Field Dependence Of Magnetoresistance Research Articles

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

We report the magnetic field dependent magnetization and magnetoresistance (MR) properties of La2/3Sr1/3MnO3 (LSMO)/ γ -Fe2O3/LSMO trilayer heterostructure 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.

Sensing characteristics and EPIR Studies on composite manganites: Role of nanoparticles in the micronsized matrix lattice

In the present communication, the electrical transport properties have been investigated for manganite-based composites consisting of different weight fractions of nanoparticles of LaMnO3 (LMO) and polycrystalline La0.7Ca0.3MnO3 (LCMO). A complex phase separation scenario has been proposed to understand the hysteretic resistive nature exhibited by manganite matrix composites. The role of complex phase separation has been discussed for the manganite composite resistivity and temperature coefficient of resistance (TCR) dependence on temperature, thermal cycle, current and LMO content as well as their sensitivity for voltage and current have also been examined. Observed electric pulse-induced resistance (EPIR) switching in these composites under different applied voltages and magnetic fields have been understood based on a complex phase separation scenario and the formation–rupture of conducting filamentary paths. Tuning of magnetic field-dependent resistance and magnetoresistance (MR) with the influence of different resistance states of LMO–LCMO composites has been understood in depth.

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.

Spin Hall magnetoresistance in antiferromagnetic α -Fe2O3/Pt bilayers: Modulation from interface magnetic state

In this work, we have prepared an antiferromagnetic insulated α-Fe2O3 film with a large out-of-plane magnetic component and studied the spin Hall magnetoresistance (SMR) in α-Fe2O3/Pt bilayers. Both angular-dependent magnetoresistance and field-dependent magnetoresistance have featured a sign change characteristic with varying temperature, which is ascribed to the competition between a modulated interface magnetic state and an antiferromagnetic bulk state of the α-Fe2O3 film. According to a generalized theoretical model, which takes the effective spin conductance into consideration, the spin transport can be mathematically expressed as the change of field dependent average spin operators with varying temperature. The critical temperature also depends on the α-Fe2O3 film thickness and the magnetic field, which are ascribed to the magnons transport and long-range order of non-collinear spin textures, respectively. Furthermore, we have given a phenomenological form to fit the SMR curves in the critical temperature interval, which further reveals the origin of SMR with complex magnetic structures.

Shubnikov–de Haas oscillations and nontrivial topological states in Weyl semimetal candidate SmAlSi

The RAlX (R = Light rare earth; X = Ge, Si) compounds, as a family of magnetic Weyl semimetal, have recently attracted growing attention due to the tunability of Weyl nodes and its interactions with diverse magnetism by rare-earth atoms. Here, we report the magnetotransport evidence and electronic structure calculations on nontrivial band topology of SmAlSi, a new member of this family. At low temperatures, SmAlSi exhibits large non-saturated magnetoresistance (MR) (as large as ∼5500% at 2 K and 48 T) and distinct Shubnikov–de Haas (SdH) oscillations. The field dependent MRs at 2 K deviate from the semiclassical (μ 0 H)2 variation but follow the power-law relation MR (μ 0 H) m with a crossover from m ∼ 1.52 at low fields (μ 0 H< 15 T) to m ∼ 1 under high fields (μ 0 H> 18 T), which is attributed to the existence of Weyl points and electron–hole compensated characteristics with high mobility. From the analysis of SdH oscillations, two fundamental frequencies originating from the Fermi surface pockets with non-trivial π Berry phases and small cyclotron mass can be identified, this feature is supported by the calculated electronic band structures with two Weyl pockets near the Fermi level. Our study establishes SmAlSi as a paradigm for researching the novel topological states of RAlX family.

Observation of Surface Superconductivity in a 3D Dirac Material

AbstractSuperconductivity becomes more interesting when it encounters dimensional constraint or topology because it is of importance for exploring exotic quantum phenomena or developing superconducting electronics. Here, the coexistence of naturally formed surface superconducting state and 3D topological Dirac state in single crystals of BaMg2Bi2 is reported. The electronic structure obtained from the first‐principles calculations demonstrates that BaMg2Bi2 is an ideal Dirac material, in which the Dirac point is very close to the Fermi level and no other energy band crosses the Fermi level. Superconductivity up to 4.77−−5.17 K can be observed under ambient pressure in the measurements of resistivity. The anisotropic upper critical field and angle dependent magnetoresistance reveals the 2D characteristic of superconductivity, indicating that superconductivity occurs on the surface of the sample and is absent in the bulk state. The study not only provides BaMg2Bi2 as a suitable platform to study the interplay between superconductivity and topological Dirac state but also indicates that MgBi‐based materials may be a promising system for exploring new superconductors.

