Showing papers on "Colossal magnetoresistance published in 2014"
TL;DR: The observation of an extremely large positive magnetoresistance at low temperatures in the non-magnetic layered transition-metal dichalcogenide WTe2 is reported, which will represent a significant new direction in the study of magnetoresistivity.
Abstract: The magnetoresistance effect in WTe2, a layered semimetal, is extremely large: the electrical resistance can be changed by more than 13 million per cent at very high magnetic fields and low temperatures. Apply a magnetic field to a magnetoresistive material and its electrical resistance changes — a technologically useful phenomenon that is harnessed, for example, in the data-reading sensors of hard drives. Mazhar Ali and colleagues have now identified a material (tungsten ditelluride or WTe2) in which the magnetoresistance effect is unusually large: the electrical resistance can be changed by more than 13 million per cent. Its remarkable magnetoresitance is evident at very high magnetic fields and at extremely low temperatures, so practical applications are not yet in prospect. But this finding suggests new directions in the study of magnetoresistivity that could ultimately lead to new uses of this effect. 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 sensors1, in magnetic memory2, and in hard drives3 at room temperature, and their rarity has motivated many fundamental studies in materials physics at low temperatures4. 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.
1,364 citations
TL;DR: In this article, angle-resolved photoelectron spectroscopy was used to investigate the electronic structure basis of magnetoresistance in layered nonmagnetic tungsten ditelluride.
Abstract: 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.
232 citations
Book•
12 Mar 2014
TL;DR: In this article, the discovery of Manganites and the Colossal Magnetoresistance Effect was discussed. But the main focus was on phase diagrams and basic properties of the Manganite model.
Abstract: 1. Why Manganites Are Interesting.- 2. The Discovery of Manganites and the Colossal Magnetoresistance Effect.- 3. Phase Diagrams and Basic Properties of Manganites.- 4. Preliminary Theoretical Considerations: Coulombic and Jahn Teller Effects.- 5. Models for Manganites.- 6. The One-Orbital Model: Phase Diagram and Dominant Correlations.- 7. Monte Carlo Simulations and Application to Manganite Models.- 8. Mean-Field Approximation.- 9. Two-Orbitals Model and Orbital Order.- 10. Charge Ordering: CE-States, Stripes, and Bi-Stripes.- 11. Inhomogeneities in Manganites: The Case of La1?xCaxMnO3.- 12. Optical Conductivity.- 13. Glassy Behavior and Time-Dependent Phenomena.- 14. Inhomogeneities in La1?xSrxMnO3 and Pr1?xCaxMnO3.- 15. Inhomogeneities in Layered Manganites.- 16. An Elementary Introduction to Percolation.- 17. Competition of Phases as the Origin of the CMR.- 18. Pseudogaps and Photoemission Experiments.- 19. Charge-Ordered Nanoclusters above TC: the Smoking Gun of Phase Separation?.- 20. Other Compounds with Large MR and/or Competing FM AF Phases.- 21. Brief Introduction to Giant Magnetoresistance (GMR).- 22. Discussion and Open Questions.- References.
229 citations
TL;DR: This work reports a Na5/8MnO2 superstructure with a pronounced static CJTE that is coupled to an unusual Na vacancy ordering that demonstrates the strong interaction between alkali ordering, displacement, and electronic and magnetic structure, and underlines the important role that structural details play in determining electronic behaviour.
Abstract: The cooperative Jahn-Teller effect (CJTE) refers to the correlation of distortions arising from individual Jahn-Teller centres in complex compounds. The effect usually induces strong coupling between the static or dynamic charge, orbital and magnetic ordering, which has been related to many important phenomena such as colossal magnetoresistance and superconductivity. Here we report a Na5/8MnO2 superstructure with a pronounced static CJTE that is coupled to an unusual Na vacancy ordering. We visualize this coupled distortion and Na ordering down to the atomic scale. The Mn planes are periodically distorted by a charge modulation on the Mn stripes, which in turn drives an unusually large displacement of some Na ions through long-ranged Na-O-Mn(3+)-O-Na interactions into a highly distorted octahedral site. At lower temperatures, magnetic order appears, in which Mn atomic stripes with different magnetic couplings are interwoven with each other. Our work demonstrates the strong interaction between alkali ordering, displacement, and electronic and magnetic structure, and underlines the important role that structural details play in determining electronic behaviour.
