Showing papers on "Colossal magnetoresistance published in 2013"

Bifurcated Polarization Rotation in Bismuth-Based Piezoelectrics

Abstract: ABO3 perovskite-type solid solutions display a large variety of structural and physical properties, which can be tuned by chemical composition or external parameters such as temperature, pressure, strain, electric, or magnetic fields. Some solid solutions show remarkably enhanced physical properties including colossal magnetoresistance or giant piezoelectricity. It has been recognized that structural distortions, competing on the local level, are key to understanding and tuning these remarkable properties, yet, it remains a challenge to experimentally observe such local structural details. Here, from neutron pair-distribution analysis, a temperature-dependent 3D atomic-level model of the lead-free piezoelectric perovskite Na0.5Bi0.5TiO3 (NBT) is reported. The statistical analysis of this model shows how local distortions compete, how this competition develops with temperature, and, in particular, how different polar displacements of Bi3+ cations coexist as a bifurcated polarization, highlighting the interest of Bi-based materials in the search for new lead-free piezoelectrics.

Large magnetoresistance in high mobility topological insulator Bi2Se3

Abstract: We report the magnetotransport properties of individual Bi2Se3 nanoplates. The carrier Hall mobility is up to 104 cm2/Vs. A large positive linear magnetoresistance (MR) approaching to 400% without sign of saturation was observed at 14 T. By angular dependence measurements, we demonstrate that the linear MR originates from a two-dimensional transport. Furthermore, by comparing the Hall mobility and longitudinal resistance under different temperatures, we give very clear evidence that reveals the close relationship between magnetoresistance and mobility.

Perovskite‐like Mn2O3: A Path to New Manganites

Abstract: Among complex oxides, perovskite-based manganites play a special role in science and technology. They demonstrate colossal magnetoresistance, and can be employed as memory and resistive switching elements or multiferroics. The perovskite structure ABO3 has two different cation sites: B-sites that are octahedrally coordinated by oxygen, and cuboctahedrally-coordinated (often heavily distorted) Asites. The magnetic and transport properties of perovskite manganites are largely determined by the Mn O Mn interactions in the perovskite framework of corner-sharing MnO6 octahedra. Although the A cations do not directly participate in these interactions, they control the Mn valence and the geometry of the Mn O Mn bonds. Complex phenomena, such as charge and orbital ordering, often accompany chemical substitutions on the A-site. Requirements on formal charge and ionic radius are usually different for cations adopting theA or B positions and prevent A/B mixing. Small and often highly charged transition-metal B-cations are unfavorable for the large 12coordinated A-site. Partial filling of the A-position with transition metals is, nevertheless, possible in a unique class of A-site ordered perovskites AA’3B4O12 (where A= alkali, alkali-earth, rare-earth, Pb, or Bi cations, A’=Cu or Mn, and B= transition metals, Ga, Ge, Sb, or Sn). A key ingredient of such compounds is the A’ cation that should be prone to a first-order Jahn–Teller effect (Cu or Mn). An oxygen environment suitable for such transition-metal cations at the A’ position is created by the aaa octahedral tilt system (in Glazer s notation) with a notably large magnitude of the tilt (for example, in CaCu3Ti4O12 the Ti O Ti bond angle is only 140.78). The tilt creates a square-planar anion coordination, favorable for Jahn–Teller-active A’ cations. The ap= ffiffiffi

Spin Seebeck Effect and Thermal Colossal Magnetoresistance in Graphene Nanoribbon Heterojunction

Abstract: 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.

Emergent phenomena in manganites under spatial confinement

Abstract: 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.

Functional oxide interfaces

Abstract: Functional perovskite oxides are recognized for their stunningly rich physics and for their potential as next-generation electronic materials. Their properties include high Tc superconductivity, colossal magnetoresistance, record-high dielectric/ferroelectric/piezoelectric performances, multiferroic behavior, resistive switching behavior, giant thermoelectric and magnetocaloric effects, giant ionic conduction, and catalytic behavior. Due to their intrinsic chemical and crystal similarities, functional oxides can be stacked in multilayer heterostructures exhibiting an astonishing degree of epitaxial perfection. Such artificial systems not only allow one to combine in a single device the functionalities of their individual layers, but often reveal an even wider range of emergent novel properties that can be surprisingly different from those of the single building blocks. The goal of this issue of MRS Bulletin is to present the state of the art of oxide interfaces in inscience and technology. Here we provide an introduction to their properties, serving as a base for the following topical articles.