Spin chirality induced large topological Hall effect in magnetic Weyl semimetallic Eu2Ir2O7 (111) thin films

Antiferromagnetic (AFM) pyrochlore iridates are a fertile ground to hunt for a Weyl semimetallic state characterized by a linear crossing of two nondegenerate bands near the Fermi level ${E}_{F}$. Here, we demonstrate evidence of low-temperature anomalous and topological Hall effects in an antiferromagnetic ${\mathrm{Eu}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$(111) epitaxial thin film. The observed anomalous Hall effect is explained in terms of the momentum space Berry curvature associated with the Weyl nodes in the electronic band structure. The topological Hall effect reaches a large value ${\ensuremath{\rho}}_{xy}^{\text{THE}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}10\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\text{cm}$ at 2 K. The topological nature of the Hall effect is attributed to the nonzero scalar spin chirality of the all-in-all-out/all-out-all-in (AIAO/AOAI) type noncoplanar AFM spin structure. The magnetoresistance (MR) shows a prominent negative variation ($\mathrm{MR}\ensuremath{\sim}10%$ at 2 K) below 10 K. The field dependence of MR below 5 K varies quadratically in the low-field regime, and above 40 kOe it shows a linear trend. The quadratic to linear crossover of the MR is explained by the field-induced ($H$) spin canting (spin chirality) of the static spins in the AIAO/AOAI spin structure. In the intermediate-temperature region MR of $15\ensuremath{-}25$ K exhibits a hysteretic response which is associated with field-induced domain switching of the AIAO/AOAI spin structure. This work highlights the interplay of magnetism and topology in a spin-orbit-coupled correlated electron system and unravels the possibility for realizing the Weyl phase in antiferromagnetic ${\mathrm{Eu}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$(111) thin films.

LiMo8O10: Polar Crystal Structure with Infinite Edge-Sharing Molybdenum Octahedra.

Polycrystalline LiMo8O10 was prepared in a sealed Mo crucible at 1380 °C for 48 h using the conventional high-temperature solid-state method. The polar tetragonal crystal structure (space group I41md) is confirmed based on the Rietveld refinement of powder neutron diffraction and 7Li/6Li solid-state NMR. The crystal structure features infinite chains of Mo4O5 (i.e., Mo2Mo4/2O6/2O6/3) as a repeat unit containing edge-sharing Mo6 octahedra with strong Mo-Mo metal bonding along the chain. X-ray absorption near-edge spectroscopy of the Mo-L3 edge is consistent with the formal Mo valence/configuration. Magnetic measurements reveal that LiMo8O10 is paramagnetic down to 1.8 K. Temperature-dependent resistivity [ρ(T)] measurement indicates a semiconducting behavior that can be fitted with Mott's variable range hopping conduction mechanism in the temperature range of 215 and 45 K. The ρ(T) curve exhibits an exponential increase below 5 K with a large ratio of ρ1.8/ρ300 = 435. LiMo8O10 shows a negative field-dependent magnetoresistance between 2 and 25 K. Heat capacity measurement fitted with the modified Debye model yields the Debye temperature of 365 K.

Microstructure and magnetoresistance driven magnetocapacitance in ex-situ combustion derived BaTiO3-CoFe2O4 bulk magnetodielectric composites

