Quasilinear Magnetoresistance Research Articles

Highly sensitive magnetic properties and large linear magnetoresistance in antiferromagnetic CrxSe（0.875 ≤x ≤ 1）single crystals

CrxSe (x ≤ 1) is a class of quasi-layered binary compounds with potential applications in spintronics due to its intriguing antiferromagnetic properties. In this work, CrxSe single crystals with high Cr content (x = 0.87, 0.91 and 0.95) were grown, and their magnetic and transport properties were investigated in detail. It is found that with small increase of Cr content, the Néel temperature (TN) of the samples can dramatically increase from 147 K to 257 K, accompanied with obvious changes in the magnetic anisotropy and hysteresis. The phenomena of field-induced spin-flop transitions were unveiled in these alloys, indicating their comparatively low anisotropy. The magnetoresistance (MR) of the three compounds showed positive dependence at low temperatures and particularly, non-saturated linear positive MR was observed in Cr0.91Se and Cr0.95Se, with a large value of 16.2% achieved in Cr0.91Se (10 K, 9 T). The calculated Fermi surface and MR showed that the quasi-linear MR is a product of carrier compensation. Our work revealed highly sensitive magnetic and transport properties in the Cr-Se compounds, which can lay foundation when constructing further antiferromagnetic spintronic devices based on them.

Quasi-linear and Plateaus-like Tunneling Magnetoresistance in Graphene-based Tunable Magnetic Barrier Nanostructures

The effect of electrostatic and magnetic vector potentials pattern on electrical properties and the tunneling magnetoresistance in graphene junction with periodic magnetic vector potentials are theoretically investigated using the transfer matrix method. The magnetic structure on graphene can control the direction of the magnetizations which correspond to the parallel and anti-parallel (AP) configurations. In AP magnetic structures with the applied gate voltage pattern, USUBA/SUB (U₁ = U₂), the shift of the conductance-peak position as a function of Fermi energy. The peak corresponds to resonant tunneling, where the incidence energy of the tunneling electron equals the confinement energy, and the conductance peak decrease approximately linearly with increasing electrostatic potential. The peak position occurs at ESUBF/SUB = 0.5U where it is shifted to higher Fermi energy with higher gate potential, but for the case of USUBB/SUB (U₁ = -U₂), the peak height is reduced rapidly, and the width increase as gate potential increases. Because of the periodic magnetic field with zero spatial average in the antiparallel structure, we found that the minimum conductivity decreases with increasing magnetic energy. They show suppression of Klein tunneling which occurs in the zero-conductance plateaus and leads to the robust magnetoresistance plateau and large positive magnetoresistance appears below magnetic energy. For the case of USUBA/SUB and ESUBF/SUB more than magnetic energy, we found that the quasi-linear magnetoresistance feature is applied by an electric field instead of the usual magnetically driven magnetoresistance.

Weak antilocalization effect and triply degenerate state in Cu-doped CaAuAs

The effect of 50% Cu doping at the Au site in the topological Dirac semimetal CaAuAs is investigated through electronic band structure calculations, electrical resistivity, and magnetotransport measurements. Electronic structure calculations suggest a broken-symmetry-driven topological phase transition from the Dirac to triple-point state in CaAuAs via alloy engineering. The electrical resistivity of both the CaAuAs and ${\mathrm{CaAu}}_{0.5}{\mathrm{Cu}}_{0.5}\mathrm{As}$ compounds shows metallic behavior. Nonsaturating quasilinear magnetoresistance (MR) behavior is observed in CaAuAs. On the other hand, MR of the doped compound shows a pronounced cusplike feature in the low-field regime. Such behavior of MR in ${\mathrm{CaAu}}_{0.5}{\mathrm{Cu}}_{0.5}\mathrm{As}$ is attributed to the weak antilocalization (WAL) effect. The WAL effect is analyzed using different theoretical models, including the semiclassical $\ensuremath{\sim}\sqrt{B}$ one which accounts for the three-dimensional WAL and the modified Hikami-Larkin-Nagaoka model. A strong WAL effect is also observed in the longitudinal MR, which is well described by the generalized Altshuler-Aronov model. Our study suggests that the WAL effect originates from weak disorder and the spin-orbit coupled bulk state. Interestingly, we have also observed the signature of chiral anomaly in longitudinal MR when both the current and field are applied along the $c$ axis. The Hall resistivity measurements indicate that the charge conduction mechanism in these compounds is dominated by the holes with a concentration $\ensuremath{\sim}{10}^{20}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ and mobility $\ensuremath{\sim}{10}^{2}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{2}\phantom{\rule{4pt}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{4pt}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$.