228 citations
TL;DR: Temperature-dependent measurements of the resistance and anisotropic magnetoresistance highlight the large, entangled tunabilities of the ordinary charge and spin-dependent transport in a spintronic device utilizing the antiferromagnet semiconductor.
Abstract: The change in the electrical properties of a ferromagnetic under the influence of a magnetic field depends strongly on field orientation Marti et al now show that this so-called anisotropic magnetoresistance is also evident in antiferromagnetic semiconductors, making them useful in spintronics
147 citations
TL;DR: In this article, the current understanding and fundamental issues related to the size effects on the magnetic properties and charge ordering in perovskite oxides are reviewed, which covers lattice structure, magnetic and electronic properties in both ferromagnetic and antiferromagnetic based manganites.
Abstract: 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.
91 citations
TL;DR: In this paper, a reversible control of ferromagnetic phase transition in manganite films through ionic liquid gating is reported, where the formation and annihilation of an insulating and magnetically hard phase in the magnetically soft matrix, which randomly nucleates and grows across the film instead of initiating at the surface and spreading to the bottom, is directly observed.
Abstract: The electronic phase transition has been considered as a dominant factor in the phenomena of colossal magnetoresistance, metal-insulator transition, and exchange bias in correlated electron systems. However, the effective manipulation of the electronic phase transition has remained a challenging issue. Here, the reversible control of ferromagnetic phase transition in manganite films through ionic liquid gating is reported. Under different gate voltages, the formation and annihilation of an insulating and magnetically hard phase in the magnetically soft matrix, which randomly nucleates and grows across the film instead of initiating at the surface and spreading to the bottom, is directly observed. This discovery provides a conceptually novel vision for the electric-field tuning of phase transition in correlated oxides. In addition to its fundamental significance, the realization of a reversible metal-insulator transition in colossal magnetoresistance materials will also further the development of four-state memories, which can be manipulated by a combination of electrode gating and the application of a magnetic field.
80 citations
TL;DR: In this article, the transport properties of a ferromagnetic topological insulator thin film fabricated into a field effect transistor device were investigated, and the authors observed 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.
Abstract: 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.
58 citations
TL;DR: In this article, the authors predict a magnetoresistance induced by the interfacial Rashba spin-orbit coupling in normal metal/ferromagnetic insulator bilayers, which depends on the angle between current and magnetization directions.
Abstract: We predict a magnetoresistance induced by the interfacial Rashba spin-orbit coupling in normal metal/ferromagnetic insulator bilayers It depends on the angle between current and magnetization directions as found for the ``spin Hall magnetoresistance'' mechanism, ie, the combined action of spin Hall and inverse spin Hall effects By the identical phenomenology it is not obvious whether the magnetoresistance reported by Nakayama et al [Phys Rev Lett 110, 206601 (2013)] is a bulk metal or interface effect The interfacial Rashba-induced magnetoresistance may be distinguished from the bulk metal spin Hall magnetoresistance by its dependence on the metal film thickness
49 citations
TL;DR: In this paper, the spin injection efficiency was increased by employing 1.6 nm-thick MgO tunnel barrier, resulting in large non-local magnetoresistance in two-terminal scheme.
Abstract: 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 ohm 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.
44 citations
TL;DR: In this paper, negative magnetoresistance (MR) in a GaAs/AlGaAs quantum well is reported, which, at low temperatures, is manifested by a drop of the resistivity by more than an order of magnitude at a magnetic field $B\ensuremath{\approx}1$ kG.
