Showing papers on "Colossal magnetoresistance published in 2011"
TL;DR: Theoretical analysis identifies spin-dependent hybridization of molecular and electrode orbitals as the cause of the large magnetoresistance across a single, non-magnetic hydrogen phthalocyanine molecule contacted by the ferromagnetic tip of a scanning tunnelling microscope.
Abstract: A single magnetic molecule between ferromagnetic contacts exhibits a 60% magnetoresistance effect and nearly metallic conduction at the same time.
297 citations
TL;DR: In this article, dilute fluorinated graphene was created using a clean, controlled, and reversible approach, and the zero-field resistance was reduced by a factor of 40 at the highest field of 9 T and shows no sign of saturation.
Abstract: Adatoms offer an effective route to modify and engineer the properties of graphene. In this work, we create dilute fluorinated graphene using a clean, controlled, and reversible approach. At low carrier densities, the system is strongly localized and exhibits an unexpected, colossal negative magnetoresistance. The zero-field resistance is reduced by a factor of 40 at the highest field of 9 T and shows no sign of saturation. Unusual staircaselike field dependence is observed below 5 K. The magnetoresistance is highly anisotropic. These observations cannot be explained by existing theories, but likely require adatom-induced magnetism and/or a metal-insulator transition driven by quantum interference.
154 citations
TL;DR: In this paper, a comprehensive review of recent developments in studies of strain effects in transition metal oxide ultra-thin films and nano/microwires is presented, focusing on the work of strain-controlled electromechanical response in piezoelectric oxides and strain-induced metal-insulator transitions as well as domain physics in strongly correlated electron oxides.
Abstract: Transition metal oxides offer a wide spectrum of properties which provide the foundation for a broad range of potential applications. Many of these properties originate from intrinsic coupling between lattice deformation and nanoscale electronic and magnetic ordering. Lattice strain thus has a profound influence on the electrical, optical, and magnetic properties of these materials. Recent advances in materials processing have led to the synthesis of low-dimensional single-crystal transition metal oxides, namely, epitaxial ultra-thin films and free-standing nano/microwires. Unlike bulk materials, these systems allow external tuning of uniform strain in these materials to tailor their properties and functionalities. This paper provides a comprehensive review of recent developments in studies of strain effects in transition metal oxide ultra-thin films and nano/microwires. In epitaxial thin films, biaxial strain is developed as a result of lattice mismatch between the film and the substrate. By choosing different substrates, a wide range of strain can be established at discrete values that allows for exploration of new phase space, enhancement of order parameters, creation of complicated domain textures, and stabilization of new phases. On the other hand, continuous tuning of uniaxial strain is possible in nano/microwires, where a variety of phase transitions and their dynamics could be probed at the single or few-domain scale. We focus on the work of strain-controlled electromechanical response in piezoelectric oxides and strain-induced metal–insulator transitions as well as domain physics in strongly correlated electron oxides. Related nanoscale device applications such as strain sensing and power generation will be highlighted as well.
145 citations
TL;DR: It is reported that the magnetic Néel temperature of the multiferroic compound BiFeO(3) is suppressed to around room temperature by heteroepitaxial misfit strain, providing a unique example of a concurrent magnetic and ferroelectric transition at the same temperature among proper ferroelectrics, taking a step toward room temperature magnetoelectric applications.
Abstract: Strong spin-lattice coupling in condensed matter gives rise to intriguing physical phenomena such as colossal magnetoresistance and giant magnetoelectric effects. The phenomenological hallmark of such a strong spin-lattice coupling is the manifestation of a large anomaly in the crystal structure at the magnetic transition temperature. Here we report that the magnetic Neel temperature of the multiferroic compound BiFeO(3) is suppressed to around room temperature by heteroepitaxial misfit strain. Remarkably, the ferroelectric state undergoes a first-order transition to another ferroelectric state simultaneously with the magnetic transition temperature. Our findings provide a unique example of a concurrent magnetic and ferroelectric transition at the same temperature among proper ferroelectrics, taking a step toward room temperature magnetoelectric applications.
138 citations
TL;DR: In this article, an energy-efficient technique for electrically modulating magnetoresistance was demonstrated in multiferroic anisotropic magnetorsistance (AMR) and GMR heterostructures using a giant electric field induced magnetic anisotropy caused by a strong magnetoelectric coupling.
