Showing papers on "Magnetoresistance published in 2021"

Tunable magnetoresistance of core-shell structured polyaniline nanocomposites with 0-, 1-, and 2-dimensional nanocarbons

Abstract: Core-shell structured polyaniline (PANI) nanocomposites with tunable magnetoresistance (MR) were obtained through the facial surface-initiated polymerization method with assistance of zero-, one-, and two-dimensional nanocarbons (carbon black, carbon fiber, carbon tube, and graphene). The improved dielectric properties and typical semiconducting behavior were observed in the PANI nanocomposites. And the quasi 3D electron conduction mechanism was observed in all the samples through Mott variable range hopping model, indicating that dimension of the nanocarbons does not affect the charge transport mechanism. Meanwhile, positive MR was observed in all the samples, and the MR value can be controlled by nanocarbons. When nanocarbon loading is 10.0 wt%, MR of graphene/PANI, carbon fiber/PANI, carbon black/PANI, and carbon tube/PANI were 15.6%, 14.7%, 9.5%, and 1.5%, respectively. The positive MR phenomenon was analyzed by the wave functional shrinkage model. The magnetic field and nanocarbons’ effects on the localization length, density of state at the Fermi level, average hopping length, and hopping energy were systematically studied. This work provides the guideline for the fabrication of tunable magnetic sensor or information storage device. Tunable magnetoresistance was reported in the polyaniline nanocomposites with zero-, one-, and two-dimensional nanocarbons as fillers.

Demonstration of Nanosecond Operation in Stochastic Magnetic Tunnel Junctions.

Abstract: Magnetic tunnel junctions operating in the superparamagnetic regime are promising devices in the field of probabilistic computing, which is suitable for applications like high-dimensional optimization or sampling problems. Further, random number generation is of interest in the field of cryptography. For such applications, a device's uncorrelated fluctuation time-scale can determine the effective system speed. It has been theoretically proposed that a magnetic tunnel junction designed to have only easy-plane anisotropy provides fluctuation rates determined by its easy-plane anisotropy field and can perform on a nanosecond or faster time-scale as measured by its magnetoresistance's autocorrelation in time. Here, we provide experimental evidence of nanosecond scale fluctuations in a circular-shaped easy-plane magnetic tunnel junction, consistent with finite-temperature coupled macrospin simulation results and prior theoretical expectations. We further assess the degree of stochasticity of such a signal.

Scale-invariant magnetoresistance in a cuprate superconductor

Abstract: Cranking up the field Cuprate superconductors have many unusual properties even in the “normal” (nonsuperconducting) regions of their phase diagram. In the so-called “strange metal” phase, these materials have resistivity that scales linearly with temperature, in contrast to the usual quadratic dependence of ordinary metals. Giraldo-Gallo et al. now find that at very high magnetic fields—up to 80 tesla—the resistivity of the thin films of a lanthanum-based cuprate scales linearly with magnetic field as well, again in contrast to the expected quadratic law. This dual linear dependence presents a challenge for theories of the normal state of the cuprates. Science, this issue p. 479 At high magnetic fields up to 80 tesla, the resistivity of a thin-film La-based cuprate scales linearly with the field. The anomalous metallic state in the high-temperature superconducting cuprates is masked by superconductivity near a quantum critical point. Applying high magnetic fields to suppress superconductivity has enabled detailed studies of the normal state, yet the direct effect of strong magnetic fields on the metallic state is poorly understood. We report the high-field magnetoresistance of thin-film La2–xSrxCuO4 cuprate in the vicinity of the critical doping, 0.161 ≤ p ≤ 0.190. We find that the metallic state exposed by suppressing superconductivity is characterized by magnetoresistance that is linear in magnetic fields up to 80 tesla. The magnitude of the linear-in-field resistivity mirrors the magnitude and doping evolution of the well-known linear-in-temperature resistivity that has been associated with quantum criticality in high-temperature superconductors.