Quantum oscillations and quasilinear magnetoresistance in the topological semimetal candidate ScSn2

Novel compounds with two-dimensional square lattices formed by group IV or V elements (Si, Sn, Ge, Bi, and Sb) have been attracting a great deal of attention in recent times, mainly because of the possible emergence of various topological phases therein. Here, we successfully grow the single crystals of Sn-square-net based material $\mathrm{Sc}{\mathrm{Sn}}_{2}$, and systematically perform their magnetization and magnetotransport measurements. Clear quantum oscillations emerge in the magnetization isotherms along different field orientations, from which nonzero Berry phases are extracted, implying that $\mathrm{Sc}{\mathrm{Sn}}_{2}$ harbors three-dimensional Fermi surfaces and nontrivial electronic states. Similar to many other topological semimetals with extremely large magnetoresistance, $\mathrm{Sc}{\mathrm{Sn}}_{2}$ shows field-induced resistivity enhancement as well, which has been proven to be not of a gap opening origin. Besides, at low temperature, large magnetoresistance with a quasilinear field dependence is observed. Our analysis of the magnetotransport data finds that the quasilinear magnetoresistance in $\mathrm{Sc}{\mathrm{Sn}}_{2}$ cannot be understood by several familiar mechanisms proposed in the literature. These findings are expected to have far reaching implications for both the fundamental understanding and magnetoresistance device application of topological semimetal materials.

Magnetotransport properties of the topological nodal-line semimetal CaCdSn

Topological nodal-line semimetals support protected band crossings which form nodal lines or nodal loops between the valence and conduction bands and exhibit novel transport phenomena. Here we address the topological state of the nodal-line semimetal candidate material, CaCdSn, and report magnetotransport properties of its single crystals grown by the self-flux method. Our first-principles calculations show that the electronic structure of CaCdSn harbors a single nodal loop around the $\Gamma$ point in the absence of spin-orbit coupling (SOC) effects. The nodal crossings in CaCdSn are found to lie above the Fermi level and yield a Fermi surface that consists of both electron and hole pockets. CaCdSn exhibits high mobility ($\mu \approx 3.44\times 10^4$ cm$^2$V$^{-1}$s$^{-1}$) and displays a field-induced metal-semiconductor like crossover with a plateau in resistivity at low temperature. We observe an extremely large and quasilinear non-saturating transverse as well as longitudinal magnetoresistance (MR) at low temperatures ($\approx 7.44\times 10^3 \%$ and $\approx 1.71\times 10^3\%$, respectively, at 4K). We also briefly discuss possible reasons behind such a large quasilinear magnetoresistance and its connection with the nontrivial band structure of CaCdSn.

Inhomogeneous superconductivity and quasilinear magnetoresistance at amorphous LaTiO3/SrTiO3 interfaces

We have studied the transport properties of LaTiO3/SrTiO3 (LTO/STO) heterostructures. In spite of 2D growth observed in reflection high energy electron diffraction, transmission electron microscopy images revealed that the samples tend to amorphize. Still, we observe that the structures are conducting, and some of them exhibit high conductance and/or superconductivity. We established that conductivity arises mainly on the STO side of the interface, and shows all the signs of the two-dimensional electron gas usually observed at interfaces between STO and LTO or LaAlO3, including the presence of two electron bands and tunability with a gate voltage. Analysis of magnetoresistance (MR) and superconductivity indicates the presence of spatial fluctuations of the electronic properties in our samples. That can explain the observed quasilinear out-of-plane MR, as well as various features of the in-plane MR and the observed superconductivity.

