Showing papers on "Colossal magnetoresistance published in 2015"
TL;DR: In this paper, a unidirectional magnetoresistance observed in bilayer metal films was used to add directional sensitivity to conventional magnetic sensors based on anisotropic magnetic sensors.
Abstract: A unidirectional magnetoresistance observed in bilayer metal films could be used to add directional sensitivity to conventional magnetic sensors based on anisotropic magnetoresistance.
369 citations
TL;DR: In this paper, the angular dependence of the magnetoresistance in a WTe2 single crystal was studied and the significant anisotropic magnetotransport behavior in different magnetic field directions and violation of the Kohler's rule was observed.
Abstract: Recently, the WTe2 semimetal, as a typical layered transition-metal dichalcogenide, attracted much attention due to an extremely large, non-saturating parabolic magnetoresistance in the perpendicular field. Here, we report a systematic study of the angular dependence of the magnetoresistance in a WTe2 single crystal. The significant anisotropic magnetotransport behavior in different magnetic field directions and violation of the Kohler's rule are observed. Unexpectedly, when the applied field and excitation current are both parallel to the tungsten chains of WTe2, an exotic large longitudinal linear magnetoresistance as high as 1200% at 15T and 2K is identified. These results imply that the WTe2 semimetal, due to its balanced hole and electron populations, seems to be the first material for which a large longitudinal linear magnetoresistance appears when the external magnetic field is parallel to the applied current. Finally, our work may stimulate studies of double-carrier correlated materials and the corresponding quantum physics.
179 citations
TL;DR: In this paper, the Shubnikov-de Haas oscillations of the magnetoresistance under ambient and high pressure have been studied for WTe2 single crystals, and four Fermi surfaces are identified, and two of them are found to persist to high pressure.
Abstract: 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.
138 citations
TL;DR: In this paper, the role of the double exchange mechanism is maximized in La 0.7Ca 0.3MnO3, leading to the concurrent metal-insulator transition and ferromagnetic transition as well as CMR effect.
Abstract: 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.
109 citations
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TL;DR: In this article, the local and non-local magnetoresistive response of thin Pt strips on yttrium iron garnet has been studied, and it has been shown that the spin Hall magnetoresistance vanishes at liquid Helium temperatures.
Abstract: 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. [1]. 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.
103 citations
TL;DR: The results demonstrate that graphene heterostructures may be promising for magnetic field sensing applications and suggest the possibility of a graphene-based gate tunable thermal switch.
Abstract: 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.
88 citations
TL;DR: In this article, structural, magnetic and magnetotransport properties of polycrystalline La0.5Ca 0.5Mn1−xBixO3 (x=0, 0.02 and 0.05) were reported.
69 citations
TL;DR: In this article, the experimental evidences of conductive filaments, the transport and switching mechanisms, and the memory performances and enhancing methods of perovskite oxide based filamentary RRAM cells have been summarized and discussed.
68 citations
TL;DR: It is demonstrated in a clean way that phase separation is at the origin of CMR in LaMnO3, and the insulator-to-metal transition at 32 GPa is well described using the percolation theory.
Abstract: 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.
66 citations
TL;DR: A ferrimagnetic double perovskite, Mn2 FeReO6, synthesized at high pressure which has a high Curie temperature of 520 K and magnetizations of up to 5.0 μB which greatly exceed those for other double perOVskite ferrimagnets.
Abstract: Ferrimagnetic A2BB′O6 double perovskites, such as Sr2FeMoO6, are important spin-polarized conductors. Introducing transition metals at the A-sites offers new possibilities to increase magnetization and tune magnetoresistance. Herein we report a ferrimagnetic double perovskite, Mn2FeReO6, synthesized at high pressure which has a high Curie temperature of 520 K and magnetizations of up to 5.0 μB which greatly exceed those for other double perovskite ferrimagnets. A novel switching transition is discovered at 75 K where magnetoresistance changes from conventional negative tunneling behavior to large positive values, up to 265 % at 7 T and 20 K. Neutron diffraction shows that the switch is driven by magnetic frustration from antiferromagnetic Mn2+ spin ordering which cants Fe3+ and Re5+ spins and reduces spin-polarization. Ferrimagnetic double perovskites based on A-site Mn2+ thus offer new opportunities to enhance magnetization and control magnetoresistance in spintronic materials.