Anisotropic superconducting properties of Kagome metal CsV3Sb5

Abstract: We systematically measure the superconducting (SC) and mixed state properties of high-quality CsV3Sb5 single crystals with Tc ~ 35 K We find that the upper critical field Hc2(T) exhibits a large anisotropic ratio of Hc2^(ab)/Hc2^(c) ~ 9 at zero temperature and fitting its temperature dependence requires a minimum two-band effective model Moreover, the ratio of the lower critical field, Hc1^(ab)/Hc1^(c), is also found to be larger than 1, which indicates that the in-plane energy dispersion is strongly renormalized near Fermi energy Both Hc1(T) and SC diamagnetic signal are found to change little initially below Tc ~ 35 K and then to increase abruptly upon cooling to a characteristic temperature of ~28 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 ~ 28 K, the orientation of this two-fold anisotropy displays a peculiar twist by an angle of 60o 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

Two-fold symmetric superconductivity in few-layer NbSe2

Abstract: The strong Ising spin–orbit coupling in certain two-dimensional transition metal dichalcogenides can profoundly affect the superconducting state in few-layer samples. For example, in NbSe2, this effect combines with the reduced dimensionality to stabilize the superconducting state against magnetic fields up to ~35 T, and could lead to topological superconductivity. Here we report a two-fold rotational symmetry of the superconducting state in few-layer NbSe2 under in-plane external magnetic fields, in contrast to the three-fold symmetry of the lattice. Both the magnetoresistance and critical field exhibit this two-fold symmetry, and it also manifests deep inside the superconducting state in NbSe2/CrBr3 superconductor-magnet tunnel junctions. In both cases, the anisotropy vanishes in the normal state, demonstrating that it is an intrinsic property of the superconducting phase. We attribute the behaviour to the mixing between two closely competing pairing instabilities, namely the conventional s-wave instability typical of bulk NbSe2 and an unconventional d- or p-wave channel that emerges in few-layer NbSe2. Our results demonstrate the unconventional character of the pairing interaction in few-layer transition metal dichalcogenides and highlight the exotic superconductivity in this family of two-dimensional materials. A two-fold rotational symmetry is observed in the superconducting state of NbSe2. This is strikingly different from the three-fold symmetry of the lattice, and suggests that a mixed conventional and unconventional order parameter exists in this material.

Incoherent transport across the strange-metal regime of overdoped cuprates

Abstract: Strange metals possess highly unconventional electrical properties, such as a linear-in-temperature resistivity1-6, an inverse Hall angle that varies as temperature squared7-9 and a linear-in-field magnetoresistance10-13. Identifying the origin of these collective anomalies has proved fundamentally challenging, even in materials such as the hole-doped cuprates that possess a simple bandstructure. The prevailing consensus is that strange metallicity in the cuprates is tied to a quantum critical point at a doping p* inside the superconducting dome14,15. Here we study the high-field in-plane magnetoresistance of two superconducting cuprate families at doping levels beyond p*. At all dopings, the magnetoresistance exhibits quadrature scaling and becomes linear at high values of the ratio of the field and the temperature, indicating that the strange-metal regime extends well beyond p*. Moreover, the magnitude of the magnetoresistance is found to be much larger than predicted by conventional theory and is insensitive to both impurity scattering and magnetic field orientation. These observations, coupled with analysis of the zero-field and Hall resistivities, suggest that despite having a single band, the cuprate strange-metal region hosts two charge sectors, one containing coherent quasiparticles, the other scale-invariant 'Planckian' dissipators.

Two-dimensional magneto-photoconductivity in non-van der Waals manganese selenide

Abstract: Deficient intrinsic species and suppressed Curie temperatures (Tc) in two-dimensional (2D) magnets are major barriers for future spintronic applications. As an alternative, delaminating non-van der Waals (vdW) magnets can offset these shortcomings and involve robust bandgaps to explore 2D magneto-photoconductivity at ambient temperature. Herein, non-vdW α-MnSe2 is first delaminated as quasi-2D nanosheets for the study of emerging semiconductor, ferromagnetism and magneto-photoconductivity behaviors. Abundant nonstoichiometric surfaces induce the renormalization of the band structure and open a bandgap of 1.2 eV. The structural optimization strengthens ferromagnetic super–exchange interactions between the nearest-neighbor Mn2+, which enables us to achieve a high Tc of 320 K well above room temperature. The critical fitting of magnetization and transport measurements both verify that it is of quasi-2D nature. The above observations are evidenced by multiple microscopic and macroscopic characterization tools, in line with the prediction of first-principles calculations. Profiting from the negative magnetoresistance effect, the self-powered infrared magneto-photoconductivity performance including a responsivity of 330.4 mA W−1 and a millisecond-level response speed are further demonstrated. Such merits stem from the synergistic modulation of magnetic and light fields on photogenerated carriers. This provides a new strategy to manipulate both charge and spin in 2D non-vdW systems and displays their alluring prospects in magneto-photodetection.

