite to high-temperature superconductivity, is caused by an almost unretarted electron-phonon interaction sufficient to overcome the direct Coulomb repulsion in the strong-coupling limit, where electrons become polarons and bipolarons (real-space electron or hole pairs dressed by phonons). The long-range Froehlich electron-phonon interaction has been identified as the most essential in cuprates providing "superlight" lattice polarons and bipolarons. A number of key observations have been predicted and/or explained with polarons and bipolarons including unusual isotope effects, normal state (pseudo)gaps, upper critical fields, etc. Here some kinetic, magnetic, and more recent thermomagnetic normal state measurements are interpreted in the framework of the strong-coupling theory, including the Nernst effect and normal state diamagnetism. Remarkably, a similar strong-coupling approach offers a simple explanation of CMR in ferromagnetic oxides, while the conventional double-exchange (DEX) model, proposed half a century ago and generalised more recently to include the electronphonon interaction, is in conflict with a number of modern experiments. Among these experiments are site-selective spectroscopies, which have shown that oxygen p-holes are current carriers rather than d-electrons in ferromagnetic manganites (and in cuprates) ruling out DEX mechanism of CMR. Also some samples of ferromagnetic manganites manifest an insulating-like optical conductivity at all temperatures contradicting the DEX notion that their ferromagnetic phase is metallic. On the other hand, the pairing of oxygen holes into heavy bipolarons in the

  6. 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.

  7. Anomalously large anisotropic magnetoresistance in a perovskite manganite

    PubMed Central

    Li, Run-Wei; Wang, Huabing; Wang, Xuewen; Yu, X. Z.; Matsui, Y.; Cheng, Zhao-Hua; Shen, Bao-Gen; Plummer, E. Ward; Zhang, Jiandi

    2009-01-01

    The signature of correlated electron materials (CEMs) is the coupling between spin, charge, orbital and lattice resulting in exotic functionality. This complexity is directly responsible for their tunability. We demonstrate here that the broken symmetry, through cubic to orthorhombic distortion in the lattice structure in a prototype manganite single crystal, La0.69Ca0.31MnO3, leads to an anisotropic magneto-elastic response to an external field, and consequently to remarkable magneto-transport behavior. An anomalous anisotropic magnetoresistance (AMR) effect occurs close to the metal-insulator transition (MIT) in the system, showing a direct correlation with the anisotropic field-tuned MIT in the system and can be understood by means of a simple phenomenological model. A small crystalline anisotropy stimulates a “colossal” AMR near the MIT phase boundary of the system, thus revealing the intimate interplay between magneto- and electronic-crystalline couplings. PMID:19706504

  8. 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

  9. 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

  10. 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

  11. 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.

  12. 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

  13. 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.

  14. Structure, Electrical Transport and Magneto-Resistance Properties of La5/8Ca3/8MnO3 Manganite Synthesized with Different Manganese Precursors

    NASA Astrophysics Data System (ADS)

    Navasery, M.; Halim, S. A.; Lim, K. P.; Chen, S. K.; Roslan, A. S.; Abd-Shukor, R.

    We synthesized the polycrystalline manganite of La5/8Ca3/8MnO3 with three different manganese routes prepared through a solid state reaction method. The effects of the manganese route selection on the structure, electrical transport and magneto-transport properties were examined in this study. The samples were characterized using X-ray diffraction (XRD) and SEM to identify their structure and morphology. XRD analysis confirmed that all samples were in single phase with orthorhombic structure and belonged to the Pnma space group. The average grain sized samples with manganese route of Mn2O3 and MnCO3 had a grain size of 1.2-8.7 μm and 2-7.5 μm, respectively. For the MnO2 route, the sample had a small melt-like shape with higher porosity. The metal-insulator transition temperature, TMI, for LCMO (Mn2O3), LCMO (MnO2) and LCMO (MnCO3) samples were 270 K, 266 K and 258 K, respectively. All the samples showed negative magneto-resistance with significant increase in value near the TMI temperature. The highest CMR (colossal magneto-resistance) ratio was found in LCMO (Mn2O3), -22.06% at 270 K, followed by -16.69% for LCMO (MnO2) at 80 K, and 15.2% for LCMO (MnCO3) at 100 K in a 1 T magnetic field.

  15. Ru(4+) induced colossal magnetoimpedance in Ru doped perovskite manganite at room temperature.

    PubMed

    Singh, Brajendra

    2016-05-14

    We have demonstrated Ru(4+) induced colossal magnetoimpedance (MI) at room temperature in a ∼1 Tesla magnetic field with a pulsed laser deposited La0.7Ca0.3Mn0.7Ru0.3O3 thin film. This composition showed a large negative ∼12% MI in the low frequency range (<5 MHz), a colossal positive MI > 120% in the intermediate frequency range (5 MHz to ∼13 MHz) and a negative MI in the high frequency range (∼13 MHz to 40 MHz) at room temperature. XAS data confirmed the predominant Ru valence state was 4+ in La0.7Ca0.3Mn0.7Ru0.3O3. Ru(4+) induced (i) charge carrier localization and (ii) reduced hole carrier density enhances the MI in this composition, which otherwise was not significant in mixed valences Mn(3+)/Mn(4+) containing La0.7Ca0.3MnO3 and Ru(4+)/Ru(5+) and Mn(3+)/Mn(4+) mixed valences containing Ru = 0.1 and Ru = 0.2 compositions in La0.7Ca0.3Mn1-xRuxO3 (0 ≤x≤ 0.3) thin films. PMID:27109569

  16. Large magnetic entropy change above 300 K in a colossal magnetoresistive material La0.7Sr0.3Mn0.98Ni0.02O3

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong; Tho, Nguyen Duc; Chau, Nguyen; Yu, Seong-Cho; Kurisu, M.

    2005-05-01

    A thorough study of the magnetocaloric effect (MCE) in a colossal magnetoresistive compound of La0.7Sr0.3Mn0.98Ni0.02O3 has been made. The large magnetic entropy change of 7.65 J/kg K upon an applied field of 70 kOe has been found to occur at 350 K, which allows magnetic refrigeration at room temperature. It is interesting to note that, even in high magnetic fields, the magnetic entropy change versus temperature distribution is much more uniform than that of gadolinium and several polycrystalline perovskite manganites, which is desirable for an Ericson-cycle magnetic refrigerator. It is found that such a small amount (˜2%) of substitution of Mn3+ by a magnetic ion (Ni3+ or Co3+) in the perovskite manganite can favor the spin order and hence the MCE. Undoubtedly, this observation opens a window to explore the active magnetic refrigeration at high temperatures.

  17. 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

  18. Spin wave damping in colossal magnetoresistive La0.7Ca0.3MnO3

    NASA Astrophysics Data System (ADS)

    Helton, Joel; Jones, Susumu; Stone, Matthew; Shulyatev, Dmitry; Parshall, Daniel; Lynn, Jeffrey

    The hole-doped perovskite La0.7Ca0.3MnO3 is best known for the colossal magnetoresistance displayed at a combined ferromagnetic and metal-insulator phase transition (Tc=257 K). Previous studies have reported that the spin wave excitations in the ferromagnetic phase become anomalously damped near the Brillouin zone boundary, though a later work suggested that this was a measurement artifact due to an optical phonon branch. We have used the ARCS time-of-flight neutron spectrometer to investigate the spin wave excitations of La0.7Ca0.3MnO3 at T=100 K and find a damping for spin waves at energies exceeding 20 meV that cannot be explained solely by proximity to the phonon branch. With additional measurements using the BT7 triple-axis neutron spectrometer, the spin wave damping is explored as a function of reduced wavevector, excitation energy, and temperature.

  19. Low field anisotropic colossal magnetoresistance in Sm0.53Sr0.47MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Srivastava, Manoj K.; Singh, M. P.; Kaur, Amarjeet; Razavi, F. S.; Singh, H. K.

    2011-12-01

    Sm0.53Sr0.47MnO3 (SSMO) thin films (thicknesses ˜200 nm) were deposited by on-axis dc magnetron sputtering on the single crystal LSAT (001) substrates. These films are oriented along the out of plane c-direction. The ferromagnetic and insulator-metal transition occurs at TC ˜ 96 and TIM ˜ 91 K, respectively. The magnetization easy axis is observed to lie in the plane of the film while the magnetic hard axis is found to be along the normal to this. The magnetotransport of the SSMO films, which was measured as a function of angle (θ) between the magnetic field (H) and plane of the film, shows colossal anisotropy. Magnetoresistance (MR) decreases drastically as θ increases from 0° (H//easy axis) to 90° (H//hard axis). The out-of-plane anisotropic MR is as high as 88% at H = 3.6 kOe and 78 K. The colossal anisotropy has been explained in terms of the magnetic anisotropies at play and the magnetic domain motion in applied magnetic field.

  20. Improved tunneling magnetoresistance at low temperature in manganite junctions grown by molecular beam epitaxy

    SciTech Connect

    Werner, R.; Kleiner, R.; Koelle, D.; Petrov, A. Yu.; Davidson, B. A.; Mino, L. Alvarez

    2011-04-18

    We report resistance versus magnetic field measurements for a La{sub 0.65}Sr{sub 0.35}MnO{sub 3}/SrTiO{sub 3}/La{sub 0.65}Sr{sub 0.35}MnO{sub 3} tunnel junction grown by molecular-beam epitaxy, that show a large field window of extremely high tunneling magnetoresistance (TMR) at low temperature. Scanning the in-plane applied field orientation through 360 deg., the TMR shows fourfold symmetry, i.e., biaxial anisotropy, aligned with the crystalline axis but not the junction geometrical long axis. The TMR reaches {approx}1900% at 4 K, corresponding to an interfacial spin polarization of >95% assuming identical interfaces. These results show that uniaxial anisotropy is not necessary for large TMR, and lay the groundwork for future improvements in TMR in manganite junctions.

  1. Charge inhomogeneities in the colossal magnetoresistant manganites from the local atomic structure

    SciTech Connect

    Billinge, S. J. L.; Petkov, V.; Proffen, T.; Kwei, G. H.; Sarrao, J. L.; Shastri, S. D.; Kycia, S.

    2000-01-12

    The authors have measured atomic pair distribution functions (PDF) of La{sub 1{minus}x}Ca{sub x}MnO{sub 3} using high energy x-ray diffraction. This approach yields accurate PDFs with very high real-space resolution. It also avoids potential pitfalls from the more usual neutron measurements that magnetic scattering is present in the measurement, that the neutron scattering length of manganese is negative leading to partial cancellation of PDF peaks, and that inelasticity effects might distort the resulting PDF. They have used this to address the following questions which do not have a satisfactory answer: (1) What are the amplitudes and natures of the local Jahn-Teller and polaronic distortions in the CMR region. (2) Is the ground-state of the ferromagnetic metallic phase delocalized or polaronic. (3) As one moves away from the ground-state, by raising temperature or decreasing doping, towards the metal insulator transition, how does the state of the material evolve?

  2. Sr0.9K0.1Zn1.8Mn0.2As2: A ferromagnetic semiconductor with colossal magnetoresistance

    NASA Astrophysics Data System (ADS)

    Yang, Xiaojun; Chen, Qian; Li, Yupeng; Wang, Zhen; Bao, Jinke; Li, Yuke; Tao, Qian; Cao, Guanghan; Xu, Zhu-An

    2014-09-01

    A bulk diluted magnetic semiconductor (Sr,K)(Zn,Mn)2As2 was synthesized with decoupled charge and spin doping. It has a hexagonal CaAl2Si2-type structure with the (Zn,Mn)2As2 layer forming a honeycomb-like network. Magnetization measurements show that the sample undergoes a ferromagnetic transition with a Curie temperature of 12 K and magnetic moment reaches about 1.5 μ\\textit{B}/\\text{Mn} under μ_0H= 5 \\text{T} and T= 2 \\text{K} . Surprisingly, a colossal negative magnetoresistance, defined as [ρ(H)-ρ(0)]/ρ(0) , up to -38{%} under a low field of μ_0H= 0.1 \\text{T} and to -99.8{%} under μ_0H= 5 \\text{T} , was observed at T= 2 \\text{K} . The colossal magnetoresistance can be explained based on the Anderson localization theory.

  3. Colossal Magnetoresistance Without Mn3+/Mn4+ Double Exchange in the Stoichiometric Pyrochlore Tl2Mn2O7

    PubMed

    Subramanian; Toby; Ramirez; Marshall; Sleight; Kwei

    1996-07-01

    Structural analysis from powder neutron and single-crystal x-ray diffraction data for a sample of the Tl2Mn2O7 pyrochlore, which exhibits colossal magnetoresistance (CMR), shows no deviations from ideal stoichiometry. This analysis gives an Mn-O distance of 1.90 angstroms, which is significantly shorter than the Mn-O distances (1.94 to 2.00 angstroms) observed in phases based on LaMnO3 perovskites that exhibit CMR. Both results in Tl2Mn2O7 indicate oxidation states very close to Tl23+Mn24+O7. Thus, Tl2Mn2O7 has neither mixed valence for a double-exchange magnetic interaction nor a Jahn-Teller cation such as Mn3+, both of which were thought to have an important function in CMR materials. An alternate mechanism for CMR in Tl2Mn2O7 based on magnetic ordering driven by superexchange and strong spin-fluctuation scattering above the Curie temperature is proposed here. PMID:8688054

  4. 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

  5. A nanomagnetic study of phase transition in manganite thin films and ballistic magnetoresistance in magnetic nanocontacts

    NASA Astrophysics Data System (ADS)

    Chung, Seok-Hwan

    This work focuses on two largely unexplored phenomena in micromagnetics: the temperature-driven paramagnetic insulator to ferromagnetic (FM) metallic phase transition in perovskite manganite and ballistic magnetoresistance in spin-polarized nanocontacts. To investigate the phase transition, an off-the-shelf commercial scanning force microscope was redesigned for operation at temperatures from 350 K to 100 K. This adaptation is elaborated in this thesis. Using this system, both ferromagnetic and charge-ordered domain structures of (La 1-xPrx)0.67Ca0.33MnO3 thin film were observed by magnetic force microscopy (MFM) and electric force microscopy (EFM) operated in the vicinity of the peak resistance temperature (Tp). Predominantly in-plane oriented FM domains of sub-micrometer size emerge below Tp and their local magnetic moment increased as the temperature is reduced. Charge-ordered insulating regions show a strong electrostatic interaction with an EFM tip at a few degrees above Tp and the interaction correlates well with the temperature dependence of resistivity of the film. Cross-correlation analysis between topography and magnetic structure on several substrates indicates FM domains form on the flat regions of the surface, while charge ordering occurs at surface protrusions. In the investigation of ballistic magnetoresistance, new results on half-metallic ferromagnets formed by atomic or nanometer contacts of CrO2-CrO 2 and CrO2-Ni are presented showing magnetoconductance as high as 400%. Analysis of the magnetoconductance versus conductance data for all materials known to exhibit so-called ballistic magnetoresistance strongly suggests that magnetoconductance of nanocontacts follows a universal mechanism. If the maximum magnetoconductance is normalized to unity and the conductance is scaled with the resistivity of the material, then all data points fall onto a universal curve independent of the contact material and the transport mechanism. The analysis has been

  6. 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.

  7. Modeling of colossal magnetoresistance in La0.67Ca0.33MnO3/Pr0.67Ca0.33MnO3 superlattices: Comparison with individual (La1-yPry)0.67Ca0.33MnO3 films

    NASA Astrophysics Data System (ADS)

    Hühn, S.; Jungbauer, M.; Michelmann, M.; Massel, F.; Koeth, F.; Ballani, C.; Moshnyaga, V.

    2013-05-01

    Colossal magnetoresistance (CMR) and nm-scale electronic inhomogeneity close to the first order phase transition in perovskite manganites, e.g., (La1-yPry)0.67Ca0.33MnO3 still remain a puzzling phenomenon. We experimentally model a metal-insulator phase coexistence by growing a short period (LCMOn/PCMOn)m superlattices (SLs) with the same thickness for both components. CMR effect was studied as a function of the individual layer thickness n = 2-8 and then compared with chemically homogeneous (La1-yPry)0.67Ca0.33MnO3 LPCMO films. We show that SLs can be superimposed in the phase diagram of LPCMO. The results also point out the importance of the nm-scale electronic rather than chemical separation for realization of the CMR effect as well as limits the lowest boundary for the thickness of an individual manganite material to n ˜4u.c.

  8. 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.

  9. 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.

  10. 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

    2016-04-14

    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. PMID:27031679

  11. Coherent orbital waves during an Ultrafast Photo-induced Isulator-metal Transition in a magnetoresistive manganite

    SciTech Connect

    ULTRAS-INFM-CNR Dipartimento di Fisica, Politecnico di Milano, Italy; Department of Physics - Cavalleri Group, Clarendon Laboratory, University of Oxford, U.K.; Correlated Electron Research Center, Tsukuba, Japan; Schoenlein, Robert William; Polli, D.; Rini, M.; Wall, S.; Schoenlein, R.W.; Tomioka, Y.; Tokura, Y.; Cerullo, G.; Cavalleri, A.

    2007-06-01

    Photo-excitation can drive strongly correlated electron insulators into competing conducting phases1,2, resulting in giant and ultrafast changes of their electronic and magnetic properties. The underlying non-equilibrium dynamics involve many degrees of freedom at once, whereby sufficiently short optical pulses can trigger the corresponding collective modes of the solid along temporally coherent pathways. The characteristic frequencies of these modes range between the few GHz of acoustic vibrations3 to the tens or even hundreds of THz for purely electronic excitations. Virtually all experiments so far have used 100 fs or longer pulses, detecting only comparatively slow lattice dynamics4,5. Here, we use sub-10-fs optical pulses to study the photo-induced insulator-metal transition in the magneto-resistive manganite Pr0.7Ca0.3MnO3. At room temperature, we find that the time-dependent pathway towards the metallic phase is accompanied by coherent 31 THz oscillations of the optical reflectivity, significantly faster than all lattice vibrations. These high-frequency oscillations are suggestive of coherent orbital waves6,7, crystal-field excitations triggered here by impulsive stimulated Raman scattering. Orbital waves are likely to be initially localized to the small polarons of this room-temperature manganite, coupling to other degrees of freedom at longer times, as photo-domains coalesce into a metallic phase.

  12. Magnetic and charge ordering in nanosized manganites

    SciTech Connect

    Zhang, T. Wang, X. P.; Fang, Q. F.; Li, X. G.

    2014-09-15

    Perovskite manganites exhibit a wide range of functional properties, such as colossal magneto-resistance, magnetocaloric effect, multiferroic property, and some interesting physical phenomena including spin, charge, and orbital ordering. Recent advances in science and technology associated with perovskite oxides have resulted in the feature sizes of microelectronic devices down-scaling into nanoscale dimensions. The nanoscale perovskite manganites display novel magnetic and electronic properties that are different from their bulk and film counterparts. Understanding the size effects of perovskite manganites at the nanoscale is of importance not only for the fundamental scientific research but also for developing next generation of electronic and magnetic nanodevices. In this paper, the current understanding and the fundamental issues related to the size effects on the magnetic properties and charge ordering in manganites are reviewed, which covers lattice structure, magnetic and electronic properties in both ferromagnetic and antiferromagnetic based manganites. In addition to review the literatures, this article identifies the promising avenues for the future research in this area.

  13. Magnetic and charge ordering in nanosized manganites

    NASA Astrophysics Data System (ADS)

    Zhang, T.; Wang, X. P.; Fang, Q. F.; Li, X. G.

    2014-09-01

    Perovskite manganites exhibit a wide range of functional properties, such as colossal magneto-resistance, magnetocaloric effect, multiferroic property, and some interesting physical phenomena including spin, charge, and orbital ordering. Recent advances in science and technology associated with perovskite oxides have resulted in the feature sizes of microelectronic devices down-scaling into nanoscale dimensions. The nanoscale perovskite manganites display novel magnetic and electronic properties that are different from their bulk and film counterparts. Understanding the size effects of perovskite manganites at the nanoscale is of importance not only for the fundamental scientific research but also for developing next generation of electronic and magnetic nanodevices. In this paper, the current understanding and the fundamental issues related to the size effects on the magnetic properties and charge ordering in manganites are reviewed, which covers lattice structure, magnetic and electronic properties in both ferromagnetic and antiferromagnetic based manganites. In addition to review the literatures, this article identifies the promising avenues for the future research in this area.

  14. Colossal thermoelectric power in charge ordered lanthanum calcium manganites (La0.5Ca0.5MnO3)

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Lanthanum calcium manganites (La0.5Ca0.5MnO3) 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 (TC). 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 < TC. Mott's polaronic contribution of charge carriers are considered to interpret TEP in the high temperature region (T > TC). The optimal Mn4+-Mn3+ concentration in charge ordered La0.5Ca0.5MnO3 was examined by X-ray Photoelectron Spectroscopy analysis which confirms the charge ordered nature of this compound.

  15. 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.

  16. 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.

  17. 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

  18. 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

  19. 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.

  20. Theory of strain-controlled magnetotransport and stabilization of the ferromagnetic insulating phase in manganite thin films.

    PubMed

    Mukherjee, Anamitra; Cole, William S; Woodward, Patrick; Randeria, Mohit; Trivedi, Nandini

    2013-04-12

    We show that applying strain on half-doped manganites makes it possible to tune the system to the proximity of a metal-insulator transition and thereby generate a colossal magnetoresistance (CMR) response. This phase competition not only allows control of CMR in ferromagnetic metallic manganites but can be used to generate CMR response in otherwise robust insulators at half-doping. Further, from our realistic microscopic model of strain and magnetotransport calculations within the Kubo formalism, we demonstrate a striking result of strain engineering that, under tensile strain, a ferromagnetic charge-ordered insulator, previously inaccessible to experiments, becomes stable. PMID:25167302

  1. Strongly bias-dependent tunnel magnetoresistance in manganite spin filter tunnel junctions.

    PubMed

    Prasad, Bhagwati; Zhang, Wenrui; Jian, Jie; Wang, Haiyan; Blamire, Mark G

    2015-05-20

    A highly unconventional bias-dependent tunnel magnetoresistance (TMR) response is observed in Sm0.75 Sr0.25 MnO3 -based nanopillar spin filter tunnel junctions (SFTJs) with two different behaviors in two different thickness regimes of the barrier layer. Thinner barrier devices exhibit conventional SFTJ behaviors; however, for larger barrier thicknesses, the TMR-bias dependence is more complex and reverses sign at higher bias. PMID:25845706

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    Ultra-thin films of the electron doped manganite La0.8Ce0.2MnO3 were grown in a layer-by-layer growth mode on SrTiO3 (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 Ce4+ and Mn2+ 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-Tc cuprates.

  3. 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.

  4. Resonant magnetoresistance in the vicinity of a phase transition

    SciTech Connect

    Atsarkin, V. A. Demidov, V. V.

    2013-01-15

    The change in the electrical conductivity of manganite films upon microwave pumping in the magnetic resonance conditions is investigated. The temperature dependence of the effect correlates with the temperature variation of colossal magnetoresistance (CMR), passing through a maximum at the Curie point. The results are interpreted using a model that assumes a decrease in the absolute value vertical bar M vertical bar of the magnetic moment of the sample under the action of magnetoresonant saturation, which leads to an increase in resistance in accordance with the CMR mechanism. Theoretical analysis based on the Landau-Lifshitz-Bloch equation confirms the correctness of this model and ensures good agreement with experiment.

  5. Spin glass-like behavior, giant magnetocaloric and giant magnetoresistance effect in PrPb manganites

    NASA Astrophysics Data System (ADS)

    Chau, N.; Hanh, D. T.; Tho, N. D.; Luong, N. H.

    2006-08-01

    The Pr 1-xPb xMnO 3 ( x=0.1-0.5) perovskites have been fabricated by solid-state reaction. The X-ray diffraction patterns show that the samples are of single phase with orthorhombic structure. The field-cooled (FC) and zero-field-cooled (ZFC) thermomagnetic curves measured at low field and low temperatures exhibit the spin glass-like state. The Curie temperature of samples increased with increase in Pb content. The maximum magnetic entropy change |Δ Sm| max reaches the giant values of 3.91 and 3.68 J/kg K for quite low magnetic field change of 1.35 T for the samples x=0.1 and 0.4, respectively. The resistance measurements show that there is insulator-metal phase transition on the R( T) curves for samples with x⩾0.3. The giant magnetoresistance effect is also observed for all samples studied.

  6. 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

  7. 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)

  8. 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

  9. Emergent phenomena in manganites under spatial confinement

    NASA Astrophysics Data System (ADS)

    Shen, Jian; Z. Ward, T.; F. Yin, L.

    2013-01-01

    It is becoming increasingly clear that the exotic properties displayed by correlated electronic materials such as high-Tc superconductivity in cuprates, colossal magnetoresistance (CMR) in manganites, and heavy-fermion compounds are intimately related to the coexistence of competing nearly degenerate states which couple simultaneously active degrees of freedom—charge, lattice, orbital, and spin states. The striking phenomena associated with these materials are due in a large part to spatial electronic inhomogeneities, or electronic phase separation (EPS). In many of these hard materials, the functionality is a result of the soft electronic component that leads to self-organization. In this paper, we review our recent work on a novel spatial confinement technique that has led to some fascinating new discoveries about the role of EPS in manganites. Using lithographic techniques to confine manganite thin films to length scales of the EPS domains that reside within them, it is possible to simultaneously probe EPS domains with different electronic states. This method allows for a much more complete view of the phases residing in a material and gives vital information on phase formation, movement, and fluctuation. Pushing this trend to its limit, we propose to control the formation process of the EPS using external local fields, which include magnetic exchange field, strain field, and electric field. We term the ability to pattern EPS “electronic nanofabrication." This method allows us to control the global physical properties of the system at a very fundamental level, and greatly enhances the potential for realizing true oxide electronics.

  10. Piezoresistivity in films of nanocrystalline manganites.

    PubMed

    Sarkar, Jayanta; Raychaudhuri, A K

    2007-06-01

    Rare earth manganites having perovskite structure are susceptible to lattice strain. So far most investigations have been done with hydrostatic pressure or biaxial strain. We have observed that hole doped rare-earth manganites, which are known to display colossal magnetoresistance (CMR) also show change in its resistance under the influence of uniaxial strain. We report the direct measurement of piezoresistive response of La0.67Ca0.33MnO3 (LCMO) and La0.67Sr0.33MnO3 (LSMO) of this manganite family. The measurements were carried out on nanostructured polycrystalline films of LCMO and LSMO grown on oxidized Si(100) substrates. The piezoresistance was measured by bending the Si cantilevers (on which the film is grown) in flexural mode both with compressive and tensile strain. At room temperature the gauge factor approximately 10-20 and it increases to a large value near metal-insulator transition temperature (Tp) where the resistivity shows a peak. PMID:17654992

  11. 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

  12. 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.

  13. Colossal magnetoresistance in La 0.7Ca 0.3-xHg xMnO 3 (0⩽ x⩽0.2) system over wide temperature range

    NASA Astrophysics Data System (ADS)

    Shelke, Vilas; Khatarkar, Subhash; Yadav, Rashmi; Anshul, Avneesh; Singh, R. K.

    2010-05-01

    The divalent substitutions in rare-earth manganites create quenched disorders; those are responsible for the modification of magnetoelectronic properties through competition of two phases. In this regards, the substitution of divalent Hg is rarely studied. Here, we present the results on effect of Hg 2+ substitution in LCMO manganites. We have synthesized polycrystalline samples with nominal compositions La 0.7Ca 0.3-xHg xMnO 3 (0⩽ x⩽0.2) by the standard solid-state reaction method. The X-ray diffraction data revealed monophasic nature without a signature of Hg related or any other impurity phase. The ac susceptibility measurement showed variation in the magnetic transition temperature as well as the transition width. The electrical resistivity measurement showed variation in metal-insulator transition temperature. The magnetoresistance (MR) measurements were carried out at 5 T magnetic field. The samples show varying magnitude of magnetoresistance as high as 74.48%. The distinct feature seen with Hg substitution is the increase in the magnitude of MR and temperature range over which MR value is sustained. It also improves the microstructure of the samples.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Giant Coulomb blockade magnetoresistance

    SciTech Connect

    Zhang, Xiaoguang; Wen, Z. C.; Wei, H. X.; Han, Prof. X. F.

    2010-01-01

    We show that the Coulomb blockade voltage can be made to depend strongly on the electron spin in a thin magnetic granular layer inserted in the middle of an insulating layer of a tunnel junction. This strong spin dependence is predicted from the spin-dependent inter-granular conductance through any of the following effects within the granular layer, giant magnetoresistance (GMR), tunneling magnetoresistance (TMR), colossal magnetoresistance (CMR), or GMR through a polymer spacer. The resulting Coulomb blockade magnetoresistance (CBMR) ratio can exceed the magnetoresistance ratio of the granular layer itself by orders of magnitude. Unlike other magenetoresistance effects, the CBMR effect does not require magnetic electrodes.

  20. 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.

  1. Colossal electroresistance and magnetoresistance effect in polycrystalline perovskite cobaltites Nd{sub 1−x}Sr{sub x}CoO{sub 3} (x = 0.1, 0.2, 0.3)

    SciTech Connect

    Zhang, Li; Li, Xia; Wang, Feifei; Wang, Tao; Shi, Wangzhou

    2013-03-15

    Highlights: ► Samples of cobaltites Nd{sub 1−x}Sr{sub x}CoO{sub 3} were synthesized by solid state reaction method. ► Different currents were applied to study the electroresistance effect. ► Resistivity of the samples decrease dramatically with increase of the currents. ► Non-linear current–voltage (I–V) characteristics are observed. ► Current can have influence on the low field magnetoresistance of the samples. - Abstract: Polycrystalline samples of cobaltites Nd{sub 1−x}Sr{sub x}CoO{sub 3} (x = 0.1, 0.2, 0.3) with the perovskite structure were synthesized by conventional solid state reaction method. Different currents ranging from 1 μA to 1 mA were applied to study the electroresistance (ER) effect. Temperature dependence of resistivity for the samples decrease dramatically with increase of the currents in the low temperature and non-linear current–voltage (I–V) characteristics are observed. The maximum ER ratio (defined as ER = (ρ{sub 1} {sub mA} − ρ{sub L})/ρ{sub L} × 100%) of the all samples is more than −99%, which indicates a colossal electroresistance (CER) effect has found in these compounds. What is more, we also found that electric current can have influence on the low field magnetoresistance (LFMR) of the samples. LFMR decrease with the increase of applied current. The experimental results were discussed by spin polarized carriers modified ferromagnetic (FM)/nonmagnetic (NM) interface and grain interior phase separation scenario.