66 citations
TL;DR: Working in the framework of semiclassical Boltzmann transport theory, it is demonstrated that the combination of spin-orbit coupling and scattering from finite-range impurities can explain the observed magnitude of the negative magnetoresistance, as well as the temperature and electron density dependence.
Abstract: The LaAlO3=SrTiO3 interface hosts a two-dimensional electron system that is unusually sensitive to the application of an in-plane magnetic field. Low-temperature experiments have revealed a giant negative magnetoresistance (dropping by 70%), attributed to a magnetic-field induced transition between interacting phases of conduction electrons with Kondo-screened magnetic impurities. Here we report on experiments over a broad temperature range, showing the persistence of the magnetoresistance up to the 20 K range—indicative of a single-particle mechanism. Motivated by a striking correspondence between the temperature and carrier density dependence of our magnetoresistance measurements we propose an alternative explanation. Working in the framework of semiclassical Boltzmann transport theory we demonstrate that the combination of spin-orbit coupling and scattering from finite-range impurities can explain the observed magnitude of the negative magnetoresistance, as well as the temperature and electron density dependence.
TL;DR: The results put forward an effective route to obtain a spin caloritronic material which can be applied in future low-power-consumption technology and indicates that the thermal spin current dominates the carrier transport while the thermal electron current is much suppressed.
Abstract: 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.
TL;DR: In this article, the structural, magnetic and magneto-transport properties of Pr0.6Sr0.4MnO3, Pr 0.3Sr 0.1MnNO3 and Pr0 0.5Sr 1.1Sr O3 perovskite manganite oxides have been investigated.
TL;DR: 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, which affects the double-exchange electron hopping and thus the colossal magnetoresistance effect.
Abstract: 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. DOI: 10.1103/PhysRevLett.114.237601 PACS numbers: 79.60.-i, 71.18.+y, 75.47.Gk, 75.47.Lx Hole-doped manganites with the general chemical formula ðLa; SrÞ x MnOy (LSMO) are typical transition metal oxides (TMOs) with perovskite structure, which have attracted tremendous interest due to the discovery of their colossal magnetoresistance (CMR). Coupling of charge, orbital, spin, and lattice degrees of freedoms results in a rich phase diagram of these materials, extending over antiferromagnetic, ferromagnetic (FM), and paramagnetic (PM) insulating and metallic states. The electron transport in manganites is coupled to their ferromagnetism and is generally described in the framework of the double-exchange (DE) mechanism. However, an important role in physics of these materials can be played by polaronic effects coupling of the electron and lattice
TL;DR: In this article, room temperature ferromagnetism and p-type conductivity of Na doped ZnO films have been observed with a crossover of positive to negative magnetoresistance with the variation of Na doping concentrations.
Abstract: Na doped ZnO films were fabricated via a hydrothermal process. The films have shown room temperature ferromagnetism and p-type conductivity. Crossover of positive to negative magnetoresistance has been observed with the variation of Na doping concentrations. The positive MR is due to p-p exchange interaction induced Zeeman splitting to suppress the hopping path of holes. The ferromagnetism is attributed to the formation of a Zn vacancy complex. The negative magnetoresistance is due to the minimization of spin-dependent scattering by the applied magnetic field.
TL;DR: This work reports the chemical solution (water-based) synthesis of high-quality epitaxial thin films of LaMnO3, free of defects at square-centimeter scales, and compatible with standard microfabrication techniques.
Abstract: Hole-doping into the Mott insulator LaMnO3 results in a very rich magneto-electric phase diagram, including colossal magnetoresistance and different types of charge and orbital ordering. On the other hand, LaMnO3 presents an important catalytic activity for oxygen reduction, which is fundamental for increasing the efficiency of solid-oxide fuel cells and other energy-conversion devices. In this work, we report the chemical solution (water-based) synthesis of high-quality epitaxial thin films of LaMnO3, free of defects at square-centimeter scales, and compatible with standard microfabrication techniques. The films show a robust ferromagnetic moment and large magnetoresistance at room temperature. Through a comparison with films grown by pulsed laser deposition, we show that the quasi-equilibrium growth conditions characteristic of this chemical process can be exploited to tune new functionalities of the material.