Abstract: We report on a colossal negative magnetoresistance (MR) in a GaAs/AlGaAs quantum well which, at low temperatures, is manifested by a drop of the resistivity by more than an order of magnitude at a magnetic field $B\ensuremath{\approx}1$ kG. In contrast to MR effects discussed earlier, the MR reported here is not parabolic, even at small $B$, and persists to much higher in-plane magnetic fields and temperatures. Remarkably, the temperature dependence of the resistivity at $B\ensuremath{\approx}1$ kG is linear over the entire temperature range studied (from 1 to 30 K) and appears to coincide with the high-temperature limit of the zero-field resistivity, hinting on the important role of acoustic phonons.
TL;DR: A paradigmatic magnetostructurally inhomogenous ground state of the geometrically frustrated α-NaMnO2 that stems from the system’s aspiration to remove magnetic degeneracy and is possible only due to the existence of near-degenerate crystal structures is reported.
Abstract: Phase inhomogeneity of otherwise chemically homogenous electronic systems is an essential ingredient leading to fascinating functional properties, such as high-Tc superconductivity in cuprates, colossal magnetoresistance in manganites and giant electrostriction in relaxors In these materials distinct phases compete and can coexist owing to intertwined ordered parameters Charge degrees of freedom play a fundamental role, although phase-separated ground states have been envisioned theoretically also for pure spin systems with geometrical frustration that serves as a source of phase competition Here we report a paradigmatic magnetostructurally inhomogenous ground state of the geometrically frustrated α-NaMnO2 that stems from the system’s aspiration to remove magnetic degeneracy and is possible only due to the existence of near-degenerate crystal structures Synchrotron X-ray diffraction, nuclear magnetic resonance and muon spin relaxation show that the spin configuration of a monoclinic phase is disrupted by magnetically short-range-ordered nanoscale triclinic regions, thus revealing a novel complex state of matter The compound α-NaMnO2is very interesting due to the complexity of its phases, which are governed by different degrees of freedom Here, the authors show that this compound possesses ground-state inhomogeneities due to geometrical frustration and simultaneously active spin and lattice degrees of freedom
TL;DR: A novel current-perpendicular-to-plane magnetoresistance effect in multilayer graphene as grown on a catalytic nickel surface by chemical vapor deposition is reported, which persists even at room temperature.
Abstract: Strong magnetoresistance effects are often observed in ferromagnet–nonmagnet multilayers, which are exploited in state-of-the-art magnetic field sensing and data storage technologies. In this work we report a novel current-perpendicular-to-plane magnetoresistance effect in multilayer graphene as grown on a catalytic nickel surface by chemical vapor deposition. A negative magnetoresistance effect of ∼104% has been observed, which persists even at room temperature. This effect is correlated with the shape of the 2D peak as well as with the occurrence of D peak in the Raman spectrum of the as-grown multilayer graphene. The observed magnetoresistance is extremely high as compared to other known materials systems for similar temperature and field range and can be qualitatively explained within the framework of “interlayer magnetoresistance” (ILMR).
TL;DR: In this paper, experimental and theoretical studies of the metal-insulator (MI) transition in manganites with colossal magnetoresistance are reviewed, focusing on the properties of these systems caused by inhomogeneities in the electronic and magnetic states of the manganite near the Curie temperature.
Abstract: Experimental and theoretical studies of the physics of the metal-insulator (MI) transition in manganites with colossal magnetoresistance are reviewed. The emphasis is on the properties of these systems caused by inhomogeneities in the electronic and magnetic states of the manganites near the Curie temperature. Experimental data supporting the existence of the Griffiths phase and theoretical treatments of the MI transition as a specific realization of a ferromagnetic-Griffiths phase transition in substituted manganites are discussed.
TL;DR: In this article, the exchange bias effect was observed in Nd2/3Ca1/3MnO3 colossal magnetoresistance perovskite below the Curie temperature of 70 K and attributed to an antiferromagnetic (AFM)-ferromagnetic spontaneous phase segregated state of this compound.
