Angular-dependent Magnetoresistance Research Articles

Twofold symmetry of the in-plane resistance in kagome superconductor Cs(V1-x Ta x )3Sb5 with enhanced superconductivity

Abstract The kagome superconductor CsV3Sb5 has attracted widespread attention due to its rich correlated electron states including superconductivity, charge density wave (CDW), nematicity, and pair density wave. Notably, the modulation of the intertwined electron orders by the chemical doping is significant to illuminate the cooperation/competition between multiple phases in kagome superconductors. In this study, we have synthesized a series of tantalum-substituted Cs(V1-x Ta x )3Sb5 by a modified self-flux method. Electrical transport measurements reveal that CDW is suppressed gradually and becomes undetectable as the doping content of x over 0.07. Concurrently, the superconductivity is enhanced monotonically from T c ~ 2.8 K at x = 0.00 to 5.2 K at x = 0.12. Intriguingly, in the absence of CDW, Cs(V1-x Ta x )3Sb5 (x = 0.12) crystals exhibit a pronounced twofold symmetry of the in-plane angular-dependent magnetoresistance (AMR) in the superconducting state, indicating the anisotropic superconducting properties in the Cs(V1-x Ta x )3Sb5. Our findings demonstrate that Cs(V1-x Ta x )3Sb5 with the non-trivial band topology is an excellent platform to explore the superconductivity mechanism and intertwined electronic orders in quantum materials.

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.

Spin-related negative magnetoresistance in germanium films

Herein, we report the transport properties of Ge films. The variable-range hopping transport at low temperatures (T≲50K) and thermal activation transport at high temperatures (T≳50K) are observed in our Ge films. In the different temperature regimes, the anomalous magnetotransport properties are observed. In the low-temperature regime (T≲15K), the negative magnetoresistance (MR) at low field and positive MR at high field can be seen. In the moderate-temperature regime (15K≲T≲100K), the positive MR curve gradually evolves from a linear curve to a parabolic curve with increasing temperature, and the MR magnitude appears to be insensitive to temperature. In the high-temperature regime (T≳100K), the positive MR value increases with increasing temperature. By considering the angular-dependent MR, we can determine that the negative MR comes from the spin-related mechanism, and the positive MR is caused by the orbital-related mechanism. However, further study is required to determine the exact mechanisms behind the anomalous magnetotransport properties.

Orbital Hall magnetoresistance in Ni/Ti bilayers

We report the observation of the orbital counterpart of the spin Hall magnetoresistance (SMR): the orbital Hall magnetoresistance (OMR). We measured angular-dependent longitudinal magnetoresistance for Ni/Ti bilayer and Ni single-layer films by rotating a magnetic field along three orthogonal planes. When the magnetic field is rotated in the plane perpendicular to the applied current direction, the angular dependence of the magnetoresistance in the Ni/Ti bilayers is consistent with the prediction of the SMR and OMR, whereas that in the Ni single-layer film can be attributed to the geometrical size effect of the anisotropic magnetoresistance. In the Ni/Ti bilayers, the magnetoresistance ratio is found to be five orders of magnitude larger than the prediction of the SMR, indicating that the OMR plays a dominant role in this system.

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.

Large linear magnetoresistance and nontrivial band topology in In3Rh

While In3Rh has been predicted to be a three-dimensional Dirac semimetal, experimental studies of its physical properties are lacking. Here, we report the angular-dependent magnetoresistance (MR) measurements of In3Rh single crystals under high magnetic fields up to 32 T. The crystals show large, non-saturating linear MR, and remarkable quantum oscillations with multi-frequencies. Analysis of the quantum oscillations reveals that there are three bands hosting a nontrivial Berry phase, which is corroborated by first-principles calculations. Our work may provide a platform for exploring topological materials in indium-rich transition metal compounds.

Large anomalous Hall magnetoresistance in partially oxidized single GdOx layer

This study investigated angular-dependent magnetoresistance in a partially oxidized single GdOx wire, wherein nonmetallic conduction was dominant. The resistivity with magnetic field being parallel (ρx), transverse (ρy), and perpendicular (ρz) to current exhibited a relation of ρz>ρx≈ρy, which is in contrast to that in case of conventional magnetoresistances. This unusual angular dependence can be attributed to the anomalous Hall magnetoresistance (AHMR), which is a novel magnetoresistance originating from anomalous Hall effect-induced spin accumulation, subsequent spin backflow, and spin-to-charge conversion, and was recently observed in metallic ferromagnets. The observed AHMR was as large as 1.5% at T = 5 K, which is orders of magnitude larger than that in case of metallic systems. Thus, the findings of this study are expected to motivate the evolution of further theoretical approaches towards a complete understanding of spin-dependent magnetotransport in granular systems.