TL;DR: Modulation of the superconducting state possessing a C-type antiferromagnetic phase in the Nd0.35Sr0.65MnO3/YBa2Cu3O7 heterostructure exhibits a field-independent behavior, indicating an enhanced flux pinning effect.
Abstract: Modulation of the superconducting state possessing a C-type antiferromagnetic phase in the Nd0.35Sr0.65MnO3/YBa2Cu3O7 heterostructure is investigated, with the Nd0.35Sr0.65MnO3 thickness (t) varying from 40 to 200 nm. Both the superconducting transition temperature and the upper critical field along the c-axis decrease with increasing t; while the in-plane coherence length increases from 2.0 up to 3.6 nm. Meanwhile, the critical current density exhibits a field-independent behavior, indicating an enhanced flux pinning effect. Furthermore, low-temperature spin canting induces a breakdown and re-entrance of the superconductivity, demonstrating a dynamic completion between the superconducting pairing and the exchange field. An unexpected colossal magnetoresistance is observed below the superconducting re-entrance temperature at t = 200 nm, which is attributed to the dominant influence of the exchange field over the pairing energy.
TL;DR: In this paper, a gravity dual for the insulator/metal phase transition and colossal magnetoresistance effect found in some manganese oxides materials was constructed within massive gravity, and the relation with the electronic phase separation was discussed.
Abstract: Within massive gravity, we construct a gravity dual for the insulator/metal phase transition and colossal magnetoresistance effect found in some manganese oxides materials. In the heavy graviton limit, a remarkable magnetic-field-sensitive DC resistivity peak appears at the Curie temperature, where an insulator/metal phase transition happens and the magnetoresistance is scaled with the square of field-induced magnetization. We find that metallic and insulating phases coexist below the Curie point and the relation with the electronic phase separation is discussed.
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TL;DR: In this article, the electronic structure of the three-dimensional colossal magnetoresistive perovskite La1-xSrxMnO3 has been established using soft-X-ray ARPES with its intrinsically sharp definition of threedimensional electron momentum.
Abstract: Electronic structure of the three-dimensional colossal magnetoresistive perovskite La1-xSrxMnO3 has been established using soft-X-ray ARPES 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 GGA+U band structure. 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.
TL;DR: CPMR is reported in degenerate semiconducting strontium titanite single crystals capped with ultrathin SrTiO3/LaAlO3 bilayers and is promising to be generalized to others oxides, and to realize devices with high-mobility carriers and interesting magnetoelectronic properties.
Abstract: 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.
TL;DR: In this paper, the authors show that the intricate pattern formation is set by a delicate balance among disorder, interactions, and material anisotropy, leading to a fractal nature of the cluster pattern.
Abstract: Inside the metals, semiconductors, and magnets of our everyday experience, electrons are uniformly distributed throughout the material. By contrast, electrons often form clumpy patterns inside of strongly correlated electronic systems (SCES) such as colossal magnetoresistance materials and high temperature superconductors. In copper-oxide-based high temperature superconductors, scanning tunneling microscopy (STM) has detected an electron nematic on the surface of the material in which the electrons form nanoscale structures which break the rotational symmetry of the host crystal. These structures may hold the key to unlocking the mystery of high temperature superconductivity in these materials, but only if the nematic also exists throughout the entire bulk of the material. Using newly developed methods for decoding these surface structures, we find that the nematic indeed persists throughout the bulk of the material. We furthermore find that the intricate pattern formation is set by a delicate balance among disorder, interactions, and material anisotropy, leading to a fractal nature of the cluster pattern. The methods we have developed can be extended to many other surface probes and materials, enabling surface probes to determine whether surface structures are confined only to the surface or whether they extend throughout the material.
TL;DR: In this paper, the electric and magnetic properties of anion-substituted antiferromagnetic MnSe1−xTex (0.4) semiconductors in the 77-700 K temperature range and magnetic fields under 1 T are studied.