  2. 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.

  3. 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.

  4. Surface electronic phase transition in colossal magnetoresistive manganese perovskites: La{sub 0.65}Sr{sub 0.35}MnO{sub 3}

    SciTech Connect

    Dulli, Hani; Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 ; Plummer, E. W.; Dowben, P. A.; Choi, Jaewu; Liou, S.-H.

    2000-07-24

    We have observed a distinct surface phase transition for an important class of giant magnetoresistance materials [La{sub 1-x}Sr{sub x}MnO{sub 3}(x=0.35)]. The surface phase transition occurs at 240 K compared to 370 K for the bulk and is fundamentally different. In the bulk, a ferromagnetic metal to paramagnetic bad-metal transition occurs, while the lower-temperature surface transition is from an insulator to a semimetal. The surface of this manganese perovskite is electronically and compositionally quite different from the bulk with important implications for the behavior of artificially grown layered transition-metal oxides and for the use of surface sensitive techniques to probe the bulk. (c) 2000 American Institute of Physics.

  5. Structural and magnetic states in layered manganites: An expanding view of the phase diagram

    SciTech Connect

    Mitchell, J. F.; Millburn, J. E.; Ling, C.; Argyriou, D. N.; Bordallo, H. N.

    2000-01-05

    Colossal magnetoresistive (CMR) manganites display a spectacular range of structural, magnetic, and electronic phases as a function of hole concentration, temperature, magnetic field, etc. A1though the bulk of research has concentrated on the 3-D perovskite manganites, the ability to study anisotropic magnetic and electronic interactions made available in reduced dimensions has accelerated interest in the layered Ruddlesden-Popper (R-P) phases of the manganite class. The quest for understanding the coupling among lattice, spin, and electronic degrees of freedom (and dimensionality) is driven by the availability of high quality materials. In this talk, the authors will present recent results on synthesis and magnetic properties of layered manganites from the La{sub 2{minus}2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} series in the Mn{sup 4+}-rich regime x >0.5. This region of the composition diagram is populated by antiferromagnetic structures that evolve from the A-type layered order to G-type ''rocksalt'' order as x increases. Between these two regimes is a wide region (0.7 < x < 0.9) where an incommensurate magnetic structure is observed. The IC structure joins spin canting and phase separation as a mode for mixed-valent manganites to accommodate FM/AF competition. Transport in these materials is dominated by highly insulating behavior, although a region close to x = 0.5 exhibits metal-nonmetal transitions and an extreme sensitivity to oxygen content. They suggest two possible explanations for this transport behavior at doping just above x = O.5: localization by oxygen defects or charge ordering of Mn{sup 3+}/Mn{sup 4+}sites.

  6. 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.

  7. Nonlinear effects and Joule heating in I-V curves in manganites

    NASA Astrophysics Data System (ADS)

    Mercone, Silvana; Frésard, Raymond; Caignaert, Vincent; Martin, Christine; Saurel, Damien; Simon, Charles; André, Gilles; Monod, Philippe; Fauth, François

    2005-07-01

    We study the influence of the Joule effect on the nonlinear behavior of the transport I-V curves in polycrystalline samples of the manganite Pr0.8Ca0.2MnO3 by using the crystalline unit-cell parameters as an internal thermometer in x-ray and neutron diffractions. We develop a simple analytical model to estimate the temperature profile in the samples. Under the actual experimental conditions we show that the internal temperature gradient or the difference between the temperature of the sample and that of the thermal bath is at the origin of the nonlinearity observed in the I-V curves. Consequences on other compounds with colossal magnetoresistance are also discussed.

  8. La0.7Ca0.3MnO3 / Mn3O4 composites: Does an insulating secondary phase always enhance the low field magnetoresistance of manganites?

    NASA Astrophysics Data System (ADS)

    Bhame, S. D.; Fagnard, J.-F.; Pekala, M.; Vanderbemden, P.; Vertruyen, B.

    2012-03-01

    Composites of magnetoresistive La0.7Ca0.3MnO3 (LCMO) with insulating Mn3O4 are useful as a model system because no foreign cation is introduced in the LCMO phase by interdiffusion during the heat treatment. Here we report the magnetotransport properties as a function of sintering temperature Tsinter for a fixed LCMO/Mn3O4 ratio. Decreasing Tsinter from 1250 °C to 800 °C causes an increase in low field magnetoresistance (LFMR) that correlates with the decrease in crystallite size (CS) of the LCMO phase. When plotting LFMR at (77 K, 0.5 T) versus 1/CS, we find that the data for the LCMO/Mn3O4 composites sintered between 800 °C and 1250 °C follow the same trend line as data from the literature for pure LCMO samples with crystallite size >˜25 nm. This differs from the LFMR enhancement observed by many authors in the "usual" manganite composites, i.e., composites where the insulating phase contains cations other than La, Ca or Mn. This difference suggests that diffusion of foreign cations into the grain boundary region is a necessary ingredient for the enhanced LFMR.

  9. Defect Induced Enhanced Low Field Magnetoresistance and Photoresponse in Pr0.6Ca0.4MnO3 thin Films

    NASA Astrophysics Data System (ADS)

    Elovaara, Tomi; Majumdar, Sayani; Huhtinen, Hannu; Paturi, Petriina

    We have investigated the effect of grain boundary related defects on the electronic transport properties of the colossal magnetoresistive low bandwidth manganite Pr0:6Ca0:4MnO3 (PCMO) thin films. A series of PCMO films were prepared by pulsed laser deposition method on MgO and STO substrates. Characterizations of the structural, magnetic and magneto-transport properties show that the films prepared on MgO substrate contain higher amount of structural defects and with decreasing deposition temperature an increasing amount of difierent crystal orientations as the level of texturing decreases. According to the low field magnetoresistance (MR) measurements, the poorly textured samples display an increased low field MR due to a grain boundary tunneling effect at low temperatures compared to the fully textured PCMO film on STO substrate. However, in spite of the level of texturing, all the samples showed a colossal magnetoresistive insulator to metal switching of almost eight orders of magnitude at low temperatures. The magnetic field required for insulator to metal transition (IMT) is much higher in PCMO samples with more structural defects. However, IMT field could be reduced over 3 T by illuminating the sample.

  10. Bond- versus site-centred ordering and possible ferroelectricity in manganites.

    PubMed

    Efremov, Dmitry V; van den Brink, Jeroen; Khomskii, Daniel I

    2004-12-01

    Transition metal oxides with a perovskite-type structure constitute a large group of compounds with interesting properties. Among them are materials such as the prototypical ferroelectric system BaTiO(3), colossal magnetoresistance manganites and the high-T(c) superconductors. Hundreds of these compounds are magnetic, and hundreds of others are ferroelectric, but these properties very seldom coexist. Compounds with an interdependence of magnetism and ferroelectricity could be very useful: they would open up a plethora of new applications, such as switching of magnetic memory elements by electric fields. Here, we report on a possible way to avoid this incompatibility, and show that in charge-ordered and orbitally ordered perovskites it is possible to make use of the coupling between magnetic and charge ordering to obtain ferroelectric magnets. In particular, in manganites that are less than half doped there is a type of charge ordering that is intermediate between site-centred and bond-centred. Such a state breaks inversion symmetry and is predicted to be magnetic and ferroelectric. PMID:15558036

  11. 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.

  12. 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.

  13. Evaluation of the effect of various mechanisms on the magnetoresistance of lanthanum manganites La0.85Sr0.15MnO3 with activation-type conductivity

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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 La0.85Sr0.15MnO3 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 s ( H > H s ). The orientational, dimensional, and magnetic mechanisms have a comparable effect on the MR for H < H 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.

  14. 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.

  15. Observation of large low field magnetoresistance in ramp-edge tunneling junctions based on doped manganite ferromagnetic electrodes and a SrTiO{sub 3} insulator

    SciTech Connect

    Kwon, C.; Jia, Q.X.; Fan, Y.; Hundley, M.F.; Reagor, D.W.; Hawley, M.E.; Peterson, D.E.

    1998-07-01

    The authors report the fabrication of ferromagnet-insulator-ferromagnet junction devices using a ramp-edge geometry based on (La{sub 0.7}Sr{sub 0.3})MnO{sub 3} ferromagnetic electrodes and a SrTiO{sub 3} insulator. The multilayer thin films were deposited using pulsed laser deposition and the devices were patterned using photolithography and ion milling. As expected from the spin-dependent tunneling, the junction magnetoresistance depends on the relative orientation of the magnetization in the electrodes. The maximum junction magnetoresistance (JMR) of 30% is observed below 300 Oe at low temperatures (T < 100 K).

  16. Effect of Quenching on Magnetoresistance Properties in the Pr 0.5Sr 0.5MnO 3 Perovskite Manganite

    NASA Astrophysics Data System (ADS)

    Boujelben, W.; Ellouze, M.; Cheikh-Rouhou, A.; Pierre, J.; Joubert, J. C.

    2002-05-01

    We report on the magnetization, resistivity and magnetoresistance (MR) measurements on polycrystalline Pr0.5Sr0.5MnO3. Quenching samples from 1400°C to room temperature in water (sample I) or in air (sample II) leads to different behaviors. Powder X-ray diffraction patterns for samples I and II could be indexed, respectively, in rhombohedral perovskite structure with R3c space group and in the orthorhombic one with Imma space group. Magnetization measurements show that both samples exhibit a paramagnetic-ferromagnetic transition at 280 K (sample I) and 265 K (sample II). At low temperature, sampleI presents a ferromagnetic spin-canted state, while sample II behaves as an antiferromagnet below 160 K. Resistivity and magnetoresistance studies show a net difference as a function of the quenching conditions.

  17. Pressure-induced colossal piezoresistance effect and the collapse of the polaronic state in the bilayer manganite (La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn2O7.

    PubMed

    Thiyagarajan, R; Manivannan, N; Arumugam, S; Esakki Muthu, S; Tamilselvan, N R; Sekar, C; Yoshino, H; Murata, K; Apostu, M O; Suryanarayanan, R; Revcolevschi, A

    2012-04-01

    We have investigated the effect of hydrostatic pressure as a function of temperature on the resistivity of a single crystal of the bilayer manganite (La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn(2)O(7). Whereas a strong insulating behaviour is observed at all temperatures at ambient pressure, a clear transition into a metallic-like behaviour is induced when the sample is subjected to a pressure (P) of ~1.0 GPa at T < 70 K. A huge negative piezoresistance ~10(6) in the low temperature region at moderate pressures is observed. When the pressure is increased further (5.5 GPa), the high temperature polaronic state disappears and a metallic behaviour is observed. The insulator to metal transition temperature exponentially increases with pressure and the distinct peak in the resistivity that is observed at 1.0 GPa almost vanishes for P > 7.0 GPa. A modification in the orbital occupation of the e(g) electron between 3d(x(2)-y(2)) and 3d(z(2)-r(2)) states, as proposed earlier, leading to a ferromagnetic double-exchange phenomenon, can qualitatively account for our data. PMID:22392884

  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. Structure, magnetic and magnetoresistance properties of Pr0.67Sr0.33MnO3 manganite oxide prepared by ball milling method

    NASA Astrophysics Data System (ADS)

    Chérif, W.; Ellouze, M.; Lehlooh, A.-F.; Elhalouani, F.; Mahmood, S. H.

    2012-07-01

    A sample of Pr0.67Sr0.33MnO3 nanoparticles was synthesized by the ball milling method. X-ray diffraction pattern of the sample showed orthorhombic system with Pnma space group. The average crystallite size of 110 nm was obtained by both Scanning Electron Microscopy and X-ray diffraction. Magnetic measurements showed para-to-ferromagnetic transition with a Curie temperature of TC=269 K. Electrical investigations showed that all our samples exhibit a semi-conducting behavior above TC and a metallic-like one at lower temperatures. The sample exhibited a large magnetoresistance of 30% at room temperature in an applied magnetic field of 2 T. The transport and the magnetic properties were interpreted in terms of the existence of magnetic polarons in the sample.

  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. 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.

  2. The structure of nanoscale polaron correlations in the layered manganites

    NASA Astrophysics Data System (ADS)

    Campbell, Branton

    2002-03-01

    Recent x-ray and neutron scattering experiments have uncovered nanoscale polaron correlations that play an essential role in the colossal magnetoresistive (CMR) behavior of the perovskite manganites. Short-range polaronic order decreases the charge-carrier mobility of the high-temperature paramagnetic state, and subsequently becomes unstable at the ferromagnetic transition, contributing to a pronounced resistivity decrease at T_C. In the bilayered perovskite system La_2-2xSr_1+2xMn_2O7 (0.3 < x < 0.5), weak x-ray diffuse scattering maxima reveal a one-dimensional incommensurate structural modulation with wavevector q = (0.3, 0, ± 1) and a correlation length of 10 to 30 Angstroms. A crystallographic analysis of the diffuse satellite intensities yields a longitudinal Jahn-Teller stretch mode suggestive of charge-density-wave fluctuations. Within the correlated regions, polaronic eg electrons form a striped pattern of occupied d(3x^2-r^2) orbitals. Dynamic polaron correlations of the zig-zag orbital type are also observed above TC and exhibit distinctly glassy behavior. These structures provide unique insights into the nature of strongly correlated polaronic systems. Collaborators: R. Osborn, D.N. Argyriou, S. Rosenkranz, L. Vasiliu-Doloc, J.F. Mitchell, S.K. Sinha, J.W. Lynn, C.D. Ling, Z. Islam, U. Ruett, and A. Berger. This work was supported by the U.S. DOE Office of Science contract No. W-31-109-ENG-38.

  3. Magnetic phase diagram of layered manganites in the highly doped regime.

    SciTech Connect

    Mitchell, J. F.; Ling, C. D.; Millburn, J. E.; Argyriou, D. N.; Berger, A.; Medarde, M.

    2000-11-02

    The naturally layered colossal magnetoresistive (CMR) manganites La{sub 2{minus}2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} exhibit an extremely varied range of magnetic and electronic behavior over a very narrow composition range between x = 0.3 and x = 0.5. The successful synthesis in our laboratories of compounds with nominally greater than 50 percent Mn{sup 4+} concentration has now allowed the study of this heretofore unexplored region of the phase diagram. Here we present detailed neutron diffraction measurements of these compounds with doping levels 0.5 < x <1.0. As predicted by simple theories, the type-A layered antiferromagnetic (AF) structure is found at x{approximately}0.5 and the type-G ''rocksalt'' AF structure at x = 1.0. Between these two extremes is found a C-type structure (ferromagnetic rods parallel to b coupled antiferromagnetically to all neighboring rods) stabilized by orbital ordering of y{sup 2} states. Also in this Mn{sup 4+}-rich regime is found a region in which no long-range magnetic order is observed. We discuss how semi-empirical models can explain the variety of magnetic structures and how structural trends as a function of doping corroborate the unifying notion of a shift from in-plane to axial orbital occupation as the Mn{sup 4+} concentration is decreased.

  4. 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.

  5. 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

  6. 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

  7. 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

  8. 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

  9. Synthesis, tailored microstructures and `colossal` magnetoresistance in oxide thin films

    SciTech Connect

    Krishnan, K.M.; Modak, A.R.; Ju, H.; Bandaru, P.

    1996-09-01

    We have grown La{sub 1-x}Sr{sub x}MnO{sub 3} films, using both pulsed laser deposition and a polymeric sol-gel route. These two growth techniques result in different microstructures, but in both cases the texture (epitaxy or polycrystallinity) can be controlled by choice of substrates and growth conditions. The crystallography and microstructure of these films were studied using XRD and high- resolution TEM. The magnetic/magnetotransport properties of these films are discussed in context of their growth and microstructural parameters.

  10. Integration of colossal magnetoresistors with GaAs

    NASA Astrophysics Data System (ADS)

    Khartsev, S. I.; Kim, J.-H.; Grishin, A. M.

    2005-10-01

    Colossal magnetoresistive (CMR) La 0.67Ca 0.33MnO 3 (LCMO) and La 0.67Sr 0.33MnO 3 (LSMO) films have been grown by pulsed laser deposition technique on GaAs(0 0 1) substrates buffered with epitaxial MgO layer. X-ray diffraction revealed strong c-axis out-of-plane orientation and strong in-plane texture of CMR/MgO bilayers on GaAs single crystal. The maximum temperature coefficient of resistivity TCR=9.0% K -1 at 223 K and 2.0% K -1 at 327 K, and the magnetoresistance Δ ρ/ ρ˜-7.95% kOe -1 and -1.47% kOe -1 have been achieved for LCMO/MgO/GaAs and LSMO/MgO/GaAs heteroepitaxial structures, respectively. Comparison with the test LCMO and LSMO films grown directly onto the bulk MgO(0 0 1) single crystal demonstrates the identity of LSMO/MgO/GaAs and LSMO/MgO films properties whereas the LCMO films grown on MgO buffered GaAs show lower transition temperature T=242 K compared to 253 K in LCMO/MgO.

  11. Extraordinary Magnetoresistance At Room Temperature In Non-Magnetic Narrow-Gap Semiconductor/Metal Composites

    NASA Astrophysics Data System (ADS)

    Solin, S. A.

    2001-03-01

    The magnetoresistance (MR) of a material object contains a physical contribution from the magnetic field dependence of the material parameters such as the mobility or carrier concentration and a geometric contribution from the dependence of the current path and output voltage on the sample shape and electrode configuration. To date, only two classes of magnetic materials, artificially layered metals which exhibit giant MR (GMR) and the manganite perovskites which exhibit colossal MR (CMR) have been considered serious candidates in the effort to improve the room temperature (RT) performance of MR sensors. For both of these classes, the physical MR dominates. In contrast, we have found that non-magnetic narrow-gap semiconductors containing patterned metallic inhomogeneities (shunts), exhibit RT geometric extraordinary MR (EMR) orders of magnitude larger than the physical MR of other materials. EMR in excess of 2000% at 0.05 Tesla and 3,000,000% at 5 T, respectively, has been observed in macroscopic ( ~ 1 mm) composite structures of InSb with patterned internal or external shunts.(S.A. Solin et al., Science 289), 1530 (2000).^,(T. Zhou, D.R. Hines and S.A. Solin, Appl. Phys. Lett., submitted.) We have been able to quantitatively account for the magnitude of the observed EMR as well as its dependence on the geometry (shape, size and placement of the shunt) using both analytic (Laplace equation with boundary conditions) and computational (Finite Element Analysis)(see the talk by L.R. Ram-Mohan et al., this conference) methods. The effect of scaling EMR structures to mesoscopic dimensions and the possible technological impact of EMR will be discussed.

  12. 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.

  13. 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.

  14. Room temperature magnetocaloric effect, critical behavior, and magnetoresistance in Na-deficient manganite La{sub 0.8}Na{sub 0.1}MnO{sub 3}

    SciTech Connect

    Khlifi, M. Dhahri, E.; Hlil, E. K.

    2014-05-21

    The La{sub 0.8}Na{sub 0.1}MnO{sub 3} oxide was prepared by the solid-state reaction and annealed in air. The X-ray diffraction data reveal that the sample is crystallized in a rhombohedral structure with R3{sup ¯}c space group. Magnetic study shows a second-order magnetic phase transition from ferromagnetic to paramagnetic state at the Curie temperature T{sub C} = 295 K. In addition, the magnetizations as a function of temperature and the magnetic field is used to evaluate the magnetic entropy change ΔS{sub M}. Then, we have deduced that the La{sub 0.8}Na{sub 0.1}MnO{sub 3} oxide has a large magnetocaloric effect at room temperature. Such effect is given by the maximum of the magnetic entropy change ΔS{sub Mmax} = 5.56, and by the Relative cooling power (RCP) factor which is equal to 235 under a magnetic field of 5 T. Moreover, the magnetic field dependence of the magnetic entropy change is used to determine the critical exponents β, γ, and δ which are found to be β = 0.495, γ = 1.083, and δ = 3.18. These values are consistent with the prediction of the mean field theory (β = 0.5, γ = 1, and δ = 3). Above all, the temperature dependence of electrical resistivity shows a metal–insulator transition at T{sub ρ}. The electrical resistivity decrease when we apply a magnetic field giving a magnetoresistance effect in the order of 60% at room temperature.

  15. Griffiths phase and the magnetic and transport properties of doped manganites

    SciTech Connect

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

    2012-07-15

    A phenomenological model is proposed to describe the magnetic and magnetoresistance properties of ferromagnetic manganites. This model is based on the methods used to describe hysteretic systems, takes into account phase separation effects, and assumes the transition of ferromagnetic manganites into the Griffiths phase at above the Curie temperature. This formalism makes it possible to describe the conducting properties of the systems in the temperature range from low temperatures to the Griffiths temperature (T{sub G}). This approach is used to qualitatively explain the experimental laws of the behavior of ferromagnetic manganites using the temperature and field dependences of the electrical resistivity and magnetization, the hysteretic properties, and the magnetoresistive effect (MRE) and to classify manganites in the magnitude of the MRE. The parameter that is responsible for the response of a system to thermal effects is the ratio of the maximum energy barrier separating various states of a system at zero temperature W{sub A}(0) to thermal fluctuation energy W{sub Cfl} at T{sub G}. The W{sub A}(0)/W{sub Cfl} ratio is found to determine the temperature range of the Griffiths phase. The relation between the magnitudes of the MRE and parameter W{sub A}(0)/W{sub Cfl} for a certain system is revealed. The behavior of the magnetization and electrical resistivity of manganites in the Griffiths phase is discussed.

  16. Effect of electric field and strain on the magnetic properties of phase separated manganites

    NASA Astrophysics Data System (ADS)

    Grant, Daniel M.

    Perovskite manganese oxide (manganites) have attracted research attention due to a wide variety of complex behaviors observed, including colossal responses to external perturbations. More recent work has focused on the competing ground states and the coexistence of magnetic and non-magnetic phases in manganites. Anisotropic resistance changes have been observed in high quality thin film manganites, possibly due to dielectrophoresis, upon application of an electric field. Dielectrophoresis is usually observed in fluid-like systems in an electric field but is surprisingly useful in explaining the transport properties of manganites due to the fluid-like behavior of competing phases. A main goal of this dissertation is to explore the role of magnetic interactions on the dielectrophoresis effects on ferromagnetic metallic regions in phase separated manganite thin films. The combined effect of electric and magnetic fields in these manganites could reveal a novel form of magnetoelectric effect. In one set of experiments, a magnetic field decreased the amount of time needed for the dielectrophoresis to lead to a large drop in the resistance along one direction, showing the importance of magnetic interactions in dielectrophoresis. In another set of experiments, breaking down the large resistance of a manganite sample produced a small change in coercive field, further confirming the relationship between electric and magnetic effects in manganites. However, the largest effect on the magnetic properties of the thin films was from confinement of the competing phases in micrometer scale structures fabricated on the thin films. Coercive field increases of about 100- 400% were observed in a certain range of film thicknesses. To analyze such behavior in manganites, high quality thin films of the phase-separated manganite (La1-xPrx)1-yCa yMnO3 (LPCMO) were grown on NdGaO3 (NGO) substrates using pulsed laser deposition. Mangetotransport, magnetization, and scanning probe microscopy

  17. The nonlinear influence of an electric field on phase transitions in ferromagnetic semiconductors: Lanthanum manganite

    NASA Astrophysics Data System (ADS)

    Povzner, A. A.; Volkov, A. G.

    2016-04-01

    We investigate nonequilibrium processes of self-heating induced by electric current in ferromagnetic semiconductors exhibiting colossal magnetoresistance (CMR) in the vicinity of the Curie temperature. The heat balance equation is solved taking into consideration localized states that appear as a result of scattering from magnetic inhomogeneities and are characterized by a percolation threshold proportional to the amplitude of spin fluctuations. The appearance of N-shaped current-voltage characteristics and hysteresis in the dependence of magnetization on electric potential difference, which are caused by the emergence of a "hot" (with respect to internal temperature) semiconductor paramagnetic phase, is revealed in the steady-state regime. The possibility of suppression of the effect of colossal magnetoresistance with increasing potential difference is indicated. The onset of self-oscillation of current and magnetization with decreasing transverse dimensions of the sample is demonstrated.

  18. Magnetic anisotropy in strained manganite films and bicrystal junctions

    NASA Astrophysics Data System (ADS)

    Demidov, V. V.; Ovsyannikov, G. A.; Petrzhik, A. M.; Borisenko, I. V.; Shadrin, A. V.; Gunnarsson, R.

    2013-04-01

    Transport and magnetic properties of La0.67Sr0.33MnO3 (LSMO) manganite thin films and bicrystal junctions were investigated. Epitaxial manganite films were grown on SrTiO3, LaAlO3, NdGaO3 (NGO), and (LaAlO3)0.3 + (Sr2AlTaO6)0.7 substrates, and their magnetic anisotropy were determined by two independent techniques of magnetic resonance spectroscopy. It was demonstrated that by using these techniques, a small (0.3%) anisotropy of crystal structure at the (110) surface plane of the orthorhombic NGO substrate leads to uniaxial magnetic anisotropy of the films in the plane of the substrate at least at the room temperature. It was found that on vicinal NGO substrates, the value of magnetic anisotropy strength can be varied in the range 100-200 Oe at T = 295 K by changing the substrate vicinal angle from 0° to 25°. Measurement of the magnetic anisotropy of manganite bicrystal junction demonstrated the presence of two ferromagnetic spin subsystems for both types of bicrystal boundaries with tilting of basal plane of manganite tilted bicrystal (TB-junction) and with rotation of crystallographic axes (RB-junction) used for comparison. The magnetoresistance of TB-junctions increases with decreasing temperature and the misorientation angle. Variation of bicrystal misorientation angle does not lead to change of misorientation of easy magnetic axes in the film parts forming TB-junction. Analysis of the voltage dependencies of bicrystal junction conductivity show that the low value of the magnetoresistance for the LSMO bicrystal junctions can be caused by two scattering mechanisms. The first one is the spin-flip of spin-polarized carriers due to the strong electron-electron interactions in a disordered layer at the bicrystal boundary at low temperatures and the second one is spin-flip by antiferromagnetic magnons at high temperatures.

  19. Quantum magnetoresistance

    SciTech Connect

    Abrikosov, A.A.

    1998-08-01

    An explanation is proposed of the unusual magnetoresistance, linear in magnetic field and positive, observed recently in nonstoichiometric silver chalcogenides. The idea is based on the assumption that these substances are basically gapless semiconductors with a linear energy spectrum. Most of the excess silver atoms form metallic clusters which are doping the remaining material to a very small carrier concentration, so that even in a magnetic field as low as 10 Oe, only one Landau band participates in the conductivity. {copyright} {ital 1998} {ital The American Physical Society}

  20. Local lattice distortions and thermal transport in perovskite manganites

    SciTech Connect

    Cohn, J.L.; Neumeier, J.J.; Popoviciu, C.P.; McClellan, K.J.; Leventouri, T.

    1997-10-01

    Measurements of thermal conductivity versus temperature and magnetic field are reported for perovskite manganites that exhibit ferromagnetic (FM), charge-ordering (CO), antiferromagnetic, and/or structural phase transitions. The data reveal a dominant lattice contribution to the heat conductivity with {kappa}{approximately}1{minus}2 W/mK near room temperature. The rather low values, implying a phonon mean free path on the order of a lattice spacing, are shown to correlate with static local distortions of the MnO{sub 6} octahedra. Modifications of the local structure are responsible for abrupt anomalies in the zero-field {kappa} at the FM, CO, and structural transitions, and for colossal magnetothermal resistance near the FM transition. {copyright} {ital 1997} {ital The American Physical Society}

  1. 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.

  2. Magnetocaloric-transport properties correlation in doped manganites

    NASA Astrophysics Data System (ADS)

    Mohamed, Abd El-Moez A.; Hernando, B.; Ahmed, A. M.

    2016-05-01

    This investigation is interested in studying the relation between magnetocaloric effect and transport properties in La0.7Ba0.3MnO3 manganite compound. The resistivity shows a metal-semiconductor transition at Tms temperature near to its reported Curie temperature (Tc). Magnetic field application decreases resistivity and increases Tms towards higher temperatures. The magnetoresistance shows a peak around Tc and increases in value with the applied magnetic field. A similar behavior has been observed between magnetic entropy change (ΔS), resistivity and magnetoresistance around Tc, this is attributed to the spin order/disorder feature that plays a main role in the magnetocaloric-transport correlation. In spite of this similarity, the correspondence among the experimental ΔS and ΔS based resistivity calculations is missing because of lattice polarons effect on resistivity as a result of the electron-phonon interaction. The magnetocaloric-magnetoresistance relation is also studied and results show the contribution of additional factors in the magnetoresistance mechanism other than spin disorder suppression as Jahn-Teller effect and electronic phase separation.

  3. 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. PMID:26306543

  4. 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.

  5. 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

  6. Intrinsic inhomogeneities of low-doped lanthanum manganites in the paramagnetic temperature range

    SciTech Connect

    Solin, N. I.

    2012-01-15

    The nature of the electrical resistivity for low-doped lanthanum manganites is elucidated. The electrical resistivity is described by the Efros-Shklovskii law (ln{rho} {radical} (T{sub 0}/T){sup -1/2}, where T{sub 0} {radical} 1/R{sub ls}) in the temperature range from T* Almost-Equal-To 300 K Almost-Equal-To T{sub C} (T{sub C} is the Curie temperature for conducting manganites) to their T{sub C} and is explained by the tunneling of carriers between localized states. The magnetoresistance is explained by a change in the size of localized states R{sub ls} in a magnetic field. The patterns of change in R{sub ls} with temperature and magnetic field strength determined from magnetotransport properties are satisfactorily described in the model of phase separation into small-radius metallic droplets in a paramagnetic matrix. The sizes R{sub ls} and their temperature dependence have been estimated through magnetic measurements. The results confirm the existence of a Griffith phase. The intrinsic inhomogeneities produced by thermodynamic phase separation determine the electrical resistivity and magnetoresistance of lanthanum manganites.

