In-plane Anisotropic Magnetoresistance Research Articles

In-plane anisotropic magnetoresistance and planar Hall effect in off-stoichiometric single crystal Mn3Ga

We report the observation of in-plane anisotropic magnetoresistance (AMR) and planar Hall effect in our recently discovered kagome antiferromagnetic off-stoichiometric single crystal of Mn3Ga. We found that the in-plane AMR is dominated by a sixfold symmetry at low temperature due to the kagome lattice magnetocrystalline anisotropy. However, an unusual fourfold symmetry is also revealed by the angular-dependent AMR measurements, which originates from the little distortion of the crystal accompanying the slight ferromagnetic transition. Moreover, we also found a clear planar Hall effect signal in off-stoichiometric single crystal of Mn3Ga, which may be related to the chiral anomaly, one of the signatures of the magnetic Weyl fermions.

Anisotropic Magnetoresistance Effect of Intercalated Ferromagnet FeTa3S6

Intercalated transition metal dichalcogenides have been widely used to study the magnetic and magnetoelectric transport properties in a strong anisotropic and spin–orbit coupling environments. In this study, ferromagnetic FeTa3S6 (also known as Fe1/3TaS2) single crystals were grown by using the chemical vapor transport method, and its magnetic and magnetoelectric transport properties were measured. The results show that FeTa3S6 has ferromagnetic ordered below 37K, with sharp switching of magnetization, butterfly-shaped double-peak magnetoresistance and anomalous Hall effect, and the magnetization and resistance have strong anisotropy. When a magnetic field is oriented parallel to the c-axis, the magnetoresistance exceeds 10% at a temperature of 10K, and negative magnetoresistance is generated when the magnetic field is larger than the switching field. When the direction of the magnetic field of 9T rotates from out-of-plane to in-plane, the anisotropic magnetoresistance exceeds 40%, and the angle-dependent Hall resistance presents a novel trend, which may be due to the existence of a topological Hall effect or other magnetic structures in the FeTa3S6 thin film. When the magnetic field of 9T rotates in the ab-plane of the sample, the in-plane anisotropic magnetoresistance conforms to the form of sin2φ. The experimental results of this study provide important information for the study of magnetic and magnetoelectric transport properties of intercalated transition metal dichalcogenides.

Spin-Momentum Locking Induced Anisotropic Magnetoresistance in Monolayer WTe2.

Monolayer WTe2 is predicted to be a quantum spin Hall insulator (QSHI), and its quantized edge transport has recently been demonstrated. However, one of the essential properties of a QSHI, spin-momentum locking of the helical edge states, has yet to be experimentally validated. Here, we measure and observe gate-controlled anisotropic magnetoresistance (AMR) in monolayer WTe2 devices. Electrically tuning the Fermi energy into the band gap, a large in-plane AMR is observed and the minimum of the in-plane AMR occurs when the applied magnetic field is perpendicular to the current direction. In line with the experimental observations, the theoretical predictions based on the band structure of monolayer WTe2 demonstrate that the AMR effect originates from spin-momentum locking in the helical edge states of monolayer WTe2. Our findings reveal that the spin quantization axis of the helical edge states in monolayer WTe2 can be precisely determined from AMR measurements.

Temperature Dependent In-Plane Anisotropic Magnetoresistance in HfTe5 Thin LayersSupported by the National Key R&D Program (Grant Nos. 2017YFB0405703, 2017YFA0205004, and 2018YFA0306600), and the National Natural Science Foundation of China (Grant Nos. 11974327, 11474265, 11674295, 11674024, and 11874193), the Fundamental Research Funds for the Central Universities (Grant Nos. WK2030020032 and WK2340000082), Anhui Initiative in Quantum Information Technologies, and the Shenzhen Fundamental

We report the observation of in-plane anisotropic magnetoresistance and planar Hall effect in non-magnetic HfTe5 thin layers. The observed anisotropic magnetoresistance as well as its sign is strongly dependent on the critical resistivity anomaly temperature T p. Below T p, the anisotropic magnetoresistance is negative with large negative magnetoresistance. When the in-plane magnetic field is perpendicular to the current, the negative longitudinal magnetoresistance reaches its maximum. The negative longitudinal magnetoresistance effect in HfTe5 thin layers is dramatically different from that induced by the chiral anomaly as observed in Weyl and Dirac semimetals. One potential underlying origin may be attributed to the reduced spin scattering, which arises from the in-plane magnetic field driven coupling between the top and bottom surface states. Our findings provide valuable insights for the anisotropic magnetoresistance effect in topological electronic systems and the device potential of HfTe5 in spintronics and quantum sensing.