Abstract: The electric and magnetic properties of anion-substituted antiferromagnetic MnSe1−xTex (0.1 ≤ x ≤ 0.4) semiconductors in the 77–700 K temperature range and magnetic fields under 1 T are studied. In the MnSe1−xTex solid solutions, negative magnetoresistance in the vicinity of the Neel temperature for x = 0.1 and for composition with x = 0.2 in the paramagnetic range below 270 K is revealed. A dependence of the magnetic susceptibility versus the prehistory of the samples is found. The model of localized spin-polarized electrons with the localization radius depending on the magnetic field is proposed for x = 0.1. In the paramagnetic range, the negative magnetoresistance and the behavior of magnetic moment are a result of orbital glass formation.
TL;DR: In this paper, the suitability of an epitaxial CaTiO3 buffer layer deposited onto (100) Si by reactive molecular-beam epitaxy (MBE) for the integration of the colossal magnetoresistive material La0.7Sr0.3MnO3 with silicon was investigated.
Abstract: We investigate the suitability of an epitaxial CaTiO3 buffer layer deposited onto (100) Si by reactive molecular-beam epitaxy (MBE) for the epitaxial integration of the colossal magnetoresistive material La0.7Sr0.3MnO3 with silicon. The magnetic and electrical properties of La0.7Sr0.3MnO3 films deposited by MBE on CaTiO3-buffered silicon (CaTiO3/Si) are compared with those deposited on SrTiO3-buffered silicon (SrTiO3/Si). In addition to possessing a higher Curie temperature and a higher metal-to-insulator transition temperature, the electrical resistivity and 1/f noise level at 300 K are reduced by a factor of two in the heterostructure with the CaTiO3 buffer layer. These results are relevant to device applications of La0.7Sr0.3MnO3 thin films on silicon substrates.
TL;DR: In this article, the authors synthesize Fe3O4 films on (110)-oriented MgO, MgAl2O4, and SrTiO3 substrates for comparative studies of the substrates' effects on magnetic and magnetoresistance properties of the films.
Abstract: Magnetite (Fe3O4) films were synthesized on (110)-oriented MgO, MgAl2O4, and SrTiO3 substrates for comparative studies of the substrates' effects on magnetic and magnetoresistance properties of the films. For the [-110] direction, the hysteresis loops of the Fe3O4 film on MgAl2O4 exhibited a good squareness with the largest coercivity of ∼1090 Oe, and the ratio of remanent magnetization to saturation magnetization was ∼0.995. For the [001] direction, positive magnetoresistance in weak magnetic fields was most distinct for the (110) SrTiO3 substrate with the largest lattice mismatch. Positive magnetoresistance in the (110) Fe3O4 films was presumably affected by imperfect atomic arrangements at anti-phase boundaries.
TL;DR: In this paper, the melting of the charge-ordered state in low bandwidth manganite PCMO ( x = 0.3 − 0.5) thin films under substantially lower magnetic field was reported.
TL;DR: In this paper, the massive magnetoresistive insulator to metal switching of almost nine orders of magnitude under the significantly reduced magnetic field is achieved by illumination for the low bandwidth manganite thin films.
Abstract: The colossal magnetoresistive insulator to metal switching of almost nine orders of magnitude under the significantly reduced magnetic field is achieved by illumination for the low bandwidth manganite thin films. Similarly, by changing the measuring bias voltage through the sample the required magnetic field for insulator–metal transition can be further fine-tuned. By applying a magnetic field of suitable strength, the samples can also be tuned to be extra sensitive to the illumination having colossal effect on the resistivity at low temperatures. This kind of utilizing of multiple external stimulants, which together change the properties of the material, could have significant impact on the new generation of phase-change memories working under affordable conditions.
TL;DR: In this article, massive magnetoresistance (CMR) ceramics were synthesized using the conventional solid-state synthesis method to investigate the effect of Bi substitution on their magnetic and electrical transport properties.