Colossal Magnetoresistance Manganites and Related Prototype Devices

Abstract: We review colossal magnetoresistance in single phase manganites, as related to the field sensitive spin charge interactions and phase separation; the rectifying property and negative/positive magnetoresistance in manganite/Nb:SrTiO3 pn junctions in relation to the special interface electronic structure; magnetoelectric coupling in manganite/ferroelectric structures that takes advantage of strain, carrier density, and magnetic field sensitivity; tunneling magnetoresistance in tunnel junctions with dielectric, ferroelectric, and organic semiconductor spacers using the fully spin polarized nature of manganites; and the effect of particle size on magnetic properties in manganite nanoparticles

Colossal magnetoresistance in manganites and related prototype devices

Abstract: We review colossal magnetoresistance in single phase manganites, as related to the field sensitive spin-charge interactions and phase separation; the rectifying property and negative/positive magnetoresistance in manganite/Nb:SrTiO3 p—n junctions in relation to the special interface electronic structure; magnetoelectric coupling in manganite/ferroelectric structures that takes advantage of strain, carrier density, and magnetic field sensitivity; tunneling magnetoresistance in tunnel junctions with dielectric, ferroelectric, and organic semiconductor spacers using the fully spin polarized nature of manganites; and the effect of particle size on magnetic properties in manganite nanoparticles.

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

Abstract: 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.

Distinct in-plane resistivity anisotropy in a detwinned FeTe single crystal: Evidence for a Hund's metal

Abstract: The in-plane resistivity anisotropy has been studied with the Montgomery method on the detwinned parent compound of the iron-based superconductor FeTe. The observed resistivity in the antiferromagnetic (AFM) direction is larger than that in the ferromagnetic (FM) direction, which is different from that observed in BaFe${}_{2}$As${}_{2}$ before. We show that the opposite resistivity anisotropy behavior in FeTe could be attributed to the strong Hund's rule coupling effects, which should be understood in a localized picture: Hund's rule coupling makes hopping along the FM direction easier than along the AFM direction in FeTe, similar to the colossal magnetoresistance observed in some manganites.

Tunneling anisotropic magnetoresistance at the single-atom limit.

Abstract: The tunneling anisotropic magnetoresistance (TAMR) of single Co atoms adsorbed on a double-layer Fe film on W(110) is observed by scanning tunneling spectroscopy. Without applying an external magnetic field the TAMR is found by comparing spectra of atoms that are adsorbed on the domains and domain walls of the Fe film. The TAMR can be as large as 12% and repeatedly changes sign as a function of bias voltage. First-principles calculations show that the hybridization between Co $d$ states of different orbital symmetries depends on the magnetization direction via spin-orbit coupling. This leads to an anisotropy of the density of states and thus induces a TAMR.

Interplay of chemical disorder and electronic inhomogeneity in unconventional superconductors

Abstract: Many of today's forefront materials, such as high-Tc superconductors, doped semiconductors, and colossal magnetoresistance materials, are structurally, chemically and/or electronically inhomogeneous at the nanoscale. Although inhomogeneity can degrade the utility of some materials, defects can also be advantageous. Quite generally, defects can serve as nanoscale probes and facilitate quasiparticle scattering used to extract otherwise inaccessible electronic properties. In superconductors, non-stoichiometric dopants are typically necessary to achieve a high transition temperature, while both structural and chemical defects are used to pin vortices and increase critical current. Scanning tunneling microscopy (STM) has proven to be an ideal technique for studying these processes at the atomic scale. In this perspective, we present an overview of STM studies on chemical disorder in unconventional superconductors, and discuss how dopants, impurities and adatoms may be used to probe, pin or enhance the intrinsic electronic properties of these materials.

Giant tunneling magnetoresistance in silicene

Abstract: 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.

