Giant Anisotropic Magnetoresistance Research Articles

Demonstration of giant anisotropic magnetoresistance, high spin filtering efficiency, and negative differential resistance in nanodevices based on oxygen doped black arsenic phosphorus nanoribbons

We investigate the electrical properties of pure black arsenic phosphorus and oxygen atom doped monolayer black arsenic phosphorus using first principle calculations. The density of states results reveals that oxygen atom doped black arsenic phosphorus is a magnetic semiconductor. The current-voltage characteristic curves of oxygen atom doped monolayer black arsenic phosphorus nanoribbons based devices have been determined using the non-equilibrium Green's function associated with the density function theory. The results demonstrate that the device made of doped black arsenic phosphorus has a substantial current difference between armchair and zigzag black arsenic phosphorus nanoribbons, implying that the device made of nanoribbons has a large anisotropic magnetoresistance. The spin filtering efficiency is nearly 100% at some bias voltage levels, and the transmission spectrums of the associated bias voltage window can explain the significant negative differential resistance. Furthermore, these findings suggest that oxygen atom doped black arsenic-phosphorus nanoribbons are suitable for spintronic devices.

Anisotropic giant magnetoresistance and Fermi surface topology in the layered compound YbBi2

Magnetoresistance in novel materials has been attracting ever-increasing attention since its mechanism is still the subject of intense debate and the physics behind these emergent phenomena remains a wild space to be explored. Here, we grow ${\mathrm{YbBi}}_{2}$ single crystals and study their anisotropic giant magnetoresistance and Fermi surface topology via de Haas--van Alphen oscillation and Hall resistivity measurements, electronic band structure calculations, and so on. A detailed analysis of the angle-dependent quantum oscillations reveals the presence of nontrivial topological electronic states and several cylindrical Fermi surface sheets extended along the $b$ axis. Hall resistivity data suggest that multiple charge carriers participate in the transport, and electron and hole densities are nearly balanced. These findings are further confirmed by theoretical calculations. After checking several possible mechanisms, the giant magnetoresistance ($\ensuremath{\sim}1.2\ifmmode\times\else\texttimes\fi{}{10}^{3}%$ at 14 T and 2 K) in ${\mathrm{YbBi}}_{2}$ is ascribed to the carrier compensation instead of topological protection and open orbits. Additionally, we also find that Fermi surface anisotropy serves as a key element for the angular magnetoresistance in this compound. Our studies show that ${\mathrm{YbBi}}_{2}$ can be not only a topologically nontrivial material, but also a prototype system to check familiar magnetoresistance mechanisms.

Anisotropic giant magnetoresistanceand de Hass–van Alphen oscillations in layered topological semimetal crystals

Here, we report an anisotropic giant magnetoresistance (GMR) effect and de Hass–van Alphen (dHvA) oscillation phenomena in nominal TaNiTe5 single crystals. TaNiTe5 exhibits the GMR effect with the maximum value of ∼3 × 103% at T = 1.7 K and B = 31 T, with no sign of saturation. The two-band model fitting of Hall resistivity indicates that the anomalous GMR effect was derived from the coexistence of electron and hole carriers. When the external magnetic field is applied to the electron–hole resonance, the GMR effect is enhanced. The dHvA oscillation data at multiple frequencies reveal the topological characteristics of high carrier mobility, low carrier effective mass, and a small Fermi surface pocket with a nontrivial Berry phase. Our work provides a new platform for the study of topological semimetals with significant anisotropic GMR effect.

Highly Tunable Spin-Orbit Torque and Anisotropic Magnetoresistance in a Topological Insulator Thin Film Attached to Ferromagnetic Layer.

We investigate spin-charge conversion phenomena in hybrid structures of topological insulator thin films and magnetic insulators. We find an anisotropic inverse spin-galvanic effect that yields a highly tunable spin-orbit torque. Concentrating on the quasiballistic limit, we also predict a giant anisotropic magnetoresistance at low dopings. These effects, which have no counterparts in thick topological insulators, depend on the simultaneous presence of the hybridization between the surface states and the in-plane magnetization. Both the inverse spin-galvanic effect and anisotropic magnetoresistance exhibit a strong dependence on the magnetization and the Fermi level position and can be used for spintronics and spin-orbit-torque-based applications at the nanoscale.