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.

Experimental observation of interfacial Rashba-Edelstein magnetoresistance in Cr/YIG heterostructures

Interfacial Rashba-type spin-orbit coupling is an attractive effect to provide spin-orbit torques without the presence of heavy metals. In this work, we report the experimental observation of the Rashba-Edelstein magnetoresistance in the Cr/YIG heterostructure, which can indicate the presence of the interfacial spin-orbit coupling. By comparing the angular-dependent magnetoresistance of the Cr/YIG and the Cr/Cu/YIG heterostructures, we identify that the magnetoresistance in the Cr/YIG heterostructure is superimposed with two parts: the Rashba-Edelstein magnetoresistance induced by the interfacial spin-orbit coupling and the anisotropic magnetoresistance induced by the magnetic proximity effect. The Rashba-Edelstein magnetoresistance shows a nonsaturated external field dependence, which can be attributed to the Hanle magnetoresistance and the interfacial antiferromagnetic ordering of the Cr layer. Our findings show an approach to obtain spin-orbit torques via the interfacial spin-orbit coupling for YIG-based devices. Furthermore, our findings also provide an understanding of the multiple couplings at the $3d$-metal/YIG interface.

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.

Influence of magnetization anisotropy on angular magnetoresistance in the antiferromagnetic topological semimetal HoSb

Magnetic rare-earth monopnictides have attracted a great deal of interest, not only because of the nontrivial topological electronic states but also due to the extremely large magnetoresistance. In this paper, we report the angular-dependent magnetization and magnetoresistance of the antiferromagnetic topological semimetal HoSb. At elevated temperatures, the angular magnetoresistance displays minima and maxima around $n\ensuremath{\pi}/2$ and $(2n+1)\ensuremath{\pi}/4$ ($n=0$, 1, 2, and 3), respectively. At low temperatures (\ensuremath{\sim}6 K), both the magnetoresistance and magnetization showcase strong angular dependence. Different from those of other rare-earth monopnictides, HoSb's angular magnetoresistance exhibits extra minima between $n\ensuremath{\pi}/2$ and $(2n+1)\ensuremath{\pi}/4$, and between $(2n+1)\ensuremath{\pi}/4$ and $(n+1)\ensuremath{\pi}/2$ ($n=0$, 1, 2, and 3), around which the magnetic phase transitions from ferromagnetic to HoP-type antiferromagnetic state, and from HoP-type antiferromagnetic to ferromagnetic state occur, suggesting the close interplay between conduction electrons and magnetism. Several possible causes have been carefully discussed for these unexpected phenomena. Our findings reveal the crucial role of magnetization anisotropy on the angular magnetoresistance in magnetic rare-earth monopnictides, and may provide a paradigm for studying the magnetization control of magnetoresistance anisotropy in other magnetic semimetals.

Detection and manipulation of the antiferromagnetic Néel vector in Cr2O3

Detection and manipulation of the N\'eel vector in antiferromagnetic materials are promising for more stable, faster, and much higher-density spintronic devices. However, the electrical manipulation of the antiferromagnetic N\'eel vector remains challenging and controversial due to the difficulty in the detection of the zero net magnetization and the unavoidable complications from thermal artifacts. In this work, by utilizing the uniaxial antiferromagnet (AFM) ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$, we demonstrate the detection and manipulation of the antiferromagnetic N\'eel vector. We reveal unambiguously the spin-dependent electrical responses of the coherent ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ N\'eel vector switching, where a symmetric Hall signal and a fourfold angular-dependent magnetoresistance are captured. We also demonstrate the in-plane arbitrary manipulation of the ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ N\'eel vector when the magnetocrystalline anisotropy energy is compensated. Our work for detecting and manipulating N\'eel vectors offers a critical guide for antiferromagnetic-based N\'eel vector switching exploration.

