Dependence Of Magnetoresistance Research Articles

Isothermal magnetization and magnetoresistive variations in trilayer (La2/3Sr1/3MnO3/γ-Fe2O3/La2/3Sr1/3MnO3) hetero-structure

Abstract We report the field dependent magnetic and magnetoresistance (MR) properties of La2/3Sr1/3MnO3 (LSMO)/γ-Fe2O3/LSMO trilayer heterostructures and single layer LSMO film grown on SiO2/Si (100) substrates utilizing Pulsed Laser Deposition technique. The metal- insulator-metal configuration is a magnetic tunnel junction topology, which is a parallel network of two metallic layers (LSMO) and one insulating layer (γ-Fe2O3) in current-in-plane (CIP) geometry. The intrinsically inhomogeneous polycrystalline trilayer film shows much lower (almost half) coercivity, compared to single layer LSMO film. The MR-H [MR = (ρ (H)-ρ (0))/ρ (0)] behavior of the films is studied under two regimes namely, Low Field Magnetoresistance (LFMR) and High Field Magnetoresistance (HFMR) at 5 K and 300 K in the field range of 0-7 T. Several equations were developed to simulate the experimental MR-H data of the studied samples. For both the films, in the LFMR region (0 T <H ≤ 1 T @ 5 K), the variation in MR exhibits a linear increase with H, followed by a logarithmic behavior in the HFMR region (1 T < H ≤ 7 T @5 K). For the trilayer film in CIP geometry, a negative MR of 16% is achieved at 5 K and 1 T field conditions, while LSMO single layer shows a negative MR of 13% at same temperature and field conditions. The MR obtained at high field (7 T) for both the films is quantitatively equal with a value of 38% @5 K and 15% @300 K. We obtained significantly better MR-H results for the trilayer in current-perpendicular-to-plane (CPP) configuration, where the two metallic layers and an insulating layer are in series. In the CPP configuration, MR is 21% @5 K and 1 T field, while it reached to 44% at 5 K and 7 T field. At room temperature, the trilayer heterostructure shows MR of 17% at 7 T field condition. At a higher field of 9 T, trilayer film in CPP mode exhibits MR value of 48% @5 K and 23%@300 K. Further, the anti-parallel and parallel magnetization states of the MIM device are well manifested in CIP and CPP geometries.

Electrical resistivity and magnetoresistance of Sr3Fe2+xMo1–xO9–3x/2 (x = 0.45, 0.60, and 1.00) prepared by the solid-state reaction

In this paper, we focus on understanding the behavior of the temperature dependence of electrical resistivity (ρ) and magnetoresistance (MR) in Sr3Fe2+xMo1–xO9–3x/2 perovskites with x = 0.45, 0.60, and 1.00. Three polycrystalline materials were synthesized using conventional solid-state reaction techniques. Rietveld analysis of room-temperature X-ray diffraction data reveals that all three compositions crystallize in tetragonal symmetry; where x = 0.45 and 0.60 undergo an I4/mcm space group, while x = 1.00 adopts a P4/mmm space group. Electrical resistivity measurements carried out at magnetic fields (0 and 1 T) reveal the presence of a transition from the ferromagnetic phase to the paramagnetic phase in the vicinity of the TMI. The metal-insulator transition temperature (TMI) decreases with increasing Fe content and rises slightly with changing magnetic field from 0 to 1 T. The magnetoresistance (MR) of the SrFeO3–δ sample (x = 1.00) has a large value of about 63.6 %, indicating that it can be exploited for certain devices. A variety of theoretical models are used to study the behavior of electrical resistivity in various temperature ranges, showing excellent agreement with experimental results.

The role of magnetic anisotropy in the magnetoresistance of Cr2O3/Al2O3 thin film antiferromagnets

The magnetic states of antiferromagnetic insulating thin films are a promising medium for information storage, but characterization of these states has proven to be challenging. One approach is via magnetotransport measurements in an adjacent heavy metal layer. To this end, we synthesized and characterized a series of Cr2O3 films and bilayers on Al2O3 substrates with three different orientations: m-plane, a-plane, and c-plane. X-ray diffraction results demonstrated orientation control of the Cr2O3 thin film, with m-plane films displaying a higher degree of mosaic spread than the a- and c-plane films. Reciprocal space maps showed that the films are mostly relaxed, although there was a small and different degree of strain in each orientation. The m-plane films were under 2% compressive strain, the a-plane film was under 0.5% compressive strain, and the c-plane film was completely relaxed to bulk values. To probe the magnetic state of the films, we measured the angular dependent magnetoresistance of Cr2O3/Pt bilayers for each orientation. We found a nontrivial temperature dependence of the sign of the magnetoresistance, pointing to the complex interplay between the exchange and anisotropy energies that vary with orientation. We propose that strain and mosaic spread may contribute to a difference in magnetic anisotropies among the samples and the resulting temperature dependence of the magnetoresistance. This work demonstrates the importance of considering the competition between antiferromagnetic exchange and magnetic anisotropy when storing information in the spin state of an antiferromagnetic insulator.