Enhanced magnetodielectric properties including magnetocapacitance have been observed in the BaTiO3-CoFe2O4 composites due to the microstructural interactions between the dielectric and magnetic phases. Based on this concept, this research work explores the frequency and field dependent magnetocapacitance and magnetoresistance of 70 wt% BaTiO3 – 30 wt% CoFe2O4 composites. Ex-situ synthesis method is adopted to form a partial 0–3 microstructure and this composite is sintered at 900 °C and 1000 °C. Phases such as pseudo-cubic BaTiO3 and cubic CoFe2O4 have been observed in both composites. Secondary phase of barium hexaferrite is observed at 1000 °C. Based on FESEM, CoFe2O4 phase is found to be embedded in the BaTiO3 matrix at 900 °C, however interconnected CoFe2O4 along with partially shrunk BaTiO3 has been observed at 1000 °C. The permittivity of composite is found to be ∼ 317 and ∼ 451 at 900 °C and 1000 °C, respectively, and the Maxwell-Wagner polarization is tuned by the microstructure. The effect of space charge is found to be relatively larger at 1000 °C. Magnetic nature is altered due to the connectivity of ferrite phases. Magnetocapacitance values are mostly analogues to the magnetoresistance behavior in both composites. The percentage of magnetocapacitance is found to be increased nearly 5 times due to the microstructural variations. Field and frequency-dependent magnetocapacitance responses along with Cole-Cole plots of composite confirmed the role of microstructural interactions and magnetoresistance.

Tunable junction magnetoresistance of Fe3−xPxO4 (P = Mn, Zn)/p-Si heterojunctions at room temperature

The tunable junction magnetoresistance of Fe3−xPxO4 (P = Mn, Zn)/p-Si heterostructures (x = 0, 0.5) is reported for potential use in future Si semiconductor-based spintronic applications. In the way that a evidence of conception, Fe3−xPxO4 (P = Mn, Zn)/p-Si heterostructures (x = 0, 0.5) were fabricated by depositing Fe3−xPxO4 (P = Mn, Zn) films on p-Si using pulsed laser deposition technique. All the heterostructures showed spin-valve as well as backward rectifying property at room temperature. Evidently, the heterostructures showed not only an electric field-dependent junction magnetoresistance (JMR) at room temperature in reverse bias but also the magnitude and sign changes of JMR with manganese (0.5) and zinc (0.5) substitutions. The electronic band structure of the heterojunctions is proposed to explain the doping and bias field-dependent JMR sign change behavior of the devices. The room temperature tunable junction magnetoresistance of Fe3−xPxO4 (P = Mn, Zn)/p-Si heterostructures at a low bias voltage and low magnetic field may open up a new favorable circumstance for Si-based and low power consuming spin valves in the near future.

Large-field magnetoresistance of nanometer scale nickel films grown on molybdenum disulfide

The magnetoresistance of thin nickel films grown on molybdenum disulfide was measured in perpendicular magnetic fields as high as 90 kOe. Films with thicknesses of 20 nm provided continuous surfaces for measurement. The magnetoresistance was found to be linear with respect to the applied magnetic field with no sign of saturation. There was also no evidence of hysteresis or temperature dependence between 100 to 300 K. STM measurement showed the deposited Ni forms a continuous film of extremely small nanoclusters. However, the field dependence of magnetoresistance was found to be significantly larger than bulk Ni, which is in turn larger than Ni with nanoscale grains. We expect the unusual magnetoresistance behavior to arise from some property of the Ni-MoS2 interface.

Band-selective gap opening by a C4-symmetric order in a proximity-coupled heterostructure Sr2VO3FeAs

Complex electronic phases in strongly correlated electron systems are manifested by broken symmetries in the low-energy electronic states. Some mysterious phases, however, exhibit intriguing energy gap opening without an apparent signature of symmetry breaking (e.g., high-TC cuprates and heavy fermion superconductors). Here, we report an unconventional gap opening in a heterostructured, iron-based superconductor Sr2VO3FeAs across a phase transition at T 0 ∼150 K. Using angle-resolved photoemission spectroscopy, we identify that a fully isotropic gap opens selectively on one of the Fermi surfaces with finite warping along the interlayer direction. This band selectivity is incompatible with conventional gap opening mechanisms associated with symmetry breaking. These findings, together with the unusual field-dependent magnetoresistance, suggest that the Kondo-type proximity coupling of itinerant Fe electrons to localized V spin plays a role in stabilizing the exotic phase, which may serve as a distinct precursor state for unconventional superconductivity.