Anisotropic magnetoresistance studies of polycrystalline La0.67Ca0.33MnO3

Abstract: We have synthesized polycrystalline La 0.67 Ca 0.33 MnO 3 by solid state reaction method and studied the structural, morphological, resistivity, magnetoresistance and anisotropic magnetoresistance properties of it with detailed analysis of anisotropic magnetoresistance. The X-ray diffraction study of our sample confirms the single phase nature of the prepared material. The temperature dependence of the DC electrical resistivity shows a peak, corresponding to metal-insulating transition, at T MI ∼264 K. Under an applied low magnetic field, the resistivity decreases from zero field resistivity and we have calculated the magnetoresistance and anisotropic magnetoresistance of our polycrystalline La 0.67 Ca 0.33 MnO 3 with respect to temperature. We found high values of magnetoresistance and anisotropic magnetoresistance at low temperatures. We have also measured the angular dependence of resistivity at different temperatures for two different currents. We have found the effect of current on the anisotropic magnetoresistance which is essential in utilizing the polycrystalline La 0.67 Ca 0.33 MnO 3 in device applications.

Phase-tunable colossal magnetothermal resistance in ferromagnetic Josephson valves

Abstract: We propose a heat valve based on the interplay between thermal transport and proximity-induced exchange splitting in Josephson tunnel junctions. We demonstrate that the junction electron heat conductance strongly depends on the relative alignment of the exchange fields induced in the superconductors. Colossal magnetothermal resistance ratios as large as ∼107% are predicted to occur under proper temperature and phase conditions, as well as suitable ferromagnet-superconductor combinations. Moreover, the quantum phase tailoring, intrinsic to the Josephson coupling, offers an additional degree of freedom for the control of the heat conductance. Our predictions for the phase-coherent and spin-dependent tuning of the thermal flux can provide a useful tool for heat management at the nanoscale.

Three-dimensional mapping of the anisotropic magnetoresistance in Fe3O4 single crystal thin films

Abstract: The anisotropic magnetoresistance (AMR) effect with a magnetic field along arbitrary directions in single crystalline (001)-oriented Fe3O4 films was studied. A cubic symmetry term, an in-plane uniaxial term, and an out-of-plane uniaxial term could be quantitatively separated. The cubic term is independent of the current direction, and decreases with increasing temperature, but both in-plane and out-of-plane uniaxial terms are found to be strongly dependent on the current orientation. This three-dimensional magnetoresistance measurement provides a quantitative method for identifying the different contributions to the AMR effect.

Impact of Crystal Chemistry upon the Physics of Strongly Correlated Electrons in Oxides

Abstract: Transition-metal oxides have been widely studied for understanding the physics of strongly electron-correlated systems. The crucial role of crystal chemistry for the discovery of three families: the high T(c) superconducting cuprates, the colossal magnetoresistance manganates, the thermoelectric, and multiferroic cobaltates, is explored.

Giant magnetoresistance: history, development and beyond

Abstract: With the discovery of giant magnetoresistance (GMR), research effort has been made to exploiting the influence of spins on the mobility of electrons in ferromagnetic materials and/or artificial structures, which has lead to the idea of spintronics. A brief introduction is given to GMR effects from scientific background to experimental observations and theoretical models. In addition, the mechanisms of various magnetoresistance beyond the GMR are reviewed, for instance, tunnelling magnetoresistance, colossal magnetoresistance, and magnetoresistance in ferromagnetic semiconductors, nanowires, organic spintronics and non-magnetic systems.

Magnetorefractive Effect in Magnetoresistive Materials

Abstract: In this chapter, we survey early and later experimental and theoretical results on the magnetorefractive effect in: (i) all-metal multilayers and granular alloys with giant magnetoresistance, (ii) metal–insulator multilayers and nanocomposites with tunnel magnetoresistance, (iii) bulk single- and polycrystals, thin films and heterostructures of manganites with colossal magnetoresistance, focusing on recent developments that have led to a better understanding of the magnetorefractive effect in the infrared and visible range of spectrum and to the recognition of unsolved problems and possible routes for the magnetorefractive effect enhancement. The possible applications of the magnetorefractive effect are also discussed.

Systematic study of magnetotransport properties and enhanced low-field magnetoresistance in thin films of La0.67Sr0.33MnO3 + Mg(O)

Abstract: La, Sr, Mn, and Mg precursors were mixed in stoichiometric ratio 0.67/0.33/1/x with solvent and were spin-coated onto (001) LaAlO3 substrates. X-ray diffraction and elemental mapping of these films indicate that for small addition of Mg precursor, Mg2+ acts as a dopant in La0.67Sr0.33MnO3 phase and for higher concentrations, MgO phase separates out. Curie temperature and metal-insulator transition temperature systematically decrease with increasing molar concentration of Mg(O). Low-field magnetoresistance of films significantly enhanced by Mg addition and for the highest amount of Mg at 10 K, values were −35.5% and −83.2% with 0.5 T and 3 T applied fields, respectively.