Cooperative orbital moments and edge magnetoresistance in monolayer WTe2

We argue that edge electrons in monolayer WTe$_2$ can possess a "cooperative" orbital moment (COM) that critically impacts its edge magnetoresistance behavior. Arising from the cooperative action of both Rashba and Ising spin orbit coupling, COM quickly achieves large magnitudes (of order few Bohr magnetons) even for relatively small spin-orbit coupling strengths. As we explain, such large COM magnitudes arise from an unconventional cooperative spin canting of edge spins when Rashba and Ising spin orbit coupling act together. Strikingly, COM can compete with spin moments to produce an unusual anisotropic edge magnetoresistance oriented at an oblique angle. In particular, this competition produces a direction along which $\mathbf{B}$ is ineffective at gapping out the edge spectrum leaving it nearly gapless. As a result, large contrasts in gap sizes manifest as $\mathbf{B}$ is rotated granting giant anisotropic magnetoresistance of 0.1-10 million % at 10 T and low temperature.

Synthesis and magnetoresistance of (Cd1−x Znx)3As2 (x = 0,007) crystals

The vapor phase growth of Cd3As2—Zn3As2 (in the following (Cd1−x Znx)3As2 solid solutions process is described. The (Cd0,993 Zn0,007)3As2 solid solution single crystals were synthesized. Scanning electron microscopy and electron diffraction data suggest high crystalline quality of studied sample. Its structure and surface morphology, indicating the presence of growth nuclei and cleavage planes, were investigated. Giant anisotropic magnetoresistance and Shubnikov — de Haas oscillations were observed at low temperatures. Obtained results suggests that peculiarities of Dirac semimetal phase persist in (Cd1−x Znx)3As2 solid solution at low zinc content. At the same time, there are indications of some differences with initial Cd3As2 properties.

Vapor-Phase Synthesis and Magnetoresistance of (Cd0.993Zn0.007)3As2 Single Crystals

We report a highly anisotropic magnetoresistance of (Cd0.993Zn0.007)3As2 single crystals, which have been synthesized by the vapor-phase growth. Scanning electron microscopy and electron diffraction data confirm the high crystalline quality of obtained samples. Studied samples exhibit specific features such as octahedral nuclei growth and step-like morphology of the surface formed by {112} planes. The giant anisotropic magnetoresistance and Shubnikov-de Haas oscillations have been observed at low temperatures. The results suggest the existence of the Dirac semimetal phase in (Cd1 −xZnx)3As2 solid solution with low zinc content. Thus, the observed magnetoresistance anisotropy is partially attributed to the chiral anomaly.

Layered Topological Insulators and Semimetals for Magnetoresistance Type Sensors

AbstractMagnetoresistance (MR) type sensors are transducers that can vary their resistances sensitively in response to an applied magnetic field. Recently, topological quantum materials have drawn the increased attention for sensor applications due to their novel MR effects. Here, a range of MR effects occurring in the layered 3D topological insulators and topological semimetals are briefly reviewed. The MR effects include the extremely large nonsaturating MR, the giant anisotropic MR, and the unique spin‐valve‐like MR. The large MR ratios, the high MR anisotropy, and the low 1/f noise allow sensors to have the high sensitivity over a wide range of temperatures and magnetic fields. It is anticipated that the layered topological quantum materials with their excellent MR performance and structural flexibility would provide an ideal platform for new‐generation magnetic sensor applications.