Quasilinear quantum magnetoresistance in pressure-induced nonsymmorphic superconductor chromium arsenide

In conventional metals, modification of electron trajectories under magnetic field gives rise to a magnetoresistance that varies quadratically at low field, followed by a saturation at high field for closed orbits on the Fermi surface. Deviations from the conventional behaviour, for example, the observation of a linear magnetoresistance, or a non-saturating magnetoresistance, have been attributed to exotic electron scattering mechanisms. Recently, linear magnetoresistance has been observed in many Dirac materials, in which the electron–electron correlation is relatively weak. The strongly correlated helimagnet CrAs undergoes a quantum phase transition to a nonmagnetic superconductor under pressure. Here we observe, near the magnetic instability, a large and non-saturating quasilinear magnetoresistance from the upper critical field to 14 T at low temperatures. We show that the quasilinear magnetoresistance may arise from an intricate interplay between a nontrivial band crossing protected by nonsymmorphic crystal symmetry and strong magnetic fluctuations.

Disruption of the Accidental Dirac Semimetal State in ZrTe_{5} under Hydrostatic Pressure.

We study the effect of hydrostatic pressure on the magnetotransport properties of zirconium pentatelluride. The magnitude of resistivity anomaly gets enhanced with increasing pressure, but the transition temperature T^{*} is insensitive to it up to 2.5GPa. In the case of H∥b, the quasilinear magnetoresistance decreases drastically from 3300% (9T) at ambient pressure to 230% (9T) at 2.5GPa. Besides, the change of the quantum oscillation phase from topological nontrivial to trivial is revealed around 2GPa. Both demonstrate that the pressure breaks the accidental Dirac node in ZrTe_{5}. For H∥c, in contrast, subtle changes can be seen in the magnetoresistance and quantum oscillations. In the presence of pressure, ZrTe_{5} evolves from a highly anisotropic to a nearly isotropic electronic system, which accompanies the disruption of the accidental Dirac semimetal state. It supports the assumption that ZrTe_{5} is a semi-3D Dirac system with linear dispersion along two directions and a quadratic one along the third.

Quasi-linear magnetoresistance and the violation of Kohler’s rule in the quasi-one-dimensional Ta4Pd3Te16 superconductor

We report on the quasi-linear in field intrachain magnetoresistance in the normal state of a quasi-one-dimensional superconductor Ta4Pd3Te16 ( K). Both the longitudinal and transverse in-chain magnetoresistance shows a power-law dependence, B, with the exponent close to 1 over a wide temperature and field range. The magnetoresistance shows no sign of saturation up to 50 T studied. The linear magnetoresistance observed in Ta4Pd3Te16 is found to be overall inconsistent with the interpretations based on the Dirac fermions in the quantum limit, charge conductivity fluctuations as well as quantum electron–electron interference. Moreover, it is observed that the Kohler’s rule, regardless of the field orientations, is violated in its normal state. This result suggests the loss of charge carriers in the normal state of this chain-containing compound, due presumably to the charge-density-wave fluctuations.

Components of strong magnetoresistance in Mn implanted Ge

Strong magnetoresistance reaching thousands of percent and non-monotonic field dependent Hall effect were measured in Mn implanted Ge samples in fields up to 60 T and analyzed in the framework of a two carriers model. The measured Hall effect and temperature dependent zero field resistance can be consistently described by parallel conductance along thick p-type Ge substrate with low concentration of highly mobile carriers and along thin Mn doped Ge layer with low mobility carriers. However, the same model is not sufficient to explain experimentally observed suppression of quadratic field dependence of magnetoresistance at low fields and absence of its saturation at high fields. Two additional mechanisms were identified: a strong quasi-linear magnetoresistance of Ge substrate that dominates the low field range and a non-saturating “3/2” power law magnetoresistance of the Mn doped Ge layer dominating the high field range.

Geometrically enhanced extraordinary magnetoresistance in semiconductor-metal hybrids

Extraordinary magnetoresistance (EMR) arises in hybrid systems consisting of semiconducting material with an embedded metallic inclusion. We have investigated such systems with the use of finite-element modeling, with our results showing good agreement to existing experimental data. We show that this effect can be dramatically enhanced by over four orders of magnitude as a result of altering the geometry of the conducting region. The significance of this result lies in its potential application to EMR magnetic field sensors utilizing more familiar semiconducting materials with nonoptimum material parameters, such as silicon. Our model has been extended further with a geometry based on the microstructure of the silver chalcogenides, consisting of a randomly sized and positioned metallic network with interspersed droplets. This model has shown a large and quasilinear magnetoresistance analogous to experimental findings.