  7. Controlled mechnical modification of manganite surface with nanoscale resolution.

    PubMed

    Kelly, Simon J; Kim, Yunseok; Eliseev, Eugene; Morozovska, Anna; Jesse, Stephen; Biegalski, Michael D; Mitchell, J F; Zheng, H; Aarts, J; Hwang, Inrok; Oh, Sungtaek; Choi, Jin Sik; Choi, Taekjib; Park, Bae Ho; Kalinin, Sergei V; Maksymovych, Peter

    2014-11-28

    We investigated the surfaces of magnetoresistive manganites, La(1-x)Ca(x)MnO3 and La(2-2x)Sr(1+2x)Mn2O7, using a combination of ultrahigh vacuum conductive, electrostatic and magnetic force microscopy methods. Scanning as-grown film with a metal tip, even with zero applied bias, was found to modify the surface electronic properties such that in subsequent scans, the conductivity is reduced below the noise level of conductive probe microscopy. Scanned areas also reveal a reduced contact potential difference relative to the pristine surface by ∼0.3 eV. We propose that contact-pressure of the tip modifies the electrochemical potential of oxygen vacancies via the Vegard effect, causing vacancy motion and concomitant changes of the electronic properties. PMID:25380080

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

    SciTech Connect

    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.

  9. Colossal magnetocapacitance effect at room temperature

    NASA Astrophysics Data System (ADS)

    Bishchaniuk, T. M.; Grygorchak, I. I.

    2014-05-01

    First nano-hybridized clathrate/cavitant structure of hierarchical architecture was synthesized. The results of investigations of the properties of initial nanoporous silica matrices MCM-41, with encapsulated in its pores of β-cyclodextrin in cavitand and cavitat (with FeSO4) states and change at room temperature in a constant magnetic field intensity of 2.75 kOe, have been presented. Phenomenon of enormous magnetocapacitance and giant negative variable-current magnetoresistance has been discovered.

  10. Transport properties and electroresistance of a manganite based heterostructure: role of the manganite-manganite interface.

    PubMed

    Gadani, Keval; Dhruv, Davit; Joshi, Zalak; Boricha, Hetal; Rathod, K N; Keshvani, M J; Shah, N A; Solanki, P S

    2016-06-29

    In this paper, we report the results of the investigations on the transport properties performed across the manganite-manganite interface in the LaMnO3-δ/La0.7Ca0.3MnO3/LaAlO3 (LMO/LCMO/LAO) heterostructure. The bilayered heterostructure was synthesized by a low cost and simple chemical solution deposition (CSD) method by employing the acetate precursor route. The same LMO/LCMO/LAO heterostructure was also grown using the dry metal oxide chemical vapor deposition (CVD) method and the results of transport characterization have been compared on the basis of wet and dry chemical methods used. XRD Φ-scan measurements were carried out to verify the structural quality and crystallographic orientations of LMO and LCMO manganite layers, for both wet and dry chemical method grown heterostructures. For wet and dry chemical methods, the temperature dependent resistance of the LMO/LCMO interface suggests the metallic nature. The asymmetric I-V curves collected at different temperatures show normal diode characteristics which get transformed to backward diode characteristics at high temperatures under high applied voltages at Vtr for both the methods. The values of Vtr are strongly dependent on the chemical method used. I-V data have been fitted using the Simmons model at different temperatures and discussed in terms of the spin-flip scattering mechanism for both wet and dry chemical method grown heterostructures. The electric field dependent electroresistance (ER) behavior of the presently studied LMO/LCMO manganite-manganite interface, grown using wet and dry chemical methods, has been understood on the basis of complex mechanisms including charge injection, formation of the depletion region, the tunneling effect, thermal processes and junction breakdown and their dependence on the applied electric field, field polarity and temperature studied. PMID:27315551

  11. 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.

  12. Large negative magnetoresistance in reactive sputtered polycrystalline GdN{sub x} films

    SciTech Connect

    Mi, W. B.; Duan, X. F.; Zhang, X. J.; Bai, H. L.; Guo, Z. B.

    2013-06-03

    Polycrystalline ferromagnetic GdN{sub x} films were fabricated at different N{sub 2} flow rates (f{sub N2}) to modify N-vacancy concentration so as to study its influence on electrotransport. Metal-semiconductor transition appears at Curie temperature (T{sub C}) of {approx}40 K. Temperature-dependent magnetoresistance (MR) shows a peak at T{sub C}. The films at f{sub N2} = 5, 10, 15, and 20 sccm show MR of -38%, -42%, -46%, and -86% at 5 K and 50 kOe, respectively. Above 15 K, MR is from colossal MR and from both colossal and tunneling MR below 15 K. The enhanced MR at f{sub N2} = 20 sccm is attributed to large spin polarization of half-metallicity in GdN{sub x} with low N vacancies.

  13. 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.

  14. Pulsed magnetic field measurement system based on colossal magnetoresistance-B-scalar sensors for railgun investigation.

    PubMed

    Stankevič, T; Medišauskas, L; Stankevič, V; Balevičius, S; Żurauskienė, N; Liebfried, O; Schneider, M

    2014-04-01

    A high pulsed magnetic field measurement system based on the use of CMR-B-scalar sensors was developed for the investigations of the electrodynamic processes in electromagnetic launchers. The system consists of four independent modules (channels) which are controlled by a personal computer. Each channel is equipped with a CMR-B-scalar sensor connected to the measurement device-B-scalar meter. The system is able to measure the magnitude of pulsed magnetic fields from 0.3 T to 20 T in the range from DC up to 20 kHz independently of the magnetic field direction. The measurement equipment circuit is electrically separated from the ground and shielded against low and high frequency electromagnetic noise. The B-scalar meters can be operated in the presence of ambient pulsed magnetic fields with amplitudes up to 0.2 T and frequencies higher than 1 kHz. The recorded signals can be transmitted to a personal computer in a distance of 25 m by means of a fiber optic link. The system was tested using the electromagnetic railgun RAFIRA installed at the French-German Research Institute of Saint-Louis, France. PMID:24784635

  15. 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

  16. 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.

  17. 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.

  18. Optical evidence of quantum rotor orbital excitations in orthorhombic manganites

    NASA Astrophysics Data System (ADS)

    Kovaleva, N. N.; Kugel, K. I.; Potůček, Z.; Kusmartseva, O. E.; Goryachev, N. S.; Bryknar, Z.; Demikhov, E. I.; Trepakov, V. A.; Dejneka, A.; Kusmartsev, F. V.; Stoneham, A. M.

    2016-05-01

    In magnetic compounds with Jahn-Teller (JT) ions (such as Mn3+ or Cu2+), the ordering of the electron or hole orbitals is associated with cooperative lattice distortions. There the role of JT effect, although widely recognized, is still elusive in the ground state properties. Here we discovered that, in these materials, there exist excitations whose energy spectrum is described in terms of the total angular momentum eigenstates and is quantized as in quantum rotors found in JT centers. We observed features originating from these excitations in the optical spectra of a model compound LaMnO3 using ellipsometry technique. They appear clearly as narrow sidebands accompanying the electron transition between the JT split orbitals at neighboring Mn3+ ions, displaying anomalous temperature behavior around the Néel temperature T N ≈ 140 K. We present these results together with new experimental data on photoluminescence found in LaMnO3, which lend additional support to the ellipsometry implying the electronic-vibrational origin of the quantum rotor orbital excitations. We note that the discovered orbital excitations of quantum rotors may play an important role in many unusual properties observed in these materials upon doping, such as high-temperature superconductivity and colossal magnetoresistance.

  19. Giant semiclassical magnetoresistance in high mobility TaAs2 semimetal

    NASA Astrophysics Data System (ADS)

    Wu, Desheng; Liao, Jian; Yi, Wei; Wang, Xia; Li, Peigang; Weng, Hongming; Shi, Youguo; Li, Yongqing; Luo, Jianlin; Dai, Xi; Fang, Zhong

    2016-01-01

    We report the observation of colossal positive magnetoresistance (MR) in single crystalline, high mobility TaAs2 semimetal. The excellent fit of MR by a single quadratic function of the magnetic field B over a wide temperature range (T = 2-300 K) suggests the semiclassical nature of the MR. The measurements of Hall effect and Shubnikov-de Haas oscillations, as well as band structure calculations, suggest that the giant MR originates from the nearly perfectly compensated electrons and holes in TaAs2. The quadratic MR can even exceed 1 200 000% at B = 9 T and T = 2 K, which is one of the largest values among those of all known semi-metallic compounds, including the very recently discovered WTe2 and NbSb2. The giant positive magnetoresistance in TaAs2 not only has a fundamentally different origin from the negative colossal MR observed in magnetic systems but also provides a nice complemental system that will be beneficial for applications in magnetoelectronic devices.

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

    NASA Astrophysics Data System (ADS)

    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

    2016-04-01

    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.

  1. 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

  2. Imaging of inhomogeneous magnetization and currents coupled with anomalous transport properties in manganites

    NASA Astrophysics Data System (ADS)

    Tokunaga, M.; Song, H.; Tokunaga, Y.; Tamegai, T.

    2006-05-01

    Using magneto-optical imaging technique, real-space distributions of magnetic fields are visualized in images of a polarized-light microscope. Application of this technique to crystals of (La1-z Prz )0.7Ca0.3MnO3 (z = 0.7) and Nd0.5Ca0.5Mn1-y Cry O3 (y = 0.03) revealed inhomogeneous magnetization and currents in the phase-separated states into ferromagnetic metal and antiferromagnetic insulator. Increase of the transport current switches this inhomogeneous current flow to homogeneous one concomitantly with abrupt increase in resistivity. Using magnetic field dependence of this switching phenomenon, operation fields for colossal magnetoresistance effects can be significantly reduced. Empirical relation between the magnitude of bias currents and transition fields is provided.

  3. Magnetoresistance of Au films

    SciTech Connect

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

    2014-01-01

    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.

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. Electrical, thermal and magnetic studies on Bi-substituted LSMO manganites

    NASA Astrophysics Data System (ADS)

    Daivajna, Mamatha D.; Rao, Ashok; Okram, G. S.

    2015-08-01

    In the present investigation detailed electrical, magnetic and thermoelectric measurements on Bi-doped L0.6-xBixSr0.4MnO3 (0≤x≤0.3) manganites have been done. All the samples are single phased. The metal-insulator transition temperatures (TMI) as well as the Curie temperature (TC) are both found to decrease with Bi-content. Magneto-resistance (MR) data shows that MR (%) increases with Bi-content thereby showing it can be used in magnetic memory based devices. Resistivity data shows that small polaron hopping (SPH) model is valid in high temperature regime. Low temperature resistivity data depicts that electron-electron scattering is mainly responsible for the conduction mechanism. High temperature thermoelectric power (TEP) data reaffirms the validity of SPH model.

  11. 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

  12. 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.

  13. 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.

  14. Anomalous oscillatory magnetoresistance in superconductors

    NASA Astrophysics Data System (ADS)

    Kunchur, Milind N.; Dean, Charles L.; Ivlev, Boris I.

    2016-08-01

    We report oscillatory magnetoresistance in various superconducting films, with a magnetic-field period Δ B ˜0.1 T that is essentially independent of sample dimensions, temperature, transport current, and the magnitude and orientation of the magnetic field, including magnetic fields oriented parallel to the film plane. The characteristics of these oscillations seem hard to reconcile with previously established mechanisms for oscillations in magnetoresistance, suggesting the possibility of another type of physical origin.

  15. Colossal anisotropy of the magnetic properties of doped lithium nitrodometalates

    NASA Astrophysics Data System (ADS)

    Antropov, V. P.; Antonov, V. N.

    2014-09-01

    We present a first-principles investigation of the electronic structure and physical properties of doped lithium nitridometalates Li2(Li1-xMx)N (LiMN) with M = Cr, Mn, Fe, Co, and Ni. The diverse properties include the equilibrium magnetic moments, magneto-crystalline anisotropy, magneto-optical Kerr spectra, and x-ray magnetic circular dichroism. We explain the colossal magnetic anisotropy in LiFeN by its unique electronic structure which ultimately leads to a series of unusual physical properties. The most unique property is a complete suppression of relativistic effects and freezing of orbital moments for in-plane orientation of the magnetization. This leads to the colossal spatial anisotropy of many magnetic properties including energy, Kerr, and dichroism effects. LiFeN is identified as an ultimate single-ion anisotropy system where a nearly insulating state can be produced by a spin orbital coupling alone. A very nontrivial strongly fluctuating and sign changing character of the magnetic anisotropy with electronic 3d-atomic doping is predicted theoretically. A large and highly anisotropic Kerr effect due to the interband transitions between atomic-like Fe 3d bands is found for LiFeN. A giant anisotropy of the x-ray magnetic circular dichroism for the Fe K spectrum and a very weak one for the Fe L2,3 spectra in LiFeN are also predicted.

  16. 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.

  17. Thermodynamic modeling of phase separation in manganites

    NASA Astrophysics Data System (ADS)

    Sacanell, J.; Parisi, F.; Campoy, J. C. P.; Ghivelder, L.

    2006-01-01

    We present a phenomenological model based on the thermodynamics of the phase separated state of manganites, accounting for its static and dynamic properties. Through calorimetric measurements on La0.225Pr0.4Ca0.375MnO3 the low temperature free energies of the coexisting ferromagnetic and charge ordered phases are evaluated. The phase separated state is modeled by free energy densities uniformly spread over the sample volume. The calculations contemplate the out of equilibrium features of the coexisting phase regime, to allow a comparison between magnetic measurements and the predictions of the model. A phase diagram including the static and dynamic properties of the system is constructed, showing the existence of blocked and unblocked regimes which are characteristics of the phase separated state in manganites.

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. Evolution of microstructure and magnetoresistive properties of (La0.65Sr0.35)0.8Mn1.2O3±Δ ceramics sintered at 800-1500 °C

    NASA Astrophysics Data System (ADS)

    Novokhatska, A.; Akimov, G.; Prylypko, S.; Revenko, Yu.; Burkhovetsky, V.

    2013-05-01

    An effect of microstructure on magnetoresistive properties of manganite ceramics (La0.65Sr0.35)0.8Mn1.2O3±Δ with superstoichiometric manganese has been studied after sintering in the temperature range of 800-1500 °C. Increase in sintering temperature to 1400 °C, an enormous growth of grains, densification of material, and rise in magnetoresistance peak from 1% to 4.8% are observed. At the same time, sintering at 1500 °C leads to a sharp increase in the grain size more than 100 μm, release of excess manganese on grain boundaries, and almost two times magnetoresistance peak rise. We propose that such radical changes are due to the presence of superstoichiometric manganese which plays a crucial role in the formation of ceramics microstructure and properties.

  3. 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. PMID:26207324

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Giant magnetoresistance in nanogranular magnets.

    SciTech Connect

    Glatz, A.; Beloborodov, I. S.; Vinokur, V. M.; Materials Science Division; Univ. of Chicago

    2008-05-01

    We study the giant magnetoresistance of nanogranular magnets in the presence of an external magnetic field and finite temperature. We show that the magnetization of arrays of nanogranular magnets has hysteretic behavior at low temperatures leading to a double peak in the magnetoresistance which coalesces at high temperatures into a single peak. We numerically calculate the magnetization of magnetic domains and the motion of domain walls in this system using a combined mean-field approach and a model for an elastic membrane moving in a random medium, respectively. From the obtained results, we calculate the electric resistivity as a function of magnetic field and temperature. Our findings show excellent agreement with various experimental data.

  9. 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

  10. 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

  11. 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.

  12. 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.

  13. Kinetic effects in manganites La{sub 1-x}Ag{sub y}MnO{sub 3} (y {<=} x)

    SciTech Connect

    Kamilov, I. K.; Gamzatov, A. G. Aliev, A. M.; Batdalov, A. B.; Abdulvagidov, Sh. B.; Mel'nikov, O. V.; Gorbenko, O. Yu.; Kaul', A. R.

    2007-10-15

    We have measured the resistivity, magnetoresistance, and thermopower of ceramic manganite samples La{sub 1-x}Ag{sub y}MnO{sub 3} (y {<=} x) doped with silver as functions of temperature (4.2-350 K) and magnetic field (up to 26 kOe). A metal-insulator phase transition is observed in all investigated samples at temperatures close to room temperature. The behavior of the resistivity and thermopower in the high-temperature paramagnetic region is interpreted using the concept of small radius polaron; the activation energy decreases with increasing doping level. The resistivity in the low-temperature ferromagnetic region is approximated by the expression {rho}{sub FM}(T) = {rho}{sub 0} + AT{sup 2} + BT{sup 4.5} presuming the existence of electron-electron and electron-magnon interactions. A resistivity minimum and a strong magnetoresistive effect are observed at low temperatures. The latter effect is associated with scattering of charge carriers at grain boundaries, which are antiferromagnetically ordered relative to one another. The temperature dependence of thermopower in the magnetically ordered phase is described in the framework of a model taking into account the drag of charge carriers by magnons.

  14. Significant enhancement of magnetoresistance with the reduction of particle size in nanometer scale.

    PubMed

    Das, Kalipada; Dasgupta, P; Poddar, A; Das, I

    2016-01-01

    The Physics of materials with large magnetoresistance (MR), defined as the percentage change of electrical resistance with the application of external magnetic field, has been an active field of research for quite some times. In addition to the fundamental interest, large MR has widespread application that includes the field of magnetic field sensor technology. New materials with large MR is interesting. However it is more appealing to vast scientific community if a method describe to achieve many fold enhancement of MR of already known materials. Our study on several manganite samples [La(1-x)Ca(x)MnO3 (x = 0.52, 0.54, 0.55)] illustrates the method of significant enhancement of MR with the reduction of the particle size in nanometer scale. Our experimentally observed results are explained by considering model consisted of a charge ordered antiferromagnetic core and a shell having short range ferromagnetic correlation between the uncompensated surface spins in nanoscale regime. The ferromagnetic fractions obtained theoretically in the nanoparticles has been shown to be in the good agreement with the experimental results. The method of several orders of magnitude improvement of the magnetoresistive property will have enormous potential for magnetic field sensor technology. PMID:26837285

  15. Significant enhancement of magnetoresistance with the reduction of particle size in nanometer scale

    NASA Astrophysics Data System (ADS)

    Das, Kalipada; Dasgupta, P.; Poddar, A.; Das, I.

    2016-02-01

    The Physics of materials with large magnetoresistance (MR), defined as the percentage change of electrical resistance with the application of external magnetic field, has been an active field of research for quite some times. In addition to the fundamental interest, large MR has widespread application that includes the field of magnetic field sensor technology. New materials with large MR is interesting. However it is more appealing to vast scientific community if a method describe to achieve many fold enhancement of MR of already known materials. Our study on several manganite samples [La1-xCaxMnO3 (x = 0.52, 0.54, 0.55)] illustrates the method of significant enhancement of MR with the reduction of the particle size in nanometer scale. Our experimentally observed results are explained by considering model consisted of a charge ordered antiferromagnetic core and a shell having short range ferromagnetic correlation between the uncompensated surface spins in nanoscale regime. The ferromagnetic fractions obtained theoretically in the nanoparticles has been shown to be in the good agreement with the experimental results. The method of several orders of magnitude improvement of the magnetoresistive property will have enormous potential for magnetic field sensor technology.

  16. Significant enhancement of magnetoresistance with the reduction of particle size in nanometer scale

    PubMed Central

    Das, Kalipada; Dasgupta, P.; Poddar, A.; Das, I.

    2016-01-01

    The Physics of materials with large magnetoresistance (MR), defined as the percentage change of electrical resistance with the application of external magnetic field, has been an active field of research for quite some times. In addition to the fundamental interest, large MR has widespread application that includes the field of magnetic field sensor technology. New materials with large MR is interesting. However it is more appealing to vast scientific community if a method describe to achieve many fold enhancement of MR of already known materials. Our study on several manganite samples [La1−xCaxMnO3 (x = 0.52, 0.54, 0.55)] illustrates the method of significant enhancement of MR with the reduction of the particle size in nanometer scale. Our experimentally observed results are explained by considering model consisted of a charge ordered antiferromagnetic core and a shell having short range ferromagnetic correlation between the uncompensated surface spins in nanoscale regime. The ferromagnetic fractions obtained theoretically in the nanoparticles has been shown to be in the good agreement with the experimental results. The method of several orders of magnitude improvement of the magnetoresistive property will have enormous potential for magnetic field sensor technology. PMID:26837285

  17. 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.

  18. 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}.

  19. 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.

  20. Designing new ferrite/manganite nanocomposites

    NASA Astrophysics Data System (ADS)

    Muscas, G.; Anil Kumar, P.; Barucca, G.; Concas, G.; Varvaro, G.; Mathieu, R.; Peddis, D.

    2016-01-01

    Two kinds of nanocomposites of transition metal oxides were synthesized and investigated. Each nanocomposite comprises nanoparticles of La0.67Ca0.33MnO3 and CoFe2O4 in similar volume fractions, however arranged with different morphologies. The temperature-dependent magnetic and electrical properties of the two systems are found to greatly differ, suggesting different degrees of interaction and coupling of their constituents. This is confirmed by magnetic field-dependent experiments, which reveal contrasted magnetization reversal and magnetoresistance in the systems. We discuss this morphology-physical property relationship, and the possibility to further tune the magnetism and magneto-transport in such nanocomposites.Two kinds of nanocomposites of transition metal oxides were synthesized and investigated. Each nanocomposite comprises nanoparticles of La0.67Ca0.33MnO3 and CoFe2O4 in similar volume fractions, however arranged with different morphologies. The temperature-dependent magnetic and electrical properties of the two systems are found to greatly differ, suggesting different degrees of interaction and coupling of their constituents. This is confirmed by magnetic field-dependent experiments, which reveal contrasted magnetization reversal and magnetoresistance in the systems. We discuss this morphology-physical property relationship, and the possibility to further tune the magnetism and magneto-transport in such nanocomposites. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07572f

  1. Magnetoresistance Anisotropy in WTe2

    NASA Astrophysics Data System (ADS)

    Thoutam, Laxman Raju; Wang, Yonglei; Xiao, Zhili; Das, Saptarshi; Luican Mayer, Adina; Divan, Ralu; Crabtree, George W.; Kwok, Wai Kwong

    We report the angle dependence of the magnetoresistance in WTe2. Being a layered material, WTe2 is considered to be electronically two-dimensional (2D). Our results demonstrate that it is in fact 3D with an anisotropy of effective mass as small as 2. We measured the magnetic field dependence of the sample resistance R(H) at various angles between the applied magnetic field with respect to the c-axis of the crystal and found that they can be scaled based on the mass anisotropy, which changes from ~2 to ~5 with decreasing temperature in the Fermi liquid state. We will also discuss the origin of the turn-on temperature behavior in this material.

  2. Competing Mechanisms in Organic Magnetoresistance

    NASA Astrophysics Data System (ADS)

    Koopmans, Bert

    2013-03-01

    A surprisingly large ``organic magnetoresistance'' (OMAR) has been found in both polymers and small molecule organic semiconductors at relatively small applied magnetic fields (~ 5 mT) and at room temperature. Unlike spin-injection devices, where the occurrence of a finite spin polarization of the current is essential for measuring a finite magnetoresistance, OMAR is generally considered to be due to spin correlations between spin carrying particles in the organic material. Although the microscopic mechanisms of hyperfine field induced spin mixing are relatively well understood, it is still intensively debated which particles are involved and how they can affect the current in such a drastic manner. In this presentation recent developments and new insights as to the underlying physics are discussed. Quantitative models will be introduced, based on different pairs of particles and mechanisms, and giving rise to effects at a variety of field scales. It will be discussed how specific device physics causes a non-trivial relation between microscopic spin-dependent reactions and macroscopic device behaviour. Finally, it will be shown how comprehensive studies on especially engineered organic systems, including polymer-fullerene blends and molecular doping, can be used to pinpoint the relevance of different mechanisms in the complementary regimes. The experimentally observed linewidth, sign and amplitude of both ``high-field'' (>100 mT) and ``low-field'' (~ 5 mT) effects, as well as their bias voltage dependence display very pronounced features as a function of fullerene doping. They provide unique fingerprints for which mechanism is of relevance. After careful analysis, this allows for identification of three earlier proposed mechanisms, involving exciton-charge, electron-hole and bipolaron (polarons of like charge) reactions. Present activities are aiming at using this insight for tailoring OMAR response by design.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Enhanced ordering temperatures in antiferromagnetic manganite superlattices.

    SciTech Connect

    May, S. J.; Ryan, P. J.; Robertson, J. L.; Kim, J.-W.; Santos, T. S.; Karapetrova, E.; Zaresty, J. L.; Zhai, X.; te Velthuis, S. G. E.; Eckstein, J. N.; Bader, S. D.; Bhattacharya, A.; Iowa State Univ.; ORNL; Univ. of Illinois

    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 through digital-synthesis techniques can dramatically enhance the antiferromagnetic ordering temperatures of manganite films. Cation-ordered (LaMnO{sub 3}){sub m}/(SrMnO{sub 3}){sub 2m} superlattices show Neel temperatures (TN) that are the highest of any La{sub 1-x}Sr{sub x}MnO{sub 3} compound, {approx}70 K greater than compositionally equivalent randomly doped La{sub 1/3}Sr{sub 2/3}MnO{sub 3}. The antiferromagnetic order is A-type, consisting of in-plane double-exchange-mediated ferromagnetic sheets coupled antiferromagnetically along the out-of-plane direction. Through 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. Designing new ferrite/manganite nanocomposites.

    PubMed

    Muscas, G; Anil Kumar, P; Barucca, G; Concas, G; Varvaro, G; Mathieu, R; Peddis, D

    2016-01-28

    Two kinds of nanocomposites of transition metal oxides were synthesized and investigated. Each nanocomposite comprises nanoparticles of La0.67Ca0.33MnO3 and CoFe2O4 in similar volume fractions, however arranged with different morphologies. The temperature-dependent magnetic and electrical properties of the two systems are found to greatly differ, suggesting different degrees of interaction and coupling of their constituents. This is confirmed by magnetic field-dependent experiments, which reveal contrasted magnetization reversal and magnetoresistance in the systems. We discuss this morphology-physical property relationship, and the possibility to further tune the magnetism and magneto-transport in such nanocomposites. PMID:26697925

  9. 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.

  10. 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.

  11. Magnetoresistance in Boron Carbide junctions

    NASA Astrophysics Data System (ADS)

    Day, Ellen; Sokolov, A.; Baruth, A.; Robertson, B. W.; Adenwalla, S.

    2007-03-01

    The properties of thin insulator layers are crucial to the performance of magnetic tunnel junctions. Commercial requirements are a device with a high tunnel magnetoresistance (TMR) with low cost and high stability. At present the vast majority of barriers are made from amorphous Al2O3 and crystalline MgO. The TMR value depends not only on the spin-dependent electronic structure of the electrodes, but on the metal-insulator interface. Oxide-type barriers may suffer from local vacancies and other type of defects, resulting in oxygen diffusion, making the TMR value unstable with time. We present TMR results obtained on a non-oxide barrier, boron carbide (B10C2) for applications in magnetic tunnel junctions. This low Z inorganic material can be grown by plasma enhanced chemical vapor deposition (PECVD) without pinholes in the ultra thin film regime. PECVD grown boron carbide is an excellent dielectric with resistivities in the range of 10^7 ohm-cm, with a band gap that can be adjusted from 0.7 eV to 1.9 eV by altering the boron to carbon ratio and to band gap values well above 2.7 eV by adding phosphorus. This creates a unique opportunity for experimental study of a broad spectrum of phenomena, related to the dielectric properties of the barrier.

  12. Tunneling anisotropic magnetoresistance in La2/3Sr1/3MnO3/LaAlO3/Pt tunnel junctions

    NASA Astrophysics Data System (ADS)

    Galceran, R.; Balcells, Ll.; Pomar, A.; Konstantinović, Z.; Bagués, N.; Sandiumenge, F.; Martínez, B.

    2016-04-01

    The magnetotransport properties of La2/3Sr1/3MnO3(LSMO)/ LaAlO3(LAO)/Pt tunneling junctions have been analyzed as a function of temperature and magnetic field. The junctions exhibit magnetoresistance (MR) values of about 37%, at H=90 kOe at low temperature. However, the temperature dependence of MR indicates a clear distinct origin than that of conventional colossal MR. In addition, tunneling anisotropic MR (TAMR) values around 4% are found at low temperature and its angular dependence reflects the expected uniaxial anisotropy. The use of TAMR response could be an alternative of much easier technological implementation than conventional MTJs since only one magnetic electrode is required, thus opening the door to the implementation of more versatile devices. However, further studies are required in order to improve the strong temperature dependence at the present stage.

  13. 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

  14. 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.

  15. 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.

  16. Evidence of spin glass like ordering and electronic phase arrest in Pr3+ doped Sm0.5Sr0.5MnO3 bulk manganites

    NASA Astrophysics Data System (ADS)

    Giri, S. K.; Panda, J.; Nath, T. K.

    2012-06-01

    The effect of doping of rare earth Pr3+ ion replacing Sm3+ in Sm0.5Sr0.5MnO3 is investigated in details. Measurements of linear and non linear ac magnetic susceptibility, resistivity, magnetoresistance on chemically synthesized (Sm0.5-xPrx)Sr0.5MnO3 shows various interesting features with doping level x=0.15. Here we observe the frequency independent FM-PM transition at higher temperature followed by a frequency dependent re-entered magnetic transition at lower temperature through complex ac susceptibility measurements. We have ascribed our observation to the formation of finite size ferromagnetic clusters which are formed as a consequence of intrinsic phase separation and undergo Spin glass-like freezing below certain temperature in this manganite. The magnetoresistance of the samples also show strong irreversibility with respect to sweeping of the field between highest positive and negative values. All these experimental results have been attributed to phase separation effect and kinetic arrest of electronically phase separated system.

  17. 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.