Anisotropic giant magnetoresistive effect in the sandwich based FexNi1−x (x ≈ 0.5) and Cu

The anisotropic effect of a giant magnetoresistance (GMR) in the three-layer FexNi1−x/Cu/FexNi1−x/Sub (x ≈ 0.5, Sub is the substrate) magnetically ordered film is analyzed experimentally and theoretically using the phenomenological approach. It is shown that in the case when the direction of the current density vector j coincides with the direction of the local magnetization vector M (j∥M) in magnetic layers, the consideration of the resistance anisotropy results in a decrease in the magnitude of the GMR effect; and while the vectors are mutually perpendicular in the film plane (j⊥M), the GMR value increases. The analysis of the size dependence (dependence of the top magnetic layer on the thickness dm2) of the magnetoresistance ratio (MR ratio) shows that, in the case of the isotropic GMR effect, when inequalities dm2 > dm1) (dm1 is the thickness of the bottom magnetic layer) hold, the indicated effect is negligible due to shunting of the top layer resistance by the base layer resistance (shunting of the base layer resistance by the top-layer resistance). In the case when the magnetic layer thicknesses are comparable in size (dm1 ~ dm2), the magnitude of the anisotropic giant magnetoresistance (AGMR) acquires its maximum (amplitude) value because of the absence of the shunting effect. The method for calculating the asymmetry parameter αlj=l0j+∕l0j– (l0js is the spin-dependent free path of charge carriers in the s = ±th spin channel of the jth magnetic layer), which characterizes the difference in the free paths of electrons in the spin conduction channels, is proposed for the first time.

Giant anisotropic magnetoresistance and planar Hall effect in Sr0.06Bi2Se3

We report the observation of giant negative anisotropic magnetoresistance and planar Hall effect in superconducting topological insulator Sr0.06Bi2Se3. It is found that giant anisotropic magnetoresistance and planar Hall effect with non-zero transverse voltage are developed by tilting the in-plane magnetic field away from the direction of the electrical current. Quantitative analyses of the measured data suggest that the observed anisotropic magnetoresistance and planar Hall effect originate from the chiral anomaly behavior of the material. The large anisotropic magnetoresistance and planar Hall effect demonstrate that this material has potential to be utilized in magnetoresistive devices with low power consumption.

Spin Direction-Controlled Electronic Band Structure in Two-Dimensional Ferromagnetic CrI3.

Manipulating physical properties using the spin degree of freedom constitutes a major part of modern condensed matter physics and is a key aspect for spintronics devices. Using the newly discovered two-dimensional van der Waals ferromagnetic CrI3 as a prototype material, we theoretically demonstrated a giant magneto band-structure (GMB) effect whereby a change of magnetization direction significantly modifies the electronic band structure. Our density functional theory calculations and model analysis reveal that rotating the magnetic moment of CrI3 from out-of-plane to in-plane causes a direct-to-indirect bandgap transition, inducing a magnetic field controlled photoluminescence. Moreover, our results show a significant change of Fermi surface with different magnetization directions, giving rise to giant anisotropic magnetoresistance. Additionally, the spin reorientation is found to modify the topological states. Given that a variety of properties are determined by band structures, our predicted GMB effect in CrI3 opens a new paradigm for spintronics applications.

Giant anisotropic magnetoresistance and planar Hall effect in the Dirac semimetal Cd3As2

Anisotropic magnetoresistance is the change tendency of resistance of a material on the mutual orientation of the electric current and the external magnetic field. Here, we report experimental observations in the Dirac semimetal Cd3As2 of giant anisotropic magnetoresistance and its transverse version, called the planar Hall effect. The relative anisotropic magnetoresistance is negative and up to -68% at 2 K and 10 T. The high anisotropy and the minus sign in this isotropic and nonmagnetic material are attributed to a field-dependent current along the magnetic field, which may be induced by the Berry curvature of the band structure. This observation not only reveals unusual physical phenomena in Weyl and Dirac semimetals, but also finds additional transport signatures of Weyl and Dirac fermions other than negative magnetoresistance.