Spin-filter induced large magnetoresistance in 2D van der Waals magnetic tunnel junctions

Abstract: Two-dimensional (2D) van der Waals (vdW) heterostructures, known as layer-by-layer stacked 2D materials in a precisely chosen sequence, have received more and more attention in spintronics for their ultra-clean interface, unique electronic properties and 2D ferromagnetism. Motivated by the recent synthesis of monolayer 1T-VSe2 with ferromagnetic ordering and a high Curie temperature above room temperature, we investigate the bias-voltage driven spin transport properties of 2D magnetic tunnel junctions (MTJs) based on VSe2 utilizing density functional theory combined with the nonequilibrium Green's function method. In the device 1T-MoSe2/1T-VSe2/2H-WSe2/1T-VSe2/1T-MoSe2, the tunneling magneto-resistance (TMR) is incredibly satisfactory up to 5600%. Based on the analysis of evanescent states, this large TMR is attributed to the spin filter effect at the interface between 1T-VSe2 and 2H-WSe2, which overcomes the low spin polarization of 1T-VSe2. Furthermore, by inserting 2H-MoSe2, the spin filter effect is enhanced with decreasing current and the TMR is drastically improved to 1.7 × 105%. This work highlights the feasibility of 2D vdW heterostructures for ultra-low power spintronic applications by electronic structural engineering.

Magnetic memory driven by topological insulators.

Abstract: Giant spin-orbit torque (SOT) from topological insulators (TIs) provides an energy efficient writing method for magnetic memory, which, however, is still premature for practical applications due to the challenge of the integration with magnetic tunnel junctions (MTJs). Here, we demonstrate a functional TI-MTJ device that could become the core element of the future energy-efficient spintronic devices, such as SOT-based magnetic random-access memory (SOT-MRAM). The state-of-the-art tunneling magnetoresistance (TMR) ratio of 102% and the ultralow switching current density of 1.2 × 105 A cm-2 have been simultaneously achieved in the TI-MTJ device at room temperature, laying down the foundation for TI-driven SOT-MRAM. The charge-spin conversion efficiency θSH in TIs is quantified by both the SOT-induced shift of the magnetic switching field (θSH = 1.59) and the SOT-induced ferromagnetic resonance (ST-FMR) (θSH = 1.02), which is one order of magnitude larger than that in conventional heavy metals. These results inspire a revolution of SOT-MRAM from classical to quantum materials, with great potential to further reduce the energy consumption.

Linear-in temperature resistivity from an isotropic Planckian scattering rate.

Abstract: A variety of ‘strange metals’ exhibit resistivity that decreases linearly with temperature as the temperature decreases to zero1–3, in contrast to conventional metals where resistivity decreases quadratically with temperature. This linear-in-temperature resistivity has been attributed to charge carriers scattering at a rate given by ħ/τ = αkBT, where α is a constant of order unity, ħ is the Planck constant and kB is the Boltzmann constant. This simple relationship between the scattering rate and temperature is observed across a wide variety of materials, suggesting a fundamental upper limit on scattering—the ‘Planckian limit’4,5—but little is known about the underlying origins of this limit. Here we report a measurement of the angle-dependent magnetoresistance of La1.6−xNd0.4SrxCuO4—a hole-doped cuprate that shows linear-in-temperature resistivity down to the lowest measured temperatures6. The angle-dependent magnetoresistance shows a well defined Fermi surface that agrees quantitatively with angle-resolved photoemission spectroscopy measurements7 and reveals a linear-in-temperature scattering rate that saturates at the Planckian limit, namely α = 1.2 ± 0.4. Remarkably, we find that this Planckian scattering rate is isotropic, that is, it is independent of direction, in contrast to expectations from ‘hotspot’ models8,9. Our findings suggest that linear-in-temperature resistivity in strange metals emerges from a momentum-independent inelastic scattering rate that reaches the Planckian limit. Angle-dependent magnetoresistance measurements of a strange-metal phase of a hole-doped cuprate show a well defined Fermi surface and an isotropic linear-in-temperature scattering rate that saturates at the Planckian limit.