Abstract: An energy-efficiency technique for electrically modulating magnetoresistance was demonstrated in multiferroic anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR) heterostructures. A giant electric field (E-field) induced magnetic anisotropy caused by a strong magnetoelectric coupling was utilized to control the orientation of magnetization and thus dynamically manipulate magnetoresistance in AMR and GMR devices. A multiband tunable AMR field sensor was designed and developed to dramatically enhance the measurement range by 15 times. In addition, two types of E-field determination of GMR in spin-valve structures are studied. The results indicate an energy efficiency approach to controlling magnetoresistance by E-field rather than magnetic field, which shows great potential for novel low power electronic and spintronic devices.
111 citations
TL;DR: This induced magnetic moment in the SrTiO3 controls the bulk magnetic and transport properties of the superlattices when the titanate layer thickness is below 1 nm.
Abstract: We report on the magnetic coupling of La0.7Sr0.3MnO3 layers through SrTiO3 spacers in La0.7Sr0.3MnO3/SrTiO3 epitaxial heterostructures. Combined aberration-corrected microscopy and electron-energy-loss spectroscopy evidence charge transfer to the empty conduction band of the titanate. Ti d electrons interact via superexchange with Mn, giving rise to a Ti magnetic moment as demonstrated by x-ray magnetic circular dichroism. This induced magnetic moment in the SrTiO3 controls the bulk magnetic and transport properties of the superlattices when the titanate layer thickness is below 1 nm.
85 citations
TL;DR: The magnetoresistance of Ni/single benzene-1,4-dithiol/Ni molecular junctions was measured by a mechanically controllable break junction method under a magnetic field.
Abstract: The magnetoresistance of Ni/single benzene-1,4-dithiol/Ni molecular junctions was measured by a mechanically controllable break junction method under a magnetic field. The negative magnetoresistance of the molecular junction as large as 30% and the anisotropic magnetoresistance of atomic contacts and tunnel junctions of Ni as large as 30% were observed.
60 citations
TL;DR: In this paper, tunneling surface current through a thin ferromagnetic barrier in a three-dimensional topological insulator is shown to possess an extraordinary response to the orientation of barrier magnetization.
Abstract: Tunneling surface current through a thin ferromagnetic barrier in a three-dimensional topological insulator is shown to possess an extraordinary response to the orientation of barrier magnetization. In contrast to conventional magnetoresistance devices that are sensitive to the relative alignment of two magnetic layers, a drastic change in the transmission current is achieved by a single layer when its magnetization rotates by 90 degrees. Numerical estimations predict a giant magnetoresistance as large as 800 % at room temperature and the proximate exchange interaction of 40 meV in the barrier. When coupled with electrical control of magnetization direction, this phenomenon may be used to enhance the gating function with potentially sharp turn-on/off for low power applications.
49 citations
TL;DR: In this article, an unexpected discovery of polarons in the metallic ground state of bilayer manganites could be an important clue to the origin of magnetoresistance in the manganite.
Abstract: Understanding the origin of colossal magnetoresistance in the manganites has proved to be one of the more difficult challenges in condensed-matter physics. An unexpected discovery of polarons in the metallic ground state of bilayer manganites could be an important clue.
37 citations
TL;DR: The CMR-B-scalar sensor based on polycrystalline La0.83Sr0.17MnO3 films is presented in this article.
Abstract: We present the design and the main characteristics of the CMR-B-scalar sensor based on polycrystalline La0.83Sr0.17MnO3 films. The sensor active volume is only 400 μm × 50 μm × 0.4 μm, and it is able to measure a magnetic induction of up to 40 T independently on its direction. The investigations of the influence of film preparation conditions on the sensitivity of the device to magnetic field amplitudes, its direction, and ambient temperature variations are presented and discussed. It is demonstrated that, for room temperature conditions, sensors based on films deposited on a lucalox substrate at a 700°C temperature are most suitable. They have a low anisotropy effect (7% at 0.5 T and 3% at higher fields) and significant magnetoresistance values (~30% at 10 T). The dynamics of a CMR response to pulsed magnetic fields is shown, and the operational speed of the sensor is discussed. Moreover, the investigations of electromotive forces induced by a "loop" effect in the bias current cable are presented. A practical solution to counter this effect is offered.
37 citations
TL;DR: In this paper, magneto-transport and magnetic properties of (1 − x )La 0.7 Ca 0.3 MnO 3 + x Al 2 O 3 composites synthesized through a solid-state reaction method combined with a high energy milling method were reported.
TL;DR: It is concluded that such nanostructure-based studies have strong potential to reveal new information about the rich physics at work in strongly correlated materials, particularly in transition metal oxides, manganites, and high temperature cuprate superconductors.