Enhancement of Rashba spin–orbit coupling by electron confinement at the LaAlO3/SrTiO3 interface

Electrical transport property is closely related to the dimensionality of carriers’ distribution. In this work, we succeed in tuning the carriers’ distribution and the Rashba spin–orbit coupling at LaAlO3/SrTiO3 interface by varying the oxygen pressure (c-PO2) adopted in crystalline LaAlO3 growth. Measurements of the in-plane anisotropic magnetoresistance and the conducting-layer thickness indicate that the carriers’ distribution changes from three to two dimensions with c-PO2 increasing, i.e. the electron confinement gets stronger. Importantly, by measuring the low-temperature out-of-plane magnetoresistance and analyzing the weak localization/weak anti-localization, we find that the strength of Rashba spin–orbit coupling can be enhanced by electron confinement. The electron confinement is a manifestation of breaking of spatial inversion symmetry. Therefore, our work reveals the intimate relationship between spatial inversion symmetry breaking and Rashba spin–orbit coupling at the LaAlO3/SrTiO3 interface, and provides a new method to tune the Rashba spin–orbit coupling, which is valuable in the application of oxide-spintronics.

Extraordinary quasi-two-dimensional magnetotransport properties of a LaAlO3/SrTiO3 heterostructure tailored with a surface TiO2 atomic sheet

Epitaxial heterostructures of lanthanum aluminate (LaAlO3) and strontium titanate (SrTiO3) exhibit extraordinary quasi-two-dimensional magnetotransport properties at low temperatures. To elucidate the mechanisms responsible for the unique properties of these interfaces, which can guide the design of novel structures having high performances, extensive analyses of the magnetotransport properties at low temperatures are required. We report the magnetotransport properties of a LaAlO3/SrTiO3 system tailored with a topmost surface atomic sheet of titanium dioxide (TiO2). Three unit cells of LaAlO3 were deposited on a reconstructed SrTiO3(001)-(13×13)-R33.7° substrate, yielding LaAlO3 covered with a single-atom-thick TiO2 sheet. The high-mobility electrons confined at the LaAlO3/SrTiO3 interface provided significantly high magnetoresistance ratios of +150% and −80% under magnetic fields perpendicular and parallel to the interface, respectively. The in-plane anisotropic magnetoresistance at 4.2 K reached approximately +30%, reflecting the Rashba spin–orbit interactions of the quasi-two-dimensional electrons. A high carrier concentration at the interface realized by the capping of LaAlO3/SrTiO3 with the surface TiO2 sheet significantly contributed to the enhancement of magnetotransport properties arising from the Ti 3d orbitals.

Symmetry breaking of in-plane anisotropic magnetoresistance with temperature in La-doped Sr2IrO4 films

Electron-doped $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$ has been the subject of much recent attention because of its similarities with hole-doped $\mathrm{L}{\mathrm{a}}_{2}\mathrm{Cu}{\mathrm{O}}_{4}$. However, direct evidence of its superconductivity has not yet been observed, which has led to various unresolved issues related to this material. In this study, a 14-nm-thick La-doped $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$ film was grown on a (001) $\mathrm{SrTi}{\mathrm{O}}_{3}$ substrate. We found that the fourfold component of the in-plane anisotropic magnetoresistance disappears and is replaced by a twofold symmetry as the temperature increases. Variable-temperature x-ray diffraction and spatially resolved optical second-harmonic generation experiments eliminate the possibility of crystal structural distortion. The temperature dependence of direct current magnetization measurements indicates that a change in the spin structure may account for the symmetry breaking, similar to the nematic ordering of iron-based and other superconductors. Remarkably, the transition temperature of the symmetry breaking is well consistent with the previously reported onset (50 K) of the low-energy gap in K-doped $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$ observed by scanning tunneling spectroscopy. Our results provide a perspective on these materials that helps elucidate the nature of magnetic interactions and explores the expected superconductivity of iridates.