Empirical relationship between x-ray photoemission spectra and electrical conductivity in a colossal magnetoresistive manganite La1−xSrxMnO3

Abstract: By using laboratory x-ray photoemission spectroscopy (XPS) and hard x-ray photoemission spectroscopy (HX-PES) at a synchrotron facility, we report an empirical semi-quantitative relationship between the valence/core-level x-ray photoemission spectral weight and electrical conductivity in La1−xSrxMnO3 as a function of x. In the Mn 2p3∕2 HX-PES spectra, we observed the shoulder structure due to the Mn3+ well-screened state. However, the intensity at x = 0.8 was too small to explain its higher electrical conductivity than x = 0.0, which confirms our recent analysis on the Mn 2p3∕2 XPS spectra. The near-Fermi level XPS spectral weight was found to be a measure of the variation of electrical conductivity with x in spite of a far lower energy resolution compared with the energy scale of the quasiparticle (coherent) peak because of the concurrent change of the coherent and incoherent spectral weight.

Magnetic properties and magnetoresistance effect of Pb2FeMoO6

Abstract: Magnetic properties and magnetoresistance effect of Pb2FeMoO6, synthesized under high pressure at high temperature, were systematically studied. The sample shows ferromagnetic behavior with Curie temperature about 243 K. The field dependent of paramagnetic susceptibility was discussed by the magnetic inhomogeneous related to Fe/Mo ions disorder. Electrical resistivity of the sample exhibits a semiconductor behavior, which can be well understood by variable-range hopping model. A maximum magnetoresistance effect value about 15% was observed at 20 K and 70 kOe. The pronounced linear magnetoresistance effect is attributed to the suppression of spin-fluctuations by the magnetic field.

Enhanced magnetoresistance in graphene nanostructure modulated by effective exchange field and Fermi velocity

Abstract: We investigate the spin-dependent transport properties of graphene nanostructures modulated by effective exchange field and Fermi velocity The Brewster-like angle of spin transport becomes large and the spin-precession length becomes short with a decrease of the Fermi velocity in effective exchange field region As a consequence, the magnetoresistance is enhanced remarkably and the number of the magnetoresistance dips increases In the graphene-based periodic velocity barrier with the modulations of the electrostatic potential and the effective exchange field, the maximum of the magnetoresistance dips is a number of times larger than that of zero electrostatic potential

Spintronic Phenomena: Giant Magnetoresistance, Tunnel Magnetoresistance and Spin Transfer Torque

Abstract: This introduction to spintronic phenomena deals with the three major physical effects of this research field: giant magnetoresistance, tunnel magnetoresistance and spin transfer torque.This presentation aims at describing the concepts in the simplest way by recalling their historical development. The correlated technical improvements mostly concerning material issues are also described showing their evolution with time.

Nanostructure induced metal-insulator transition and enhanced low-field magnetoresistance in La0.7 Sr0.3MnO3 systems.

Abstract: We investigated implications of nanostructure formation on structural and magnetotransport properties of La0.7Sr0.3MnO3 compound. The polycrystalline nanomaterials of variable grain sizes were synthesized by using sol-gel method. The structural parameters obtained by Rietveld refinement of the X-ray diffraction data indicated that the samples possess perovskite structure with orthorhombic Pnma symmetry. The X-ray Photoemission Spectra showed chemical shift in the lowest particle size sample due to oxygen deficiency. The average particle size observed through transmission electron microscopy varied from 22 nm to 34 nm. The particle size induced metal-insulator transition and substantial increase in electrical resistivity observed in these nanomaterials are in contrast with the bulk material phase diagram. We also observed temperature and magnetic field dependent colossal magnetoresistance. The low-field magnetoresistance is substantially enhanced in nanomaterials samples, making it more promising for device applications. A divergence in field cooled and zero field cooled magnetization indicated possibility of magnetic spin-glass behavior.

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

Abstract: 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.

Magnetoresistance of lanthanum manganites with activation-type conductivity

Abstract: The temperature dependence of the resistivity and magnetic moment of La0.85Ba0.15MnO3 and La0.85Sr0.15MnO3 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 TC 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 δT ≈ 20 K near TC. 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 TC in the CMR range δT.