Nanoscale domain wall devices with magnetic tunnel junction read and write

Abstract: The manipulation of fast domain wall motion in magnetic nanostructures could form the basis of novel magnetic memory and logic devices. However, current approaches for reading and writing domain walls require external magnetic fields, or are based on conventional magnetic tunnel junctions (MTJs) that are not compatible with high-speed domain wall motion. Here we report domain wall devices based on perpendicular MTJs that offer electrical read and write, and fast domain wall motion via spin–orbit torque. The devices have a hybrid free layer design that consists of platinum/cobalt (Pt/Co) or a synthetic antiferromagnet (Pt/Co/Ru/Co) into the free layer of conventional MTJs. We show that our devices can achieve good tunnelling magnetoresistance readout and efficient spin-transfer torque writing that is comparable to current magnetic random-access memory technology, as well as domain wall depinning efficiency that is similar to stand-alone materials. We also show that a domain wall conduit based on a synthetic antiferromagnet offers the potential for reliable domain wall motion and faster write speed compared with a device based on Pt/Co. Domain wall devices based on perpendicular magnetic tunnel junctions with a hybrid free layer design can offer electrical read and write, and fast domain wall motion driven via spin–orbit torque.

Magnetic Moments Induced by Atomic Vacancies in Transition Metal Dichalcogenide Flakes

Abstract: 2D magnetism plays a key role in both fundamental physics and potential device applications. However, the instability of the discovered 2D magnetic materials has been one main obstacle in deep research and potential application of 2D magnetism. Here, a localized magnetic moment induced by Pt vacancies in air-stable type-II Dirac semimetal PtSe2 flakes is reported. The localized magnetic moments give rise to the Kondo effect, evidenced by logarithmic increment of resistance with decreasing temperature and isotropic negative longitudinal magnetoresistance. Additionally, the induced magnetic moment and Kondo temperature appear to depend on thickness in the thinner samples (<10 nm). The small magnetocrystalline anisotropy revealed by first-principles calculation indicates that the magnetic moments are randomly localized instead of long-range ordered. The findings demonstrate a new means to induce magnetism in 2D non-magnetic materials.

Manipulating Ferromagnetism in Few-Layered Cr 2 Ge 2 Te 6 .

Abstract: The discovery of magnetism in 2D materials offers new opportunities for exploring novel quantum states and developing spintronic devices. In this work, using field-effect transistors with solid ion conductors as the gate dielectric (SIC-FETs), we have observed a significant enhancement of ferromagnetism associated with magnetic easy-axis switching in few-layered Cr2 Ge2 Te6 . The easy axis of the magnetization, inferred from the anisotropic magnetoresistance, can be uniformly tuned from the out-of-plane direction to an in-plane direction by electric field in the few-layered Cr2 Ge2 Te6 . Additionally, the Curie temperature, obtained from both the Hall resistance and magnetoresistance measurements, increases from 65 to 180 K in the few-layered sample by electric gating. Moreover, the surface of the sample is fully exposed in the SIC-FET device configuration, making further heterostructure-engineering possible. This work offers an excellent platform for realizing electrically controlled quantum phenomena in a single device.

Large Tunneling Magnetoresistance in van der Waals Ferromagnet/Semiconductor Heterojunctions.