  18. Possible magnetic-polaron-switched positive and negative magnetoresistance in the GdSi single crystals

    PubMed Central

    Li, Haifeng; Xiao, Yinguo; Schmitz, Berthold; Persson, Jörg; Schmidt, Wolfgang; Meuffels, Paul; Roth, Georg; Brückel, Thomas

    2012-01-01

    Magnetoresistance (MR) has attracted tremendous attention for possible technological applications. Understanding the role of magnetism in manipulating MR may in turn steer the searching for new applicable MR materials. Here we show that antiferromagnetic (AFM) GdSi metal displays an anisotropic positive MR value (PMRV), up to ~415%, accompanied by a large negative thermal volume expansion (NTVE). Around TN the PMRV translates to negative, down to ~−10.5%. Their theory-breaking magnetic-field dependencies [PMRV: dominantly linear; negative MR value (NMRV): quadratic] and the unusual NTVE indicate that PMRV is induced by the formation of magnetic polarons in 5d bands, whereas NMRV is possibly due to abated electron-spin scattering resulting from magnetic-field-aligned local 4f spins. Our results may open up a new avenue of searching for giant MR materials by suppressing the AFM transition temperature, opposite the case in manganites, and provide a promising approach to novel magnetic and electric devices. PMID:23087815

  19. Possible magnetic-polaron-switched positive and negative magnetoresistance in the GdSi single crystals.

    PubMed

    Li, Haifeng; Xiao, Yinguo; Schmitz, Berthold; Persson, Jörg; Schmidt, Wolfgang; Meuffels, Paul; Roth, Georg; Brückel, Thomas

    2012-01-01

    Magnetoresistance (MR) has attracted tremendous attention for possible technological applications. Understanding the role of magnetism in manipulating MR may in turn steer the searching for new applicable MR materials. Here we show that antiferromagnetic (AFM) GdSi metal displays an anisotropic positive MR value (PMRV), up to ~415%, accompanied by a large negative thermal volume expansion (NTVE). Around T(N) the PMRV translates to negative, down to ~-10.5%. Their theory-breaking magnetic-field dependencies [PMRV: dominantly linear; negative MR value (NMRV): quadratic] and the unusual NTVE indicate that PMRV is induced by the formation of magnetic polarons in 5d bands, whereas NMRV is possibly due to abated electron-spin scattering resulting from magnetic-field-aligned local 4f spins. Our results may open up a new avenue of searching for giant MR materials by suppressing the AFM transition temperature, opposite the case in manganites, and provide a promising approach to novel magnetic and electric devices. PMID:23087815

  20. Strain-induced anisotropic low-field magnetoresistance of La-Sr-Mn-O thin films

    NASA Astrophysics Data System (ADS)

    Choi, Kyung-Ku; Taniyama, Tomoyasu; Yamazaki, Yohtaro

    2001-12-01

    Sputtered La0.71Sr0.29Mn1.01O3-δ (LSMO) thin films on (001) SrTiO3, polycrystalline yttria-stabilized zirconia (YSZ) and (112¯0) sapphire substrates demonstrate the distinctive low-field magnetoresistance (MR) correlated with the microstructure and the strain of the films. The epitaxial LSMO film on (001) SrTiO3 shows the in-plane magnetic anisotropy with [110] easy axis and the attendant anisotropic MR. The polycrystalline films on YSZ and sapphire substrates with grain sizes from 20 to 60 nm exhibit different anisotropic feature of transport: the isotropic MR of the film on YSZ and the large anisotropy on sapphire substrates. Moreover, in the (112¯0) film plane of sapphire substrate, the [1¯100]SAP magnetic easy axis appears due to a large tensile stress, and the longitudinal MR becomes pronounced along the [0001]SAP hard axis. This implies that the anisotropy of the low-field MR is attributed to the stress induced by the thermal expansion mismatch between film and substrate. These results emphasize that the low-field MR in the polycrystalline manganite can be advanced by the strain induced magnetic anisotropy.

  1. 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.

  2. Magnetoresistance of single Permalloy circular rings

    NASA Astrophysics Data System (ADS)

    Vavassori, P.; Busato, A.; Chiapatti, A.; di Bona, A.; Valeri, S.; Metlushko, V.; Ilic, B.

    2007-09-01

    We have measured magnetoresistance in single, 1 μm external diameter, Permalloy (Ni 80Fe 20) circular rings with varied inner hole diameter of 150, 300, and 600 nm and film thickness of 25 nm. The Permalloy ring structures and the 10-nm-thick, 250-nm-wide Au nanocontacts were fabricated on a SiO 2/Si substrate using e-beam lithography. Using a four contact geometry we studied the dependence of the magnetoresistance on the direction of the applied field. The experimental data are explained by considering only the conventional anisotropic magnetoresistance effect. Numerical simulations of the current distribution within the samples combined with micromagnetic simulations of the field dependent magnetization profile, yield good agreement with the experimental data. Upon increasing the inner hole diameter (viz. decreasing the ring width) the magnetoresistance measurements show a transition of the reversal process from the "vortex nucleation-displacement-annihilation" sequence to the "onion state-reversed onion state" sequence, typical of narrow nanorings.

  3. Transient electronic structure of the photoinduced phase of Pr0.7Ca0.3MnO3 probed with soft x-ray pulses

    SciTech Connect

    Rini, M.; Zhu, Y.; Wall, S.; Tobey, R. I.; Ehrke, H.; Garl, T.; Freeland, J. W.; Tomioka, Y.; Tokura, Y.; Cavalleri, A.; Schoenlein, R. W.

    2009-04-01

    We use time-resolved x-ray absorption near-edge structure spectroscopy to investigate the electronic dynamics associated with the photoinduced insulator-to-metal phase transition in the colossal magnetoresistive manganite Pr{sub 0.7}Ca{sub 0.3}MnO{sub 3}. Absorption changes at the O K and Mn L edges directly monitor the evolution of the density of unoccupied states in the transient photoinduced phase. We show that the electronic structure of the photoinduced phase is remarkably similar to that of the ferromagnetic metallic phase reached in related manganites upon cooling below the Curie temperature.

  4. 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

  5. Electrical transport properties of manganite powders under pressure

    NASA Astrophysics Data System (ADS)

    Rodríguez, M. G.; Leyva, A. G.; Acha, C.

    2012-08-01

    We have measured the electrical resistance of micrometric to nanometric powders of the LaPryCaMnO3 (LPCMO with y=0.3) manganite for hydrostatic pressures up to 4 kbar. By applying different final thermal treatments to samples synthesized by a microwave assisted denitration process, we obtained two particular grain characteristic dimensions (40 nm and 1000 nm) which allowed us to analyze the grain size sensitivity of the electrical conduction properties of both the metal electrode interface with manganite (Pt/LPCMO) and the intrinsic intergranular interfaces formed by the LPCMO powder, conglomerate under the only effect of external pressure. We also analyzed the effects of pressure on the phase diagram of these powders. Our results indicate that different magnetic phases coexist at low temperatures and that the electrical transport properties are related to the intrinsic interfaces, as we observe evidences of a granular behavior and an electronic transport dominated by the Space Charge limited Current mechanism.

  6. Magnetoresistance of a Low-k Dielectric

    NASA Astrophysics Data System (ADS)

    McGowan, Brian Thomas

    Low-k dielectrics have been incorporated into advanced computer chip technologies as a part of the continuous effort to improve computer chip performance. One drawback associated with the implementation of low-k dielectrics is the large leakage current which conducts through the material, relative to silica. Another drawback is that the breakdown voltage of low-k dielectrics is low, relative to silica [1]. This low breakdown voltage makes accurate reliability assessment of the failure mode time dependent dielectric breakdown (TDDB) in low-k dielectrics critical for the successful implementation of these materials. The accuracy with which one can assess this reliability is currently a topic of debate. These material drawbacks have motivated the present work which aims both to contribute to the understanding of electronic conduction mechanisms in low-k dielectrics, and to improve the ability to experimentally characterize changes which occur within the material prior to TDDB failure. What follows is a study of the influence of an applied magnetic field on the conductivity of a low-k dielectric, or in other words, a study of the material's magnetoresistance. This study shows that low-k dielectrics used as intra-level dielectrics exhibit a relatively large negative magnetoresistance effect (˜2%) at room temperature and with modest applied magnetic fields (˜100 Oe). The magnetoresistance is attributed to the spin dependence of trapping electrons from the conduction band into localized electronic sites. Mixing of two-electron spin states via interactions between electron spins and the the spins of hydrogen nuclei is suppressed by an applied magnetic field. As a result, the rate of trapping is reduced, and the conductivity of the material increases. This study further demonstrates that the magnitude of the magnetoresistance changes as a function of time subjected to electrical bias and temperature stress. The rate that the magnetoresistance changes correlates to the

  7. 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.

  8. Recovery of oscillatory magneto-resistance in phase separated La0.3Pr0.4Ca0.3MnO3 epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Alagoz, H. S.; Jeon, J.; Mahmud, S. T.; Saber, M. M.; Prasad, B.; Egilmez, M.; Chow, K. H.; Jung, J.

    2013-12-01

    In-plane angular dependent magneto-resistance has been studied in La0.3Pr0.4Ca0.3MnO3 (LPCMO) manganite thin films deposited on the (100) oriented NdGaO3, and (001) oriented SrTiO3 and LaAlO3 substrates. At temperatures where the electronic phase separation is the strongest, a metastable irreversible state exists in the films whose resistivity ρ attains a large time dependent value. The ρ decreases sharply with an increasing angle θ between the magnetic field and the current, and does not display an expected oscillatory cos2θ /sin2θ dependence for all films. The regular oscillations are recovered during repetitive sweeping of θ between 0° and 180°. We discuss possible factors that could produce these unusual changes in the resistivity.

  9. 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.

  10. Novel Resistive Switching Behavior in Phase Separated Manganites

    NASA Astrophysics Data System (ADS)

    Guo, Hangwen; Ward, T. Zac; Sun, Dali; Snijders, Paul C.; Gai, Zheng; Shen, Jian

    2011-03-01

    Electronic phase separation plays a key role in many novel phenomena in complex materials. Manganites are a prime example of this class of materials and have recently come under increase scrutiny for possible application in resistive random-access memory (RRAM) technology. Here, we will discuss our recent work on spatially confined La5/8-xPrxCa3/8MnO3. We have discovered that it is possible to drive single electronic domain formation/annihilation through electric field pulsing. By measuring the I-V curve, we find such resistive switching is different from normal RRAM mechanisms in manganites and is closely related to the nature of electronic phase separation. These findings open these systems to a new understanding of the nature of electronic phase separation and begin the development of manganites for future applications in RRAM devices. Research sponsored by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy.

  11. 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.

  12. ac susceptibility studies in Fe doped La0.65Ca0.35Mn1-xFexO3: Rare earth manganites

    NASA Astrophysics Data System (ADS)

    Shah, Wiqar Hussain; Hasanain, S. K.

    2010-12-01

    The effects of Fe substitution on Mn sites in the colossal magnetoresistive compounds La0.65Ca0.35Mn1-xFexO3 with 0.00≤x≤0.10 have been studied. A careful study in the magnetic properties has been carried out by the measurement of magnetic ac susceptibility. The temperature range of colossal magnetoresistance (CMR) is greatly broadened with the addition of Fe. Substitution of Fe induces a gradual transition from a metallic ferromagnetic with a high Curie temperature (Tc=270 K) to a ferromagnetic insulator with low Tc=79 K. Increased spin disorder and decrease of Tc with increasing Fe content are evident. The variations in the critical temperature Tc and magnetic moment show a rapid change at about 4%-5% Fe. The effect of Fe is seen to be consistent with the disruption of the Mn-Mn exchange possibly due to the formation of magnetic clusters. An extraordinary behavior in the out of phase part (χ″) of ac susceptibility, characterized by double bump (shoulder), was observed around x=0.01 and 0.02. The shoulder in χ″ disappears at x≥0.04 Fe concentration. With increasing Fe concentration the χ″ peak shift to T

  13. 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.

  14. Colossal Dielectric Behavior of Ga+Nb Co-Doped Rutile TiO2.

    PubMed

    Dong, Wen; Hu, Wanbiao; Berlie, Adam; Lau, Kenny; Chen, Hua; Withers, Ray L; Liu, Yun

    2015-11-18

    Stimulated by the excellent colossal permittivity (CP) behavior achieved in In+Nb co-doped rutile TiO2, in this work we investigate the CP behavior of Ga and Nb co-doped rutile TiO2, i.e., (Ga(0.5)Nb(0.5))(x)Ti(1-x)O2, where Ga(3+) is from the same group as In(3+) but with a much smaller ionic radius. Colossal permittivity of up to 10(4)-10(5) with an acceptably low dielectric loss (tan δ = 0.05-0.1) over broad frequency/temperature ranges is obtained at x = 0.5% after systematic synthesis optimizations. Systematic structural, defect, and dielectric characterizations suggest that multiple polarization mechanisms exist in this system: defect dipoles at low temperature (∼10-40 K), polaronlike electron hopping/transport at higher temperatures, and a surface barrier layer capacitor effect. Together these mechanisms contribute to the overall dielectric properties, especially apparent observed CP. We believe that this work provides comprehensive guidance for the design of new CP materials. PMID:26512874

  15. Electron-pinned defect-dipoles for high-performance colossal permittivity materials

    NASA Astrophysics Data System (ADS)

    Hu, Wanbiao; Liu, Yun; Withers, Ray L.; Frankcombe, Terry J.; Norén, Lasse; Snashall, Amanda; Kitchin, Melanie; Smith, Paul; Gong, Bill; Chen, Hua; Schiemer, Jason; Brink, Frank; Wong-Leung, Jennifer

    2013-09-01

    The immense potential of colossal permittivity (CP) materials for use in modern microelectronics as well as for high-energy-density storage applications has propelled much recent research and development. Despite the discovery of several new classes of CP materials, the development of such materials with the required high performance is still a highly challenging task. Here, we propose a new electron-pinned, defect-dipole route to ideal CP behaviour, where hopping electrons are localized by designated lattice defect states to generate giant defect-dipoles and result in high-performance CP materials. We present a concrete example, (Nb+In) co-doped TiO2 rutile, that exhibits a largely temperature- and frequency-independent colossal permittivity (> 104) as well as a low dielectric loss (mostly < 0.05) over a very broad temperature range from 80 to 450 K. A systematic defect analysis coupled with density functional theory modelling suggests that ‘triangular’ In23+VO••Ti3+ and ‘diamond’ shaped Nb25+Ti3+ATi (A  =  Ti3+/In3+/Ti4+) defect complexes are strongly correlated, giving rise to large defect-dipole clusters containing highly localized electrons that are together responsible for the excellent CP properties observed in co-doped TiO2. This combined experimental and theoretical work opens up a promising feasible route to the systematic development of new high-performance CP materials via defect engineering.

  16. 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.

  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. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. Electrical Resistivity and Negative Magnetoresistance in (SNBry)x Crystal

    NASA Astrophysics Data System (ADS)

    Kaneto, Keiichi; Sasa, Shigehiko; Yoshino, Katsumi; Inuishi, Yoshio

    1980-11-01

    Electrical resistivity, magnetoresistance and their temperature dependences in (SNBry)x are measured for various quantity of y. By bromination, negative magnetoresistance is enhanced at 4.2 K and also appears even at 77 K, at which temperature negative magnetoresistance is not observed in undoped (SN)x. These features are remarkable for the samples heavily doped and just after doping, and are abated by pumping bromine from (SNBry)x for a few days. The possible origins for the anomalous negative magnetoresistance are discussed taking the surface state of fiber bundles or crystal due to adsorped bromine into consideration.

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

    NASA Astrophysics Data System (ADS)

    Först, 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.

    2011-12-01

    Femtosecond midinfrared pulses are used to directly excite the lattice of the single-layer manganite La0.5Sr1.5MnO4. 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.

  5. Magnetic and electrical studies on La0.4Sm0.1Ca0.5MnO3 charge ordered manganite

    NASA Astrophysics Data System (ADS)

    Krichene, A.; Solanki, P. S.; Venkateshwarlu, D.; Rayaprol, S.; Ganesan, V.; Boujelben, W.; Kuberkar, D. G.

    2015-05-01

    We have reported in this work the effect of the partial substitution of lanthanum by samarium on the structural, electrical and magnetic properties of La0.5Ca0.5MnO3. The magnetic study indicated that substitution promotes charge ordering and weakens ferromagnetism. Below TC=123 K, the compound La0.4Sm0.1Ca0.5MnO3 is a mixture of ferromagnetic and charge ordered antiferromagnetic domains. Between TC and TCO=215 K, the structure is paramagnetic with the presence of antiferromagnetic domains. The fractions of the coexisting magnetic phases are highly dependent on the applied magnetic field value. Resistivity measurements reveal the presence of an insulating-metal transition at Tρ=123 K. The equality between TC and Tρ indicates the presence of a correlation between magnetization and resistivity. For only 1 T applied field, we have reported a colossal value of magnetoresistance reaching 73% around TC. The origin of this high value is attributed to phase separation phenomenon.

  6. Colossal Aggregations of Giant Alien Freshwater Fish as a Potential Biogeochemical Hotspot

    PubMed Central

    Boulêtreau, Stéphanie; Cucherousset, Julien; Villéger, Sébastien; Masson, Rémi; Santoul, Frédéric

    2011-01-01

    The ubiquity and fascinating nature of animal aggregations are widely recognised. We report here consistent and previously undocumented occurences of aggregations of a giant alien freshwater fish, the Wels catfish (Silurus glanis). Aggregative groups were on average composed of 25 (±10 SD, ranging from 15 to 44) adults with estimated average total biomass of 651 kg (386 – 1132) and biomass density of 23 kg m−2 (14 – 40). Aggregations always occurred within the same location. No foraging, reproductive or anti-predator behaviour were observed during the aggregations. A mass-balance model estimated that these colossal aggregations of an alien species can locally release, through excretion only, up to 70 mg P m−2 h−1 and 400 mg N m−2 h−1, potentially representing the highest biogeochemical hotspots reported in freshwater ecosystems and another unexpected ecological effect of alien species. PMID:21998687

  7. 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.

  8. 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

  9. Dramatically decreased magnetoresistance in non-stoichiometric WTe2 crystals.

    PubMed

    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 (~10(5)%), 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

  10. 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

  11. 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

  12. 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.

  13. 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

  14. Effects of structural disorder in lithium manganite and titanate oxides

    NASA Astrophysics Data System (ADS)

    Chukalkin, Yu. G.; Teplykh, A. E.; Kellerman, D. G.; Gorshkov, V. S.

    2010-05-01

    The structures and magnetic states of stoichiometric lithium manganite LiMn2O4 and manganites and titanates Li1.33Mn1.67O4 and Li1.33Ti1.67O4 with excess lithium in both the initial (as-synthesized) state and after irradiation by fast ( E eff ≥ 1 MeV) neutrons with a fluence of 2 × 1020 cm-2 have been studied using neutron diffraction, X-ray diffraction, and magnetic methods. It has been established that the irradiation brings about a noticeable redistribution of manganese, titanium, and lithium cations over nonequivalent tetrahedral (8 a) and octahedral (16 d) positions of a spinel lattice. This structural disorder causes a radical change in the physical properties of the materials under study. The charge order existing in the initial LiMn2O4 sample is destroyed. There arises a strong intersublattice indirect exchange interaction Mn(8 a)-O-Mn(16 d). The disorder is accompanied by the antiferromagnet-ferrimagnet (LiMn2O4) and paramagnet-ferrimagnet (Li1.33Mn1.67O4) magnetic transitions.

  15. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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 tunneling microscopy (STM) 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. Research was supported by MSED and CNMS, which are sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U.S. Department of Energy.

  17. 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

    2014-01-01

    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. PMID:25222696

  18. Magnetoresistance in single crystalline chromium sulfides

    NASA Astrophysics Data System (ADS)

    Lee, K. D.; Won, C. J.; Song, K. M.; Hur, N.

    2011-03-01

    We studied the anisotropic magnetic and magnetotransport properties of Cr2S3 single crystals grown by using the vapor transport method. Large magnetoresistance of ˜ 46% was observed in 9 T magnetic field applied perpendicular to the c axis near the Néel temperature TN ≈ 118 K. Comparison of electric and magnetic properties of Cr2S3 crystals with different sulfur deficiencies suggested that the electron doping by the sulfur deficiency does not contribute to weak ferromagnetism. The correlation between the field-dependent magnetization and resistivity was analyzed by the polaron hopping model of magnetotransport in Cr2S3.

  19. 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.

  20. 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.

  1. 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).

  2. 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

  3. Magnetoresistive nanosensors: controlling magnetism at the nanoscale

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

  5. 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.

  6. Theory of colossal magnetoelectric response near spin-flop transition in Ni3 TeO6

    NASA Astrophysics Data System (ADS)

    Artyukhin, Sergey

    The manipulation of magnetic ordering with applied electric fields is of pressing interest for new spintronic and information storage applications. Recently, such magnetoelectric control was realized in multiferroics. However, their magnetoelectric switching is often accompanied by significant hysteresis, resulting from a large barrier, separating different ferroic states. Hysteresis prevents robust switching, unless the applied field overcomes a certain value (coercive field). I will discuss the role of a switching barrier on magnetoelectric control, in particular, in a collinear antiferromagnetic and pyroelectric Ni3TeO6. The barrier between two magnetic states in the vicinity of a spin flop transition is almost flat, and thus small changes in external electric/magnetic fields allow to switch the ferroic state through an intermediate state in a continuous manner, resulting in a colossal magnetoelectric response. This colossal magnetoelectric effect resembles the large piezoelectric effect at the morphotropic phase boundary in ferroelectrics NSF-DMREF-1233349, ONR N00014-12-1-1035.

  7. Colossal resistance switching effect in Pt/spinel-MgZnO/Pt devices for nonvolatile memory applications

    NASA Astrophysics Data System (ADS)

    Chen, Xinman; Wu, Guangheng; Jiang, Peng; Liu, Weifang; Bao, Dinghua

    2009-01-01

    We reported the discovery of colossal resistance switching effect in polycrystalline spinel-like structure MgZnO thin films with high Mg contents sandwiched by Pt electrodes. The ultrahigh resistance ratio of high resistance state to low resistance state of about seven to nine orders of magnitude with a low reset voltage of less than 1 V was obtained in this thin film system. The resistance ratio shows an increase of several orders of magnitude compared with those of previously reported resistance switching material systems including metal oxides, semiconductors, and organic molecules. This colossal resistance switching effect will greatly improve the signal-to-noise ratio and simplify the process of reading memory state for nonvolatile memory applications. Our study also provides a material base for studying the origin of resistance switching phenomenon.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  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. 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.

  15. Electrical behavior of nano-polycrystalline (La 1- yK y) 0.7Ba 0.3MnO 3 manganites

    NASA Astrophysics Data System (ADS)

    Mazaheri, M.; Akhavan, M.

    2010-11-01

    We present a study of the structural and electrical behavior of nano-polycrystalline mixed barium and alkali substituted lanthanum-based manganite, (La 1- yK y) 0.7Ba 0.3MnO 3 with y=0.0-0.3. The samples were synthesized by the polymerization complex sol-gel method. The powder X-ray diffraction (XRD) data of the samples show a single-phase character with R3¯c space group. The magnetic and electrical transport properties of the nano-polycrystalline samples have been investigated in the temperature range 50-300 K and a magnetic field up to 10 kOe. The metal-insulator transition temperature Tp of all the samples decreased with potassium doping, and also, it increased slightly with the application of magnetic field. The low field magnetoresistance, which is absent in the single-crystalline perovskite, was observed and increased with decreasing temperature. Comparing the experimental resistivity data with the theoretical models shows that the high temperature electrical behavior of these samples is in accordance with the adiabatic small polaron-hopping model. In the metal-ferromagnetic region the resistivity is found to be quite well described by ρ=ρ0+ρ2T2+ρ4.5T4.5.

  16. 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.

  17. Electronic structure basis for the extraordinary magnetoresistance in WTe2.

    PubMed

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

    2014-11-21

    The electronic structure basis of the extremely large magnetoresistance in layered nonmagnetic tungsten ditelluride has been investigated by angle-resolved photoelectron spectroscopy. Hole and electron pockets of approximately the same size were found at low temperatures, suggesting that carrier compensation should be considered the primary source of the effect. The material exhibits a highly anisotropic Fermi surface from which the pronounced anisotropy of the magnetoresistance follows. 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 of the magnetoresistance in WTe2 was identified. PMID:25479512

  18. Electronic Structure Basis for the Extraordinary Magnetoresistance in WTe2

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    The electronic structure basis of the extremely large magnetoresistance in layered nonmagnetic tungsten ditelluride has been investigated by angle-resolved photoelectron spectroscopy. Hole and electron pockets of approximately the same size were found at low temperatures, suggesting that carrier compensation should be considered the primary source of the effect. The material exhibits a highly anisotropic Fermi surface from which the pronounced anisotropy of the magnetoresistance follows. 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 of the magnetoresistance in WTe2 was identified.

  19. 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.

  20. Manganite-based heterojunction and its photovoltaic effects

    NASA Astrophysics Data System (ADS)

    Sun, J. R.; Xiong, C. M.; Shen, B. G.; Wang, P. Y.; Weng, Y. X.

    2004-04-01

    A heterojunction is fabricated by growing a La0.29Pr0.38Ca0.33MnO3 (LPCM) film on the 0.5 wt % Nb-doped SrTiO3 (STON) substrate, and its properties have been experimentally studied. In addition to fairly good rectifying behavior, the heterojunction exhibits a significant photovoltaic effect. The photovoltage on the two electrodes LPCM and STON increases almost linearly with the power of the laser beam (λ=532 nm) at a rate of ˜0.19 V/W, and no tendency to saturation is observed up to the light power of 100 mW. The lifetime of the extra carriers is between 7 and 9 ms (slightly pulse laser energy dependent), obtained from the decay of photovoltage after shutting down light illumination. The present work shows a great potential of the manganite-based heterojunction as photoelectric devices.

  1. Synthesis and characterization of LSMO manganite-based biocomposite

    NASA Astrophysics Data System (ADS)

    Keshri, Sunita; Kumar, Vivekanand; Wiśniewski, Piotr; Kamzin, Alexander S.

    2014-05-01

    In this paper we study the structural, morphological and magnetic properties of La0.67Sr0.33MnO3 (LSMO) manganite nanoparticles (NPs) and its biocomposite, obtained by mixing NPs of hydroxyapatite (HA). From the studies of X-ray diffraction and Fourier transmission of infrared spectroscopy it is evident that in the biocomposite sample both the individual phases are distinguishable from each other. The measurements of direct current (DC) magnetization and hysteresis loops reveal that the basic magnetic behaviour of LSMO-HA is similar to that of LSMO; however, the admixture of HA makes the sample magnetically softer. From the investigation of transmission electron microscopy it is observed that such a biocomposite is composed of the NPs of LSMO surrounded by HA particles, which can be found suitable for biomedical applications.

  2. Magnetic relaxation behavior in Tb-doped perovskite manganite

    NASA Astrophysics Data System (ADS)

    Zhang, Yingtang

    2011-01-01

    Tb-doped LaMnO 3 perovskite manganite has been synthesized by a conventional solid-state reaction method. The XRD patterns of the sample revealed that it has a single perovskite-type phase with orthorhombic symmetry at room temperature. The magnetic properties of the sample were investigated. The results of the static and dynamic magnetization measurements show that there is the magnetic relaxation behavior of the cluster (spin) glass in the Tb-doped LaMnO 3 sample. The outcomes of the ac nonlinear magnetization indicate that the magnetic relaxation behavior of the cluster (spin) glass was attributed to the coexistence and competition of a ferromagnetic double exchange between Mn 3+ and Mn 4+ and an antiferromagnetic superexchange coupling among Tb 3+ and Tb 3+ as well as Mn 3+ and Mn 3+.

  3. 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.

  4. Metallic ferromagnetism-insulating charge order transition in doped manganites

    NASA Astrophysics Data System (ADS)

    Phan, Van-Nham; Ninh, Quoc-Huy; Tran, Minh-Tien

    2016-04-01

    We show that an interplay of double exchange and impurity randomness can explain the competition between metal-ferromagnetic and insulating charge ordered states in doped manganites. The double exchange is simplified in the Ising type, whereas the randomness is modeled by the Falicov-Kimball binary distribution. The combined model is considered in a framework of dynamical mean-field theory. Using the Kubo-Greenwood formalism, the transport coefficients are explicitly expressed in terms of single-particle spectral functions. Dividing the system into two sublattices we have pointed out a direct calculation to the checkerboard charge order parameter and the magnetizations. Numerical results show us that the checkerboard charge order can settle inside the ferromagnetic state at low temperature. An insulator-metal transition is also found at the point of the checkerboard charge order-ferromagnetic transition.

  5. Hydrogen uptake by barium manganite at atmospheric pressure

    SciTech Connect

    Mandal, Tapas Kumar; Sebastian, Litty; Gopalakrishnan, J. . E-mail: gopal@sscu.iisc.ernet.in; Abrams, Lloyd; Goodenough, J.B.

    2004-12-02

    Investigation of the interaction of hydrogen with alkaline earth manganites (IV) AMnO{sub 3} (A = Ca, Sr, Ba), dispersed with 1 at.% Pt, has revealed an unprecedented uptake of hydrogen by BaMnO{sub 3}/Pt to the extent of {approx}1.25 mass% at moderate temperatures (190-260 deg. C) and ambient pressure. Gravimetric sorption isotherms and mass spectrometric analysis of the desorption products indicate that approximately three hydrogen atoms per mol of BaMnO{sub 3}/Pt is inserted reversibly. The nature of hydrogen in the insertion product, BaMnO{sub 3}H{sub 3}, is discussed. The work suggests the possibility of developing new hydrogen storage materials based on electropositive metal-transition metal-oxide systems.

  6. 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.

  7. Recovery of oscillatory magneto-resistance in phase separated 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.; Mahmud, S. T.; Saber, M. M.; Chow, K. H. Jung, J.; Prasad, B.; Egilmez, M.

    2013-12-02

    In-plane angular dependent magneto-resistance has been studied in La{sub 0.3}Pr{sub 0.4}Ca{sub 0.3}MnO{sub 3} (LPCMO) manganite thin films deposited on the (100) oriented NdGaO{sub 3}, and (001) oriented SrTiO{sub 3} and LaAlO{sub 3} substrates. At temperatures where the electronic phase separation is the strongest, a metastable irreversible state exists in the films whose resistivity ρ attains a large time dependent value. The ρ decreases sharply with an increasing angle θ between the magnetic field and the current, and does not display an expected oscillatory cos{sup 2}θ/sin{sup 2}θ dependence for all films. The regular oscillations are recovered during repetitive sweeping of θ between 0° and 180°. We discuss possible factors that could produce these unusual changes in the resistivity.

  8. 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.

  9. Influence of local anisotropic magnetoresistance on the total magnetoresistance of mesoscopic NiFe rings

    NASA Astrophysics Data System (ADS)

    Buntinx, Dieter; Volodin, Alexander; van Haesendonck, Chris

    2004-12-01

    The magnetoresistance of mesoscopic NiFe rings is studied by low temperature magnetotransport measurements and numerical simulations. In order not to disturb the magnetic states in the electrical transport measurements, nonmagnetic gold wires are attached to individual rings. The simulations compute the change in resistance that is caused by the anisotropic magnetoresistance (AMR) effect and are based on a combination of magnetostatics for the magnetic domain configuration and electrostatics for the current distribution. Measurements as well as simulations reveal the presence of two stable “onion” states at remanence and a stable “vortex” state near the switching fields. Moreover, a quantitative comparison between experiment and simulation is possible without the use of any free fitting parameters. Apart from the AMR effect, no additional domain wall resistance has to be introduced for the onion state. In the switching region, experiment and simulation reveal the presence of a “stressed vortex” configuration which plays a key role in the quantitative description of the magnetoresistance. The switching behavior of the NiFe rings can be modified by introducing a wedge shaped notch at the expected position of one of the domain walls in the onion state of the rings.