Tunable magnetotransport in Fe/hBN/graphene/hBN/Pt(Fe) epitaxial multilayers

Theoretical and computational analysis of the magnetotransport properties and spin-transfer torque field-induced switching of magnetization density in vertically-stacked multilayers is presented. Using epitaxially-capped free layers of Pt and Fe, atom-resolved magnetic moments and spin-transfer torques are computed at finite bias. The calculations are performed within linear response approximation to the spin-density reformulation of the van der Waals density functional theory. Dynamical spin excitations are computed as a function of a spin-transfer torque induced magnetic field along the magnetic easy axis, and the corresponding spin polarization perpendicular to the easy axis is obtained. Bias-dependent giant anisotropic magnetoresistance of up to 3200% is obtained in the nonmagnetic-metal-capped Fe/hBN/graphene/hBN/Pt multilayer architecture. Since this specific heterostructure is not yet fabricated and characterized, the predicted high performance has not been demonstrated experimentally. Nevertheless, similar calculations performed on the Fe/hBN/Co stack show that the tunneling magnetoresistance obtained at the Fermi-level is in excellent agreement with results of recent magnetotransport measurements on magnetic tunnel junctions that contain the monolayer hBN tunnel region. The magnitude of the spin-transfer torque is found to increase as the tunneling spin current increases, and this activates the magnetization switching process due to increased charge accumulation. This mechanism causes substantial spin backflow, which manifests as rapid undulations in the bias-dependent tunneling spin currents. The implication of these findings on the design of nanoscale spintronic devices with spin-transfer torque tunable magnetization density is discussed. Insights derived from this study are expected to enhance the prospects for developing and integrating artificially assembled van der Waals multilayer heterostructures as the preferred material platform for efficient engineering of spin switches for spintronic applications.

Asymmetric Coulomb oscillation and giant anisotropic magnetoresistance in doped graphene nanojunctions

We report here the charge transport behavior in graphene nanojunctions in which graphene nanodots, with relatively long relaxation time, are interfaced with ferromagnetic electrodes. Subsequently we explore the effect of substitutional doping of transition metal atoms in zigzag graphene nanodots (z-GNDs) on the charge transport under non-collinear magnetization. Only substitutional doping of transition metal atoms in z-GNDs at certain sites demonstrates the spin filtering effect with a large tunnelling magnetoresistance as high as 700%, making it actually suitable for spintronic applications. From the electrical field simulation around the junction area within the electrostatic physics model, we find that the value of electric field strength increases especially with doped graphene nanodots, as the gap between the gate electrode and tip axis is reduced from 3 nm to 1 nm. Our detailed analysis further suggests the onset of asymmetric Coulomb oscillations with varying amplitudes in graphene nanodots, on being doped with magnetic ions. Such kind of tunability in the electronic conductance can potentially be exploited in designing spintronic logic gates at nanoscale.

Magnetotransport properties of the type-II Weyl semimetal candidateTa3S2

We have investigated the magnetoresistance (MR) and Hall resistivity properties of the single crystals of tantalum sulfide, ${\mathrm{Ta}}_{3}{\mathrm{S}}_{2}$, which was recently predicted to be a new type-II Weyl semimetal. Large MR (up to $\ensuremath{\sim}8000%$ at 2 K and 16 T), field-induced metal-insulator-like transition, and nonlinear Hall resistivity are observed at low temperatures. The large MR shows a strong dependence on the field orientation, leading to a giant anisotropic magnetoresistance effect. For the field applied along the $b$ axis $(B\ensuremath{\parallel}b)$, MR exhibits quadratic field dependence at low fields and tends towards saturation at high fields; while for $B\ensuremath{\parallel}a$, MR presents quadratic field dependence at low fields and becomes linear at high fields without any trend towards saturation. The analysis of the Hall resistivity data indicates the coexistence of a large number of electrons with low mobility and a small number of holes with high mobility. Shubnikov-de Haas oscillation analysis reveals three fundamental frequencies originated from the three-dimensional Fermi surface pockets. We find that the semiclassical multiband model is sufficient to account for the experimentally observed MR in ${\mathrm{Ta}}_{3}{\mathrm{S}}_{2}$.