Peculiarity of the low temperature magnetoresistive effect in the Corbino disk with magnetic ordering

The transverse magnetoresistance (MR) hysteresis loops of a magnetically ordered Corbino disk have been studied in the temperature range 300–2 K in an external magnetic field with induction up to 1 T oriented in the plane of the disk (ϕ = 0°) and perpendicularly to its plane (ϕ = 90°). The Corbino disk is made of a thin permalloy film obtained on an insulating sitall substrate by ion-beam sputtering. Independently of the temperature and measurement geometry, the field dependences of MR in the range of weak magnetic fields up to the magnetisation saturation exhibit sharp peaks of the negative MR caused by the domain walls motion during the magnetisation reversal of the sample. The position of the peak in the magnetic field (Bp) is determined by the temperature as well as the angle between magnetic field direction and the disk plane. It was found that a temperature change in the range of T = 300–2 K leads to a change in its position in the range of 0.2–6.0 mT and 8–22 mT at ϕ = 0° and ϕ = 90°, respectively. The magnetic field direction reorientation from in-plane to out-of-pane at T = 2 K leads to the Bp change from 6 to 22 mT. In the range of strong magnetic fields above the magnetization saturation field at ϕ = 0° the positive MR component decreases with induction and has a linear non-saturable dependence down to T ≈ 40–50 K due to the magnon MR component dominance. The complete freezing of magnons at T = 2 K leads to the absence of high-field magnetoresistive effect. At ϕ = 90° in weak fields, the MR changes its sign from positive to negative due to the anisotropic MR component dominance because of the disk magnetisation reorientation perpendicular to the current lines. In a strong field it changes the slope due to the saturation of negative anisotropic MR component, as well as possible additional contribution of the positive geometric Lorentzian MR.

Anomalous magnetoresistance and magneto-thermal properties of the half-Heuslers, RPdSi (R = Y, Gd–Er)

Here, we present a detailed study on the magnetic, magneto-transport, and magneto-thermal properties of the equiatomic half-Heusler compounds with the general formula, RPdSi (R = Y and rare-earth, Gd–Er). These materials crystallize in two different superstructures of the TiNiSi-type orthorhombic unit cell with the space groups Pnma and Pmmn. Our magnetic and heat capacity measurements reveal the onset of an antiferromagnetic (AFM) ordering in the temperature range 3–16 K for all the local moments bearing RPdSi compounds, while the non-magnetic analog, YPdSi exhibits a Pauli-paramagnetic behaviour. The AFM state of these compounds can be tuned by magnetic field and temperature as demonstrated by the magnetic measurements below the Neel temperature (T N). Most importantly, this tuning of the magnetic structure is well documented in the complex temperature and field dependence of magnetoresistance (MR) and magnetocaloric effect (MCE). Our study establishes a striking correlation of the commensurate/incommensurate AFM structure with that of positive/negative MR and MCE in this series of compounds. We emphasize that such a framework applies to a large number of AFM intermetallic systems.

Significant enhancement in thermoelectric power with Iso-electronic doping in c-axis oriented MoTe2 nano bulk sheets

The search for techniques to enhance thermoelectric power as well as figure of merit is indispensable in the development of thermoelectric materials. In this work, iso-electronic substitution of Tellurium with 9% Sulfur in MoTe2 nano-bulk sheets showed an 88% room temperature enhancement in thermopower combined with a 13% increase in power factor with a negative temperature coefficient of resistivity below 80 K. To correlate the results, a two-band model was successfully applied to temperature variation of both thermopower and resistivity. The results ascribe the thermopower enhancement to the formation of a narrow sulfur impurity band, which causes, a considerable percentage of the holes to pop-up to the valence band maximum and get localized around the S2-cores, resulting in a sharp depletion in hole density available for transport. The application of the two-carrier model to the field dependent magneto resistance, supports the above proposed reduction in hole density. Our results shed light on doping induced thermopower tuning, leading to more efficient thermo-electrics.

Peculiarities of Magnetoresistance of [Fe/SiO]n Discontinuous Multilayers

The influence of the magnetic and insulator layer thickness on the crystal structure and magnetoresistive properties of [Fe/SiO]n discontinuous multilayers has been studied. The results indicate that the decreasing of Fe layer thickness within the range from 10 to 3 nm leads to the transition of microstructure of the samples from nanocrystalline to amorphous. For all investigated systems in an as-deposited state, the isotropic nature of the field dependences of magnetoresistance is observed. For samples with layer thickness dFe = 4–6 nm and dSiO = 5 nm, the transition to isotropic MR occurs after annealing to 400 K. However, for samples with Fe layer thickness of 7–10 nm, such transition is not observed regardless of the effective thickness of insulator layer and annealing temperature.