Abstract: 2D layered chalcogenide semiconductors have been proposed as a promising class of materials for low-dimensional electronic, optoelectronic, and spintronic devices. Here, all-2D van der Waals vertical spin-valve devices, that combine the 2D layered semiconductor InSe as a spacer with the 2D layered ferromagnetic metal Fe3 GeTe2 as spin injection and detection electrodes, are reported. Two distinct transport behaviors are observed: tunneling and metallic, which are assigned to the formation of a pinhole-free tunnel barrier at the Fe3 GeTe2 /InSe interface and pinholes in the InSe spacer layer, respectively. For the tunneling device, a large magnetoresistance (MR) of 41% is obtained under an applied bias current of 0.1 µA at 10 K, which is about three times larger than that of the metallic device. Moreover, the tunneling device exhibits a lower operating bias current but a more sensitive bias current dependence than the metallic device. The MR and spin polarization of both the metallic and tunneling devices decrease with increasing temperature, which can be fitted well by Bloch's law. These findings reveal the critical role of pinholes in the MR of all-2D van der Waals ferromagnet/semiconductor heterojunction devices.

Magnetic ordering through itinerant ferromagnetism in a metal-organic framework.

Abstract: Materials that combine magnetic order with other desirable physical attributes could find transformative applications in spintronics, quantum sensing, low-density magnets and gas separations. Among potential multifunctional magnetic materials, metal–organic frameworks, in particular, bear structures that offer intrinsic porosity, vast chemical and structural programmability, and the tunability of electronic properties. Nevertheless, magnetic order within metal–organic frameworks has generally been limited to low temperatures, owing largely to challenges in creating a strong magnetic exchange. Here we employ the phenomenon of itinerant ferromagnetism to realize magnetic ordering at TC = 225 K in a mixed-valence chromium(ii/iii) triazolate compound, which represents the highest ferromagnetic ordering temperature yet observed in a metal–organic framework. The itinerant ferromagnetism proceeds through a double-exchange mechanism, which results in a barrierless charge transport below the Curie temperature and a large negative magnetoresistance of 23% at 5 K. These observations suggest applications for double-exchange-based coordination solids in the emergent fields of magnetoelectrics and spintronics. The development of metal–organic magnets that combine tunable magnetic properties with other desirable physical properties remains challenging despite numerous potential applications. Now, a mixed-valent chromium–triazolate material has been prepared that exhibits itinerant ferromagnetism with a magnetic ordering temperature of 225 K, a high conductivity and large negative magnetoresistance (23%).

Tunable Tunneling Magnetoresistance in van der Waals Magnetic Tunnel Junctions with 1T-CrTe2 Electrodes.

Abstract: Two-dimensional (2D) van der Waals (vdW) heterostructures have opened new avenues for spintronic applications with novel properties. Here, by density functional theory calculations, we investigated the spin-dependent transport in vdW magnetic tunnel junctions (MTJs) composed of 1T-CrTe2 ferromagnetic electrodes. Meanwhile, graphene and h-BN are employed as tunnel barriers. It has been found that the tunneling magnetoresistance (TMR) effects of two types of vdW MTJs present analogous trends: thicknesses of barriers have a great influence on the TMR ratios, which reach up to the maximum when barriers increase to five monolayers. However, despite the similarity, the graphene-barrier junction is more promising for optimization. Through observing the energy-resolved transmission spectra of vdW MTJs, we noticed that TMR ratios of graphene-barrier junctions are tunable and could be enhanced through tuning the position of Fermi energy. Therefore, we successfully realized the TMR optimization by substitutional doping. When substituting one carbon atom with one boron atom in the graphene barrier, TMR ratios are drastically improved, and a TMR ratio as high as 6962% could be obtained in the doped seven-monolayer-barrier junction. Our results pave the way for vdW MTJ applications in spintronics.

Two-dimensional electron systems and interfacial coupling in LaCrO3/KTaO3 heterostructures

Abstract: The strong interfacial coupling at the 3d-5d transition metal-oxide interfaces has generated excitement due to the possibility of engineering a wide range of quantum phenomena and functionalities. Here, we investigate the electronic interfacial coupling and structural properties of LaCrO3/KTaO3 heterostructures. High-quality LaCrO3 films were grown on KTaO3 substrates using molecular beam epitaxy. These heterostructures show a robust two-dimensional electron gas and a metallic behavior down to liquid helium temperature. Using magnetoresistance measurements, we analyze the coupling of electronic orders between Cr 3d and Ta 5d states and observe signatures of weak anti-localization and Kondo scattering at low-temperature transport. The results provide direct evidence that a crossover (weak anti-localization to Kondo) occurs with increasing temperature as the dephasing scattering events reduce the coherence length. Our observations allow for a clear and detailed picture of two distinct quantum corrections to conductivity at low temperature.