  10. Dynamical investigations of multiferroics: hexagonal manganites and a hexaferrite.

    NASA Astrophysics Data System (ADS)

    Talbayev, Diyar

    2010-03-01

    The electrodynamic response of magnetoelectric multiferroics can provide significant insight in the microscopic origin of multiferroicity. Hexagonal manganite HoMnO3 is a robust room temperature ferroelectric with frustrated triangular antiferromagnetic order of Mn spins setting in at 72 K. Strong magnetoelectric effects were observed in HoMnO3 and related hexa-manganites, the most intriguing of which is the control of magnetization by an applied electric field. The magnetic exchange interaction between the Ho and Mn ions was identified as a possible mechanism responsible for the observation, even though the detailed knowledge about this interaction was lacking. To fill this void, we studied magnetic excitations in HoMnO3 by far-infrared spectroscopy and elucidated the ferromagnetic nature of the rare-earth/Mn exchange. Hexaferrites that display room-temperature magnetic order are also good candidates for room temperature multiferroics. We present a study of magnetic excitations in the hexaferrite Ba0.6Sr1.4Zn2Fe12O22 using optical pump-probe spectroscopy. Pump-probe spectroscopy is known as an excellent tool for manipulating and probing magnons and phonons and for studying dynamic magnetoelectric effects. In Ba0.6Sr1.4Zn2Fe12O22, we have observed a magnetic resonance using time domain pump-probe reflectance spectroscopy, revealing a modulation of the dielectric tensor by magnetization precession. The magnetic motion in the hexaferrite modifies the dielectric constant at visible wavelengths, providing a novel manifestation of the dynamic magnetoelectric coupling and a new way of detecting magnetic motion in multiferroics. Our results highlight that magnetoelectric dynamics manifests from the far-infrared through the visible and that both time-integrated and time-resolved spectroscopy are important tools in elucidating the microscopic properties of multiferroics.

  11. A possible origin for the colossally large Seebeck coefficient in FeSb2

    NASA Astrophysics Data System (ADS)

    Takahashi, Hidefumi; Okazaki, Ryuji; Terasaki, Ichiro; Yasui, Yukio

    2014-03-01

    Narrow-gap semiconductor FeSb2 has attracted interest because of the recent observation of a colossal Seebeck coefficient S ~= - 45 mV/K at 10 K.[A. Bentien et al ., EPL 80, 17008 (2007).] This compound has a small energy gap Δ ~ 5 meV and | S | rapidly increases below 40 K, suggesting that Δ is formed by an unusual mechanism such as a strong electron correlation. However, the reported maximum values of S are remarkably different from sample to sample, ranging from - 500 μV/K to - 45 mV/K. We report a systematic study of ppm-level impurity effects of magnetic and transport properties with single crystals.[H. Takahashi et al ., JPSJ. 80, 054708 (2011).] A purest sample has a small carrier concentration (<1016 cm-3 below 30 K) and a large S (- 1400 μV/K at 20 K), indicating that the large S predominantly comes from the small carrier density. Moreover, we have measured the magnetic field dependence of transport properties of the purest crystal to investigate the relation between the electronic states and transport properties. We successfully explain the results in terms of an extrinsic semiconductor with ppm-level impurities, suggesting that the large S arises from the low carrier concentration with a phonon-drag

  12. 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.

  13. 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).

  14. 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.

  15. 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.

  16. 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.

  17. Magnetoresistance of an Anderson insulator of bosons.

    PubMed

    Gangopadhyay, Anirban; Galitski, Victor; Müller, Markus

    2013-07-12

    We study the magnetoresistance of two-dimensional bosonic Anderson insulators. We describe the change in spatial decay of localized excitations in response to a magnetic field, which is given by an interference sum over alternative tunneling trajectories. The excitations become more localized with increasing field (in sharp contrast to generic fermionic excitations which get weakly delocalized): the localization length ξ(B) is found to change as ξ(-1)(B)-ξ(-1)(0)~B(4/5). The quantum interference problem maps onto the classical statistical mechanics of directed polymers in random media (DPRM). We explain the observed scaling using a simplified droplet model which incorporates the nontrivial DPRM exponents. Our results have implications for a variety of experiments on magnetic-field-tuned superconductor-to-insulator transitions observed in disordered films, granular superconductors, and Josephson junction arrays, as well as for cold atoms in artificial gauge fields. PMID:23889427

  18. 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.

  19. Magnetoresistance and localization in bosonic insulators

    NASA Astrophysics Data System (ADS)

    Müller, Markus

    2013-06-01

    We study the strong localization of hard-core bosons. Using a locator expansion we find that in the insulator, unlike for typical fermion problems, nearly all low-energy scattering paths come with positive amplitudes and hence interfere constructively. As a consequence, the localization length of bosonic excitations shrinks when the constructive interference is suppressed by a magnetic field, entailing an exponentially large positive magnetoresistance, opposite to and significantly stronger than the analogous effect in fermions. Within the forward-scattering approximation, we find that the lowest-energy excitations are the most delocalized. A similar analysis applied to random field Ising models suggests that the ordering transition is due to a delocalization initiated at zero energy rather than due to the closure of a mobility gap in the paramagnet.

  20. Giant Magnetoresistive Sensors for DNA Microarray

    PubMed Central

    Xu, Liang; Yu, Heng; Han, Shu-Jen; Osterfeld, Sebastian; White, Robert L.; Pourmand, Nader; Wang, Shan X.

    2009-01-01

    Giant magnetoresistive (GMR) sensors are developed for a DNA microarray. Compared with the conventional fluorescent sensors, GMR sensors are cheaper, more sensitive, can generate fully electronic signals, and can be easily integrated with electronics and microfluidics. The GMR sensor used in this work has a bottom spin valve structure with an MR ratio of 12%. The single-strand target DNA detected has a length of 20 bases. Assays with DNA concentrations down to 10 pM were performed, with a dynamic range of 3 logs. A double modulation technique was used in signal detection to reduce the 1/f noise in the sensor while circumventing electromagnetic interference. The logarithmic relationship between the magnetic signal and the target DNA concentration can be described by the Temkin isotherm. Furthermore, GMR sensors integrated with microfluidics has great potential of improving the sensitivity to 1 pM or below, and the total assay time can be reduced to less than 1 hour. PMID:20824116

  1. Spin Hall Magnetoresistance in Metallic Bilayers

    NASA Astrophysics Data System (ADS)

    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.

  2. 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.

  3. Magnetoresistive smart fluid (marsonpol) and devices

    NASA Astrophysics Data System (ADS)

    Reji, John; Suresh, G.; Narayanadas, D. J.

    2003-10-01

    Magnetorheological fluid, Electrorheological fluid and ferro fluids are the smart fluids known today. These fluids are either electrically conductive or non conductive. They do not exhibit variable electrical resistance or switching behavior. Of recent interest to researchers has been the development of new types of magnetoresistive materials. Such materials can be of large practical importance, as they will change their electrical resistance in the presence of a magnetic field. However, most materials only exhibit appreciable magnetoresistance under extreme conditions, such as high magnetic fields or low temperatures. A smart fluid whose electrical resistance can be varied by several orders of magnitude under nominal level of magnetic field is reported in this paper (designated MARSONPOL). In the absence of a magnetic field the fluid is an insulator having electrical resistance in the order of 108 ohm-meter and in the presence of a magnetic field the resistance of the material reduces to less than 1 ohm-meter, at room temperature of 30°C. The sharp and reversible change in resistivity makes the material transform from an insulator to conductor, rendering properties characteristic of either state, within a fraction of a second. Fluids with such characteristics are not reported in the literature making this development a breakthrough and opening up potentials for the development of several smart devices. One such device is the magnetic field sensor probe currently under development at NPOL. A capsule of MARSONPOL forms the basic sensor element. Depending on the strength of the Magnetic field, the electrical resistivity of the capsule undergoes changes. The present paper will discuss details of the smart fluid as well as features of the magnetic field sensor.

  4. 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

  5. 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

    2015-01-01

    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

  6. 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.

  7. 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.

  8. Chiral anomaly and classical negative magnetoresistance of Weyl metals

    NASA Astrophysics Data System (ADS)

    Son, D. T.; Spivak, B. Z.

    2013-09-01

    We consider the classical magnetoresistance of a Weyl metal in which the electron Fermi surface possesses nonzero fluxes of the Berry curvature. Such a system may exhibit large negative magnetoresistance with unusual anisotropy as a function of the angle between the electric and magnetic fields. In this case the system can support an additional type of plasma wave. These phenomena are consequences of the chiral anomaly in electron transport theory.

  9. Giant negative magnetoresistance in Manganese-substituted Zinc Oxide

    PubMed Central

    Wang, X. L.; Shao, Q.; Zhuravlyova, A.; He, M.; Yi, Y.; Lortz, R.; Wang, J. N.; Ruotolo, A.

    2015-01-01

    We report a large negative magnetoresistance in Manganese-substituted Zinc Oxide thin films. This anomalous effect was found to appear in oxygen-deficient films and to increase with the concentration of Manganese. By combining magnetoresistive measurements with magneto-photoluminescence, we demonstrate that the effect can be explained as the result of a magnetically induced transition from hopping to band conduction where the activation energy is caused by the sp-d exchange interaction. PMID:25783664

  10. Large, non-saturating magnetoresistance in WTe2.

    PubMed

    Ali, Mazhar N; Xiong, Jun; Flynn, Steven; Tao, Jing; Gibson, Quinn D; Schoop, Leslie M; Liang, Tian; Haldolaarachchige, Neel; Hirschberger, Max; Ong, N P; Cava, R J

    2014-10-01

    Magnetoresistance is the change in a material's electrical resistance in response to an applied magnetic field. Materials with large magnetoresistance have found use as magnetic sensors, in magnetic memory, and in hard drives at room temperature, and their rarity has motivated many fundamental studies in materials physics at low temperatures. Here we report the observation of an extremely large positive magnetoresistance at low temperatures in the non-magnetic layered transition-metal dichalcogenide WTe2: 452,700 per cent at 4.5 kelvins in a magnetic field of 14.7 teslas, and 13 million per cent at 0.53 kelvins in a magnetic field of 60 teslas. In contrast with other materials, there is no saturation of the magnetoresistance value even at very high applied fields. Determination of the origin and consequences of this effect, and the fabrication of thin films, nanostructures and devices based on the extremely large positive magnetoresistance of WTe2, will represent a significant new direction in the study of magnetoresistivity. PMID:25219849

  11. Large, non-saturating magnetoresistance in WTe2

    NASA Astrophysics Data System (ADS)

    Ali, Mazhar N.; Xiong, Jun; Flynn, Steven; Tao, Jing; Gibson, Quinn D.; Schoop, Leslie M.; Liang, Tian; Haldolaarachchige, Neel; Hirschberger, Max; Ong, N. P.; Cava, R. J.

    2014-10-01

    Magnetoresistance is the change in a material's electrical resistance in response to an applied magnetic field. Materials with large magnetoresistance have found use as magnetic sensors, in magnetic memory, and in hard drives at room temperature, and their rarity has motivated many fundamental studies in materials physics at low temperatures. Here we report the observation of an extremely large positive magnetoresistance at low temperatures in the non-magnetic layered transition-metal dichalcogenide WTe2: 452,700 per cent at 4.5 kelvins in a magnetic field of 14.7 teslas, and 13 million per cent at 0.53 kelvins in a magnetic field of 60 teslas. In contrast with other materials, there is no saturation of the magnetoresistance value even at very high applied fields. Determination of the origin and consequences of this effect, and the fabrication of thin films, nanostructures and devices based on the extremely large positive magnetoresistance of WTe2, will represent a significant new direction in the study of magnetoresistivity.

  12. 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

  13. 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

  14. Seeing oxygen disorder in YSZ/SrTiO3 colossal ionic conductor heterostructures using EELS

    NASA Astrophysics Data System (ADS)

    Pennycook, T. J.; Oxley, M. P.; Garcia-Barriocanal, J.; Bruno, F. Y.; Leon, C.; Santamaria, J.; Pantelides, S. T.; Varela, M.; Pennycook, S. J.

    2011-06-01

    Colossal ionic conductivity was recently discovered in YSZ/SrTiO3 multilayers and was explained in terms of strain- and interface-enhanced disorder of the O sublattice. In the present paper we use a combination of scanning transmission electron microscopy and electron energy loss spectroscopy (EELS) and theoretical EELS simulations to confirm the presence of a disordered YSZ O sublattice in coherent YSZ/SrTiO3 multilayers. O K-edge fine structure simulated for the strained disordered O sublattice phase of YSZ possesses blurred-out features compared to that of ordered cubic bulk YSZ, and experimental EELS fine structure taken from the strained YSZ of coherent YSZ/SrTiO3 thin films is similarly blurred out. Elemental mapping is shown to be capable of resolving ordered YSZ O sublattices. Elemental mapping of O in the coherent YSZ/STO multilayers is presented in which the O sublattice is seen to be clearly resolved in the STO but blurred out in the YSZ, indicating it to be disordered. In addition, we present imaging and EELS results which show that strained regions exist at the incoherent interfaces of YSZ islands in STO with blurred out fine structure, suggesting these incoherent regions may also support high ionic conductivities. Recently, Cavallaro et al. reported electronic conductivities in samples of incoherent disconnected islands embedded in STO that are similar to the islands described herein. The presence of a region of O depleted STO at the interface with incoherent YSZ islands is revealed by EELS elemental mapping, implying the n-type doping of STO/YSZ nanocomposites with disconnected incoherent YSZ islands.

  15. Seeing Oxygen disorder in YSZ/SrTiO3 colossal ionic conductor heterostructures using EELS

    SciTech Connect

    Pennycook, Timothy J; Oxley, Mark P; Garcia-Barriocanal, Javier; Bruno, Flavio Y.; Santamaria, J.; Pantelides, Sokrates T.; Varela del Arco, Maria; Pennycook, Stephen J

    2011-01-01

    Colossal ionic conductivity was recently discovered in YSZ/SrTiO3 multilayers and was ex- plained in terms of strain and interface-enhanced disorder of the O sublattice. In the present paper we use a combination of scanning transmission electron microscopy and electron energy loss spectroscopy (EELS) and theoretical EELS simulations to confirm the presence of a disordered YSZ O sublattice in coherent YSZ/SrTiO3 multilayers. O K-edge fine structure simulated for the strained disordered O sublattice phase of YSZ possess blurred-out features compared to that of ordered cubic bulk YSZ, and experimental EELS fine structure taken from the strained YSZ of coherent YSZ/SrTiO3 thin films is similarly blurred out. Elemental mapping is shown to be capable of resolving ordered YSZ O sublattices. Elemental mapping of O in the coherent YSZ/STO multilayers is presented in which the O sublattice is seen to be clearly resolved in the STO but blurred out in the YSZ, indicating it to be disordered. In addition, we present imaging and EELS results which show that strained regions exist at the incoherent interfaces of YSZ islands in STO with blurred out fine structure suggesting these incoherent regions may also support high ionic conductivites. Recently, Cavallaro et al. reported electronic conductivities in samples of incoherent disconnected islands embedded in STO that are similar to the islands described herein. The presence of a region of O depleted STO at the interface with incoherent YSZ islands is revealed by EELS elemental mapping, implying the n-type doping of STO/YSZ nanocomposites with disconnected incoherent YSZ islands.

  16. Tens of successive, colossal Missoula floods at north and east margins of channeled scabland

    USGS Publications Warehouse

    Waitt, Richard B.

    1983-01-01

    In deposits of Pleistocene glacial lakes in northern Idaho and Washington, beds comprising 20 to 55 varves (average = 35-40) separate each successive graded gravel or sand bed that was swiftly emplaced by a catastrophic flood from glacial Lake Missoula. The floodlaid beds are similar to rhythmic successions of 40 or more graded beds in backflooded tributaries of the lower Columbia River. This new field evidence corroborates a controversial hypothesis that the great Pleistocene floods from glacial Lake Missoula were 40 or more colossal, separate joekulhlaups, and refutes the conventional notion that any two successive graded beds were deposited by one flood. The only outlet of the 2000-km3 glacial Lake Missoula was through its great ice dam. Calculations show that each time the lake rose to about 600 m deep, it made the glacier buoyant and engendered a catastrophic discharge along the glacier bed (a joekulhlaup). A reconstructed water budget suggests that after a complete draining, the lake refilled in 3 to 6 decades; thus the hydrostatic prerequisites for a joekulhlaup were reestablished dozens of times during the late-Wisconsin episode of lake damming. Various intercalated tephra layers, radiocarbon dates, varve successions, and the Bonneville flood deposits in the region suggest that late-Wisconsin glacial Lake Missoula existed for about 2 millennia within the period 15,000 to 12,700(?) yr ago. Varve beds indicate that the mean period between Missoula floods was about 4 decades, but became shorter during the last several floods. Between 20 and 30 of the Missoula joekulhlaups occurred after the single great flood from Lake Bonneville, which according to 14C dating in the Bonneville basin by W. E. Scott and associates and by D. R. Currey occurred some time between 15,000 and 14,000 yr ago.

  17. Resistivity dependence of magnetoresistance in Co/ZnO films

    PubMed Central

    2014-01-01

    We report the dependence of magnetoresistance effect on resistivity (ρ) in Co/ZnO films deposited by magnetron sputtering at different sputtering pressures with different ZnO contents. The magnitude of the resistivity reflects different carrier transport regimes ranging from metallic to hopping behaviors. Large room-temperature magnetoresistance greater than 8% is obtained in the resistivity range from 0.08 to 0.5 Ω · cm. The magnetoresistance value decreases markedly when the resistivity of the films is less than 0.08 Ω · cm or greater than 0.5 Ω · cm. When 0.08 Ω · cm < ρ < 0.5 Ω · cm, the conduction contains two channels: the spin-dependent tunneling channel and the spin-independent second-order hopping (N = 2). The former gives rise to a high room-temperature magnetoresistance effect. When ρ > 0.5 Ω · cm, the spin-independent higher-order hopping (N > 2) comes into play and decreases the tunneling magnetoresistance value. For the samples with ρ < 0.08 Ω · cm, reduced magnetoresistance is mainly ascribed to the formation of percolation paths through interconnected elongated metallic Co particles. This observation is significant for the improvement of room-temperature magnetoresistance value for future spintronic devices. PMID:24393445

  18. 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

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

  1. 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

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

    PubMed

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

    2016-12-01

    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

  3. 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

  4. Giant magnetoresistance of copper/permalloy multilayers

    NASA Astrophysics Data System (ADS)

    Holody, P.; Chiang, W. C.; Loloee, R.; Bass, J.; Pratt, W. P., Jr.; Schroeder, P. A.

    1998-11-01

    Current perpendicular (CPP) and current in-plane (CIP) magnetoresistances (MR) have been measured on sputtered Cu/Py (Py=Permalloy) multilayers at 4.2 K. The CPP-MR is several times larger than the CIP-MR. For fixed Py layer thickness, tPy=1.5 nm, both the CPP and CIP MR's show oscillations with increasing tCu with a period similar to that previously reported for the CIP-MR. The CPP data for Cu thicknesses large enough that exchange interactions between Py layers are small are analyzed using the two spin-current model for both infinite and finite spin-diffusion length in Py. The very low coercive field of Py leads to a larger than usual uncertainty in the derived parameters, because of the uncertainty in the degree of antiparallel alignment required for the analysis. Three alternative analyses give bulk and interface spin-dependent anisotropy parameters, β, and γ, of comparable size, so that both must be considered in determining the CPP-MR. Our preferred values, based upon an assumed IPysf=5.5+/-1 nm, are β=0.65+/-0.1 and γ=0.76+/-0.1. These values produce good fits to the CPP-MR's of Co/Cu/Py/Cu multilayers.

  5. 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.

  6. 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%.

  7. 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

  8. Magnetoresistive magnetometer for space science applications

    NASA Astrophysics Data System (ADS)

    Brown, P.; Beek, T.; Carr, C.; O'Brien, H.; Cupido, E.; Oddy, T.; Horbury, T. S.

    2012-02-01

    Measurement of the in situ dc magnetic field on space science missions is most commonly achieved using instruments based on fluxgate sensors. Fluxgates are robust, reliable and have considerable space heritage; however, their mass and volume are not optimized for deployment on nano or picosats. We describe a new magnetometer design demonstrating science measurement capability featuring significantly lower mass, volume and to a lesser extent power than a typical fluxgate. The instrument employs a sensor based on anisotropic magnetoresistance (AMR) achieving a noise floor of less than 50 pT Hz-1/2 above 1 Hz on a 5 V bridge bias. The instrument range is scalable up to ±50 000 nT and the three-axis sensor mass and volume are less than 10 g and 10 cm3, respectively. The ability to switch the polarization of the sensor's easy axis and apply magnetic feedback is used to build a driven first harmonic closed loop system featuring improved linearity, gain stability and compensation of the sensor offset. A number of potential geospace applications based on the initial instrument results are discussed including attitude control systems and scientific measurement of waves and structures in the terrestrial magnetosphere. A flight version of the AMR magnetometer will fly on the TRIO-CINEMA mission due to be launched in 2012.

  9. 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.

  10. 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.

  11. 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.

  12. 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. PMID:24727201

  13. Classical and quantum routes to linear magnetoresistance.

    PubMed

    Hu, Jingshi; Rosenbaum, T F

    2008-09-01

    The hallmark of materials science is the ability to tailor the microstructure of a given material to provide a desired response. Carbon mixed with iron provides the steel of buildings and bridges; impurities sprinkled in silicon single crystals form the raw materials of the electronics revolution; pinning centres in superconductors let them become powerful magnets. Here, we show that either adding a few parts per million of the proper chemical impurities to indium antimonide, a well-known semiconductor, or redesigning the material's structure on the micrometre scale, can transform its response to an applied magnetic field. The former approach is purely quantum mechanical; the latter a classical outgrowth of disorder, turned to advantage. In both cases, the magnetoresistive response--at the heart of magnetic sensor technology--can be converted to a simple, large and linear function of field that does not saturate. Harnessing the effects of disorder has the further advantage of extending the useful applications range of such a magnetic sensor to very high temperatures by circumventing the usual limitations imposed by phonon scattering. PMID:18719705

  14. 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.

  15. Biquadratic and ring exchange interactions in orthorhombic perovskite manganites

    NASA Astrophysics Data System (ADS)

    Fedorova, Natalya; Ederer, Claude; Spaldin, Nicola; Scaramucci, Andrea

    We use ab initio electronic structure calculations within the GGA+U approximation to density functional theory (DFT) to determine the microscopic exchange interactions in the series of orthorhombic rare-earth manganites (o-RMnO3). Our motivation is to construct a model Hamiltonian (excluding effects due to spin-orbit coupling), which can provide an accurate description of the magnetism in these materials. First we map the exchange couplings for several representatives of o-RMnO3 series onto a Heisenberg Hamiltonian and find a clear deviation from the Heisenberg-like behavior. We demonstrate that this deviation can be explained only by the presence of relatively strong higher order exchange interactions (biquadratic and four-spin ring couplings) and show that they have the strongest effect in compounds, where nearest-neighbor exchange interactions are weakened due to the presence of large GdFeO3-type distortion. Finally we discuss how these higher order terms determine magnetic ground states, influence magnetic excitations and define the multiferroic properties of o-RMnO3.

  16. Biquadratic and ring exchange interactions in orthorhombic perovskite manganites

    NASA Astrophysics Data System (ADS)

    Fedorova, Natalya S.; Ederer, Claude; Spaldin, Nicola A.; Scaramucci, Andrea

    2015-04-01

    We use ab initio electronic structure calculations within the generalized gradient approximation (GGA+U) to density functional theory to determine the microscopic exchange interactions in the series of orthorhombic rare-earth manganites, o-R MnO3 . Our motivation is to construct a model Hamiltonian (excluding effects due to spin-orbit coupling), which can provide an accurate description of the magnetism in these materials. First, we consider TbMnO3, which exhibits a spiral magnetic order at low temperatures. We map the exchange couplings in this compound onto a Heisenberg Hamiltonian and observe a clear deviation from the Heisenberg-like behavior. We consider first the coupling between magnetic and orbital degrees of freedom as a potential source of non-Heisenberg behavior in TbMnO3, but conclude that it does not explain the observed deviation. We find that higher order magnetic interactions (biquadratic and four-spin ring couplings) should be taken into account for a proper treatment of the magnetism in TbMnO3 as well as in the other representatives of the o-R MnO3 series with small radii of the R cation.

  17. 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.

  18. 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.

  19. Transport properties of silver-calcium doped lanthanum manganite

    NASA Astrophysics Data System (ADS)

    Cherif, B.; Rahmouni, H.; Smari, M.; Dhahri, E.; Moutia, N.; Khirouni, K.

    2015-01-01

    Electrical properties of silver-calcium doped lanthanum manganite (La0.5Ca0.5-xAgxMnO3 with 0.0

  20. Electrical switching to probe complex phases in a frustrated manganite

    NASA Astrophysics Data System (ADS)

    Asthana, Saket; Fujiwara, Kohei; Tanaka, Hidekazu

    2014-06-01

    Electrical switching was used to investigate complex phases induced by Cr-substitution in (Pr1/3Sm2/3)2/3Sr1/3MnO3. This system was expected to transform from a Type I (Mn4+/Mn3+≈3/7) to Type II (Mn4+/Mn3+≈1) manganite at critical Cr content, satisfying a virtual Mn4+/Mn3+ ratio close to unity. The phase diagram of (Pr1/3Sm2/3)2/3Sr1/3Mn0.8Cr0.2O3 including charge/spin ordered/disordered phases was probed by electrical switching. The ferromagnetic insulating phase at <~100 K, located next to the charge-ordered antiferromagnetic phase, exhibited a sudden rise in conductivity upon electric-field biasing. This resulted from the melting of charge ordering, and demonstrated the presence of a crossover regime of two coexisting magnetic orderings.

  1. Performance of Lanthanum Strontium Manganite Electrodes at High Pressure

    SciTech Connect

    Thomsen, Edwin C.; Coffey, Greg W.; Pederson, Larry R.; Marina, Olga A.

    2009-06-15

    The high-pressure performance of lanthanum strontium manganite (LSM), LSM-zirconia, and LSM/ceria composite electrodes was studied by impedance spectroscopy and dc methods. Electrode resistances decreased in proportion to P(O2)1/2 for the LSM electrode in both cathodic and anodic directions to at least 100 atm, a decrease that was attributed to dissociative oxygen adsorption, surface diffusion, and related phenomena. For the LSM-20/zirconia composite electrode, resistances decreased in proportion to P(O2)1/4 across the entire pressure range considered. Two principal features appeared in the impedance spectra, one that showed a P(O2)1/4 dependence attributed to charge transfer reactions, and one that was nearly pressure-independent, possibly due to transport in the zirconia portion of the composite. For the LSM-20/ceria composite electrode, resistances decreased as P(O2)0.3-0.4 at high pressure, depending on temperature. Two features appeared in the impedance spectra: one at low to intermediate frequency having a P(O2)1/2 dependence and one at high frequency having a P(O2)1/4 dependence. These features are attributed to dissociative oxygen adsorption and to charge transfer reactions, respectively. Results suggest that cathodic losses can be substantially lowered by operation of solid oxide fuel cells at greater than ambient pressure.

  2. Unraveling electronic and magnetic structure at cuprate-manganite interfaces

    NASA Astrophysics Data System (ADS)

    Freeland, John

    2014-03-01

    Oxide interfaces offer a rich variety of physics and a pathway to create new classes of functional oxide materials. The interface between the cuprate high-temperature superconductors and ferromagnetic manganites is of particular interest due to the strongly antagonistic nature of the superconducting and ferromagnetic phases. Advancements in the synthesis of oxide heterostructure offers the opportunity to merge these two dissimilar oxides with atomic precision to understand the fundamental limits of bringing such states into close proximity. However, the main challenge is to understand the physical framework that describes the behavior of strongly correlated electrons near oxide interfaces. One aspect that will be addressed here is the use of advanced tools to gain detailed electronic and magnetic information from the boundary region. In this talk, recent work will be addressed both in connection to visualizing the interface with spatially resolved tools as well as harnessing layer-by-layer growth to explore the limits in ultrathin superlattices. These insights allow us to better understand the physics behind the interfacial spin and orbital reconstruction observed in this system. Work at Argonne is supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.

  3. Investigation of the resistive properties of HTS/manganite bilayers

    NASA Astrophysics Data System (ADS)

    Nurgaliev, T.; Blagoev, B.; Štrbik, V.; Chromik, Š.; Sojková, M.

    2016-03-01

    Temperature dependences of the resistivity of manganite La0.7Ca0.3MnO3 (LCMO) films deposited on LaAlO3 and SrTiO3 substrates by RF magnetron sputtering were shown to be successfully simulated in the whole temperature range (covering metal, insulator and metal-insulator transition regions) using a phenomenological phase-coexistence transport model. Quantitative data on the internal parameters of these films were obtained. The possibility was also considered for investigation of individual resistive characteristics and excess conductivity of a high temperature superconducting (HTS) YBa2Cu3O7-x (YBCO) thin film in the vicinity of T C included into a YBCO/LCMO bilayer structure. It was shown that the considered YBCO film in the temperature range from 85.5 K to 114.9 K behaves as a two-dimensional system with respect to the fluctuations in the superconducting order parameter, while a three-dimensional regime is observed in a narrow range of temperatures at T < 85.5 K. Such behavior was assumed to be partly due to the FM LCMO component of the bilayer, the spin-polarized charge carriers of which enter into the YBCO film and cause a "breaking" of superconducting pairs in the superconducting gap and pseudogap regimes.

  4. 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.

  5. 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.