Unusual giant anisotropic magnetoresistance in manganite strips

Manganites have been known to exhibit giant anisotropic magnetoresistance (GAMR) near metal-insulator transition temperatures. Interestingly, we observed a second GAMR peak at lower temperatures in manganite strips fabricated from epitaxial thin films. The second low-temperature GAMR peak is highly sensitive to magnetic field and vanishes quickly upon increasing of magnetic field. We attribute the emergent GAMR behavior to spatial confinement effect on electronic phase separation in manganite strips.

Giant anisotropic magnetoresistance in insulating ultrathin (Ga,Mn)As

Molecular-beam epitaxy grown, 5 nm thick annealed Ga0.95Mn0.05As films demonstrate transition from metallic to insulating state for sheet resistances near resistance quantum, which we connect with the two-dimensional hole localization. Below the metal-insulator transition we found the giant anisotropic magnetoresistance (GAMR) effect, which depends on the orientation of magnetization to crystallographic axes and demonstrates the twofold symmetry angular dependence. The GAMR manifests itself in positive magnetoresistance near 50% at T=1.7 K for H//[110] crystallographic direction in contrast to smaller negative magnetoresistance for H//[11¯0] direction. We connect the GAMR with formation of high- and low-resistance states with different localization due to anisotropic spin-orbit interaction.

Anisotropic giant magnetoresistance near the Mott transition in pressurizedCa2RuO4

We have observed an anisotropic and giant magnetoresistance (MR) in the $4d$-electron Mott transition system of ${\text{Ca}}_{2}{\text{RuO}}_{4}$. On the border of the Mott transition $(\ensuremath{\sim}2\text{ }\text{GPa})$, the MR effect at $\ensuremath{\sim}10\text{ }\text{T}$ reaches $\ensuremath{\sim}\ensuremath{-}55%$ at ${T}_{\text{C}}$ for longitudinal and $\ensuremath{\sim}+120%$ at low temperatures for the transverse effects. The negative MR is most likely interpreted as a reduction in a ferromagnetic (FM) fluctuation at ${T}_{\text{C}}$. In contrast, the large positive effect is actually rare and is characteristic of the mixed state where the FM metallic islands are flecked with the insulating phases. We discuss the reason of the peculiar MR from the viewpoint of the ``anisotropic magnetism,'' the ``tunnel MR,'' and the ``orbital physics.''

Field-induced phase transitions and giant magnetoresistance in Dy Co single crystals

Electrical resistivity and calorimetric measurements on Dy 3 Coshow that below the Neel temperature (TN=44 K) the non-collinear antiferromagnetic structure exhibits field-induced magnetic phase transitions of a first-order type along all principal axes, accompanied by a strongly anisotropic giant magnetoresistance and by a change of the Sommerfeld coefficient of the specific heat. Quantum tunnelling of the magnetization appears to be possible for T < 0.6 K.

Laser Ablated CuCo Thin Films Exhibiting Controlled Anisotropic Giant Magnetoresistance

AbstractControlled microstructured thin films with nominal composition Cu95Co5 have been deposited on glass substrates by pulsed laser ablation at room temperature, in vacuum, for different target speed rotation. Atomic Force Microscopy, AFM, studies have shown a surface roughness not higher than 0.5 nm, for the as-deposited samples, which do not exhibit magnetoresistive, MR, behaviour. X-ray diffraction analysis show broad diffraction peaks, slightly shifted from pure Cu reflection peaks. After annealing, the samples show GMR. The AFM investigations reveal a surface roughness of =6.8 nm and =9.2 nm for the samples prepared with high and low target speed rotation, respectively. Furthermore the GMR data correspond to a strong anisotropic behaviour. A reversible MR is exhibited, for all the films, exclusively for perpendicular to the films plane applied magnetic field. Hysteretic MR behaviour is observed for any other direction: in the range of 70-80 deg., coercive MR fields from 0.17 Tesla to 0.05 Tesla are observed for the samples obtained at 10 rpm to 32 rpm respectively target speed rotation. These properties are discussed in terms of the shape anisotropy of magnetic Co nanoparticles.