Anomalous Hall effect in ferrimagnetic metal RMn6Sn6 (R = Tb, Dy, Ho) with clean Mn kagome lattice.

Abstract: Kagome lattice, made of corner-sharing triangles, provides an excellent platform for hosting exotic topological quantum states. Here we systematically studied the magnetic and transport properties of RMn6Sn6 (R = Tb, Dy, Ho) with clean Mn kagome lattice. All the compounds have a collinear ferrimagnetic structure with different easy axis at low temperature. The low-temperature magnetoresistance (MR) is positive and has no tendency to saturate below 7 T, while the MR gradually declines and becomes negative with the increasing temperature. A large intrinsic anomalous Hall conductivity about 250 {\Omega}-1cm-1, 40 {\Omega}-1cm-1, 95 {\Omega}-1cm-1 is observed for TbMn6Sn6, DyMn6Sn6, HoMn6Sn6, respectively. Our results imply that RMn6Sn6 system is an excellent platform to discover other intimately related topological or quantum phenomena and also tune the electronic and magnetic properties in future studies.

Observation of the Orbital Rashba-Edelstein Magnetoresistance

Abstract: We report the observation of magnetoresistance (MR) originating from the orbital angular momentum transport (OAM) in a Permalloy (Py) / oxidized Cu (Cu*) heterostructure: the orbital Rashba-Edelstein magnetoresistance. The angular dependence of the MR depends on the relative angle between the induced OAM and the magnetization in a similar fashion as the spin Hall magnetoresistance (SMR). Despite the absence of elements with large spin-orbit coupling, we find a sizable MR ratio, which is in contrast to the conventional SMR which requires heavy elements. By varying the thickness of the Cu* layer, we confirm that the interface is responsible for the MR, suggesting that the orbital Rashba-Edelstein effect is responsible for the generation of the OAM. Through Py thickness-dependence studies, we find that the effective values for the spin diffusion and spin dephasing lengths of Py are significantly larger than the values measured in Py / Pt bilayers, approximately by the factor of 2 and 4, respectively. This implies that another mechanism beyond the conventional spin-based scenario is responsible for the MR observed in Py / Cu* structures originated in a sizeable transport of OAM. Our findings not only unambiguously demonstrate the current-induced torque without using any heavy element via the OAM channel but also provide an important clue towards the microscopic understanding of the role that OAM transport can play for magnetization dynamics.

Anomalous Hall effect in ferrimagnetic metal RMn6Sn6 (R = Tb, Dy, Ho) with clean Mn kagome lattice

Abstract: Kagome lattice, made of corner-sharing triangles, provides an excellent platform for hosting exotic topological quantum states. Here, we systematically studied the magnetic and transport properties of RMn6Sn6 (R = Tb, Dy, Ho) with clean Mn kagome lattice. All the compounds have a collinear ferrimagnetic structure with different easy axis at low temperature. The low-temperature magnetoresistance (MR) is positive and has no tendency to saturate below 7 T, while the MR gradually declines and becomes negative with the increasing temperature. A large intrinsic anomalous Hall conductivity about 250, 40, and 95 Ω−1 cm−1 is observed for TbMn6Sn6, DyMn6Sn6, and HoMn6Sn6, respectively. Our results imply that RMn6Sn6 system is an excellent platform to discover other intimately related topological or quantum phenomena and also tune the electronic and magnetic properties in future studies.

Van Der Waals Epitaxial Growth and Phase Transition of Layered FeSe 2 Nanocrystals.