High-field immiscibility of electrons belonging to adjacent twinned bismuth crystals

Bulk bismuth has a complex Landau spectrum. The small effective masses and the large g-factors are anisotropic. The chemical potential drifts at high magnetic fields. Moreover, twin boundaries further complexify the interpretation of the data by producing extra anomalies in the extreme quantum limit. Here, we present a study of angle dependence of magnetoresistance up to 65 T in bismuth complemented with Nernst, ultrasound, and magneto-optic data. All observed anomalies can be explained in a single-particle picture of a sample consisting of two twinned crystals tilted by 108° and with two adjacent crystals keeping their own chemical potentials despite a shift between chemical potentials as large as 68 meV at 65 T. This implies an energy barrier between adjacent twinned crystals reminiscent of a metal- semiconductor Schottky barrier or a p-n junction. We argue that this barrier is built by accumulating charge carriers of opposite signs across a twin boundary.

Excellent temperature dependence of retention energy and large tunnel magnetoresistance of MTJs with strain-induced magnetic anisotropy for SOT-MRAMs with high write efficiency

Excellent temperature dependence of retention energy and large tunnel magnetoresistance of MTJs with strain-induced magnetic anisotropy for SOT-MRAMs with high write efficiency

Генерация и детектирование спинового тока в гетероструктурах иридат/манганит

Kotel'nikov Institute of Radioengineering and Electronics of Russian Academy of Sciences The results of experimental studies on spin current at the interface of iridate/manganite heterostructure SrIrO3/La0.7Sr0.3MnO3 consisted of oxide epitaxial films with nanometer thickness are presented. A pure spin current was induced by microwave irradiation in GHz frequency band under conditions of ferromagnetic resonance. The spin current was detected due to inverse spin-Hall effect measuring the spectral characteristics of charge current arising on electrically conductive SrIrO3 film with strong spin-orbit interaction. The spin-Hall angle, which characterizes the efficiency of spin current conversion to the charge current, was determined by measurements of the angular dependences of spin magnetoresistance of the iridate/manganite interface.

Unconventional superconductivity in PdxBi2Se3 whiskers

Studies of temperature dependence of magnetoresistance for PdxBi2Se3 whiskers in the temperature range 1.6-77K in magnetic field up to 10 T were carried out. Crystals were grown by chemical transport reaction method in closed bromide system. The source and crystallization zone temperatures were 1100 K and 780 K, respectively. Doping of the crystals was carried out during the growth process with palladium impurity to concentrations of (1 – 2) × 1019 cm−3. In the low-temperature region beginning at a temperature of 5 K and reaching a temperature 3.5 K, a sharp decrease in resistance was observed, which is associated with the transition to superconducting state. Based on the analysis of the temperature dependence of the resistance at fixed magnetic fields, the Curie temperature Tc1=5.3 K and Tc2=3.5 K as well as the upper critical magnetic field Bc2=1.45 T and 0.25 T were determined. The established parameters indicates in II type supercondor. This is indicated by the ratio Δ0/kBTc = 2.0, which exceeds BCS limit of 1.76 and indicates a relatively large value of the superconducting gap Δ0=0.8 meV. The determined ratio A/γ2, which establishes the relationship between the electron-electron and electron-phonon interaction, is about of 2ao, which indicates a strong fermionic interaction with phonons in the PdxBi2Se3 superconductor. The estimated value of the ratio of the Curie temperature to the effective Fermi temperature equal to 0.04 also falls within the range of 0.01 ⩽ Tc/TF ⩽ 0.1, which confirms the unconventional superconductivity in the investigated whiskers.