Abstract: Colossal magnetoresistance (CMR) ceramics with starting composition of La0.7−x
Bi
x
Ce0.3MnO3 (x = 0–0.15) were synthesized using the conventional solid-state synthesis method to investigate the effect of Bi substitution on their magnetic and electrical transport properties. The undoped sample (x = 0) showed paramagnetic to ferromagnetic (PM-FM) transition at Curie temperature, T
c = 248 K and metal to insulator (MI) transition at T
MI = 231 K which decreases with Bi content (0 < x < 0.15) indicating weakening of FM phase. At x = 0.15, the susceptibility, χ′ was observed to decrease below 83 K which indicates presence of antiferromagnetic (AFM) clusters in the sample. The decrease in T
c and T
MI is suggested to be due to the weakening of DE-like interaction involving Mn2+ and Mn3+ as a result of the hybridization between Bi3+ 6 s
2 lone pair with O orbital which increases electron localization. Fitting of the experimental data in the metallic region to scattering models suggested scattering involving electron-electron, electron-magnon, Kondo-like spin-dependant scattering, and electron-phonon interaction. On the other hand, fitting in the insulating region suggests resistivity behavior obeys the adiabatic small polaron hopping (SPH) model.
TL;DR: Das et al. as discussed by the authors presented a dynamical mean field theory study of the charge and orbital correlations in finite-size (LCMO) nanoclusters, and showed that upon further reducing the system size, quantum confinement effects come into play: the nanocluster turns insulating again and the charge disproportionation between Mn sites and the orbital polarization are enhanced.
Abstract: We present a dynamical mean-field theory study of the charge and orbital correlations in finite-size ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3}$ (LCMO) nanoclusters. Upon nanostructuring LCMO to clusters of 3 nm diameter, the size reduction induces an insulator-to-metal transition in the high-temperature paramagnetic phase. This is ascribed to the reduction in charge disproportionation between Mn sites with different nominal valence [H. Das et al., Phys. Rev. Lett. 107, 197202 (2011)]. Here we show that upon further reducing the system size to nanoclusters of a few atoms, quantum confinement effects come into play. These lead to the opposite effect: the nanocluster turns insulating again and the charge disproportionation between Mn sites and the orbital polarization are enhanced. Electron doping by means of external gate voltage on few-atom nanoclusters is found to trigger a site- and orbital-selective Mott transition. Our results suggest that LCMO nanoclusters could be employed for the realization of technological devices, exploiting the proximity to the Mott transition and its control by size and gate voltage.
TL;DR: In this paper, the effect of annealing time in polycrystalline bulk La0.7Sr0.3MnO3 in composition range (0.1) is presented.
Abstract: A study of Mn-site substitution by Ni2+ and the effect of annealing time in polycrystalline bulk La0.7Sr0.3MnO3 in composition range (0 ≤ x ≤ 0.1) is presented. This study involves structural, electrical, magnetoresistance, and thermoelectric power (TEP) measurements. X-ray diffraction was used to examine the structure for the as-prepared and annealed samples, and it shows that there is no change in structure with annealing time. Electrical resistivity and magnetoresistance are strongly affected by annealing process, where there is a dramatic increase in resistivity with annealing time and an enhancement in magnetoresistance in different temperature ranges. Moreover, conduction mechanisms above and below transition temperature (Tms) are discussed, since, variable-range hopping and small-polaron hopping models are applied above Tms, in addition to some experimental relations below it. In addition, the TEP sign changes from positive to negative with doping and annealing.
TL;DR: In this paper, it has been found that the inclusion of ZrO2 content decreases the conductivity, magnetization and metal-semiconductor transition, whereas it increases the low field magnetoresistance.
Abstract: (La07Sr03MnO3)1−x /(ZrO2)
x
(x = 00–0150, step 0025) composites have been prepared via solid state reaction process The X-ray diffraction and scanning electron microscopic observations indicate that there are ZrO2 grains separated from La07Sr03MnO3 matrix It has been found that the inclusion of ZrO2 content decreases the conductivity, magnetization and metal–semiconductor transition, whereas it increases the low field magnetoresistance Possible effects of grain boundaries on the low field magnetoresistance have been discussed The small ZrO2 grains are trapped between La07Sr03MnO3 grains may be acting as a barrier for spin-polarized tunneling and enhance the low-field magnetoresistance