Abstract: Strongly correlated materials exhibit an amazing variety of phenomena, including metal-insulator transitions, colossal magnetoresistance, and high temperature superconductivity, as strong electron-electron and electron–phonon couplings lead to competing correlated ground states. Recently, researchers have begun to apply nanostructure-based techniques to this class of materials, examining electronic transport properties on previously inaccessible length scales, and applying perturbations to drive systems out of equilibrium. We review progress in this area, particularly emphasizing work in transition metal oxides (Fe3O4, VO2), manganites, and high temperature cuprate superconductors. We conclude that such nanostructure-based studies have strong potential to reveal new information about the rich physics at work in these materials.
TL;DR: It is shown that spin ordering in manganites can be controlled by depositing isolated ferromagnetic nanodots at the surface, indicating that electronic phase separation can becontrolled by the presence of magnetic nanodot density.
Abstract: In strongly correlated electronic systems, the global transport behavior depends sensitively on spin ordering. We show that spin ordering in manganites can be controlled by depositing isolated ferromagnetic nanodots at the surface. The exchange field at the interface is tunable with nanodot density and makes it possible to overcome dimensionality and strain effects in frustrated systems to greatly increasing the metal-insulator transition and magnetoresistance. These findings indicate that electronic phase separation can be controlled by the presence of magnetic nanodots.
TL;DR: This work presents resonant soft x-ray scattering results from small bandwidth manganites, which show that the CE-type spin ordering at the phase boundary is stabilized only below the canted antiferromagnetic transition temperature and enhanced by ferromagnetism in the macroscopically insulating state (FM-I).
Abstract: We present resonant soft x-ray scattering results from small bandwidth manganites $(\mathrm{Pr},\mathrm{Ca}){\mathrm{MnO}}_{3}$, which show that the CE-type spin ordering (SO) at the phase boundary is stabilized only below the canted antiferromagnetic transition temperature and enhanced by ferromagnetism in the macroscopically insulating state (FM-I). Our results reveal the fragility of the CE-type ordering that underpins the colossal magnetoresistance effect in this system, as well as an unexpected cooperative interplay between FM-I and CE-type SO which is in contrast to the competitive interplay between the ferromagnetic metallic state and CE-type ordering.
TL;DR: The magnetic properties of a Cd1−xMnxGeAs2: MnAs hybrid micro-composite have the signature of ferromagnetic order at room temperature as discussed by the authors, which is interpreted in terms of an effective medium approximation with the value and shape of the magnetoresistance depending on the structural and electronic properties of the semiconductor rather than on its magnetic properties.
TL;DR: In this article, a model based on the theory of the magnetorefractive effect has been proposed to qualitatively explain the magnetic and charge homogeneity of manganite films.
Abstract: Complex experimental investigations of the structural, optical, and magneto-optical properties (magnetotransmission, magnetoreflection, and transversal Kerr effect, as well as the magnetoresistance, of La0.7Ca0.3MnO3 epitaxial films indicate that magnetoreflection and magnetotransmission in manganite films can reach giant values and depend strongly on the magnetic and charge homogeneity of the films, their thickness, and spectral range under investigation. It has been shown that the optical enhancement of the magnetorefractive effect occurs in thin films as compared to manganite crystals. In the region of the minimum of the reflectance near the first phonon band, the resonance-like magnetorefractive effect has been observed, which is accompanied by change of the sign of the magnetoreflection. A model based on the theory of the magnetorefractive effect has been proposed to qualitatively explain this behavior.
TL;DR: The structurally modified nanoclusters at the CMR temperature were found to be ferromagnetic and exhibit much higher electrical conductivity than previously proposed, substantially alter the current understanding of these nanocluster on the material’s functionality.
Abstract: 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 La(1-x)Ca(x)MnO(3) (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.
TL;DR: In this paper, a brief review of properties of the ferromagnetic manganites La1 − x ε, Ca 1 − ε, MnO3 is given, with special attention paid to effects observed near the Curie temperature.
Abstract: A brief review of properties of the ferromagnetic manganites La1 − x
Ca
x
MnO3 is given. Lattice properties, magnetic properties, transport phenomena, magnetic resonance, and the results of neutron diffraction and optical studies are considered. Special attention is paid to effects observed near the Curie temperature.
TL;DR: In this paper, the authors investigated the strain-induced low-temperature behavior of Si1−xGex whiskers' magnetoresistance and estimated the prospects for the creation of physical values and sensing elements on the basis operating in strong magnetic fields.
TL;DR: In this article, a temperature dependence of La 0.85 Ag 0.15 MnO 3 resistivity in the temperature interval between 77 and 340 K and magnetic fields up to 26kOe was presented.