Magnetoresistance behavior across the critical region in ferrimagnet FeCr2Te4 single crystal

In this paper, we carried out a systematic study on the magnetic and electrical transport properties of weak-itinerant ferrimagnet FeCr2Te4 single crystal. We observe a substantial suppression of electron-magnon scattering and spin-fluctuation scattering coefficients with increasing magnetic field below the magnetic ordering temperature ≈123 K. Temperature dependent magnetoresistance exhibits a maximum in the close vicinity of the Curie temperature (Tc) associated with paramagnetic to ferrimagnetic transition. Our Hall resistivity measurements suggest that the obtained carrier concentration is directly related to the magnetoresistance behavior near the transition temperature. Angle dependent measurements show that the magnetoresistance is anisotropic near Tc.

Non-Fermi-Liquid Behavior of Superconducting SnH4.

The chemical interaction of Sn with H2 by X-ray diffraction methods at pressures of 180-210GPa is studied. A previously unknown tetrahydride SnH4 with a cubic structure (fcc) exhibiting superconducting properties below TC = 72 K is obtained; the formation of a high molecular C2/m-SnH14 superhydride and several lower hydrides, fcc SnH2 , and C2-Sn12 H18 , is also detected. The temperature dependence of critical current density JC (T) in SnH4 yields the superconducting gap 2Δ(0)= 21.6 meV at 180GPa. SnH4 has unusual behavior in strong magnetic fields: B,T-linear dependences of magnetoresistance and the upper critical magnetic field BC2 (T) ∝ (TC - T). The latter contradicts the Wertheimer-Helfand-Hohenberg model developed for conventional superconductors. Along with this, the temperature dependence of electrical resistance of fcc SnH4 in non-superconducting state exhibits a deviation from what is expected for phonon-mediated scattering described by the Bloch-Grüneisen model and is beyond the framework of the Fermi liquid theory. Such anomalies occur for many superhydrides, making them much closer to cuprates than previously believed.

Angular dependence of antisymmetric magnetoresistance in Co-Tb thin films with artificial domain wall inclination

We report the observation of angular-dependent antisymmetric magnetoresistance (MR) in artificially deformed Co-Tb Hall bar structures with perpendicular magnetization. Simultaneous transport measurements and domain imaging show that the antisymmetric MR results from the generation of a single domain wall (DW) inclination due to the restricted geometry and is further proportional to the inclination-associated geometry factor. The results are well described by a theoretical model that is supported by analytic and numerical calculations of the nonequilibrium current and Hall voltage distribution in the vicinity of the inclined DW. This finding provides a straightforward and effective approach to control DW geometries, leading to various DW-based spintronic device applications.

Anisotropic proximity–induced superconductivity and edge supercurrent in Kagome metal, K 1− x V 3 Sb 5

Materials with Kagome nets are of particular importance for their potential combination of strong correlation, exotic magnetism, and electronic topology. KV 3 Sb 5 was discovered to be a layered topological metal with a Kagome net of vanadium. Here, we fabricated Josephson Junctions of K 1− x V 3 Sb 5 and induced superconductivity over long junction lengths. Through magnetoresistance and current versus phase measurements, we observed a magnetic field sweeping direction–dependent magnetoresistance and an anisotropic interference pattern with a Fraunhofer pattern for in-plane magnetic field but a suppression of critical current for out-of-plane magnetic field. These results indicate an anisotropic internal magnetic field in K 1− x V 3 Sb 5 that influences the superconducting coupling in the junction, possibly giving rise to spin-triplet superconductivity. In addition, the observation of long-lived fast oscillations shows evidence of spatially localized conducting channels arising from edge states. These observations pave the way for studying unconventional superconductivity and Josephson device based on Kagome metals with electron correlation and topology.

Unusual Transport Properties with In-plane Magnetic Field in SrxBi2Se3 Single Crystals

A topological insulator Bi2Se3 becomes a topological superconductor by doping Cu or Sr. Due to the nematicity of these Ax Bi2Se3 (A = Cu, Sr) materials, physical quantities show two-fold rotational symmetry as a function of in-plane magnetic field angle φ despite their three-fold structural symmetry in the plane. In this study, single crystals of Sr x Bi2Se3 (0.0 ≤ x ≤ 0.17) were grown by the self-flux method. Using these crystals, extensive measurements of the magnetoresistivity as a function of φ (ρ(φ)) were performed. Angular dependence of magnetoresistance shows an unusual cos(φ) term, which can be related to the c-axis current as well as higher harmonics components. Origins of higher harmonics components of ρ(φ) are discussed.