  6. The Effects of Fringe Fields on Organic Magnetoresistance

    NASA Astrophysics Data System (ADS)

    Harmon, Nicholas; Macià, Ferran; Wang, Fujian; Wohlgenannt, Markus; Kent, Andrew; Flatté, Michael

    2013-03-01

    The importance of random hyperfine fields is now widely acknowledged as a vital ingredient for the phenomena of organic magnetoresistance (OMAR). Recent experiments (Phys. Rev. X 2 021013 (2012)) have shown that another type of random field - fringe fields due to a nearby ferromagnet - can also dramatically affect magnetoconductivity. A theoretical analysis of the fringe field OMAR is challenging due to the different properties of the fringe fields when compared to the hyperfine fields. For instance, the range of fringe field strengths is 1-2 orders of magnitude larger than that of the hyperfine couplings. The correlation length between fringe fields is also larger by the same degree. We use a recent theory of OMAR that is well-suited to numerically calculate the magnetoresistance with both hyperfine and fringe fields present. We find agreement with key features of experimental fringe-field magnetoresistance dependences on applied magnetic field, including the field values of extrema of the magnetoresistance, the region of large magnetoresistance effects from the fringe fields, and the sign of the effect. This work was supported by an ARO MURI.

  7. 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.

  8. 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.

  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. 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

  11. 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

  12. Nanoscale dissipation and magnetoresistive 1/f noise in spin valves

    NASA Astrophysics Data System (ADS)

    Diao, Zhu; Nowak, E. R.; Haughey, K. M.; Coey, J. M. D.

    2011-09-01

    Spatial correlations of 1/f noise in yoke-shaped, giant magnetoresistance spin valve sensors are reported. An upper bound of 135 nm, corresponding to a magnetic volume of <105 nm3, is determined for the lateral size of the magnetic fluctuators responsible for the magnetoresistive 1/f noise in regions where the resistance susceptibility is large. The normalized noise power is found to scale inversely with the separation between voltage taps along the arm of the yoke, also consistent with a local noise mechanism. The magnetoresistive 1/f noise is associated with quasiequilibrium fluctuations in the micromagnetic structure having a length scale set by the disorder formed during the deposition and processing of the materials stack.

  13. Ballistic Anisotropic Magnetoresistance of Single-Atom Contacts.

    PubMed

    Schöneberg, J; Otte, F; Néel, N; Weismann, A; Mokrousov, Y; Kröger, J; Berndt, R; Heinze, S

    2016-02-10

    Anisotropic magnetoresistance, that is, the sensitivity of the electrical resistance of magnetic materials on the magnetization direction, is expected to be strongly enhanced in ballistic transport through nanoscale junctions. However, unambiguous experimental evidence of this effect is difficult to achieve. We utilize single-atom junctions to measure this ballistic anisotropic magnetoresistance (AMR). Single Co and Ir atoms are deposited on domains and domain walls of ferromagnetic Fe layers on W(110) to control their magnetization directions. They are contacted with nonmagnetic tips in a low-temperature scanning tunneling microscope to measure the junction conductances. Large changes of the magnetoresistance occur from the tunneling to the ballistic regime due to the competition of localized and delocalized d-orbitals, which are differently affected by spin-orbit coupling. This work shows that engineering the AMR at the single atom level is feasible. PMID:26783634

  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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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.

  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. Magnetization reversal in permalloy ferromagnetic nanowires investigated with magnetoresistance measurements

    NASA Astrophysics Data System (ADS)

    Oliveira, A. B.; Rezende, S. M.; Azevedo, A.

    2008-07-01

    The magnetization reversal process in single Permalloy (Ni81Fe19) nanowires has been investigated by magnetoresistance measurements as a function of the angle between the applied field and the wire direction. The Permalloy nanostructures fabricated on an ultrathin film by atomic force microscopy consist of two large rectangular pads connected by a nanowire with the shape of a long thin narrow tape. For each field direction in the plane of the film the dependence of the magnetoresistance on the field value exhibits two main contributions: one from the pads and one from the nanowire. The contribution from the pads is due to a usual anisotropic magnetoresistance characteristic of coherent magnetization rotation, whereas the contribution from the nanowire is an abrupt transition at the switching field. The dependence of the switching field on the in-plane field angle is quantitatively described by a model of nucleation field with the buckling magnetization rotation mode.

  18. 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

  19. Large Magnetoresistance Effects in Novel Layered Rare Earth Halides

    NASA Astrophysics Data System (ADS)

    Kremer, R. K.; Ryazanov, M.; Simon, A.

    We give a survey of the structures, electric, magnetic and magnetoresistance properties of the two novel low dimensional rare-earth halide systems, GdI2 and GdIHy (2/3 < y ≤ 1). The large magnetoresistance e.ect observed for GdI2 can be understood on the basis of a conventional spin disorder scattering mechanism, however, strongly magni.ed by the structural anisotropy and the special topology of the Fermi surface. Bound magnetic polarons are formed in GdIHy leading to a metal insulator transition below ~ 30 K. The mobility of the magnetic polarons can be e.ectively modi.ed by external magnetic .fields resulting in the large experimentally found magnetoresistance.

  20. Linear field amplification for magnetoresistive sensors

    NASA Astrophysics Data System (ADS)

    Trindade, I. G.; Fermento, R.; Sousa, J. B.; Chaves, R. C.; Cardoso, S.; Freitas, P. P.

    2008-05-01

    In this article, we describe the fabrication and characterization of a spin valve (SV) magnetoresistive (MR) sensor, located in the gap of two magnetically soft flux guides (FGs) that enhance the sensor magnetic field sensitivity, while keeping in the sensor a quasilinear Barkhausen-noise-free response. Top pinned SV sensors were fabricated into stripes, having lengths of 100μm and widths of 2 and 3μm, by optical lithography and ion-milling etching. The FGs consisted of poles and yokes of an amorphous alloy of Co88.4Zr3.3Nb8.3, prepared by physical vapor deposition and were lithographically defined by a lift-off process. The SV sensor MR responses to applied uniform magnetic fields Ha, when either isolated or located in the gap of two types of FGs, were characterized in terms of the saturation field, coercive force, and sensitivity. The impact of the FG geometry in the magnetic field amplification and sensor response characteristics were studied. Magnetic force microscopy analysis was performed to identify the presence of multidomain states in the FGs and of a remanent field in their gap. SV sensors in the gap of FGs using long poles and having a sensing area of 1000μm2 exhibit a linear sensitivity of 50mV/Oe in the field range of a couple of oersteds. The SV sensor in the gap of magnetically soft FGs exhibits enhanced hysteresis, characterized by a coercive force of approximately 1Oe. Two schemes are proposed to reduce the hysteresis in the sensor response.

  1. Magnetoresistive-based static tester for actuators

    NASA Astrophysics Data System (ADS)

    Borme, J.; Freitas, A. S.; Cardoso, S.; Almeida, J. M.; Chaves, R. C.; Freitas, P. P.

    2008-04-01

    A static tester for precision actuators is proposed. It is intended to test the functioning of future actuators to be used in hard drive read heads. The design allows a simple fabrication of a nanometer-scale position measurement system that can measure lateral, vertical, and angular displacements. The tester consists of (a) a reference magnetic layer of CoCrPt, (150×100μm2, 600nm thick) and (b) a sequence of four spin-valve sensors. The tested sensors have crossed anisotropies, 6.9% magnetoresistance with a linear response, 0.5%/mT sensitivity, coercive field less than 0.1mT and resistance of 1680Ω in the parallel state. A noise level of 6nV/√Hz was measured at thermal background for 0.2mA of applied current. The lateral displacement is measured by the two spin valves in the center. While the magnetic element is passing over these sensors, the measured signal on each of them varies in opposite directions, allowing a precise measurement of the center position. The two outer spin valves are sensitive to the angular orientation of the magnetic element. The relative movements of the spin valves and magnetic element are controlled by computer using piezoelectric crystals and step motors. Since the sensors are measuring the in-plane component of the field, the signal measured decreases rapidly with sensor-to-plane distance. An appropriate range for flight height is about 30μm. Simulations of the signal are in agreement with measurements.

  2. 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

  3. 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.

  4. 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.

  5. Detection of magnetic resonance signals using a magnetoresistive sensor

    DOEpatents

    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.

  6. Spin Hall magnetoresistance induced by a nonequilibrium proximity effect.

    PubMed

    Nakayama, H; Althammer, M; Chen, Y-T; Uchida, K; Kajiwara, Y; Kikuchi, D; Ohtani, T; Geprägs, S; Opel, M; Takahashi, S; Gross, R; Bauer, G E W; Goennenwein, S T B; Saitoh, E

    2013-05-17

    We report anisotropic magnetoresistance in Pt|Y(3)Fe(5)O(12) bilayers. In spite of Y(3)Fe(5)O(12) being a very good electrical insulator, the resistance of the Pt layer reflects its magnetization direction. The effect persists even when a Cu layer is inserted between Pt and Y(3)Fe(5)O(12), excluding the contribution of induced equilibrium magnetization at the interface. Instead, we show that the effect originates from concerted actions of the direct and inverse spin Hall effects and therefore call it "spin Hall magnetoresistance." PMID:25167435

  7. Tunneling Spectroscopy Study of Spin-Polarized Quasiparticle Injection Effects in Cuparate/Manganite Heterostructures

    NASA Technical Reports Server (NTRS)

    Wei, J. Y. T.; Yeh, N. C.; Vasquez, R. P.

    1998-01-01

    Scanning tunneling spectroscopy was performed at 4.2K on epitaxial thin-film heterostructures comprising YBa2Cu3O7 and La0.7Ca0.3MnO3, to study the microscopic effects of spin-polarized quasiparticle injection from the half-metallic ferromagnetic manganite on the high-Tc cuprate superconductor.

  8. 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

  9. Magnetoresistive performance and comparison of supermagnetic nanoparticles on giant magnetoresistive sensor-based detection system

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Wang, Yi; Tu, Liang; Feng, Yinglong; Klein, Todd; Wang, Jian-Ping

    2014-07-01

    Giant magnetoresistive (GMR) biosensors have emerged as powerful tools for ultrasensitive, multiplexed, real-time electrical readout, and rapid biological/chemical detection while combining with magnetic particles. Finding appropriate magnetic nanoparticles (MNPs) and its influences on the detection signal is a vital aspect to the GMR bio-sensing technology. Here, we report a GMR sensor based detection system capable of stable and convenient connection, and real-time measurement. Five different types of MNPs with sizes ranging from 10 to 100 nm were investigated for GMR biosensing. The experiments were accomplished with the aid of DNA hybridization and detection architecture on GMR sensor surface. We found that different MNPs markedly affected the final detection signal, depending on their characteristics of magnetic moment, size, and surface-based binding ability, etc. This work may provide a useful guidance in selecting or preparing MNPs to enhance the sensitivity of GMR biosensors, and eventually lead to a versatile and portable device for molecular diagnostics.

  10. 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.

  11. Pressure dependence of resistivity and magnetoresistance in Pr-doped La0.7Ca0.3MnO3

    NASA Astrophysics Data System (ADS)

    Jani, H. K.; Maheswar Repaka, D. V.; Mahendiran, R.

    2013-05-01

    We report the effects of magnetic field (μ0H = 0-7 T) and hydrostatic pressure (P = 1 bar to 9.53 kbar) on electrical resistivity in the phase separated manganite La0.3Pr0.4Ca0.3MnO3. The resistivity shows a first-order transition from paramagnetic insulating to ferromagnetic metallic state at a temperature T = TIM in ambient pressure and zero magnetic field. The first-order transition becomes second-order with increasing pressure and/or magnetic field. Both hydrostatic pressure and magnetic field decrease the magnitude resistivity and shift the resistivity peak at T = TIM towards high temperature with different rates (dTIM/dH = 13.5 K/T for P = 1 bar, 8.8 K/T for P = 9.53 kbar, and dTIM/dP ˜ 4.42 K/kbar in zero field). However, the magnitude of the magnetoresistance decreases with increasing pressure. Baroresistance in the absence of magnetic field for ΔP = 9.53 kbar reaches nearly 100% around 150 K. Interestingly, while the resistivity at a constant temperature shows irreversible behaviour upon cycling the direction of magnetic field at ambient pressure, the irreversibility is eliminated under hydrostatic pressure. Our results indicate that pressure eliminates phase separation by converting the paramagnetic polaronic phase into ferromagnetic metallic phase in the vicinity of phase coexistence.

  12. Magnetoresistance of Bloch-wall-type magnetic structures induced in NiFe/CoSm exchange-spring bilayers

    NASA Astrophysics Data System (ADS)

    Mibu, K.; Nagahama, T.; Shinjo, T.; Ono, T.

    1998-09-01

    The magnetoresistance originating from magnetic structures with gradually rotating magnetic moments, like a Bloch wall, was investigated using soft-magnetic (NiFe)/hard-magnetic (CoSm) bilayers, whose magnetic structures were well characterized. The magnetoresistance was measured with an electric current in the film plane; the magnetoresistance in this geometry corresponds to that due to a current parallel to a Bloch wall. The main feature of the magnetoresistance curves was ruled by the anisotropic magnetoresistance. It was found that a giant magnetoresistance-type effect coexisted; the effect was very small in comparison with the anisotropic magnetoresistance effect.

  13. Investigation of continuous changes in the electric-field-induced electronic state in Bi(1-x)Ca(x)FeO(3-δ).

    PubMed

    Ikeda-Ohno, Atsushi; Lim, Ji Soo; Ohkochi, Takuo; Yang, Chan-Ho; Seidel, Jan

    2014-09-01

    Amongst the most interesting phenomena in correlated oxide systems are the doping-driven competitions between energetically similar ground states found in, e.g., high-Tc superconductors and colossal magnetoresistance manganites. It has recently been reported that doped multiferroics also exhibit this generic concept of phase competition. Here, we employ photoelectron emission microscopy (PEEM) to demonstrate evidence of systematic changes in the electronic structure of Bi(1-x)Ca(x)FeO(3-δ) treated by electrically controlled hole carrier doping, the outcome of which clearly correlates with the local modulation of electronic conductivity observed in the same material. PMID:25041934

  14. 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

  15. 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%.

  16. Tuning magnetic nanostructures and flux concentrators for magnetoresistive sensors

    NASA Astrophysics Data System (ADS)

    Yin, Xiaolu; Liu, Yen-Fu; Ewing, Dan; Ruder, Carmen K.; De Rego, Paul J.; Edelstein, A. S.; Liou, Sy-Hwang

    2015-09-01

    The methods for the optimization of the magnetoresistive (MR) sensors are to reduce sources of noises, to increase the signal, and to understand the involved fundamental limitations. The high-performance MR sensors result from important magnetic tunnel junction (MTJ) properties, such as tunneling magnetoresistance ratio (TMR), coercivity (Hc), exchange coupling field (He), domain structures, and noise properties as well as the external magnetic flux concentrators. All these parameters are sensitively controlled by the magnetic nanostructures, which can be tuned by varying junction free layer nanostructures, geometry, and magnetic annealing process etc. In this paper, we discuss some of efforts that an optimized magnetic sensor with a sensitivity as high as 5,146 %/mT. This sensitivity is currently the highest among all MR-type sensors that have been reported. The estimated noise of our magnetoresistive sensor is 47 pT/Hz1/2 at 1 Hz. This magnetoresistance sensor dissipates only 100 μW of power while operating under an applied voltage of 1 V at room temperature.

  17. Large magnetoresistance and electronic anisotropy in NbAs2

    NASA Astrophysics Data System (ADS)

    Shen, Bing; Jiang, Shan; Ni, Ni

    Recently, extremely large magnetoresistance (XMR) was discovered in semimetal such as WTe2 LaSb and so on, triggering extensive reseach on these materials and the origin of XMR. In this talk, we will report the transport properties of non-magnetic layered pnictide material NbAs2. Large transverse magnetoresistance is observed. At 10 K, the magnetoresistance is around 13000 % in the field of 9 T and shows no saturation behavior. The temperature dependent resistivity at various fields exhibits metal-to-semiconductor transition behavior around 100 K, which is coincident with the sudden increase of the Hall signal in the same temperature region. The angle dependent magnetoresistance at various temperatures follows the 3D scaling behavior with the mass anisotropy around 1.3-1.4, indicative of its 3D electron structure. Quantum oscillation data reveal the existence of at least three Fermi pockets in this material. Work at UCLA was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES) under Award Number DE-SC0011978.

  18. Spin Hall magnetoresistance in ultra thin Pt/LSMO

    NASA Astrophysics Data System (ADS)

    Lei, Na; Bai, Yu; Ding, Zhao; Shao, Jian; Wei, Wengang; Yin, Lifeng; Wu, Yizheng; Shen, Jian

    Spin Hall magnetoresistance (SMR) in a non-/ ferro- magnetic (NM/FM) bilayer is an angular dependence of resistance of the NM layer on the magnetization of FM layer. It provides an easy approach to the spin Hall effect in a simple bilayer system, however similar effects mixed in the system and might complicated the data analysis and interpretation. Here we present a case of ultra thin Pt/LSMO, in which LSMO (bellow 7 unit cells) layer is an insulating magnetic oxide with Curie temperature of 120K. Below 120K, our results clearly show the coexistence of the anisotropic magnetoresistance (AMR) and SMR effects. However, far away above Curie temperature, where the LSMO is paramagnetic, the magnetoresistance doesn't disappear but even increase, which is distinct from the case of Pt/YIG. Here it is neither SMR nor AMR, and an additional mechanism is required. Anomalous Hall effect was also performed, which is consistent with SMR measurement. We propose some physical pictures which could attribute to this magnetoresistance in paramagnetic state.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. Spin Hall magnetoresistance in ferromagnetic insulator/normal metal hybrids

    NASA Astrophysics Data System (ADS)

    Althammer, Matthias

    2014-03-01

    Pure spin currents, i.e. the net flow of spin angular momentum without an accompanying charge current, represent a new paradigm for spin transport and spintronics. We have experimentally studied a new type of magnetoresistance effect, which arises from the interaction of charge and spin current flows in ferromagnetic insulator/normal metal hybrid structures. In more detail, we measured the resistance of yttrium iron garnet(YIG)/Pt, YIG/nonferromagnet/Pt, nickel ferrite/Pt, and magnetite/Pt hybrid structures as a function of the magnitude and the orientation of an external magnetic field. The resistance changes observed can be quantitatively traced back to the combined action of spin Hall and inverse spin Hall effect in the Pt metal layer, and are thus termed spin Hall magnetoresistance (SMR) [ 1 , 2 ] . We show that the SMR is qualitatively different from the conventional anisotropic magnetoresistance effect arising in magnetic metals. From the magnetoresistance measurements in YIG/Au/Pt and YIG/Cu/Pt structures and from x-ray magnetic circular dichroism measurements on YIG/Pt heterostructures we exclude a static proximity magnetization in Pt as the origin of the magnetoresistance, in contrast to the mechanism proposed by Huang et al. [ 3 ] . Furthermore, the SMR enables us to quantify the spin Hall angle as a function of temperature in our Pt layers. In addition, we analyze the anomalous Hall type contribution of the SMR to quantify the imaginary part of the spin mixing conductance. Financial support by the DFG via SPP 1538 (project no. GO 944/4) and the Nanoinitiative Munich (NIM) is gratefully acknowledged.

  4. Characterization and Application of Large Magnetoresistance in Organic Semiconductors

    NASA Astrophysics Data System (ADS)

    Wohlgenannt, Markus

    2007-03-01

    Recent years have seen a surge in interest in magnetoresistive and spintronic properties of organic semiconductors, whereas this field was previously almost exclusively concerned with their electrooptical properties. We report on the extensive experimental characterization of a recently discovered large and intriguing magnetoresistive effect in organic light- emitting diodes that reaches up to 10% at room temperature for magnetic fields, B = 10mT. This magnetoresistive effect is therefore amongst the largest of any bulk material. The study includes a range of materials that show greatly different chemical structure, mobility, hyperfine and spin-orbit coupling strength. We show that the applied magnetic field affects the carrier transport inside the bulk semiconductor. By demonstrating that the effect is critically altered by the presence of strong spin- orbit coupling and that it does not occur in fullerene devices, we prove that the transport in organics sensitively depends on spin-dynamics induced by hyperfine interaction with the hydrogen protons. We discuss a possible relation between organic magnetoresistance and other magnetic field effects in organics that were known long before its discovery. As a possible mechanism we describe how Pauli's principle restricts carrier hopping between singly occupied sites near the Fermi level. However, spin-mixing by the hyperfine interaction may partially lift this restriction. Since the devices we describe can be manufactured cheaply they hold promise for applications where large numbers of magnetoresistive devices are needed, such as magnetic random- access-memory (MRAM); and applications related to organic light- emitting diode displays such as touch screens where the position of a magnetic stylus is detected (patent pending). We will show a video of a simple demonstrator device.

  5. Magnetism at grain boundary interfacesin the colossal permittivity dielectric material; In+Nb Co-Doped Rutile

    NASA Astrophysics Data System (ADS)

    Berlie, Adam; Terry, Ian; Cottrell, Stephen; Hu, Wanbiao; Liu, Yun

    With the emphasis in recent years on understanding novel materials with potential technological applications this work seeks to understand magnetic ordering within the colossal-permittivity material, In+Nb co-doped rutile (TiO2). Evidence for a spin-freezing transition was reported from a step like feature in the dielectic data below 50 K but this was largly glossed over. Within this work we show that below 300 K there is a slowing down of magnetic fluctuations associated with the electronic magnetism due to the defect-dipoles created by the co-doping, but the muon spectroscopy results are strongly suggestive of the behaviour being localised to the edges/interfaces of particles/grains. The TC is strongly dependent on the doping level of the samples that presents novel way to control the magnetism and ultimately magneto-electric coupling within a dielectric material.

  6. Structural, Magnetic and Spectroscopic Studies of Thin Manganite Films

    NASA Astrophysics Data System (ADS)

    Tyson, T. A.

    2003-03-01

    Starting from early experiments [1], evidence has been found for a close coupling of strain and the magnetotransport properties of manganite films. The characteristic feature found is that the metal to insulator transition temperature (TMI) is suppressed in very thin films [2]. In addition, studies show that the magnetic transition temperature (Tc) and TMI decouple in ultrathin films [3]. Systematic magnetization studies reveal that strain induces strong magnetic anisotropy [4]. Theoretical work also points to the sensitivity of Tc to biaxial strain [5]. Most studies have focused on single bulk properties. In order to understand the correlations between strain and the transport and magnetic properties we have examined the structure of films on multiple length scales. The local structure of films have been studies by x-ray absorption spectroscopy. The long -range structure has been studied by high-resolution x-ray diffraction and the microstructure has been studied by AFM measurements. These measurements are correlated with bulk magnetization and transport studies. Insight is gained on the evolution of lattice strain and Jahn-Teller distortions with thickness. Direct evidence is found for the arrest of charge ordering with strain and the existence of strain induced insulating regions of films. The magnetic ordering and transport properties as a function of strain as compared with bandstructure calculations. This work is supported by NSF Career Grant DMR-9733862 and DMR-0209243. Collaborators: Q. Qian, M. Deleon (NJIT), C. Dubourdiu (CNRS), J. Bai (ORNL), W. Prellier, A. Biswas, R. L. Greene (U. Maryland) [1] S. Jin et al., Appl. Phys. Lett. 67, 557 (1995). [2] (a) J. Z. Sun et al. Appl. Phys. Lett. 74, 3017 (1999). (b) F. S. Razi et al., Appl. Phys. Lett 76, 155 (2000) [3] J. Aarts et al., Appl. Phys. Lett. 72, 2975 (1998). (b) R. A. Rao et al., J. Appl. Phys. 85, 4794 (1999). [4] (a) X. W. Wu et al., Phys. Rev. B 61, 501 (2000). (b) J. O'Donnell et al., Appl. Phys

  7. Structure, magnetism and transport of the perovskite manganites Ln {sub 0.5}Ca{sub 0.5}MnO{sub 3} (Ln=Ho, Er, Tm, Yb and Lu)

    SciTech Connect

    Yoshii, Kenji . E-mail: yoshiike@spring8.or.jp; Abe, Hideki; Ikeda, Naoshi

    2005-12-15

    It was found that the manganese perovskite oxides Ln {sub 0.5}Ca{sub 0.5}MnO{sub 3} (Ln=Ho, Er, Tm, Yb and Lu) have an orthorhombic structure (space group Pnma). The Mn-O-Mn angles were calculated to be {approx}148-150{sup o}, revealing an existence of a large crystallographic distortion in these oxides. Electrical resistivity measurements indicated both an insulating nature and a small magnetoresistance effect, both of which are owing to narrow bandwidths of the Mn-3d electrons arising from the crystallographic distortion. DC magnetization measurements showed the three characteristic temperatures, which could be assigned to charge-order, antiferromagnetism of Mn moments, and possible glassy states. All of these temperatures were decreased for the heavier Ln ions, which is explained in connection with both a difference of ionic radii of Ln {sup 3+} and Ca{sup 2+}, and a lowering of electron transfer. The charge-ordering transition was not clearly observed only for Lu{sub 0.5}Ca{sub 0.5}MnO{sub 3} containing the smallest lanthanide ion, plausibly due to a large randomness of magnetic interactions arising from the ionic radii difference of Lu{sup 3+} and Ca{sup 2+}. In addition, preliminary measurements of AC dielectric response suggested that these manganites belong to a so-called multiferroic system.

  8. Evidence of glassy ferromagnetic phase and kinetic arrest of electronic phase in Sm0.35Pr0.15Sr0.5MnO3 manganites

    NASA Astrophysics Data System (ADS)

    Giri, S. K.; Nath, T. K.

    2012-07-01

    The effect of doping of rare earth Pr3+ ion as a replacement of Sm3+ in Sm0.5Sr0.5MnO3 is investigated. Temperature dependent dc and ac magnetic susceptibility, resistivity, magnetoresistance measurements on chemically synthesized (Sm0.5-xPrx)Sr0.5MnO3 show various unusual features with doping level x=0.15. The frequency independent ferromagnetic to paramagnetic transition at higher temperature (∼191 K) followed by a frequency dependent reentrant magnetic transition at lower temperature (∼31 K) has been observed. The nature of this frequency dependent reentrant magnetic transition is described by a critical slowing down model of spin glasses. From non-linear ac susceptibility measurements it has been confirmed that the finite size ferromagnetic clusters are formed as a consequence of intrinsic phase separation, and undergo spin glass-like freezing below a certain temperature. There is an unusual observation of a 2nd harmonic peak in the non-linear ac susceptibility around this reentrant magnetic transition at low temperature (∼31 K). Arrott plots at 10 and 30 K confirm the existence of glassy ferromagnetism below this low temperature reentrant transition. Electronic- and magneto-transport measurements show a strong magnetic field-temperature history dependence and strong irreversibility with respect to the sweeping of magnetic field. These results are attributed to the effect of phase separation and kinetic arrest of the electronic phase in this phase separated manganite at low temperatures.

  9. An investigation of low temperature electronic phase arrest in Sm{sub 0.55}Sr{sub 0.45}MnO{sub 3} phase separated manganite

    SciTech Connect

    Giri, S. K. Nath, T. K.

    2014-02-07

    The temperature dependence of electronic-transport and magneto-transport of polycrystalline Sm{sub 0.55}Sr{sub 0.45}MnO{sub 3} manganite at low temperatures has been investigated in detail. The low temperature resistivity data show a distinct minimum in the resistivity versus temperature plots for all fields. The low temperature resistivity upturn below this minimum has been fitted to an expression, which includes three terms, namely, residual resistivity, inelastic scattering, and electron-electron (e-e) interaction or Kondo effects. It has been found that the dominating mechanism is e-e interaction. The resistivity of the sample shows strong dependence on the magnetic field–temperature history. The electronic-transport property clearly confirms that the electronic phase of the sample gets arrested to a low resistive state during field cooling and cannot return to its original state even after the magnetic field is removed. The magnetoresistance of the sample also shows a strong irreversibility with respect to the sweeping of the magnetic field between its highest positive and negative values. Moreover, the resistivity of the sample is found to be time dependent. All the observed phenomena have been explained through the phase separation scenario and kinetic arrest of electronic phase.

  10. 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.

  11. 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

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

    PubMed

    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

  13. Magnetoresistive performance and comparison of supermagnetic nanoparticles on giant magnetoresistive sensor-based detection system

    PubMed Central

    Wang, Wei; Wang, Yi; Tu, Liang; Feng, Yinglong; Klein, Todd; Wang, Jian-Ping

    2014-01-01

    Giant magnetoresistive (GMR) biosensors have emerged as powerful tools for ultrasensitive, multiplexed, real-time electrical readout, and rapid biological/chemical detection while combining with magnetic particles. Finding appropriate magnetic nanoparticles (MNPs) and its influences on the detection signal is a vital aspect to the GMR bio-sensing technology. Here, we report a GMR sensor based detection system capable of stable and convenient connection, and real-time measurement. Five different types of MNPs with sizes ranging from 10 to 100 nm were investigated for GMR biosensing. The experiments were accomplished with the aid of DNA hybridization and detection architecture on GMR sensor surface. We found that different MNPs markedly affected the final detection signal, depending on their characteristics of magnetic moment, size, and surface-based binding ability, etc. This work may provide a useful guidance in selecting or preparing MNPs to enhance the sensitivity of GMR biosensors, and eventually lead to a versatile and portable device for molecular diagnostics. PMID:25043673

  14. Dual magnetoresistive heads for high-density magnetic recording

    NASA Astrophysics Data System (ADS)

    Trindade, Isabel Maria Goncalves

    2000-11-01

    In this thesis, novel magnetoresistive heads were developed and tested. The head designs had been proposed and analyzed with 3-D micromagnetic simulations. The dual magnetoresistive heads were of technological interest because they could provide higher linear resolution than conventional magnetoresistive heads, with less micro- fabrication complexity. As the demands for higher storage capacity and higher data rate increase, it is important to investigate alternative transducer designs that can provide suitable signal to noise ratio at smaller bits (smaller track-widths, narrower separation between tracks and smaller bit lengths). Dual magnetoresistive heads with track-widths of 2 microns and gap lengths of 80 nm were fabricated by micro-fabrication techniques. Thin film materials incorporating magnetic materials, metals and insulators were developed and prepared by sputtering. Optical lithography processes were developed and used to pattern the films with lateral dimensions of the order of a micron. Read-elements on wafers were characterized by Kerr microscope imaging and magnetoresistance measurements. The characterization involved single domain state stabilization, antiparallel magnetic state and electrical and magnetic mismatch between the two permalloy stripes of the dual magnetoresistive read- elements. The read-elements were built into nano-sliders and tested on spin stands with either two arm actuators (one for the read head, another for the write head) or a commercial Gukiz spin stand provided with one actuator for two separate heads. The time-domain response, spectral response, cross track-profile, off-track response and adjacent track interference were tested and the experimental results compared to theoretical models. The head performance on longitudinal medium with an areal magnetic product of Mrδ = 0-5 memu/cm2 and Mr δ = 1 memu/cm2 indicate that the head operated mainly in a linear regime, with a signal output amplitude directly proportional to the

  15. A Raman Study of the Origin of Oxygen Defects in Hexagonal Manganite Thin Films

    NASA Astrophysics Data System (ADS)

    Chen, Xiang-Bai; Hien Nguyen Thi, Minh; Yang, In-Sang; Lee, Daesu; Noh, Tae-Won

    2012-12-01

    Oxygen defects are usually unavoidable when synthesizing oxide thin films. We study the origin of the oxygen defects in hexagonal manganite HoMnO3 epitaxial thin films through Raman scattering spectroscopy. Our results show that the oxygen defects in hexagonal HoMnO3 thin films have distinct effects on different phonon modes and on magnon scattering. Our analyses indicate that the oxygen defects in hexagonal HoMnO3 thin films mainly originate from the basal O3 and/or O4 oxygen vacancies. Furthermore, our analyses of oxygen defects predict that the Mn 3d orbitals would be more strongly hybridized with the apical O1 and/or O2 2p orbitals than the basal O3 and/or O4 2p orbitals. This prediction is consistent with our resonant Raman scattering study and earlier first-principle calculations of the electronic structures of hexagonal manganites.