Abstract: We present the temperature dependence of La 0.85 Ag 0.15 MnO 3 resistivity in the temperature interval between 77 and 340 K and magnetic fields up to 26 kOe. We offer a method of separating tunnel magnetoresistance from total magnetoresistance. A change in both the magnetic entropy, which is caused by the magnetocaloric effect ( MCE ), and the magnetoresistance are shown to be connected through a simple relationship to La 0.85 Ag 0.15 MnO 3 .
TL;DR: In this paper, a correlation between the giant magnetoimpedance effect and permeability change was found, where the magnetoresistance is mainly dominated by the change of transverse imaginary permeability.
TL;DR: In this paper, the authors theoretically investigated the magnetoresistance effect of an ultrathin Bi2Se3 film sandwiched between two ferromagnetic insulators (FIs) and found that the conductance is quantized to be e2/h and vanishing, respectively, for parallel and antiparallel magnetization configurations of the two FIs.
Abstract: We theoretically investigate the magnetoresistance effect of an ultrathin Bi2Se3 film sandwiched between two ferromagnetic insulators (FIs). It is found that the conductance is quantized to be e2/h and vanishing, respectively, for parallel and antiparallel magnetization configurations of the two FIs, which stems from a transition of the Bi2Se3 film from the quantum anomalous Hall phase to a conventional insulator. This quantum magnetoresistance is robust against disorder scattering.
TL;DR: In this paper, a method of obtaining thin films of La0.85Ag0.15MnO3 using the chemical solution approach of polymer-assisted deposition was reported.
Abstract: We report a method of obtaining thin films of La0.85Ag0.15MnO3 using the chemical solution approach of polymer-assisted deposition. Epitaxial films with 25-30 nm thickness have been grown on single-crystal substrates of LaAlO3 (001) and SrTiO3 (001) exhibiting ferromagnetic Curie and metal-insulator transition temperatures shifted due to differences in the relaxation mechanisms of epitaxial misfit. High values of colossal magneto-resistance (−60% at 287 K and 5 T) were obtained in the case of LaAlO3 substrates which indicate that silver-doped manganite oxides have potential for room temperature applications.
TL;DR: In this article, the effects of doping on magnetic and electrical transport mechanism of polycrystalline samples La0.7Ca0.3Mn1−xAlxO3 (x=0,0.02, 0.04,0.,06,0,08,01) have been investigated.
Abstract: The effects of doping on magnetic and electrical transport mechanism of polycrystalline samples La0.7Ca0.3Mn1−xAlxO3 (x=0,0.02,0.04,0.06,0.08,0.1) have been investigated. Magnetization data reveal that long-range ferromagnetic ordering persists in all samples and the saturation moment decreases linearly as x increases. Resistivity data have been fitted with the variable range hopping model to estimate the density of state at Fermi level. It was observed that the substitution of Al in the series leads to a decrease in conductivity of the doped manganites samples, with conduction being controlled by the disorder induced localization of charge carriers.
TL;DR: In this paper, the effects of tetravalent hafnium doping on the structural, transport, and magnetic properties of polycrystalline La1−xHfxMnO3 (LHMO) (0.05 to 0.3) were investigated systematically.
Abstract: The effects of tetravalent hafnium doping on the structural, transport, and magnetic properties of polycrystalline La1−xHfxMnO3 (LHMO) (0.05 ≤ x ≤ 0.3) were investigated systematically. LHMO exhibited a typical colossal magnetoresistance effect via the double-exchange between Mn2+ and Mn3+ ions, instead of that between Mn3+ and Mn4+ ions in hole-doped manganites. A phase diagram was obtained for the first time through magnetization and resistance measurements in a broad temperature range. As the Hf concentration varied from x = 0.05 to 0.3, the Curie point and metal-to-insulator transition temperature increased significantly, whereas the magnetization and resistivity decreased remarkably. An abnormal enhancement of the magnetization was observed at about 42 K. It was further confirmed that a second magnetic phase MnO2 in LHMO gives rise to such a phenomenon. The possible causes are discussed in detail. The dynamic magnetic properties of LHMO, including relaxation and aging processes, were studied, demonstrating a spin-glass state at low temperature accompanied by a ferromagnetic phase.
TL;DR: In this article, the authors investigated the electrical and thermoelectric properties of Sn2P2S6 under strong compression up to 20 GPa and found an I-M-type transition by a monotonic and reversible lowering of electrical resistivity by 9-10 orders.
Abstract: We report results of investigation of electrical and thermoelectric properties of Sn2P2S6 under strong compression up to 20 GPa. An “insulator-metal”(I-M)-type transition was discovered by a monotonic and reversible lowering of electrical resistivity by 9–10 orders. The energy gap (Eg = 2.3 eV) was estimated to decrease to ∼0.25–0.3 eV at 20 GPa. X-ray diffraction and Raman studies on samples recovered from the high pressure experiments confirm a conservation of the original monoclinic lattice. Thus, a colossal “band-gap engineering” potential is revealed in this optical material. Sn2P2S6 is a potential candidate for emergent multi-functional switches, between transparent “insulator” state and conducting state with magneto-dependent properties.