Energy Spectrum of the Valence Band in HgTe Quantum Wells on the Way from a Two- to Three-Dimensional Topological Insulator

The magnetic field and temperature dependences of longitudinal magnetoresistance and the Hall effect have been measured in order to determine the energy spectrum of the valence band in HgTe quantum wells with the width dQW = 20–200 nm. The comparison of hole densities determined from the period of Shubnikov–de Haas oscillations and the Hall effect shows that states at the top of the valence band are doubly degenerate in the entire dQW range, and the cyclotron mass {{m}_{h}} determined from the temperature dependence of the amplitude of Shubnikov–de Haas oscillation increases monotonically from 0.2{{m}_{0}} to 0.3{{m}_{0}} ({{m}_{0}} is the mass of the free electron) with increasing hole density p from 2 times {{10}^{{11}}} to 6 times {{10}^{{11}}} cm–2. The determined dependence has been compared to theoretical dependences {{m}_{h}}(p,{{d}_{{{text{QW}}}}}) calculated within the four-band kP model. These calculations predict an approximate stepwise increase in {{m}_{h}} owing to the pairwise merging of side extrema with increasing hole density, which should be observed at p = (4{-} 4.5) times {{10}^{{11}}} and 4 × 1010 cm–2 for dQW = 20 and 200 nm, respectively. The experimental dependences are strongly inconsistent with this prediction. It has been shown that the inclusion of additional factors (electric field in the quantum well, strain) does not remove the contradiction between the experiment and theory. Consequently, it is doubtful that the mentioned kP calculations adequately describe the valence band at all dQW values.

Anomalous Hall effect in ferromagnetic LaCo2As2 and ferrimagnetic NdCo2As2

We conducted a comparative study of the magnetic and transport properties of single-crystalline LaCo2As2 and NdCo2As2. LaCo2As2 is a soft metallic ferromagnet which exhibits purely intrinsic anomalous Hall effect (AHE) due to Co-3d electrons. With Nd-4f electronic magnetism, ferrimagnetic NdCo2As2 manifests pronounced sign reversal and multiple hysteresis loops in temperature- and field-dependent magnetization, Hall resistivity, and magnetoresistance, due to complicated magnetic structural changes. We reveal that the AHE for NdCo2As2 is stemming from the Co sub-lattice and deduce its phase diagram which includes magnetic compensation and two meta-magnetic phase transitions. The sensitivity of the Hall effect on the details of the magnetic structures in ferrimagnetic NdCo2As2 provides a unique opportunity to explore the magnetic interaction between 4f and 3d electrons and its impact on the electronic structure.

Magnetotransport property of oxygen-annealed Fe1+y Te thin films

Fe-based superconductors are one of the current research focuses. FeTe is unique in the series of FeSe1−x Te x , since it is nonsuperconducting near the FeTe side in the phase diagram in contrast to the presence of superconductivity in other region. However, FeTe thin films become superconducting after oxygen annealing and the mechanism remains elusive. Here, we report the temperature dependences of resistivity, Hall effect and magnetoresistance (MR) of a series of FeTe thin films with different amounts of excess Fe and oxygen. These properties show dramatic changes with excess Fe and oxygen incorporation. We found the Hall coefficients are positive for the oxygen-annealed samples, in contrast to the transition from positive to negative below 50 K for the vacuum-annealed samples. For all samples, both the resistivity and Hall coefficient show a dramatic drop, respectively, at around 50 K–75 K, implying coexistence of superconductivity and antiferromagnetic order for the oxygen-annealed samples. The vacuum-annealed samples show both positive and negative values of MR depending on temperature, while negative MR dominates for the oxygen-annealed samples. We also found that oxygen annealing reduces the excess Fe in FeTe, which has been neglected before. The results are discussed in terms of several contributions, and a comparison is made between the oxygen-annealed FeTe thin films and FeSe1−x Te x . This work is helpful for shedding light on the understanding of oxygen-annealed FeTe thin films.

Spin mixing conductance and spin magnetoresistance of the iridate/manganite interface

We present results on experimental studies of spin current, measured under spin pumping at ferromag-netic resonance in wide frequency band 2-20 GHz for SrIrO3/La0.7Sr0.3MnO3 heterostructures fabricated by RF magnetron sputtering at high temperature. The epitaxial growth of the thin film in heterostructure by a cube-on-cube mechanism was confirmed by XRD and TEM analysis. Taking into account the con-tribution of anisotropic magnetoresistance the spin current was estimated as 1/3 of the total response. We show that both real and imaginary parts of spin mixing conductance are valuable for heterostructures with strong spin-orbit interaction in SrIrO3. Imaginary part of spin mixing conductance was estimated by means of shift of ferromagnetic resonance field of La0.7Sr0.3MnO3 layer in heterostructure. The spin mag-netoresistance was evaluated from angular dependencies of magnetoresistance measured in planar Hall configuration. In order to extract the influence of anisotropic magnetoresistance a La0.7Sr0.3MnO3 film was measured as well. The spin Hall angle for heterostructure was found higher than for interface Pt/ La0.7Sr0.3MnO3.