Abstract: Exchange bias (EB) phenomena have been observed in Nd2/3Ca1/3MnO3 colossal magnetoresistance perovskite below the Curie temperature $T_{C}$ = 70 K and attributed to an antiferromagnetic (AFM) - ferromagnetic (FM) spontaneous phase segregated state of this compound. Field cooled magnetic hysteresis loops exhibit shifts toward negative direction of the magnetic field axis. The values of exchange field $H_{EB}$ and coercivity $H_{C}$ are found to be strongly dependent of temperature and strength of the cooling magnetic field $H_{cool}$. These effects are attributed to evolution of the FM phase content and a size of FM clusters. A contribution to the total magnetization of the system due to the FM phase has been evaluated. The exchange bias effect decreases with increasing temperature up to $T_{C}$ and vanishes above this temperature with disappearance of FM phase. Relaxation of a non-equilibrium magnetic state of the compound manifests itself through a training effect also observed while studying EB in Nd2/3Ca1/3MnO3.
TL;DR: In this paper, the exchange bias effect decreases with increasing temperature up to TC and vanishes above this temperature with disappearance of the antiferromagnetic-ferromagnetic (FM) spontaneous phase segregated state of this compound.
Abstract: Exchange bias (EB) phenomena have been observed in Nd2/3Ca1/3MnO3 colossal magnetoresistance perovskite below the Curie temperature TC ∼ 70 K and attributed to an antiferromagnetic–ferromagnetic (FM) spontaneous phase segregated state of this compound. Field cooled magnetic hysteresis loops exhibit shifts toward negative direction of the magnetic field axis. The values of exchange field HEB and coercivity HC are found to be strongly dependent of temperature and strength of the cooling magnetic field Hcool. These effects are attributed to evolution of the FM phase content and a size of FM clusters. A contribution to the total magnetization of the system due to the FM phase has been evaluated. The exchange bias effect decreases with increasing temperature up to TC and vanishes above this temperature with disappearance of FM phase. Relaxation of a non-equilibrium magnetic state of the compound manifests itself through a training effect also observed while studying EB in Nd2/3Ca1/3MnO3.
TL;DR: In this article, the giant magnetoresistance and magnetoelectric effects of Z-type hexaferrite Sr3Co2Fe24O41 were investigated, and the results reveal great potential for emerging applications of multifunctional magnet-electric ferrite materials.
Abstract: The giant magnetoresistance and magnetoelectric (ME) effects of Z-type hexaferrite Sr3Co2Fe24O41 were investigated. The present experiments indicated that an induced magnetoelectric current in a transverse conical spin structure not only presented a nonlinear behavior with magnetic field and electric field but also depended upon a sweep rate of the applied magnetic field. More interestingly, the ME current induced magnetoresistance was measured, yielding a giant room temperature magnetoresistance of 32.2% measured at low magnetic fields (∼125 Oe). These results reveal great potential for emerging applications of multifunctional magnetoelectric ferrite materials.
TL;DR: In this paper, the magnetic proximity effect was extended to Ta which has been reported to have a negative spin Hall angle and the size of the MR ratio observed (∼10−5) and its magnetization direction dependence are similar to that reported in Pt/yttrium iron garnet, both of which can be explained by spin Hall magnetoresistance theory.
Abstract: In this work, the investigation of magnetic proximity effect was extended to Ta which has been reported to have a negative spin Hall angle. Magnetoresistance (MR) and Hall measurements for in-plane and out-of-plane applied magnetic field sweeps were carried out at room temperature. The size of the MR ratio observed (∼10−5) and its magnetization direction dependence are similar to that reported in Pt/yttrium iron garnet, both of which can be explained by the spin Hall magnetoresistance theory. Additionally, a flip of magnetoresistance polarity is observed at 4 K in the temperature dependent measurements, which can be explained by the magnetic proximity effect induced anisotropic magnetoresistance at low temperature. Our findings suggest that both magnetic proximity effect and spin Hall magnetoresistance have contribution to the recently observed unconventional magnetoresistance effect.
TL;DR: In this paper, the influence of excess manganese on structure defects and functional properties of (Nd0.7Sr0.3)1−xMn1+xO3 ceramics annealed at 1200 and 1500°C was investigated.