TL;DR: In this paper, double perovskite oxide PrSrMnCoO6 (cubic, Fm3¯m) has been studied in fields up to 7 T.
Abstract: Magnetoresistance and magnetocaloric effect of a double perovskite oxide PrSrMnCoO6 (cubic, Fm3¯m) has been studied in fields up to 7 T. This compound is semiconductor-like and its electrical resistivity increases by 5 orders while going from 300 to 50 K. Giant magnetoresistance of ∼40% is observed at 200 K in 7 T field. PrSrMnCoO6 orders ferromagnetically at ∼150 K and shows a maximum magnetic entropy change of ∼4.6 J/kg/K for 5 T field change in the temperature range of 110–190 K. This nearly constant magnetocaloric effect over a broad temperature span is highly suitable for Ericsson-cycle magnetic refrigeration.
TL;DR: In this article, an epitaxial Pr0.65(Ca0.7Sr0.3)0.35MnO3 thin film was grown on orthorhombic (110) NdGaO3 substrate which breaks the lattice symmetry and affects the phase separated ground state, which is related to the anisotropic coupling and competition between the double exchange interaction and the Jahn-Teller distortion.
Abstract: We investigate epitaxial Pr0.65(Ca0.7Sr0.3)0.35MnO3 thin film grown on orthorhombic (110) NdGaO3 substrate which breaks the lattice symmetry and affects the phase separated ground state. As a result of the anisotropic substrate strain, giant in-plane magnetic and magnetotransport anisotropy are observed, which is related to the anisotropic coupling and competition between the double-exchange interaction and the Jahn-Teller distortion. Furthermore, the in-plane anisotropy shows a distinct enhancement near the metal-insulator transition, implying a significant contribution from the phase separation to the anisotropic transport behaviors. V C 2011 American Institute of Physics. [doi:10.1063/1.3643442] Since the discovery of “colossal magnetoresistance” (CMR), 1‐3 perovskite manganites have drawn significant attention due to both the fundamental science and the potential applications. In these materials, the complex and strong coupling between spin, charge, orbital, and lattice degrees of freedom gives rise to multiple competing phases with essentially distinct physical properties. Moreover, these phases are quite “soft” in the sense that their free energies are close to each another, thus forming a delicate balance which is very sensitive to internal/external perturbations, such as electric field (current), 4,5 light, 6 phonon, 7 and strain, 8‐13 in addition to magnetic field. Among these tuning parameters, strain stands out as it is ubiquitous in thin films and devices, and it has been shown that strain also can significantly affect the charge, spin, and orbital orders in manganite thin films. 14‐18
TL;DR: In this article, the magnetotransport properties of Fe(3)Se(4) nanowire arrays in anodic aluminum oxide (AAO) porous membrane were investigated.
Abstract: We report the magnetotransport properties of Fe(3)Se(4) nanowire arrays in anodic aluminum oxide (AAO) porous membrane. The temperature dependence of resistance of Fe(3)Se(4) nanowires at a zero field shows thermal activated behavior below 295 K. The exponential relationship in resistance is consistent with the model of strong localization with variable-range hopping (VRH) for a finite one-dimensional wire. Resistance versus magnetic field curves below 100 K show small positive magnetoresistance (MR). The field dependencies of log[R(H)/R(0)] explain the positive MR as the effect of magnetic field on the VRH conduction. (C) 2011 American Institute of Physics. [doi:10.1063/1.3544508]
TL;DR: In this paper, a sharp drop in resistance and a magnetization anomaly have been observed in La2/3Ca1/3MnO3 film in zero magnetic field at the BaTiO3 substrate structural phase transition temperature, due to the substrate clamping/strain effect, which is confirmed by Raman scattering.
Abstract: A sharp drop in resistance and a magnetization anomaly have been observed in La2/3Ca1/3MnO3 film in zero magnetic field at the BaTiO3 substrate structural phase transition temperature, due to the substrate clamping/strain effect, which is confirmed by Raman scattering. However, the anomalies for both resistance and magnetization were eliminated by a strong external magnetic field. These phenomena indicate that strain can cause colossal resistance and a change in magnetization which resembles the magnetic field effect. The interplay of the external forces (strain and magnetic field) is a good demonstration of the strong coupling between spin and lattice in colossal magnetoresistance materials.