Angular-dependent magnetoresistance in Cr1/3NbS2 single crystals

We present a comprehensive study of angular-dependent magnetoresistance (MR) in the layered chiral helimagnet Cr1/3NbS2 (CNS), which realizes a magnetic soliton lattice. It was found that, at temperatures below Curie temperature, CNS showed a negative magnetoresistance related to the emergence of a chiral soliton lattice state when a magnetic field was applied parallel to the ab-plane (H ‖ ab-plane). When the magnetic field was applied parallel to the c-axis (H ‖ c-axis), however, the negative MR disappeared and a positive MR appeared around zero field at low temperatures. Detailed analysis and modeling indicate that the positive MR is due to the weak anti-localization effect arising from the strong spin–orbit coupling of CNS.

Fermi Surface Structure and Isotropic Stability of Fulde-Ferrell-Larkin-Ovchinnikov Phase in Layered Organic Superconductor β″-(BEDT-TTF)2SF5CH2CF2SO3

The Fermi surface structure of a layered organic superconductor β″-(BEDT-TTF)2SF5CH2CF2SO3 was determined by angular-dependent magnetoresistance oscillations measurements and band-structure calculations. This salt was found to have two small pockets with the same area: a deformed square hole pocket and an elliptic electron pocket. Characteristic corrugations in the field dependence of the interlayer resistance in the superconducting phase were observed at any in-plane field directions. The features were ascribed to the commensurability (CM) effect between the Josephson vortex lattice and the periodic nodal structure of the superconducting gap in the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase. The CM effect was observed in a similar field region for various in-plane field directions, in spite of the anisotropic nature of the Fermi surface. The results clearly showed that the FFLO phase stability is insensitive to the in-plane field directions.

Magnetic-Field-Induced Spin Nematicity in FeSe1 – x S x and FeSe1 – y Te y Superconductor SystemsSupported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0300300 and 2017YFA0303003), the National Natural Science Foundation of China (Grant Nos. 12061131005, 11834016, and 11888101), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant Nos. XDB25000000), and the

The angular-dependent magnetoresistance (AMR) of the ab plane is measured on the single crystals of iron-chalcogenide FeSe1–x S x (x = 0, 0.07, 0.13 and 1) and FeSe1–y Te y (y = 0.06, 0.61 and 1) at various temperatures under fields up to 9 T. A pronounced twofold-anisotropic carrier-scattering effect is identified by AMR, and attributed to a magnetic-field-induced spin nematicity that emerges from the tetragonal normal-state regime below a characteristic temperature T sn. This magnetically polarized spin nematicity is found to be ubiquitous in the isoelectronic FeSe1–x S x and FeSe1–y Te y systems, no matter whether the sample shows an electronic nematic order at T s ≲ T sn, or an antiferromagnetic order at T N < T sn, or neither order. Importantly, we find that the induced spin nematicity shows a very different response to sulfur substitution from the spontaneous electronic nematicity: The spin-nematic T sn is not suppressed but even enhanced by the substitution, whereas the electronic-nematic T s is rapidly suppressed, in the FeSe1–x S x system. Furthermore, we find that the superconductivity is significantly suppressed with the enhancement of the induced spin nematicity in both FeSe1–x S x and FeSe1–y Te y samples.

Anisotropic Superconducting Properties of Kagome Metal CsV3Sb5 Supported by the National Natural Science Foundation of China (Grant Nos. 11834016, 11888101, 12061131005, 51771224 and 61888102), the National Key Research and Development Projects of China (Grant Nos. 2017YFA0303003 and 2018YFA0305800), the Key Research Program and Strategic Priority Research Program of Frontier Sciences of the Chinese Academy of Sciences (Grant Nos. QYZDY-SSW-SLH001, XDB33010200

We systematically measure the superconducting (SC) and mixed state properties of high-quality CsV3Sb5 single crystals with T c ∼ 3.5 K. We find that the upper critical field H c2(T) exhibits a large anisotropic ratio of at zero temperature and fitting its temperature dependence requires a minimum two-band effective model. Moreover, the ratio of the lower critical field, , is also found to be larger than 1, which indicates that the in-plane energy dispersion is strongly renormalized near Fermi energy. Both H c1(T) and SC diamagnetic signal are found to change little initially below T c ∼ 3.5 K and then to increase abruptly upon cooling to a characteristic temperature of ∼2.8 K. Furthermore, we identify a two-fold anisotropy of in-plane angular-dependent magnetoresistance in the mixed state. Interestingly, we find that, below the same characteristic T ∼ 2.8 K, the orientation of this two-fold anisotropy displays a peculiar twist by an angle of 60° characteristic of the Kagome geometry. Our results suggest an intriguing superconducting state emerging in the complex environment of Kagome lattice, which, at least, is partially driven by electron-electron correlation.