TL;DR: This work fabricated a self-assembled nanocomposite composed of magnetic CoFe2O4 mesocrystal in Sr-doped manganites and induced an additional magnetic perturbation to spin-polarized electrons, resulting in a significantly enhanced magnetoresistance in the nanocomPOSite.
Abstract: Mesocrystal, a new class of crystals as compared to conventional and well-known single crystals and polycrystalline systems, has captured significant attention in the past decade. Recent studies have been focused on the advance of synthesis mechanisms as well as the potential on device applications. In order to create further opportunities upon functional mesocrystals, we fabricated a self-assembled nanocomposite composed of magnetic CoFe2O4 mesocrystal in Sr-doped manganites. This combination exhibits intriguing structural and magnetic tunabilities. Furthermore, the antiferromagnetic coupling of the mesocrystal and matrix has induced an additional magnetic perturbation to spin-polarized electrons, resulting in a significantly enhanced magnetoresistance in the nanocomposite. Our work demonstrates a new thought toward the enhancement of intrinsic functionalities assisted by mesocrystals and advanced design of novel mesocrystal-embedded nanocomposites.
TL;DR: In this article, the electrical resistivity is fitted with the phenomenological percolation model which is based on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions.
TL;DR: A subnanometer scale map of the transition metal oxidation state profile across the interface between the high Tc superconductor YBa2Cu3O7-δ and the colossal magnetoresistance compound (La,Ca)MnO3 is produced.
Abstract: Here we study the electronic properties of cuprate-manganite interfaces. By means of atomic resolution electron microscopy and spectroscopy, we produce a subnanometer scale map of the transition metal oxidation state profile across the interface between the high Tc superconductor YBa_(2)Cu_(3)O_(7−δ) and the colossal magnetoresistance compound (La,Ca)MnO_(3). A net transfer of electrons from manganite to cuprate with a peculiar nonmonotonic charge profile is observed. Model calculations rationalize the profile in terms of the competition between standard charge transfer tendencies (due to band mismatch), strong chemical bonding effects across the interface, and Cu substitution into the Mn lattice, with different characteristic length scales.
20 Oct 2014
TL;DR: In this paper, a detailed analysis of the magnetotransport properties of small polarons in thin films of the low bandwidth manganite Pr0.68Ca0.32MnO3 with different degrees of preparation-induced octahedral disorder is presented.
Abstract: The colossal magnetoresistance effect (CMR), the drop of the electric resistance by orders of magnitude in a strong magnetic field, is a fascinating property of strongly correlated electrons in doped manganites. Here, we present a detailed analysis of the magnetotransport properties of small polarons in thin films of the low bandwidth manganite Pr0.68Ca0.32MnO3 with different degrees of preparation-induced octahedral disorder. The crystal and defect structure is investigated by means of high-resolution transmission electron microscopy. We apply the small polaron theory developed by Firsov and Lang in order to study the hopping mobility in the paramagnetic phase and its changes due to the formation of the antiferromagnetic charge ordered (CO) and the ferromagnetic metallic phases. Although it represents a single particle theory, reasonable estimates of small polaron properties such as formation energy, activation energy and transfer integral are possible, if the effects of interactions and disorder are taken into account. Beyond the well-known effect of the magnetic double exchange on the transfer integral, we show that the emergence of band transport of small polarons in the CMR transition sensibly depends on the degree of octahedral disorder, the polaron–polaron interactions and the resulting long range order leading to a structural phase transition in the CO phase.
TL;DR: It is revealed that a significant part of the lattice effects originates in the magnetically driven delocalization of charge carriers, consistent with the scenario of percolating magnetic polarons.
Abstract: The coupling of magnetic and electronic degrees of freedom to the crystal lattice in the ferromagnetic semimetal EuB(6), which exhibits a complex ferromagnetic order and a colossal magnetoresistance effect, is studied by high-resolution thermal expansion and magnetostriction experiments. EuB(6) may be viewed as a model system, where pure magnetism-tuned transport and the response of the crystal lattice can be studied in a comparatively simple environment, i.e., not influenced by strong crystal-electric field effects and Jahn-Teller distortions. We find a very large lattice response, quantified by (i) the magnetic Gruneisen parameter, (ii) the spontaneous strain when entering the ferromagnetic region, and (iii) the magnetostriction in the paramagnetic temperature regime. Our analysis reveals that a significant part of the lattice effects originates in the magnetically driven delocalization of charge carriers, consistent with the scenario of percolating magnetic polarons. A strong effect of the formation and dynamics of local magnetic clusters on the lattice parameters is suggested to be a general feature of colossal magnetoresistance materials.