Normal-state properties of the quasi-one-dimensional superconductor Ta4Pd3Te16

We examined the physical properties of the quasi-one-dimensional superconductor Ta4Pd3Te16 in the normal state by detailed measurements of susceptibility, in-plane anisotropic resistivity, magnetoresistance, Hall resistivity, and Seebeck coefficient. The large Wilson ratio, as inferred from normal-state susceptibility, indicates strong electron–electron interaction. The Hall and Seebeck coefficients show not only significant temperature-dependent behavior, indicating the multiband effect, but also an obvious anomaly around T1 = 40 K. Analyses of both the Hall resistivity and thermopower using a two-band model indicate that the electrons dominate the electrical transport at low temperatures. Our results imply that it is the quantum fluctuations of the charge order taking place in the temperature range 30–50 K that may result in the abnormal normal-state properties of Ta4Pd3Te16.

Effect of Sb content on anisotropic magnetoresistance in a (Ga, Mn)(As, Sb) ferromagnetic semiconductor thin film.

The effect of Sb content on the in-plane anisotropic magnetoresistance (AMR) of the quaternary ferromagnetic semiconductor (Ga, Mn)(As, Sb) was investigated. The results showed that the strain increased with Sb content, but the hole density was found to fluctuate. Dominant cubic and uniaxial symmetries were observed for the current along the [110] crystalline direction. The dependence of the symmetry on the Sb content was demonstrated for the longitudinal AMR, which mainly results from the alteration of the local stain relaxation and the hole density. A phenomenological analysis showed that the variation of the AMR coefficients is a good explanation for the observed experimental results.

Giant planar Hall effect in the Dirac semimetal ZrTe5−δ

Recently, giant planar Hall effect originating from chiral anomaly has been predicted in nonmagnetic Dirac/Weyl semimetals. ZrTe5 is considered to be an intriguing Dirac semimetal at the boundary of weak topological insulators and strong topological insulators, though this claim still remains controversial. Here, we report the observation in ZrTe5 of the giant planar Hall resistivity that shows two different magnetic-field dependences as predicted by theory and a maximum at the Lifshitz transition temperature. We found that the giant planar Hall resistivity fades out with decreasing the thickness of ZrTe5 nanoplates, which may be ascribed to the vanishing of the 3D nature of the samples. In addition, we have observed a nontrivial Berry phase, chiral-anomaly-induced negative longitudinal magnetoresistance, and a giant in-plane anisotropic magnetoresistance in these ZrTe5 nanoplates. All the experimental observations demonstrated coherently that ZrTe5 is a Dirac semimetal.

Anisotropic electronic transport and Rashba effect of the two-dimensional electron system in (110) SrTiO3 -based heterostructures

The two-dimensional electron system in (110)Al$_2$O$_{3-\delta}$/SrTiO$_3$ heterostructures displays anisotropic electronic transport. Largest and lowest conductivity and electron mobility $\mu$ are observed along the $[001]$ and $[1\bar{1}0]$ direction, respectively. The anisotropy of the sheet resistance and $\mu$ likewise leads to a distinct anisotropic normal magnetotransport (MR) for T < 30K. However, at temperatures T<5K and magnetic field B<2T MR is dominated by weak antilocalization.Despite the rather strong anisotropy of the Fermi surfaces, the in-plane anisotropic magnetoresistance (AMR) displays two-fold non-crystalline anisotropy. However, the AMR-amplitude is found to be anisotropic with respect to the current direction, leading to a 60% larger AMR amplitude for current I along the $[001]$ direction compared to I parallel to $[1\bar{1}0]$. Tight binding calulations evidence an anisotropic Rashba-induced band splitting with dominant linear k-dependence. In combination with semiclassical Boltzmann theory the non-crystalline AMR is well described, despite the anisotropic Fermi surface.