Abstract: Layered iron chalcogenides (FeX, X = S, Se, Te) provide excellent platforms to study intertwined phase transitions, superconductivity, and magnetism. However, layered iron dichalcogenides (FeX2 , X = S, Se, Te) are rarely reported and their intrinsic properties are still unknown. Here, phase-pure layered iron diselenide (FeSe2 ) nanocrystals are epitaxially grown on mica by the sublimed-salt-assisted chemical vapor deposition method at atmospheric pressure. The layered atomic structure of FeSe2 is confirmed by X-ray diffraction and atomic-resolution scanning transmission electron microscopy. Electrical transport shows that the layered FeSe2 is a metal with high conductivity and a phase transition at ≈11 K. The phase transition manifests itself as a kink in the temperature-dependent resistivity, as well as anomalous magnetoresistance (MR) appearing around the phase-transition temperature. The MR changes from negative to positive, accompanied by large hysteresis near the phase-transition temperature upon cooling. The negative MR and hysteresis might originate from magnetic field suppression scattering of spin fluctuations and competition of magnetic interactions induced by the phase transition, respectively. Layered iron dichalcogenide will be potential candidate to explore novel quantum phenomena and other applications.

Large and robust charge-to-spin conversion in sputtered conductive WTex with disorder

Abstract: Summary Topological materials with large spin-orbit coupling and immunity to disorder-induced symmetry breaking show great promise for efficiently converting charge to spin. Here, we report that long-range disordered sputtered WTex thin films exhibit local chemical and structural order similar to those of Weyl semimetal WTe2 and conduction behavior that is consistent with semimetallic Weyl fermion. We find large charge-to-spin conversion properties and electrical conductivity in thermally annealed sputtered WTex films that are comparable with those in crystalline WTe2 flakes. Besides, the strength of unidirectional spin Hall magnetoresistance in annealed WTex/Mo/CoFeB heterostructure is 5–20 times larger than typical spin-orbit torque (SOT) layer/ferromagnet heterostructures reported at room temperature. We further demonstrate room-temperature damping-like SOT-driven magnetization switching of in-plane magnetized CoFeB. These large charge-to-spin conversion properties that are robust in the presence of long-range disorder and thermal annealing pave the way for industrial application of a new class of sputtered semimetals.

Spin-texture-driven electrical transport in multi-Q antiferromagnets

Abstract: Unusual magnetic textures can be stabilized in f-electron materials due to the interplay between competing magnetic interactions, complex Fermi surfaces, and crystalline anisotropy. Here we investigate CeAuSb2, an f-electron incommensurate antiferromagnet hosting both single-Q and double-Q spin textures as a function of magnetic fields (H) applied along the c axis. Experimentally, we map out the field-temperature phase diagram via electrical resistivity and thermal expansion measurements. Supported by calculations of a Kondo lattice model, we attribute the puzzling magnetoresistance enhancement in the double-Q phase to the localization of the electronic wave functions caused by the incommensurate magnetic texture. The magnetic, electronic, and structural properties of a quantum material are intrinsically linked. In f-electron systems, such as cerium-based materials, this interplay can be exceedingly complex. Here, the authors investigate the antiferromagnet CeAuSb2 using a Kondo lattice model in order to resolve the changes in conductance that occur with variations in the magnetic spin texture as function of applied magnetic field.

Magnetotransport in semiconductors and two-dimensional materials from first principles

Abstract: Studies of transport in magnetic fields are key for research in semiconductors and quantum materials. However, accurately predicting magnetotransport phenomena and the microscopic mechanisms governing them remains challenging. Here, the authors develop an approach to solve numerically the electron Boltzmann equation in a magnetic field using first-principles electron-phonon interactions. The magnetoresistance, Hall coefficient, and Hall factor of various semiconductors and two-dimensional materials are accurately predicted. These advances extend the scope of first-principles studies of transport to include applied magnetic fields.

Chirality-Dependent Hall Effect and Antisymmetric Magnetoresistance in a Magnetic Weyl Semimetal.

Abstract: Weyl semimetals host a variety of exotic effects that have no counterpart in conventional materials, such as the chiral anomaly and magnetic monopole in momentum space. These effects give rise to unusual transport properties, including a negative magnetoresistance and a planar Hall effect, etc. Here, we report a new type of Hall and magnetoresistance effect in a magnetic Weyl semimetal. Unlike antisymmetric (with respect to either magnetic field or magnetization) Hall and symmetric magnetoresistance in conventional materials, the discovered magnetoresistance and Hall effect are antisymmetric in both magnetic field and magnetization. We show that the Berry curvature, the tilt of the Weyl node, and the chiral anomaly synergically produce these phenomena. Our results reveal a unique property of Weyl semimetals with broken time reversal symmetry.