TL;DR: A series of polycrystalline La0.85−xSmxK0.15MnO3 (x = 0.05, 0.1 and 0.15) have been synthesized by standard solid state reaction method to study effects of substituting La3+ by Sm3+ ion on the structural, electrical and magnetic properties as discussed by the authors.
TL;DR: In this article, the authors present experimental evidence on the existence of an effective antiferromagnetic coupling between the ferromagnetic nanodomains in epitaxial thin films of a classical CMR material.
Abstract: A commonly believed picture of colossal magnetoresistance (CMR) effect is related to a first-order phase transition and electronic phase separation with coexisting ferromagnetic metallic and antiferromagnetic insulating phases. However, the underlying mechanism, i.e., the characteristic energy scale of the interacting phases and their spatial extent, is still under debate. Here we present experimental evidence on the existence of an effective antiferromagnetic coupling between the ferromagnetic nanodomains in epitaxial thin films of a classical CMR material $({\mathrm{La}}_{1\ensuremath{-}y}{\mathrm{Pr}}_{y}){}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_{3}$ with Pr doping, $y$ = 0.375 and 0.4. This coupling yields to peculiar low-field CMR behavior with magnetic hysteresis and slow resistance relaxation, both induced by the magnetization reversal. The coercive field obeys a square-root temperature dependence for $T\ensuremath{\ll}{T}_{\mathrm{C}}$ and increases anomalously close to the phase transition. We modeled the magnetic structure within the phase-separation scenario as an assembly of single-domain ferromagnetic nanoparticles, antiferromagnetically coupled (pinned) by correlated Jahn-Teller polarons. The concentration of polarons increases drastically close to phase transition as indicated by the third harmonic of the electrical conductivity as well as Raman spectroscopy.
Abstract: We propose and demonstrate gold nanoparticle decorated graphene as an ideal system for studying carrier inhomogeneity induced magnetoresistance. Large linear magnetoresistance has been realized in the system and the magnitude can be tuned by a gate. By detailed study, we provide an empirical expression, which reveals the dependence of the magnetoresistance on density fluctuations and mobility. The induced magnetoresistance is temperature independent and can be strongly enhanced by the high mobility of graphene, hence offers potential for magnetic sensor applications.
TL;DR: Evidence of systematic changes in the electronic structure of Bi(1-x)Ca(x)FeO(3-δ) treated by electrically controlled hole carrier doping is demonstrated, the outcome of which clearly correlates with the local modulation of electronic conductivity observed in the same material.
Abstract: 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 Bi1−xCaxFeO3−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.
TL;DR: In this paper, singly occupied carrier traps, produced by electrical stress or irradiation within organic semiconductors, can cause spin blockades and the large room-temperature magnetoresistance known as organic magnetoreistance.
Abstract: We predict that singly occupied carrier traps, produced by electrical stress or irradiation within organic semiconductors, can cause spin blockades and the large room-temperature magnetoresistance known as organic magnetoresistance. The blockade occurs because many singly occupied traps can only become as doubly occupied in a spin-singlet configuration. Magnetic-field effects on spin mixing during transport dramatically modify the effects of this blockade and produce magnetoresistance. We calculate the quantitative effects of these traps on organic magnetoresistance from percolation theory and find a dramatic nonlinear dependence of the saturated magnetoresistance on trap density, leading to values ∼20%, within the theory's range of validity.
TL;DR: In this article, low doped colossal magnetoresistance La 1− x Ba x MnO 3+ δ nanoparticles are synthesized by a sol-gel method along with the parent compound LaMnO 3 + δ.