Electrical Properties and Thermal Annealing Effects of Polycrystalline MoS2-MoSX Nanowalls Grown by Sputtering Deposition Method

Straightforward growth of nanostructured low-bandgap materials is a key issue in mass production for electronic device applications. We report here facile nanowall growth of MoS2-MoSX using sputter deposition and investigate the electronic properties of the nanowalls. MoS2-MoSX nanowalls become gradually thicker and taller, with primarily (100)-plane growth directions, with increasing deposition time. Nanowalls combine with nearby walls when a rapid thermal annealing (RTA, 200 °C–500 °C) process is applied. All samples have conventional low-bandgap semiconductor behavior with exponential resistance increase as measurement temperature decreases. The 750 nm-thick MoS2-MoSX nanowalls have a sheet carrier mobility of up to 2 cm2·V−1·s−1 and bulk carrier concentration of ~1017–1019 cm−3 range depending on RTA temperature. Furthermore, perpendicular field-dependent magnetoresistance at 300 K shows negative magnetoresistance behavior, which displays resistance decay by applying a magnetic field (MR ratio in the −1 % range at 5 T). Interestingly, 400 °C RTA treated samples show a resistance upturn when applying an external magnetic field of more than 3 T. Our research suggests tuneability of MoS2 nanowall size and mesoscopic electronic transport properties.

Magnetoresistive Properties of Multilayer Film Systems Based on Permalloy and Silver

In this paper, the experimental investigation focuses on the magnetoresistive properties of nanosized film systems. Their structure changes from layered to granular due to transition from bilayer FM/NM (FM is a ferromagnetic material, NM is a nonmagnetic material) to [FM/NM]n multilayer film at a constant total thickness of samples. As ferromagnetic and nonmagnetic materials were chosen permalloy Ni80Fe20 (Py) and Ag, respectively. It was demonstrated that the shape of the field dependences of magnetoresistance depends on the number of bilayer Py/Ag. For as-deposited [Py/Ag]n/S at n = 8, 16, the transition from the antiferromagnetic ordering of magnetic moments to ferromagnetic one occurs under an external magnetic field. As a result, the resistivity of the samples reduced, and the giant magnetoresistive effect was realized. The increase of the number of bilayers repeats from 2 to 16 at the unchanged total thickness of the system leads to the growth of the magnetoresistance from 0.1 % to 0.35 %. During annealing up to 600 K, the magnetoresistive effect is reduced, but it does not disappear completely

Percolation conductivity model in A site-deficient La0.8−xoxNa0.2−xoxMnO3 manganites and universal model of magnetic field-dependent resistivity and magnetoresistance behavior

The electrical and magnetoresistance behaviors of La0.8−xoxNa0.2−xoxMnO3 [with x = 0 (N0) and 0.1 (N0.1)] polycristalline samples were investigated. Resistance measurements versus temperature under different magnetic applied fields were performed to investigate the electronic transport as well as the magnetoresistance properties. The metal/insulator transition temperature decreases from 280 K for x = 0 to 275 K for x = 0.1. The electrical conduction in these compounds has been well described in the context of the percolation model based on the phase separation of ferromagnetic metallic regions with paramagnetic insulating ones. The temperature-dependent resistance shows the existence of a minimum at low temperature. This behavior is due to the existence of a competition between inelastic and elastic interactions expressed by Kondo-like spin-dependent scattering. An empirical model was used to describe the variation of the magetoresistance and normalized resistance as a function of the magnetic applied field. The model was successfully widely tested on several magnetic specimens and the evolution of the fitting parameters was discussed in detail.

Magnetism and magnetoresistance in the critical region of a dilute ferromagnet

We present detailed experimental measurements and simulations of the field-dependent magnetization and magnetoresistance in the vicinity of the Curie temperature in the highly disordered dilute ferromagnetic semiconductor (Ga,Mn)As. The observed dependence of the magnetization on external magnetic field and temperature is consistent with three-dimensional Heisenberg equation of state calculations including a narrow distribution of critical temperatures. The magnetoresistance shows a peak at the Curie temperature due to the suppression of magnetic scattering in an applied magnetic field, which is well-described by considering changes in the square of the magnetization induced by the magnetic field.