Broadband Terahertz Probes of Anisotropic Magnetoresistance Disentangle Extrinsic and Intrinsic Contributions

Abstract: Anisotropic magnetoresistance (AMR) is a ubiquitous and versatile probe of magnetic order in contemporary spintronics research. Its origins are usually ascribed to extrinsic effects (i.e., spin-dependent electron scattering), whereas intrinsic (i.e., scattering-independent) contributions are neglected. Here, we measure AMR of polycrystalline thin films of the standard ferromagnets Co, Ni, Ni81Fe19, and Ni50Fe50 over the frequency range from dc to 28 THz. The large bandwidth covers the regimes of both diffusive and ballistic intraband electron transport and, thus, allows us to separate extrinsic and intrinsic AMR components. Analysis of the THz response based on Boltzmann transport theory reveals that the AMR of the Ni, Ni81Fe19, and Ni50Fe50 samples is of predominantly extrinsic nature. However, the Co thin film exhibits a sizable intrinsic AMR contribution, which is constant up to 28 THz and amounts to more than 2/3 of the dc AMR contrast of 1%. These features are attributed to the hexagonal structure of the Co crystallites. They are interesting for applications in terahertz spintronics and terahertz photonics. Our results show that broadband terahertz electromagnetic pulses provide new and contact-free insights into magnetotransport phenomena of standard magnetic thin films on ultrafast timescales.

Contrasting physical properties of the trilayer nickelates Nd 4 Ni 3 O 10 and Nd 4 Ni 3 O 8

Abstract: We report the crystal structures and physical properties of trilayer nickelates Nd4Ni3O10 and Nd4Ni3O8. Measurements of magnetization and electrical resistivity display contrasting behaviors in the two compounds. Nd4Ni3O10 shows a paramagnetic metallic behavior with a metal-to-metal phase transition ( T ∗) at about 162 K, as revealed by both magnetic susceptibility and resistivity. Further magnetoresistance and Hall coefficient results show a negative magnetoresistance at low temperatures and the carrier type of Nd4Ni3O10 is dominated by hole-type charge carriers. The significant enhancement of Hall coefficient and resistivity below T ∗ suggests that effective charge carrier density decreases when cooling through the transition temperature. In contrast, Nd4Ni3O8 shows an insulating behavior. In addition, this compound shows a paramagnetic behavior with the similar magnetic moment as that of Nd4Ni3O10 derived from the Curie-Weiss fitting. This may suggest that the magnetic moments in both systems are contributed by Nd3+ ions. By applying pressures up to about 49 GPa, the insulating behavior is still present and becomes even stronger under a high pressure. Our results suggest that the different Ni configurations (Ni1+/2+ or Ni2+/3+) and the changes of coordination environment of Ni sites may account for the contrasting behaviors in trilayer nickelates Nd4Ni3O10 and Nd4Ni3O8.

Colossal Magnetoresistance without Mixed Valence in a Layered Phosphide Crystal.

Abstract: Materials with strong magnetoresistive responses are the backbone of spintronic technology, magnetic sensors, and hard drives. Among them, manganese oxides with a mixed valence and a cubic perovskite structure stand out due to their colossal magnetoresistance (CMR). A double exchange interaction underlies the CMR in manganates, whereby charge transport is enhanced when the spins on neighboring Mn3+ and Mn4+ ions are parallel. Prior efforts to find different materials or mechanisms for CMR resulted in a much smaller effect. Here an enormous CMR at low temperatures in EuCd2 P2 without manganese, oxygen, mixed valence, or cubic perovskite structure is shown. EuCd2 P2 has a layered trigonal lattice and exhibits antiferromagnetic ordering at 11 K. The magnitude of CMR (104 %) in as-grown crystals of EuCd2 P2 rivals the magnitude in optimized thin films of manganates. The magnetization, transport, and synchrotron X-ray data suggest that strong magnetic fluctuations are responsible for this phenomenon. The realization of CMR at low temperatures without heterovalency leads to a new regime for materials and technologies related to antiferromagnetic spintronics.