Columnar growth structure dependent soft magnetic and electrical transport properties of Co nanocrystalline films evaporated with a high magnetic field

Control and improvement of the magnetic and electrical properties of magnetic nanocrystalline films are very essential for their applications in spintronics and magnetic storages. This paper studies the effects of high magnetic field (HMF) on the microstructure, soft magnetic and electrical transport properties of the Co nanocrystalline films. It was found that the Co films without HMF were disordered stack of spherical nanoparticles. The stack changed to columnar structure with the HMF application. Furthermore, this columnar crystal changed to columnar stack of spherical nanoparticles with the increase of evaporation temperature under HMF. HMF induced a part of the c-axis preferred orientation in the Co films aligning along the direction of HMF. The varied growth structure and preferred orientation led to the change from the in-plane magnetic anisotropy (without HMF) to isotropy in the Co films due to the application of HMF at a higher evaporation temperature. The saturation magnetization of the Co films with columnar crystals obtained by HMF was much larger than that of the films composed of spherical nanoparticles because of the dense atom arrangement. The decrease of the grain boundaries due to the changed growth structure under HMF remarkably reduced the coercivity and resistivity of the Co films. The changed growth structure under HMF also induced and improved the in-plane anisotropic magnetoresistance of the Co films. These results indicate that the adjustment of columnar growth structure by HMF effectively control and improve the soft magnetic and electrical transport properties of the Co films.

Theoretical study on the perpendicular anisotropic magnetoresistance using Rashba-type ferromagnetic model

We investigated the anisotropic magnetoresistance (AMR) effects in ferromagnetic-metal multi-layers stacked on non-magnetic insulators in the context of microscopic theory. We represented this situation with tight-binding models that included the exchange and Rashba fields, where the Rashba field was assumed to originate from spin–orbit interactions as junction effects with the insulator. To describe the AMR ratios, the DC conductivity was calculated based on the Kubo formula. As a result, we showed that the Rashba field induced both perpendicular and in-plane AMR effects and that the perpendicular AMR effect rapidly decayed with increasing film thickness.

Signature of surface state coupling in thin films of the topological Kondo insulatorSmB6from anisotropic magnetoresistance

The temperature and thickness dependencies of the in-plane anisotropic magnetoresistance (AMR) of SmB$_6$ thin films are reported. We find that the AMR changes sign from negative ($\rho_{||}<\rho_{\perp}$) at high temperatures to positive ($\rho_{||}>\rho_{\perp}$) at low temperatures. The temperature, T$_s$, at which this sign change occurs, decreases with increasing film thickness $t$ and T$_s$ vanishes for $t$ $>$ 30 nm. We interpret our results in the framework of a competition between two components: a negative bulk contribution and a positive surface AMR.

Anisotropic magneto-transport properties of electron gases at SrTiO3 (111) and (110) surfaces

Electron gases at the surfaces of insulating (111)- and (110)-oriented SrTiO3 (STO) single crystals have been created using Ar+-irradiation and their magneto-transport properties are characterized. Fully metallic behaviors with sheet carrier density of ∼1014 cm−2 and low-temperature-mobilities as large as 8600 cm2 V−1 s−1 are obtained. Intrinsic in-plane anisotropic magnetoresistance (AMR) has been obtained by applying current along different crystal axes to subtract the Lorentz force effect. The results yield nearly 6-fold and 2-fold components for the (111)-and (110)-surfaces. A symmetry breaking in AMR for the (111)-surfaces with ordering temperature TO ∼ 30 K is also observed. In contrast, the out-of-plane AMR does not show anisotropy associated with crystal axes, suggesting a two-dimensional nature of the effect. Our results demonstrate that electron gases at (111)- and (110)-oriented STO surfaces are a promising playground for both fundamental research and all-oxide device applications.