I–V characteristic and magnetoresistance of homogeneous materials

A formula providing the current across a slab of homogeneous conducting material under bias and subjected to a perpendicular magnetic field, is presented in both the high and low temperature regime. The current is expressed in terms of the applied voltage, V, the magnetic field, B, temperature, T, mobility and resistivity of the material, μ and ρs at zero magnetic field and at temperature T. Furthermore, the sample dimensions enter the expression for the current. The formula in question enables obtaining the magnetoresistance of the slab in terms of the above parameters in the cases under constant bias and under constant current. Several experimental results are compared with theoretical predictions, e.g., switch from positive to negative magnetoresistance. Furthermore, it is shown that there exists a critical value for a certain dimensionless collective parameter, above which for small magnetic fields the magnetoresistance becomes negative, while for values below is positive. The quasi-linear magnetoresistance, observed in experiments at high magnetic fields, is also adequately reproduced.

Quasilinear magnetoresistance in an almost two-dimensional band structure

We present a theoretical study of the orbital magnetoresistance in a unixial anisotropic metal within the relaxation-time approximation. The appearance of a new dimensionless scale, delta=4t_perp/epsilon_F, allows the possibility of a new region at intermediate fields where the magnetoresistance is linear in applied magnetic field for currents flowing along the unixial direction. (Here, t_perp characterizes the bandwidth along the unixial direction.) In the limit of large anisotropy (small delta), corresponding to a quasi-two-dimensional metal made up of weakly coupled layers, we obtain an analytic expression for the magnetoresistance valid for all magnetic fields. We test our analytic results numerically and we compare our expressions with the c-axis magnetoresistance of Sr_2RuO_4.

Magnetoresistance and Hall coefficient of inhomogeneous metals

In strong magnetic fields, most metals have highly anisotropic transport coefficients, and these have long been known to be much influenced by sample inhomogeneities. This paper reports a detailed theoretical study of such effects. Various approximations for calculating the effective transport coefficients of inhomogeneous solids are rederived from a unified point of view; these are then used for a variety of model calculations appropriate to metals with open Fermi surfaces. A small concentration of crystallites with open orbits embedded in a free-electron metal is shown to give rise to a strictly linear transverse magnetoresistance (TMR) at strong magnetic fields. The linear coefficient is strongly dependent on the orientation of the open orbit in the plane perpendicular to the magnetic field $\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}$. Extended-orbit crystallites in a free-electron metal produce a TMR which is initially linear, but saturates at sufficiently strong field. The Hall coefficient ${R}_{H}$ is unchanged from its free-electron value to first order in the concentration of defects. A striking geometrical effect is predicted, the TMR from open-orbit crystallites saturating in geometries such that current distortions are unable to propagate parallel to $\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}$. The TMR and Hall coefficient of a free-electron metal containing a larger concentration of open-orbit crystallites is calculated in the effective-medium theory (EMT). The TMR is found to saturate at strong fields, in agreement with previous results of Stachowiak, while the Hall coefficient falls off as 1/${\mathrm{H}}^{2}$ at strong fields, except in flat-plate samples with $\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}$ perpendicular to the plate, in which case it is predicted to saturate at its free-electron value for a sufficiently large concentration of open-orbit crystallites, but to fall off quadratically for lower concentrations. In contrast, calculations within a non-self-consistent approximation give a strictly linear TMR and a Hall coefficient which saturates at a value below the free-electron coefficient. Possible explanations for the discrepancy are discussed. Calculations in the EMT for a model polycrystal with extended-orbit crystallites reveal a broad field region of quasi-linear magnetoresistance, as found previously by Stachowiak, and a reduced Hall coefficient, as well as a conspicuous geometrical effect. The possible relation of these model calculations to experiments of polycrystalline noble metals is examined, but no quantitative theory for these metals is given.