Evidence of magnetoelectronic electromagnon-mediated transport in flexoelectronic heterostructures

The superposition of atomic vibrations and flexoelectronic effect gives rise to a cross correlation between free charge carriers and temporal magnetic moment of phonons in conducting heterostructures under an applied strain gradient. The resulting dynamical coupling is expected to give rise to quasiparticle excitations called magnetoelectronic electromagnons that carry electronic charge and temporal magnetic moment. Here, we report experimental evidence of magnetoelectronic electromagnons in the freestanding degenerately doped $p$-Si based heterostructure thin film samples. These quasiparticle excitations give rise to long-distance ($>100 \ensuremath{\mu}\mathrm{m}$) spin transport, demonstrated using spatially modulated transverse magnetothermoelectric and nonlocal resistance measurements. The magnetoelectronic electromagnons are nonreciprocal and give rise to large magnetochiral anisotropy $(0.352\phantom{\rule{0.16em}{0ex}}{\mathrm{A}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{T}}^{\ensuremath{-}1})$ that diminishes at lower temperatures. The superposition of nonreciprocal magnetoelectronic electromagnons gives rise to longitudinal and transverse modulations in charge carrier density, spin density, and magnetic moment, demonstrated using the Hall effect and edge dependent magnetoresistance measurements, which can also be called inhomogeneous magnetoelectronic multiferroic effect. These quasiparticle excitations are analogous to photons where time dependent polarization and temporal magnetic moment replace electric and magnetic field, respectively, and most likely topological because they manifest topological Nernst effect. Hence, the magnetoelectronic electromagnon can potentially give rise to quantum interference and entanglement effects in conducting solid state systems at room temperature in addition to efficient spin transport.

Strain-induced massless Dirac fermion state of the molecular conductor α-(BEDT-TTF)2I3

Uniaxial pressure can dramatically change the properties of low-dimensional systems and induce electronic phase transitions. The first-discovered molecular massless Dirac electron system α-(BEDT-TTF)2I3 has intensively been studied because of its unique features, such as the Fermi energy being very close to the Dirac point, strong electron correlation, and the quantum phase transition from the charge-ordered insulating state. However, the Dirac state is realized only under high pressure of 15 kbar, which limits the measurement of physical properties (e.g., experimental determination of band dispersion and density of states). Here, we demonstrate that the Dirac state of α-(BEDT-TTF)2I3 can be realized by applying uniaxial bending strain without confining it in a pressure cell. Uniaxial strain below 1% completely suppresses the metal–insulator transition observed at ambient pressure. Under strain, a characteristic temperature dependence of magnetoresistance associated with the formation of the n = 0 Landau level is observed, indicating the realization of the massless Dirac state.

Temperature dependence of angular-dependent magnetoresistance in epitaxial Fe(001) film

Angular-dependent magnetoresistance (ADMR) of an epitaxial Fe(001) film is investigated with current along hard and easy axes in-plane at different temperatures. The temperature dependences of ordinary magnetoresistance (OMR), anisotropic magnetoresistance (AMR), and magnetocrystalline anisotropy magnetoresistance (MMR) in ADMR were determined. As temperature decreases, negative OMR and positive AMR with a twofold symmetry show increasing and decreasing amplitudes, respectively. The amplitude of MMR with twofold and fourfold symmetries is almost invariable with both temperature and magnetic field. Meantime, when current was applied at hard and easy axes, MMR contributes an anti-phase signal to ADMR. Our findings of OMR, AMR, and MMR in the Fe(001) ADMR are of great significance to the understanding of magnetoresistance in magnetic films.

Antiferromagnetic hysteresis above the spin-flop field

Magnetocrystalline anisotropy is essential in the physics of antiferromagnets and commonly treated as a constant, not depending on an external magnetic field. However, we demonstrate that in CoO the anisotropy should necessarily depend on the magnetic field, which is shown by the spin Hall magnetoresistance of the CoO|Pt device. Below the N\'eel temperature CoO reveals a spin-flop transition at 240 K at 7.0 T, above which a hysteresis in the angular dependence of magnetoresistance unexpectedly persists up to 30 T. This behavior is shown to agree with the presence of the unquenched orbital momentum, which can play an important role in antiferromagnetic spintronics.