Signature of enhanced spin-orbit interaction in the magnetoresistance ofLaTiO3/SrTiO3interfaces onδdoping

We present a study of modulation of spin-orbit interaction (SOI) at the interface of LaTiO$_3$/SrTiO$_3$ by $\delta$-doping with an iso-structural ferromagnetic perovskite LaCoO$_3$. The sheet carrier density at the interface decreases exponentially with $\delta$-doping thickness. We have explored that the spin-orbit scattering time ($\tau_{so}$) can be decreased by nearly 3 orders of magnitude, whereas the inelastic scattering time ($\tau_{i}$) remains almost constant with $\delta$-doping thickness. We have also observed that the $\tau_{i}$ varies almost inversely proportional to temperature and $\tau_{so}$ remains insensitive to temperature, which suggest that the spin relaxation in these interfaces follows D'yakonov-Perel mechanism. The observed in-plane anisotropic magnetoresistance is attributed to the mixing of the spin up and spin down states of d-band at Fermi level due to SOI.

Current dependence of colossal anisotropic magnetoresistance in La0.3Pr0.4Ca0.3MnO3 microbridges

The effect of the bias current on the in-plane colossal anisotropic magnetoresistance (C-AMR) is investigated in spatially confined La0.3Pr0.4Ca0.3MnO3 microbridges. Dramatic increases of the C-AMR are found when the bias current is reduced. For example, in one of the samples, the C-AMR changed from ∼900% to over ∼24 000% as the current is decreased from 1 μA to 10 nA. The results indicate that the bias current can be used to manipulate the C-AMR in spatially confined manganite thin films via changes to the nature of the anisotropic percolation within the samples.

Temperature dependence of in-plane magnetic anisotropy and anisotropic magnetoresistance in (Ga,Mn)As codoped with Li

We evaluate the temperature dependence of in-plane magnetic anisotropy and anisotropic magnetoresistance (AMR) in (Ga,Mn)As codoped with Li by magnetotransport measurements. We find that the signs of in-plane uniaxial anisotropy and AMR change at the same temperature of ∼75 K, and that the sign of planar Hall effect does not depend on temperature.

Transverse anisotropic magnetoresistance effects in pseudo-single-crystal γ′-Fe4N thin films

Transverse anisotropic magnetoresistance (AMR) effects, for which magnetization is rotated in an orthogonal plane to the current direction, were investigated at various temperatures, in order to clarify the structural transformation from a cubic to a tetragonal symmetry in a pseudo-single-crystal Fe4N film, which is predicted from the usual in-plane AMR measurements by the theory taking into account the spin-orbit interaction and crystal field splitting of 3d bands. According to a phenomenological theory of AMR, which derives only from the crystal symmetry, a cos 2θ component (C2tr) exists in transverse AMR curves for a tetragonal system but does not for a cubic system. In the Fe4N film, the C2tr shows a positive small value (0.12%) from 300 K to 50 K. However, the C2tr increases to negative value below 50 K and reaches to -2% at 5 K. The drastic increasing of the C2tr demonstrates the structural transformation from a cubic to a tetragonal symmetry below 50 K in the Fe4N film. In addition, the out-of-plane and in-plane lattice constants (c and a) were precisely determined with X-ray diffraction at room temperature using the Nelson-Riely function. As a result, the positive small C2tr above 50 K is attributed to a slightly distorted Fe4N lattice (c/a = 1.002).

Disentangling interface and bulk contributions to the anisotropic magnetoresistance in Pt/Co/Pt sandwiches

We report on interfacial contributions to the anisotropic magnetoresistance (AMR) in Co layers sandwiched between Pt. Utilizing the Fuchs-Sondheimer formalism interface contributions can be separated from bulklike AMR. We demonstrate that for all-metal systems interfacial AMR is also present when varying the magnetization within the film plane. This interfacial in-plane AMR is two times smaller than the contribution that arises when the magnetization is varied within the plane perpendicular to the current direction. This finding is in contrast to the spin Hall MR found for ferromagnetic insulator/Pt bilayers revealing the existence of different MR effects at the interfaces of Pt with conducting and insulating ferromagnets.