  16. 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

  17. 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.

  18. 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.

  19. 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

  20. 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

  1. 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.

  2. 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.

  3. 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

  4. Hall effect in the extremely large magnetoresistance semimetal WTe2

    NASA Astrophysics Data System (ADS)

    Luo, Yongkang; Li, H.; Dai, Y. M.; Miao, H.; Shi, Y. G.; Ding, H.; Taylor, A. J.; Yarotski, D. A.; Prasankumar, R. P.; Thompson, J. D.

    2015-11-01

    We systematically measured the Hall effect in the extremely large magnetoresistance semimetal WTe2. By carefully fitting the Hall resistivity to a two-band model, the temperature dependencies of the carrier density and mobility for both electron- and hole-type carriers were determined. We observed a sudden increase in the hole density below ˜160 K, which is likely associated with the temperature-induced Lifshitz transition reported by a previous photoemission study. In addition, a more pronounced reduction in electron density occurs below 50 K, giving rise to comparable electron and hole densities at low temperature. Our observations indicate a possible electronic structure change below 50 K, which might be the direct driving force of the electron-hole "compensation" and the extremely large magnetoresistance as well. Numerical simulations imply that this material is unlikely to be a perfectly compensated system.

  5. Giant magnetoresistance in the variable-range hopping regime

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    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.

  6. Magneto-Resistance in thin film boron carbides

    NASA Astrophysics Data System (ADS)

    Echeverria, Elena; Luo, Guangfu; Liu, J.; Mei, Wai-Ning; Pasquale, F. L.; Colon Santanta, J.; Dowben, P. A.; Zhang, Le; Kelber, J. A.

    2013-03-01

    Chromium doped semiconducting boron carbide devices were fabricated based on a carborane icosahedra (B10C2H12) precursor via plasma enhanced chemical vapor deposition, and the transition metal atoms found to dope pairwise on adjacent icosahedra site locations. Models spin-polarized electronic structure calculations of the doped semiconducting boron carbides indicate that some transition metal (such as Cr) doped semiconducting boron carbides may act as excellent spin filters when used as the dielectric barrier in a magnetic tunnel junction structure. In the case of chromium doping, there may be considerable enhancements in the magneto-resistance of the heterostructure. To this end, current to voltage curves and magneto-transport measurements were performed in various semiconducting boron carbide both in and out plane. The I-V curves as a function of external magnetic field exhibit strong magnetoresistive effects which are enhanced at liquid Nitrogen temperatures. The mechanism for these effects will be discussed in the context of theoretical calculations.

  7. Linear magnetoresistance in mosaic-like bilayer graphene

    NASA Astrophysics Data System (ADS)

    Kisslinger, Ferdinand; Ott, Christian; Heide, Christian; Kampert, Erik; Butz, Benjamin; Spiecker, Erdmann; Shallcross, Sam; Weber, Heiko B.

    2015-08-01

    The magnetoresistance of conductors usually has a quadratic dependence on magnetic field, however, examples exist of non-saturating linear behaviour in diverse materials. Assigning a specific microscopic mechanism to this unusual phenomenon is obscured by the co-occurrence and interplay of doping, mobility fluctuations and a polycrystalline structure. Bilayer graphene has virtually no doping fluctuations, yet provides a built-in mosaic tiling due to the dense network of partial dislocations. We present magnetotransport measurements of epitaxial bilayer graphene that exhibits a strong and reproducible linear magnetoresistance that persists to B = 62 T at and above room temperature, decorated by quantum interference effects at low temperatures. Partial dislocations thus have a profound impact on the transport properties in bilayer graphene, a system that is frequently assumed to be dislocation-free. It further provides a clear and tractable model system for studying the unusual properties of mosaic conductors.

  8. Complexity in Transition Metal Oxides

    NASA Astrophysics Data System (ADS)

    Dagotto, Elbio; Alvarez, Gonzalo; Moreo, Adriana

    2004-03-01

    Recent computational results in the context of models for manganites and cuprates will be briefly discussed. It is argued that correlations in quenched disorder -- needed to mimic cooperative Jahn-Teller effects -- are important to have colossal magnetoresistance in 3D. A related recently discussed metal-insulator transition induced by disorder in a one-orbital model with cooperative phonons is intuitively explained [1]. In addition, it is argued that colossal effects should be far more common than currently known, and they may appear in cuprate superconductors as well [2]. [1] J. Burgy et al., cond-mat/0308456; C. Sen, G. Alvarez, and E. Dagotto, preprint. [2] See also Adriana Moreo, invited talk, March APS 04; G. Alvarez, M. Mayr et al., preprint.

  9. Interaction-induced huge magnetoresistance in a high mobility two-dimensional electron gas

    SciTech Connect

    Bockhorn, L.; Haug, R. J.; Gornyi, I. V.; Schuh, D.; Wegscheider, W.

    2013-12-04

    A strong negative magnetoresistance is observed in a high-mobility two-dimensional electron gas in a GaAs/Al{sub 0.3}Ga{sub 0.7}As quantum well. We discuss that the negative magnetoresistance consists of a small peak induced by a combination of two types of disorder and a huge magnetoresistance explained by the interaction correction to the conductivity for mixed disorder.

  10. 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

  11. Giant positive magnetoresistance in metallic VOx thin films

    NASA Astrophysics Data System (ADS)

    Rata, A. D.; Kataev, V.; Khomskii, D.; Hibma, T.

    2003-12-01

    We report on giant positive magnetoresistance (MR) effect observed in VOx thin films, epitaxially grown on SrTiO3 substrate. The MR effect depends strongly on temperature and oxygen content and is anisotropic. At low temperatures its magnitude reaches 70% in a magnetic field of 5 T. Strong electron-electron interactions in the presence of strong disorder may qualitatively explain the results. An alternative explanation, related to a possible magnetic instability, is also discussed.

  12. Anomalous magneto-resistance in single crystals of silver chalcogenides

    NASA Astrophysics Data System (ADS)

    Zhang, Chenglong; Liu, Haiwen; Hua, Wei; Yuan, Zhunjun; Sun, Junliang; Xie, Xincheng; Jia, Shuang

    2015-03-01

    Silver chalcogenides have been known as quantum materials for over fifteen years but no single crystal was ever studied before. Very recently, we developed a method for growth of single crystals. Our measurements of magneto-resistance (MR) showed strong Shubnikov-de Haas (SdH) oscillations associated with a very low quantum limit. When the field is beyond this limit we observed a negative, longitudinal MR, which is believed as a fingerprint of chiral anomaly in Weyl Fermion systems.

  13. Spin-memory effect and negative magnetoresistance in hopping conductivity

    NASA Astrophysics Data System (ADS)

    Agam, Oded; Aleiner, Igor L.; Spivak, Boris

    2014-03-01

    We propose a mechanism for negative isotropic magnetoresistance in the hopping regime. It results from a memory effect encrypted into spin correlations that are not taken into account by the conventional theory of hopping conductivity. The spin correlations are generated by the nonequilibrium electric currents and lead to the decrease of the conductivity. The application of the magnetic field destroys the correlations thus enhancing the conductance. This effect can occur even at magnetic fields as small as a few gauss.

  14. Handheld, giant magnetoresistive-sensor-based eddy current probes

    NASA Astrophysics Data System (ADS)

    Brady, S. K.; Palmer, D. D.

    2012-05-01

    The minimum crack length detectable with conventional eddy current probes increases dramatically as the thickness of metal through which the inspection is performed increases. The skin depth phenomenon is unavoidable, and demands low frequency inspection, hindering sensitivity. However, one time derivative introduced by Faraday's Law can be avoided by using giant magnetoresistive sensors to detect eddy currents instead of conventional coils, improving sensitivity. The theory will be explained, along with some probe designs and the observed benefits in sensitivity.

  15. [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

  16. Negative magnetoresistance in Dirac semimetal Cd3As2.

    PubMed

    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 × 10(17) cm(-3) at 300 K to 2.2 × 10(16) 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

  17. 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

  18. 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

  19. 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

  20. Spin–orbit coupling induced magnetoresistance oscillation in a dc biased two-dimensional electron system.

    PubMed

    Wang, C M; Lei, X L

    2014-06-11

    We study dc-current effects on the magnetoresistance oscillation in a two-dimensional electron gas with Rashba spin-orbit coupling, using the balance-equation approach to nonlinear magnetotransport. In the weak current limit the magnetoresistance exhibits periodical Shubnikov-de Haas oscillation with changing Rashba coupling strength for a fixed magnetic field. At finite dc bias, the period of the oscillation halves when the interbranch contribution to resistivity dominates. With further increasing current density, the oscillatory resistivity exhibits phase inversion, i.e., magnetoresistivity minima (maxima) invert to maxima (minima) at certain values of the dc bias, which is due to the current-induced magnetoresistance oscillation. PMID:25932474

  1. Negative huge magnetoresistance in high-mobility 2D electron gases: DC-current dependence

    NASA Astrophysics Data System (ADS)

    Iñarrea, J.; Bockhorn, L.; Haug, R. J.

    2016-07-01

    Two-dimensional electron gases with very high mobility show a huge or giant negative magnetoresistance at low temperatures and low magnetic fields. We present an experimental and theoretical work on the influence of the applied current on the negative huge magnetoresistance of these systems. We obtain an unexpected and strong nonlinear behavior consisting in an increase of the negative huge magnetoresistance with increasing current, in other words, for increasing current the magnetoresistance collapses at small magnetic fields. This nonlinearity is explained by the subtle interplay of elastic scattering within Landau levels and between Landau levels.

  2. Enhancement of Low-field Magnetoresistance in Self-Assembled Epitaxial La0.67Ca0.33MnO3:NiO and La0.67Ca0.33MnO3:Co3O4 Composite Films via Polymer-Assisted Deposition

    NASA Astrophysics Data System (ADS)

    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

    2016-07-01

    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.

  3. 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

  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. Effect of interface-induced exchange fields on cuprate-manganite spin switches.

    PubMed

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

    2012-05-18

    We examine the anomalous inverse spin switch behavior in La0.7Ca0.3MnO3(LCMO)/YBa2Cu3O7-δ (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. PMID:23003184

  6. Phonons and colossal thermal expansion behavior of Ag3Co(CN)6 and Ag3Fe(CN)6.

    PubMed

    Mittal, R; Zbiri, M; Schober, H; Achary, S N; Tyagi, A K; Chaplot, S L

    2012-12-19

    Recently colossal volume thermal expansion has been observed in the framework compounds Ag(3)Co(CN)(6) and Ag(3)Fe(CN)(6). We have measured phonon spectra using neutron time-of-flight spectroscopy as a function of temperature and pressure. Ab initio calculations were carried out for the sake of analysis and interpretation. Bonding is found to be very similar in the two compounds. At ambient pressure, modes in the intermediate frequency part of the vibrational spectra in the Co compound are shifted slightly to higher energies as compared to the Fe compound. The temperature dependence of the phonon spectra gives evidence for a large explicit anharmonic contribution to the total anharmonicity for low-energy modes below 5 meV. We have found that modes are mainly affected by the change in size of the unit cell, which in turn changes the bond lengths and vibrational frequencies. Thermal expansion has been calculated via the volume dependence of phonon spectra. Our analysis indicates that Ag phonon modes within the energy range 2-5 meV are strongly anharmonic and major contributors to thermal expansion in both systems. The application of pressure hardens the low-energy part of the phonon spectra involving Ag vibrations and confirms the highly anharmonic nature of these modes. PMID:23174851

  7. Effects of Multiple Treatments of Low-Temperature Colossal Supersaturation on Tribological Characteristics of Austenitic Stainless Steels

    SciTech Connect

    Qu, Jun; Blau, Peter Julian; Zhang, Ligong; Xu, Hanbing

    2008-01-01

    An alternative carburization process, low-temperature colossal supersaturation (LTCSS), has demonstrated significant improvement on both wear- and corrosion-resistance for austenitic stainless steel surfaces in recent literature. This study explores the effects of multiple treatments of LTCSS on tribological characteristics for Type 316 stainless steel. Thicker carburized layers were produced by multiple LTCSS treatments, with 30, 45, and 55 m for one, two, and four treatments, respectively. Although the hardness remains unchanged at low-load microindentation, multiple treatments have showed higher values in both microindentation and scratch hardness tests when deeper penetrations occurred under heavier loads. The friction and wear characteristics of Type 316 stainless steel with multiple LTCSS treatments were evaluated in non-lubricated unidirectional sliding (pin-on-disk) against Type 440C stainless steel. While little change was observed on friction behavior, substantial further improvement on wear-resistance has been achieved for the multiple treatments. In addition, the wear of the counterface was also largely reduced when rubbing against a multiple-treated surface.

  8. Successive Magnetic-Field-Induced Transitions and Colossal Magnetoelectric Effect in Ni_{3}TeO_{6}.

    PubMed

    Kim, Jae Wook; Artyukhin, S; Mun, E D; Jaime, M; Harrison, N; Hansen, A; Yang, J J; Oh, Y S; Vanderbilt, D; Zapf, V S; Cheong, S-W

    2015-09-25

    We report the discovery of a metamagnetic phase transition in a polar antiferromagnet Ni_{3}TeO_{6} 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/cm^{2}, 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 T transition. The high-field transition involves a competition between multiple different exchange interactions which drives the polarization change through the exchange-striction mechanism. The resultant spin structure is rather counterintuitive and complex, thus providing new insights on design principles for materials with strong magnetoelectric coupling. PMID:26451580

  9. 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.

  10. 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.

  11. 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.

  12. Magnetoresistance of quasi-Bloch-wall induced in NiFe/CoSm exchange-spring bilayers

    NASA Astrophysics Data System (ADS)

    Mibu, K.; Nagahama, T.; Ono, T.; Shinjo, T.

    1998-01-01

    The magnetoresistance (MR) originating from a magnetic structure with continuous rotation of magnetic moments was studied using soft-magnetic/hard-magnetic bilayers. The feature of the MR curves was explained with anisotropic magnetoresistance (AMR) applying to twisted magnetic structures. The giant magnetoresistance (GMR)-type effect was found to be very small compared with the AMR effect.

  13. Mechanism of the hysteretic behavior of the magnetoresistance of granular HTSCs: The universal nature of the width of the magnetoresistance hysteresis loop

    SciTech Connect

    Balaev, D. A. Dubrovskii, A. A.; Shaikhutdinov, K. A.; Popkov, S. I.; Gokhfeld, D. M.; Gokhfeld, Yu. S.; Petrov, M. I.

    2009-02-15

    The hysteretic behavior of the magnetoresistance R(H) of granular high-temperature superconductors (HTSCs) of the Y-Ba-Cu-O, Bi-Ca-Sr-Cu-O, and La-Sr-Cu-O classical systems is investigated for transport current densities lower and higher than the critical density (at H = 0). All systems exhibit universal behavior of the width of the magnetoresistance hysteresis loop: independence of transport current under identical external conditions. This means that flux trapping in HTSC grains is the main mechanism controlling the hysteretic behavior of the magnetoresistance of granular HTSCs, while pinning of Josephson vortices in the intragranular medium makes no appreciable contribution to the formation of magnetoresistance hysteresis (when transport current flows through the sample). Experimental data on relaxation of residual resistance after the action of a magnetic field also confirm this conclusion.

  14. Electrical, Magnetic and Thermal Transport Behavior of Divalent/Tetravalent Doped LaMnO3 Manganites

    NASA Astrophysics Data System (ADS)

    Varshney, Dinesh; Mansuri, Irfan; Kaurav, N.; Kuo, Y. K.

    2011-07-01

    We report the investigations of electrical magnetic and thermal properties of La0.7-x CexCa0.3MnO3 (0.00.3) manganites. The metal-semiconducting transitions (TMS) are observed for all doped manganites at ˜255 K, ˜235 K ˜220 K and ˜154 K. The magnetic susceptibility measurement confirms that the sample undergoes a transition from paramagnetic to ferromagnetic phase at a particular temperature (TC). It is noticed that the TC is nearly equal to the TMS. Specific heat measurements depict a pronounced anomaly near the TC, indicating the magnetic ordering and magnetic inhomogeneity in the samples.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. Angular magnetoresistance in semiconducting undoped amorphous carbon thin films

    NASA Astrophysics Data System (ADS)

    Sagar, Rizwan Ur Rehman; Saleemi, Awais Siddique; Zhang, Xiaozhong

    2015-05-01

    Thin films of undoped amorphous carbon thin film were fabricated by using Chemical Vapor Deposition and their structure was investigated by using High Resolution Transmission Electron Microscopy and Raman Spectroscopy. Angular magnetoresistance (MR) has been observed for the first time in these undoped amorphous carbon thin films in temperature range of 2 ˜ 40 K. The maximum magnitude of angular MR was in the range of 9.5% ˜ 1.5% in 2 ˜ 40 K. The origin of this angular MR was also discussed.

  1. Nonlinear spin current and magnetoresistance of molecular tunnel junctions.

    PubMed

    Waldron, Derek; Haney, Paul; Larade, Brian; MacDonald, Allan; Guo, Hong

    2006-04-28

    We report on a theoretical study of spin-polarized quantum transport through a Ni-bezenedithiol(BDT)-Ni molecular magnetic tunnel junction (MTJ). Our study is based on carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism, so that microscopic details of the molecular MTJ are taken into account from first principles. A magnetoresistance ratio of approximately 27% is found for the Ni-BDT-Ni MTJ which declines toward zero as bias voltage is increased. The spin currents are nonlinear functions of bias voltage, even changing sign at certain voltages due to specific features of the coupling between molecular states and magnetic leads. PMID:16712257

  2. 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.

  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. Angular magnetoresistance in semiconducting undoped amorphous carbon thin films

    SciTech Connect

    Sagar, Rizwan Ur Rehman; Saleemi, Awais Siddique; Zhang, Xiaozhong

    2015-05-07

    Thin films of undoped amorphous carbon thin film were fabricated by using Chemical Vapor Deposition and their structure was investigated by using High Resolution Transmission Electron Microscopy and Raman Spectroscopy. Angular magnetoresistance (MR) has been observed for the first time in these undoped amorphous carbon thin films in temperature range of 2 ∼ 40 K. The maximum magnitude of angular MR was in the range of 9.5% ∼ 1.5% in 2 ∼ 40 K. The origin of this angular MR was also discussed.

  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. Interfacial contribution to thickness dependent in-plane anisotropic magnetoresistance

    NASA Astrophysics Data System (ADS)

    Tokaç, M.; Wang, M.; Jaiswal, S.; Rushforth, A. W.; Gallagher, B. L.; Atkinson, D.; Hindmarch, A. T.

    2015-12-01

    We have studied in-plane anisotropic magnetoresistance (AMR) in cobalt films with overlayers having designed electrically interface transparency. With an electrically opaque cobalt/overlayer interface, the AMR ratio is shown to vary in inverse proportion to the cobalt film thickness; an indication that in-plane AMR is a consequence of anisotropic scattering with both volume and interfacial contributions. The interface scattering anisotropy opposes the volume scattering contribution, causing the AMR ratio to diminish as the cobalt film thickness is reduced. An intrinsic interface effect explains the significantly reduced AMR ratio in ultra-thin films.

  7. Ultrahigh magnetoresistance at room temperature in molecular wires.

    PubMed

    Mahato, R N; Lülf, H; Siekman, M H; Kersten, S P; Bobbert, P A; de Jong, M P; De Cola, L; van der Wiel, W G

    2013-07-19

    Systems featuring large magnetoresistance (MR) at room temperature and in small magnetic fields are attractive owing to their potential for applications in magnetic field sensing and data storage. Usually, the magnetic properties of materials are exploited to achieve large MR effects. Here, we report on an exceptionally large (>2000%), room-temperature, small-field (a few millitesla) MR effect in one-dimensional, nonmagnetic systems formed by molecular wires embedded in a zeolite host crystal. This ultrahigh MR effect is ascribed to spin blockade in one-dimensional electron transport. Its generic nature offers very good perspectives to exploit the effect in a wide range of low-dimensional systems. PMID:23828887

  8. 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.

  9. Fusion-neutron effects on magnetoresistivity of copper stabilizer materials

    SciTech Connect

    Guinan, M.W.; Van Konynenburg, R.A.

    1983-02-24

    The objective of this work is to quantify the changes which occur in the magnetoresistivity of coppers (having various purities and pretreatments, and at magnetic fields up to 12 T during the course of sequential fusion neutron irradiations at about 4/sup 0/K and anneals to room temperature. In conjunction with work in progress by Coltman and Klabunde of ORNL, the results should lead to engineering design data for the stabilizers of superconducting magnets in fusion reactors. These magnets are expected to be irradiated during reactor operation and warmed to room temperature periodically during maintenance.

  10. Damping in free layers of tunnel magneto-resistance readers

    NASA Astrophysics Data System (ADS)

    Lu, Lei; Wang, Zihui; Mead, Griffin; Kaiser, Christian; Leng, Qunwen; Wu, Mingzhong

    2014-07-01

    Damping properties in the free layers of tunnel magneto-resistance (TMR) readers were reported. The study used a free layer sample consisting of the same stacking structure as in TMR readers, involved comprehensive ferromagnetic resonance (FMR) measurements, and included numerical analysis of the FMR data. The results indicate that the free layer shows a Gilbert damping constant of 8.1 × 10-3. When the free layer is magnetized with a field which is not normal to the film plane, two-magnon scattering also occurs, although its contribution to the relaxation is at least 2.5 times smaller than the Gilbert contribution.

  11. Large magnetic-entropy change above room temperature in the colossal magnetoresistance La 0.7Sr 0.3Mn 1- xNi xO 3 materials

    NASA Astrophysics Data System (ADS)

    Choudhury, Md. A.; Akhter, S.; Minh, D. L.; Tho, N. D.; Chau, N.

    2004-05-01

    Magnetic and magnetocaloric properties of the series La 0.7Sr 0.3Mn 1- xNi xO 3 ( x=0.00, 0.01, 0.02, 0.03, and 0.05) have been investigated. The X-ray diffraction analysis shows that all perovskites studied have the rhombohedral structure. The field-cooled and zero-field-cooled thermomagnetic curves measured at low field show that there is spin-glass (or cluster-glass)-like state in the samples. It is found that the magnetic-entropy change |Δ Smax| has reached the highest value of 3.54 J/kg K at 13.5 kOe for the composition with x=0.02.

  12. Structural Characterisation of Complex Oxide & Rare Earth Manganite Thing Films by Microscopy

    NASA Astrophysics Data System (ADS)

    Jehanathan, Neerushana

    This PhD thesis presents the work on specific complex oxides and rare earth manganite thin films which were characterized mainly by transmission electron microscopy (TEM). The scientific results are divided in two main parts: the first part is devoted to the complex oxide films and the second to the rare earth manganite films. I. Complex oxides: The compositional influence of Cr, Al and Y on the microstructure of Mg-Cr-O, Mg-Al-O, Mg-Y-0 and Y-Al-O films synthesized by a reactive magnetron sputtering technique is reported. The study was based on a series of films with a range of compositions (metal ratios) deposited on Si substrates (without external substrate heating). The film thickness is about 1 μm (±200 nm). The effect of high temperatures (973 K to 1223 K) on the microstructural evolution of Mg-AlO, Mg-Cr-O and Y-Al-O films with specific metal ratios is also reported. II. Rare Earth Manganite Films: The microstructure and defect characterisation of hexagonal ReMnO3 (Re=Y, Tb, Dy, Ho and Er) thin films and multilayers is reported. The effect of off-stoichiometry on the microstructure of some hexagonal ReMnO3 (Re=Er, Dy and Ho) films with specific cationic ratios is also discussed. These thin films and multilayers were deposited on (111) YSZ and (111) Pt/TiO2/SiO 2/Si (stack) substrates by liquid injection metal organic chemical vapour deposition (MOCVD). The thickness of the films and multilayers is between 10 nm and 500 nm.

  13. Perovskite-structure TlMnO₃: a new manganite with new properties.

    PubMed

    Yi, Wei; Kumagai, Yu; Spaldin, Nicola A; Matsushita, Yoshitaka; Sato, Akira; Presniakov, Igor A; Sobolev, Alexey V; Glazkova, Yana S; Belik, Alexei A

    2014-09-15

    We synthesize a new member of the AMnO3 perovskite manganite family (where A is a trivalent cation)--thallium manganite, TlMnO3--under high-pressure (6 GPa) and high-temperature (1500 K) conditions and show that the structural and magnetic properties are distinct from those of all other AMnO3 manganites. The crystal structure of TlMnO3 is solved and refined using single-crystal X-ray diffraction data. We obtain a triclinically distorted structure with space group P1̅ (No. 2), Z = 4, and lattice parameters a = 5.4248(2) Å, b = 7.9403(2) Å, c = 5.28650(10) Å, α = 87.8200(10)°, β = 86.9440(10)°, and γ = 89.3130(10)° at 293 K. There are four crystallographic Mn sites in TlMnO3 forming two groups based on the degree of their Jahn-Teller distortions. Physical properties of insulating TlMnO3 are investigated with Mössbauer spectroscopy and resistivity, specific heat, and magnetization measurements. The orbital ordering, which persists to the decomposition temperature of 820 K, suggests A-type antiferromagnetic ordering with the ferromagnetic planes along the [-101] direction, consistent with the measured collinear antiferromagnetism below the Néel temperature of 92 K. Hybrid density functional calculations are consistent with the experimentally identified structure, insulating ground state, and suggested magnetism, and show that the low symmetry originates from the strongly Jahn-Teller distorted Mn(3+) ions combined with the strong covalency of the Tl(3+)-O bonds. PMID:25163034

  14. 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.

  15. 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.

  16. Strong orbital correlations in a Fe-substituted spin-glass-manganite

    SciTech Connect

    Granado, E.; Azimonte, C.; Souza, R.A.; Souza-Neto, N.M.; Urbano, R.R.; Perez, C.A.; Ramos, A.Y.; Lynn, J.W.; Bychkov, G.L.; Shiryaev, S.V.; Barilo, S.N.

    2005-08-01

    The compound La{sub 0.66}Ba{sub 0.40}Mn{sub 0.61}Fe{sub 0.33}O{sub 3} shows anisotropic magnetic correlations with no long-range order. Specific heat measurements suggest these correlations represent the bulk. Orbital correlations of Mn{sup 3+}e{sub g} electrons, surviving in an environment of largely disordered exchange interactions, are invoked to account for this magnetic state. These results argue in favor of a strain-field mechanism for orbital ordering in manganites.

  17. Science and technology of reduced-dimensional magnetic materials

    SciTech Connect

    Heffner, R.H.; Bishop, A.R.; Hundley, M.F.; Jia, Q.; Neumeier, J.J.; Trugman, S.A.; Thompson, J.D.; Wu, X.D.; Zhang, J.

    1998-12-31

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). This work involved the synthesis of single crystal and thin film samples of magnetoresistive manganites (LaMnO{sub 3} doped with Ca and Sr) and the characterization of their electronic transport properties to understand the underlying physical mechanisms responsible for the colossal magnetoresistance (CMR) of these materials. The experimental program was supplemented by a modeling effort that sought to develop microscopic mathematical models of the observed phenomena. The authors succeeded in finding an important relation between the magnetization and resistivity in these materials, which helps to explain the importance of lattice distortions accompanied by clusters of ferromagnetic spins (called spin-lattice polarons) in the CMR phenomena. In addition, they developed rudimentary tunnel junctions of CMR-insulator-CMR multilayers that will lead to possible applications of these materials as magnetic sensors.

  18. Theory of the negative magnetoresistance in magnetic metallic multilayers

    SciTech Connect

    Hood, R.Q.; Falicov, L.M. |

    1993-04-01

    The Boltzman equation is solved for a system consisting of alternating ferromagnetic normal metallic layers. The in-plane conductance of the film is calculated for two configurations: successive ferromagnetic layers aligned parallel and antiparallel to each other. Results explain the giant negative magnetoresistance encountered in these systems when an initial antiparallel arrangement is changed into a parallel configuration by application of an extemal magnetic field. The calculation depends on geometric parameters (the thicknesses of the layers); intrinsic metal parameters (number of conduction electrons, magnetization and effective masses in the layers); bulk sample properties (conductivity relaxation times); and interface scattering properties (diffuse scattering versus potential scattering at the interfaces). It is found that a large negative magnetoresistance requires, in general, considerable asymmetry in the interface scattering for the two spin orienmtions. All qualitative features of the experiments are reproduced. Quantitative agreement can be achieved with sensible values of the parameters. The effect can be conceptually explained based on considerations of phase-space availability for an electron of a given spin orientation as it travels through the multilayer sample in the various configurations and traverses the interfaces.

  19. 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

  20. 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.

  1. Unidirectional spin Hall magnetoresistance in ferromagnet/normal metal bilayers

    NASA Astrophysics Data System (ADS)

    Avci, Can Onur; Garello, Kevin; Ghosh, Abhijit; Gabureac, Mihai; Alvarado, Santos F.; Gambardella, Pietro

    2015-07-01

    Magnetoresistive effects are usually invariant on inversion of the magnetization direction. In non-centrosymmetric conductors, however, nonlinear resistive terms can give rise to a current dependence that is quadratic in the applied voltage and linear in the magnetization. Here we demonstrate that such conditions are realized in simple bilayer metal films where the spin-orbit interaction and spin-dependent scattering couple the current-induced spin accumulation to the electrical conductivity. We show that the longitudinal resistance of Ta|Co and Pt|Co bilayers changes when reversing the polarity of the current or the sign of the magnetization. This unidirectional magnetoresistance scales linearly with current density and has opposite sign in Ta and Pt, which we associate with the modification of the interface scattering potential induced by the spin Hall effect in these materials. Our results suggest a route to control the resistance and detect magnetization switching in spintronic devices using a two-terminal geometry, which applies also to heterostructures including topological insulators.