Non-Planar Geometrical Effects on the Magnetoelectrical Signal in a Three-Dimensional Nanomagnetic Circuit.

Expanding nanomagnetism and spintronics into three dimensions (3D) offers great opportunities for both fundamental and technological studies. However, probing the influence of complex 3D geometries on magnetoelectrical phenomena poses important experimental and theoretical challenges. In this work, we investigate the magnetoelectrical signals of a ferromagnetic 3D nanodevice integrated into a microelectronic circuit using direct-write nanofabrication. Due to the 3D vectorial nature of both electrical current and magnetization, a complex superposition of several magnetoelectrical effects takes place. By performing electrical measurements under the application of 3D magnetic fields, in combination with macrospin simulations and finite element modeling, we disentangle the superimposed effects, finding how a 3D geometry leads to unusual angular dependences of well-known magnetotransport effects such as the anomalous Hall effect. Crucially, our analysis also reveals a strong role of the noncollinear demagnetizing fields intrinsic to 3D nanostructures, which results in an angular dependent magnon magnetoresistance contributing strongly to the total magnetoelectrical signal. These findings are key to the understanding of 3D spintronic systems and underpin further fundamental and device-based studies.

Angular dependence of magnetoresistance and planar Hall effect in semimetals in strong magnetic fields

The semiclassical transport theory is especially powerful for investigating galvanomagnetic effects. Generally, the semiclassical theory is applicable only in weak fields because it does not consider Landau quantization. Herein, we extend the conventional semiclassical theory by considering Landau quantization through the field dependence of carrier density in semimetals. The extended semiclassical theory is applicable even in strong fields, where Landau quantization is noticeable. Using this new approach, we explain the qualitative change in the angular dependence of transverse magnetoresistance (TMR), anisotropic magnetoresistance (AMR), and planar Hall effect (PHE) in bismuth with an increase in the magnetic field. This unveils the puzzle of nontrivial field-induced changes in TMR, AMR, and PHE observed recently in semimetal bismuth.

Angular dependent magnetoresistance in organic spin valves

Vertical organic spin valve (OSV)-based organic spintronic devices with additional degree of freedom to utilize and control the magnetoresistance (MR) by spin of electrons, have attracted a lot of interests for both foundation science and future functional device applications. Herein the effects of temperature, bias voltage and direction of magnetic field on the MR of the OSV are investigated to disclose the mechanisms. Specifically, the MR shows angular dependence with the value tuned from negative to positive by rotating the field direction from in-plane to out-of-plane, corresponding to the angular dependent spin moment. A domain-switch model is proposed to simulate the resistance changes in OSV device. The research provides a new route to tune the MR in organic spintronic devices, which is significant for future functional device applications.

Absence of spin Hall magnetoresistance in Pt/(CoNi)n multilayers

We systematically studied the magnetoresistance effect in a Pt/(CoNi)n multilayer system with perpendicular magnetic anisotropy and the fcc (111) texture. The angular dependence of magnetoresistance, including high-order cosine terms, was observed in a plane perpendicular to the electrical current; this was attributed to the geometrical-size effects caused by crystal symmetry, the ordered arrangement of grains, and the anisotropic interface magnetoresistance effect caused by the breaking of the symmetry at interfaces. Based on the accuracy of our experimental results, the magnitude of spin Hall magnetoresistance (SMR) in Pt/(CoNi)n was expected to be below $1\times10^{-4}$. However, on evaluating the spin Hall angle of $\geq$ 0.07 for Pt using spin-torque ferromagnetic resonance measurements, the theoretical magnitude of SMR in our samples was estimated to exceed $7\times10^{-4}$. This absence of SMR in the experimental results can be explained by the Elliott-Yafet spin relaxation of itinerant electrons in the ferromagnetic metal, which indicates that the boundary conditions of the spin current in the heavy metal/ferromagnetic insulator may not be applicable to all-metallic heterostructures.