  2. 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.

  3. 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.

  4. Large tunneling magnetoresistance in octahedral Fe3O4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Mitra, Arijit; Barick, Barun; Mohapatra, Jeotikanta; Sharma, H.; Meena, S. S.; Aslam, M.

    2016-05-01

    We have observed large tunneling Magnetoresistance (TMR) in amine functionalized octahedral nanoparticle assemblies. Amine monolayer on the surface of nanoparticles acts as an insulating barrier between the semimetal Fe3O4 nanoparticles and provides multiple tunnel junctions where inter-granular tunneling is plausible. The tunneling magnetoresistance recorded at room temperature is 38% which increases to 69% at 180 K. When the temperature drops below 150 K, coulomb staircase is observed in the current versus voltage characteristics as the charging energy exceeds the thermal energy. A similar study is also carried out with spherical nanoparticles. A 24% TMR is recorded at room temperature which increases to 41% at 180 K for spherical particles. Mössbauer spectra reveal better stoichiometry for octahedral particles which is attainable due to lesser surface disorder and strong amine coupling at the <111> facets of octahedral Fe3O4 nanoparticles. Less stoichiometric defect in octahedral nanoparticles leads to a higher value of spin polarization and therefore larger TMR in octahedral nanoparticles.

  5. 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

  6. Angle Dependence of the Orbital Magnetoresistance in Bismuth

    NASA Astrophysics Data System (ADS)

    Collaudin, Aurélie; Fauqué, Benoît; Fuseya, Yuki; Kang, Woun; Behnia, Kamran

    2015-04-01

    We present an extensive study of angle-dependent transverse magnetoresistance in bismuth, with a magnetic field perpendicular to the applied electric current and rotating in three distinct crystallographic planes. The observed angular oscillations are confronted with the expectations of semiclassic transport theory for a multivalley system with anisotropic mobility and the agreement allows us to quantify the components of the mobility tensor for both electrons and holes. A quadratic temperature dependence is resolved. As Hartman argued long ago, this indicates that inelastic resistivity in bismuth is dominated by carrier-carrier scattering. At low temperature and high magnetic field, the threefold symmetry of the lattice is suddenly lost. Specifically, a 2 π /3 rotation of magnetic field around the trigonal axis modifies the amplitude of the magnetoresistance below a field-dependent temperature. By following the evolution of this anomaly as a function of temperature and magnetic field, we map the boundary in the (field, temperature) plane separating two electronic states. In the less symmetric state, confined to low temperature and high magnetic field, the three Dirac valleys cease to be rotationally invariant. We discuss the possible origins of this spontaneous valley polarization, including a valley-nematic scenario.

  7. 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.

  8. Advanced Magnetoresistance Sensing of Rotation Rate for Biomedical Applications

    NASA Astrophysics Data System (ADS)

    Avram, Marioara; Volmer, Marius; Avram, Andrei

    2008-06-01

    We propose to build a non-Newtonian fluids viscosimeter, in order to measure the viscosity of biological fluids such as blood. The system is based on a rotating microgear wheel and a magnetoresistive sensor with a non-contacting transduction mechanism to transform the rotor rotation rate into an electrical signal. As the rotor turns, the field from this microscopic magnet will modulate the resistance of a bar of a low coercitivity material such as Permalloy, with an in-plane uniaxial magnetization, placed nearby, close to the rotor flanges. The change in resistivity provides an electrical signal with frequency proportional to the rotation rate, and hence the fluid velocity. The rotor is fabricated from polysilicon and coated with a soft magnetic material. The magnetoresistive sensor is formed of two Wheatstone bridges orientated on the X and Y axes. As the microgear wheel rotates, a tooth passing by the sensing GMR of the Wheatstone bridge changes the magnetic field, thus enabling us to measure the velocity of the gear wheel. The gear wheel has the outer diameter of 200 μm and is obtained by using the cut and refill technique. The basis for fabrication of movable parts is the use of sacrificial layers that act both as spacers and also to keep the parts attached to the silicon wafer during fabrication.

  9. 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).

  10. Imaging Ferromagnetic Tracers with a Magnetoresistive Sensors Array

    NASA Astrophysics Data System (ADS)

    Leyva, Juan A.; Carneiro, Antonio A. O.; Murta, Luís O.; Baffa, O.

    2006-09-01

    The aim of this work was to study the feasibility to obtain images from a distribution of ferromagnetic tracers using a magnetoresistive multichannel sensor array (MRA). A magnetic imaging system formed by a linear array composed of 12 magnetoresistive sensors (Honeywell HMC 1001) was constructed covering a scanning area of (16×18) cm2. The signal was pre-processed for off-set correction and interpolation to generate a matrix of (256×256). The point spread function of the MRA was evaluated and the sensors were spaced accordingly. The magnetic images were generated by mapping the response of the MRA at short distances from the presence of a magnetite powder dispersed in planar phantoms with different shapes. The phantoms were magnetized by a pulse field of approximately 80 mT produced by a Helmholtz coil. Using the Wiener filtering, the magnetic source images were obtained. We conclude that this biomagnetic method can be successfully used to generate planar functional images of the gastrointestinal tract using magnetic markers in the near field.

  11. 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.

  12. Theory of magnetoresistance due to lattice dislocations in face-centred cubic metals

    NASA Astrophysics Data System (ADS)

    Bian, Q.; Niewczas, M.

    2016-06-01

    A theoretical model to describe the low temperature magneto-resistivity of high purity copper single and polycrystals containing different density and distribution of dislocations has been developed. In the model, magnetoresistivity tensor is evaluated numerically using the effective medium approximation. The anisotropy of dislocation-induced relaxation time is considered by incorporating two independent energy bands with different relaxation times and the spherical and cylindrical Fermi surfaces representing open, extended and closed electron orbits. The effect of dislocation microstructure is introduced by means of two adjustable parameters corresponding to the length and direction of electron orbits in the momentum space, which permits prediction of magnetoresistance of FCC metals containing different density and distribution of dislocations. The results reveal that dislocation microstructure influences the character of the field-dependent magnetoresistivity. In the orientation of the open orbits, the quadratic variation in magnetoresistivity changes to quasi-linear as the density of dislocations increases. In the closed orbit orientation, dislocations delay the onset of magnetoresistivity saturation. The results indicate that in the open orbit orientations of the crystals, the anisotropic relaxation time due to small-angle dislocation scattering induces the upward deviation from Kohler's rule. In the closed orbit orientations Kohler's rule holds, independent of the density of dislocations. The results obtained with the model show good agreement with the experimental measurements of transverse magnetoresistivity in deformed single and polycrystal samples of copper at 2 K.

  13. Extremely large magnetoresistance in few-layer graphene/boron–nitride heterostructures

    PubMed Central

    Gopinadhan, Kalon; Shin, Young Jun; Jalil, Rashid; Venkatesan, Thirumalai; Geim, Andre K.; Neto, Antonio H. Castro; Yang, Hyunsoo

    2015-01-01

    Understanding magnetoresistance, the change in electrical resistance under an external magnetic field, at the atomic level is of great interest both fundamentally and technologically. Graphene and other two-dimensional layered materials provide an unprecedented opportunity to explore magnetoresistance at its nascent stage of structural formation. Here we report an extremely large local magnetoresistance of∼2,000% at 400 K and a non-local magnetoresistance of >90,000% in an applied magnetic field of 9 T at 300 K in few-layer graphene/boron–nitride heterostructures. The local magnetoresistance is understood to arise from large differential transport parameters, such as the carrier mobility, across various layers of few-layer graphene upon a normal magnetic field, whereas the non-local magnetoresistance is due to the magnetic field induced Ettingshausen–Nernst effect. Non-local magnetoresistance suggests the possibility of a graphene-based gate tunable thermal switch. In addition, our results demonstrate that graphene heterostructures may be promising for magnetic field sensing applications. PMID:26388149

  14. Structural and magnetic inhomogeneities, phase transitions, 55Mn nuclear magnetic resonance, and magnetoresistive properties of La0.6 - x Nd x Sr0.3Mn1.1O3-δ ceramics

    NASA Astrophysics Data System (ADS)

    Pashchenko, A. V.; Pashchenko, V. P.; Prokopenko, V. K.; Revenko, Yu. F.; Kisel, N. G.; Kamenev, V. I.; Sil'cheva, A. G.; Ledenev, N. A.; Burkhovetskii, V. V.; Levchenko, G. G.

    2014-05-01

    The structure, lattice imperfection, and properties of ceramic samples La0.6 - x Nd x Sr0.3Mn1.1O3-δ ( x = 0-0.4) have been investigated using the X-ray diffraction, resistive, magnetic (χac, 55Mn NMR), magnetoresistive and microscopic methods. It has been shown that there is a satisfactory agreement between the concentration decrease in the lattice parameters a of the rhombohedral ( x = 0, 0.1, 0.2) and cubic ( x = 0.3, 0.4) perovskite structures and the average ionic radii for the lattice containing anion vacancies, cation vacancies, and nanostructured clusters with Mn2+ ions in A-positions. With an increase in the neodymium concentration x, the vacancy-type imperfection increases, the cluster-type imperfection decreases, the temperatures of metal-semiconductor phase transition T ms and ferromagnetic-paramagnetic phase transition T C decrease, and the content of the ferromagnetic phase decreases. The anomalous hysteresis is associated with the appearance of unidirectional exchange anisotropy induced in a clustered perovskite structure consisting of a ferromagnetic matrix and a planar antiferromagnetic cluster coherently coupled with it. An analysis of the asymmetrically broadened 55Mn NMR spectra has revealed a high-frequency electronic double exchange (Mn3+-O2--Mn4+) ↔ (Mn4+-O2--Mn3+) and an inhomogeneity of the magnetic and charge states of manganese due to the heterogeneous environment of the manganese ions by other ions and defects. The observed changes in the resonant frequency and width of the resonance curve are caused by changes in the ratio Mn3+/Mn4+ and magnetic inhomogeneity. An increase in the neodymium concentration x leads to a decrease in the ferromagnetic phase content determined from the dependences 4π Nχac( T) and the 55Mn NMR curves. The phase diagram characterizes an interrelation between the composition, the imperfection of the structure, and the transport, magnetic, and magnetoresistive properties of lanthanum neodymium manganite

  15. Grain morphology and size disorder effect on the transport and magnetotransport in Sol-Gel grown nanostructured manganites

    NASA Astrophysics Data System (ADS)

    Kuberkar, D. G.; Doshi, R. R.; Solanki, P. S.; Khachar, Uma; Vagadia, Megha; Ravalia, Ashish; Ganesan, V.

    2012-09-01

    Nanostructured polycrystalline La0.7Ca0.3MnO3 (LCMO) and Nd0.7Sr0.3MnO3 (NSMO) manganites have been successfully synthesized at various temperatures ranging between 700 and 1100 °C using Sol-Gel method. Crystalline nature and morphology of the samples have been studied using XRD (Rietveld analysis) and TEM measurements. SEM studies reveal nanostructured grain morphology of LCMO and NSMO samples. It is observed that, with increase in sintering temperature, crystallinity and grain morphology get improved resulting in better transport. A strong dependence of transport on size variance has been observed in the systems studied. The modified transport and better magnetotransport properties of the manganites have been observed due to the large surface to volume ratio (surface contribution) in the nanostructured manganites. The observation of large low temperature MR in both the manganite systems and the interplay between the intrinsic and extrinsic MR components has been explained in the light of spin polarized tunneling effect, grain morphology, grain boundary nature and size disorder effect.

  16. Magnetic charges and magnetoelectricity in hexagonal rare-earth manganites and ferrites

    NASA Astrophysics Data System (ADS)

    Ye, Meng; Vanderbilt, David

    2015-07-01

    Magnetoelectric (ME) materials are of fundamental interest and show broad potential for technological applications. The common dominant contribution to the ME response is the lattice-mediated one, which is proportional to both the Born electric charge Ze and its analog, the dynamical magnetic charge Zm. Our previous study has shown that exchange striction acting on noncollinear spins induces much larger magnetic charges than those that depend on spin-orbit coupling. The hexagonal manganites R MnO3 and ferrites R FeO3 (R =Sc, Y, In, Ho-Lu) exhibit strong couplings between electric, magnetic, and structural degrees of freedom. The transition-metal ions in the basal plane antiferromagnetically coupled through super-exchange so as to form a 120∘ noncollinear spin arrangement. In this paper, we present a theoretical study of the magnetic charges, and of the spin-lattice and spin-electronic ME constants, in these hexagonal manganites and ferrites. We clarify the conditions under which exchange striction leads to enhanced Zm values and anomalously large in-plane spin-lattice ME effects.

  17. Cooperative phonon effects in the metal-insulator transitions of manganite and nickelate perovskites

    NASA Astrophysics Data System (ADS)

    Brierley, Richard T.; Guzmán Verri, Gian G.; Littlewood, Peter B.

    Metal-insulator transitions in manganite and nickelate perovskites depend on the competition between the electron kinetic energy, which favors the metallic phase, and the electron-phonon coupling and Coulomb interaction, which favor localization. The size of the A-site cation controls the relative rotation of the octahedral structural units of the perovskite in the range of 0 - 15°. This is accompanied by changes in the metal-insulator transition temperature from 0 - 600K . This effect is commonly attributed to modification in the electron bandwidth from changes in orbital overlap. Although previous theoretical studies of these materials include the electron-phonon interaction, they typically do not consider cooperative phonon effects. Using a phenomenological model of the perovskite structure, we show that the long-range anisotropic forces arising from inter-site phonon interactions are modulated by changes in the octahedral rotation. We demonstrate using statistical mechanical calculations that these changes in the strain interaction can capture the variation in transition temperature with tolerance factor observed in both the manganites and nickelates.

  18. 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.

  19. Controlled lateral anisotropy in correlated manganite heterostructures by interface-engineered oxygen octahedral coupling

    NASA Astrophysics Data System (ADS)

    Huijben, Mark

    Ultimate miniaturization of magnetic random access memory (MRAM) devices is expected by the utilization of spin-transfer torques, because they present an efficient means to switch elements with a very high magnetic anisotropy. To overcome the low switching speed in current collinearly magnetized devices, new routes are being explored to realize magnetic tunnel junction stacks with non-collinear magnetization between two magnetic electrodes. Controlled in-plane rotation of the magnetic easy axis in manganite heterostructures by tailoring the interface oxygen network would provide a promising direction for non-collinear magnetization in correlated oxide magnetic tunneling junctions. 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. Membership Pending.

  20. 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.

  1. Development of Uncooled Micro-bolometer Arrays Based on Hole-doped Rare-Earth Manganites

    NASA Astrophysics Data System (ADS)

    Tanyi, E.; Yong, Grace; Keshavarz, Camron; Sharma, Prakash; Rubin, Christopher; Kolagani, Rajeswari; Gross, Steven

    2013-03-01

    Material properties indicate that rare earth manganites have a competitive advantage over VOx which is a material commonly employed as bolometric sensors in state of the art uncooled imaging arrays. We will present the results of our work on developing manganite thin films for uncooled micro-bolometer arrays. By fine tuning the cation composition and stoichiometry, we have identified material compositions suitable for uncooled bolometer operation and developed thin films of these materials by Pulsed Laser Deposition (PLD) on Si. For hetero-epitaxy on Si, we employ lattice engineering schemes to circumvent problems such as chemical incompatibility and amorphization of the substrate surface due to the native oxide. We are in the process of fabricating single test bolometers and micro-bolometer arrays. We will discuss the results of materials development and device fabrication efforts and will present performance parameters and estimated figures of merit for test bolometers. We will also discuss efforts towards understanding and alleviating material problems such as the residual stresses in the thin film heterostructures which are of critical importance for the fabrication of suspended microstructures. We acknowledge support from the NSF grant ECCS 1128586 at Towson University.

  2. 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

  3. Kinetic study of the formation of oxygen vacancy on lanthanum manganite electrodes

    SciTech Connect

    Jiang, Y.; Wang, S.; Zhang, Y.; Yan, J.; Li, W.

    1998-02-01

    Strontium doped lanthanum manganite (LSM) has been considered one of the most promising cathode materials for solid oxide fuel cells (SOFC). The electrochemical reduction of oxygen on lanthanum manganite (LSM) electrodes has been investigated by cyclic voltammetry, alternating current (ac) impedance, and, in particular, potential step. An emphasis was given to the study of the kinetics of the formation of oxygen vacancy, which is shown to be the main cause for the reversed hysteresis in cyclic voltammograms and for the increase in the electrochemical activity of oxygen reduction on the cathodically polarized LSM electrode observed in both ac impedance and in potential step experiments. The potential step experiments show that the oxygen vacancy concentration increases exponentially with time when the LSM is under a cathodic polarization. In the present study, the rate controlling step for the formation of oxygen vacancies is the oxygen vacancy generation step. The cathodic current rising from the reaction on oxygen vacancies can make a significant contribution to the total reduction current.

  4. 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 .

  5. Scanning tunneling microscopy for laterally resolved measurements of magnetoresistance through a point contact

    NASA Astrophysics Data System (ADS)

    Wahlström, Erik; Bručas, Rimantas; Hanson, Maj

    2006-03-01

    Using a scanning tunneling microscope for point contact measurements, we obtained laterally resolved information of the magnetoresistive properties of nanostructured spin-valve elements. A good correlation is found between magnetization and magnetoresistance curves of single-domain elliptical elements (450nm by 150nm), for magnetic fields applied along their long and short axes. In ring-shaped elements (inner and outer diameters 1.8 and 2.2μm), different magnetoresistance curves are acquired as different points around the ring are probed. The observed switching can be related to the onion state of the rings, and it clearly demonstrates a lateral resolution ⩽100nm.

  6. Giant magnetoresistance in the cluster glass regime of Co-Ga alloys

    NASA Astrophysics Data System (ADS)

    Mohammad Yasin, Sk; Saha, Ritwik; Srinivas, V.; Kasiviswanathan, S.; Nigam, A. K.

    2016-05-01

    A detailed study of low temperature electrical transport properties of CoxGa100-x (x = 54, 55.5, 57) alloy has been carried out. The origin of the resistivity anomalies and correlation between magnetic and electrical transport properties are identified through an elaborate analysis. The weak localization and enhanced electron-electron interaction effects partially support the electrical transport properties of the system. Further, the observed magnetoresistance can be well represented by localized model along with quantum corrections. The low temperature magnetoresistance value near critical composition is comparable to that reported in giant magnetoresistance materials.

  7. 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.

  8. The magnetization process and magnetoresistance of exchange-spring bilayer systems

    NASA Astrophysics Data System (ADS)

    Nagahama, T.; Mibu, K.; Shinjo, T.

    1998-01-01

    A perfectly reversible magnetization process was observed in NiFe/CoSm bilayers. During this process, the magnetic moments in the soft magnetic layer (NiFe) are pinned at the interface with the hard magnetic layer (CoSm), so that the direction of the magnetic moment distributes successively like a Bloch wall. The characteristic reversible magnetization process is explained by an atomic layer model. The magnetoresistance also exhibits a reversible change reflecting the magnetization process. The basic feature of the reversible magnetoresistance curve is understood to be anisotropic magnetoresistance.

  9. 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

  10. Evidence of weak localization in quantum interference effects observed in epitaxial La0.7Sr0.3MnO3 ultrathin films.

    PubMed

    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 T(1/2) 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

  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. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 360 degree domain walls monitored by anisotropic magnetoresistance measurements

    NASA Astrophysics Data System (ADS)

    Nam, Chunghee; Ross, C. A.

    2013-03-01

    This study investigates the electrical observation of the formation of a 360° magnetic domain wall (360DW) in an elliptical Co ring structure. Because the 360DW consists of two 180° domain walls, a decrease in resistance is observed in the switching process due to anisotropic magnetoresistance (AMR). Certain AMR measurements exhibit an increase in the resistance in the switching process, indicating that a flux-closure vortex state is formed without first forming a 360DW state. The difference between the 360DW and vortex state in the switching process reflects differences in the DW depinning mechanism from the onion state. The minor loop of the AMR measurements is also dependent on the initial magnetic configuration between the 360DW and the vortex state.

  1. Low-field giant magnetoresistance in layered magnetic rings

    NASA Astrophysics Data System (ADS)

    Castaño, F. J.; Morecroft, D.; Ross, C. A.

    2006-12-01

    The low-field magnetization reversal of NiFe/Cu/Co multilayer mesoscopic elliptical and circular rings has been investigated via magnetoresistance measurements and micromagnetic modeling. Minor loop measurements, in which the NiFe layer is cycled for a fixed Co layer configuration, show qualitatively different behavior depending on whether the Co layer is present in a vortex or an onion state. Micromagnetic simulations are in excellent agreement with the experimental data and confirm the dominant role played by magnetostatic interactions between the Co and NiFe layers, as a result of stray fields from the domain walls present in the layers. Multiple stable remanent resistance levels can be obtained by cycling the rings at modest fields.

  2. Raman scattering investigation of large positive magnetoresistance material WTe2

    NASA Astrophysics Data System (ADS)

    Kong, W.-D.; Wu, S.-F.; Richard, P.; Lian, C.-S.; Wang, J.-T.; Yang, C.-L.; Shi, Y.-G.; Ding, H.

    2015-02-01

    We have performed polarized Raman scattering measurements on WTe2, for which an extremely large positive magnetoresistance has been reported recently. We observe 5 A1 phonon modes and 2 A2 phonon modes out of 33 Raman active modes, with frequencies in good accordance with first-principles calculations. The angular dependence of the intensity of the peaks observed is consistent with the Raman tensors of the C2v point group symmetry attributed to WTe2. Although the phonon spectra suggest neither strong electron-phonon nor spin-phonon coupling, the intensity of the A1 phonon mode at 160.6 cm-1 shows an unconventional decrease with temperature decreasing, for which the origin remains unclear.

  3. Correlation of crystal quality and extreme magnetoresistance of WTe2

    NASA Astrophysics Data System (ADS)

    Ali, Mazhar N.; Schoop, Leslie; Xiong, Jun; Flynn, Steven; Gibson, Quinn; Hirschberger, Max; Ong, N. P.; Cava, R. J.

    2015-06-01

    High-quality single crystals of WTe2 were grown using a Te flux followed by a cleaning step involving self-vapor transport. The method is reproducible and yields consistently higher-quality single crystals than are typically obtained via halide-assisted vapor transport methods. Magnetoresistance (MR) values at 9 tesla and 2 kelvin as high as 1.75 million %, nearly an order of magnitude higher than previously reported for this material, were obtained on crystals with residual resistivity ratio (RRR) of approximately 1250. The MR follows a near B 2 law (B = 1.95(1)) and, assuming a semiclassical model, the average carrier mobility for the highest-quality crystal was found to be 167,000 \\text{cm}^2/\\text{Vs} at 2 K. A correlation of RRR, MR ratio and average carrier mobility (μ\\textit{avg}) is found with the cooling rate during the flux growth.

  4. 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.

  5. 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

  6. 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 .

  7. 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. PMID:25554336

  8. Impurity-Assisted Tunneling Magnetoresistance under a Weak Magnetic Field

    NASA Astrophysics Data System (ADS)

    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.

  9. Longitudinal Magnetoresistance and “Chiral" Coupling in Silver Chalcogenides

    NASA Astrophysics Data System (ADS)

    Xu, Jie; Zhang, Duan-Ming

    2011-03-01

    A complex longitudinal magnetoresistance (MR//) effect in the non-stoichiometric silver chalcogenides (include the silver selenide and telluride) has been found, however the mechanism for the MR// effect is not clear now. In this work, a new random resistor network for MR// effect is proposed based on the experimental observation. The network is constructed from six-terminal resistor units and the mobility of carries within the network has a Gaussian distribution. Considering the non-zero transverse-longitudinal coupling in materials, the resistance matrix of the six-terminal resistor unit is modified. It is found that the material has the “chiral" transverse-longitudinal couplings, which is suggested a main reason for the complex MR// effect. The model predictions are compared with the experimental results. A three dimension (3D) visualization of current flow within the network demonstrates the “current jets" phenomenon in the thickness of materials clearly.

  10. On-chip magnetoresistive detection of resonance in microcantilevers

    NASA Astrophysics Data System (ADS)

    Patil, S. B.; Guedes, A.; Freitas, P. P.; Cardoso, S.; Chu, V.; Conde, J. P.

    2009-07-01

    Magnetoresistive spin-valve sensors were used to provide on-chip detection of the mechanical resonance of a thin silicon microelectromechanical systems cantilever. The spin-valve sensor was placed underneath the free end of the cantilever. A CoCrPt thin-film permanent magnet was placed on top of the amorphous silicon/Al cantilever. The cantilever was electrostatically actuated and its deflection creates a change in the magnetic field that can be sensed by the spin-valve sensor. The resonance frequency of the structure in the megahertz range is detected by the measurement of the spin-valve sensor output. Minimum deflection detection limit is determined to be 0.06 Å/Hz1/2.

  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. 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. Spin-valley filter and tunnel magnetoresistance in asymmetrical silicene magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Wang, Dali; Huang, Zeyuan; Zhang, Yongyou; Jin, Guojun

    2016-05-01

    The spin and valley transports and tunnel magnetoresistance are studied in a silicene-based asymmetrical magnetic tunnel junction consisting of a ferromagnetic tunnel barrier, sandwiched between a ferromagnetic electrode and a normal electrode. For such an asymmetrical silicene junction, a general formulism is established. The numerical results show that the spin-valley resolved conductances strongly depend on the magnetization orientation of the ferromagnetic tunnel barrier, and the fully spin-valley polarized current can be realized by tuning a perpendicularly applied electric field. We also find that the tunnel magnetoresistance in this case can be effectively modified by the external electric field when the conductance is fully spin-valley polarized. In particular, the exchange field in the ferromagnetic electrode can further substantially enhance the tunnel magnetoresistance of the system. Our work provides a practical method for electric and magnetic manipulation of valley/spin polarization and tunnel magnetoresistance.

  14. Drastic Pressure Effect on the Extremely Large Magnetoresistance in WTe2 : Quantum Oscillation Study

    NASA Astrophysics Data System (ADS)

    Cai, P. L.; Hu, J.; He, L. P.; Pan, J.; Hong, X. C.; Zhang, Z.; Zhang, J.; Wei, J.; Mao, Z. Q.; Li, S. Y.

    2015-07-01

    The quantum oscillations of the magnetoresistance under ambient and high pressure have been studied for WTe2 single crystals, in which extremely large magnetoresistance was discovered recently. By analyzing the Shubnikov-de Haas oscillations, four Fermi surfaces are identified, and two of them are found to persist to high pressure. The sizes of these two pockets are comparable, but show increasing difference with pressure. At 0.3 K and in 14.5 T, the magnetoresistance decreases drastically from 1.25 ×105% under ambient pressure to 7.47 ×103% under 23.6 kbar, which is likely caused by the relative change of Fermi surfaces. These results support the scenario that the perfect balance between the electron and hole populations is the origin of the extremely large magnetoresistance in WTe2 .

  15. Extremely large and significantly anisotropic magnetoresistance in ZrSiS single crystals

    NASA Astrophysics Data System (ADS)

    Lv, Yang-Yang; Zhang, Bin-Bin; Li, Xiao; Yao, Shu-Hua; Chen, Y. B.; Zhou, Jian; Zhang, Shan-Tao; Lu, Ming-Hui; Chen, Yan-Feng

    2016-06-01

    Recently, the extremely large magnetoresistance (MR) observed in transition metal telluride, like WTe2, attracted much attention because of the potential applications in magnetic sensor. Here, we report the observation of extremely large magnetoresistance as 3.0 × 104% measured at 2 K and 9 T magnetic field aligned along [001]-ZrSiS. The significant magnetoresistance change (˜1.4 × 104%) can be obtained when the magnetic field is titled from [001] to [011]-ZrSiS. These abnormal magnetoresistance behaviors in ZrSiS can be understood by electron-hole compensation and the open orbital of Fermi surface. Because of these superior MR properties, ZrSiS may be used in the magnetic sensors.

  16. Drastic Pressure Effect on the Extremely Large Magnetoresistance in WTe2: Quantum Oscillation Study.

    PubMed

    Cai, P L; Hu, J; He, L P; Pan, J; Hong, X C; Zhang, Z; Zhang, J; Wei, J; Mao, Z Q; Li, S Y

    2015-07-31

    The quantum oscillations of the magnetoresistance under ambient and high pressure have been studied for WTe2 single crystals, in which extremely large magnetoresistance was discovered recently. By analyzing the Shubnikov-de Haas oscillations, four Fermi surfaces are identified, and two of them are found to persist to high pressure. The sizes of these two pockets are comparable, but show increasing difference with pressure. At 0.3 K and in 14.5 T, the magnetoresistance decreases drastically from 1.25×10(5)% under ambient pressure to 7.47×10(3)% under 23.6 kbar, which is likely caused by the relative change of Fermi surfaces. These results support the scenario that the perfect balance between the electron and hole populations is the origin of the extremely large magnetoresistance in WTe2. PMID:26274436

  17. Hanle Magnetoresistance in Thin Metal Films with Strong Spin-Orbit Coupling

    NASA Astrophysics Data System (ADS)

    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 /Y3Fe5O12 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.

  18. 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

  19. 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.

  20. Comparison of a prototype magnetoresistive biosensor to standard fluorescent DNA detection.

    PubMed

    Schotter, J; Kamp, P B; Becker, A; Pühler, A; Reiss, G; Brückl, H

    2004-05-15

    We present a comparative analysis of a magnetoresistive biosensor to standard fluorescent DNA detection. The biosensor consists of giant magnetoresistive (GMR) type Cu/Ni(80)Fe(20) multilayers in the second antiferromagnetic coupling maximum. Each of the 206 elements of the magnetoresistive biosensor is patterned into a spiral-shaped line that can cover the area of a typical DNA spot (70 microm diameter). The probe DNA is assembled on top of the sensor elements in different concentrations ranging from 16 pg/microl to 10 ng/microl. Complementary biotin-labeled analyte DNA is hybridized to the probe DNA at a concentration of 10 ng/microl. A number of different commercially available magnetic microspheres are investigated to determine the most appropriate markers. The experimental comparison shows that the relative sensitivity of the magnetoresistive biosensor is superior to the fluorescent detection at low probe DNA concentrations. PMID:15046745