When a three-dimensional (3D) ferromagnetic topological insulator thin film is magnetized out-of-plane, conduction ideally occurs through dissipationless, one-dimensional (1D) chiral states that are characterized by a quantized, zero-field Hall conductance. The recent realization of this phenomenon - the quantum anomalous Hall effect - provides a conceptually new platform for studies of edge-state transport, distinct from the more extensively studied integer and fractional quantum Hall effects that arise from Landau level formation. An important question arises in this context: how do these 1D edge states evolve as the magnetization is changed from out-of-plane to in-plane? We examine this question by studying the field-tilt driven crossover from predominantly edge state transport to diffusive transport in Cr-doped (Bi,Sb)2Te3 thin films, as the system transitions from a quantum anomalous Hall insulator to a gapless, ferromagnetic topological insulator. The crossover manifests itself in a giant, electrically tunable anisotropic magnetoresistance that we explain using the Landauer-Buttiker formalism. Our methodology provides a powerful means of quantifying edge state contributions to transport in temperature and chemical potential regimes far from perfect quantization.
We reveal the giant magnetoresistance induced by the spin-polarized current in the ferromagnet (F_1)/topological insulator (TI)/ferromagnet (F_2) junction, where two ferromagnets are deposited on the diffusive surface of the TI. We can increase and reduce the value of the giant magnetoresistance by tuning the spin-polarized current, which is controlled by the magnetization configurations. The property is intuitively understood by the non-equilibrium spin-polarized current, which plays the role of an effective electrochemical potential on the surface of the TI.
We study an effect of moderate magnetic field on variable range hopping conductivity in arrays of ferromagnetic granules separated by tunnel barriers. It is shown that the resulting magnetoresistance can be significantly larger than the standard "giant" magnetoresistance in Fe-N-Fe-N... multilayers. The effect is related to a gain in densities of states available for the virtual processes within the intermediate granules due to magnetic-field induced alignment of the granule magnetizations.
We report a numerical study on Aharonov-Bohm (AB) effect and giant magnetoresistance in rectangular rings made of graphene nanoribbons (GNRs). We show that in low energy regime where only the first subband of contact GNRs contributes to the transport, the transmission probability can be strongly modulated, i.e., almost fully suppressed, when tuning a perpendicular magnetic field. On this basis, strong AB oscillations with giant negative magnetoresistance can be achieved at room temperature. The magnetoresistance reaches thousands % in perfect GNR rings and a few hundred % with edge disordered …
Anomalous Hall-like signals in platinum in contact with magnetic insulators are common observations that could be explained by either proximity magnetization or spin Hall magnetoresistance. In this work, longitudinal and transverse magnetoresistances are measured in a pure gold thin film on the ferrimagnetic insulator Y$_3$Fe$_5$O$_{12}$ (Yttrium Iron Garnet, YIG). We show that both the longitudinal and transverse magnetoresistances have quantitatively consistent scaling in YIG/Au and in a YIG/Pt reference system when applying the Spin Hall magnetoresistance framework. No contribution of an an…
A quasiclassical theory of giant magnetoresistance in nanoscale point contacts between different ferromagnetic metals is developed. The contacts were sorted by three types of mutual positions of the conduction spin-subband bottoms which are shifted one against another by the exchange interaction. A model of linear domain wall has been used to account for the finite contact length. The magnetoresistance is plotted against the size of the nanocontact. In heterocontacts the magnetoresistance effect turned out to be not only negative, as usual, but can be positive as well. Relevance of the results…
We conducted a systematic angular dependence study of nonlinear magnetoresistance in NiFe/Pt bilayers at variable temperature and field using the Wheatstone bridge method. We successfully disentangled magnon magnetoresistance from other types of magnetoresistances based on their different temperature and field dependences. Both the spin Hall/anisotropic and magnon magnetoresistances contain sine phi and sine 3 phi components with phi the angle between current and magnetization, but they exhibit different field and temperature dependence. The competition between different types of magnetoresist…
We report on theoretical studies of the recently discovered negative giant magnetoresistance in ultraclean two-dimensional electron systems at low temperatures. We adapt a transport model to a ultraclean scenario and calculate the elastic scattering rate (electron-charged impurity) in a regime where the Landau level width is much smaller than the cyclotron energy. We obtain that for low magnetic fields the scattering rate and, as a consequence, the longitudinal magnetoresistance dramatically drop because of the small density of states between Landau levels. We also study the dependence of this…
Anisotropic magnetoresistance is the change tendency of resistance of a material on the mutual orientation of the electric current and the external magnetic field. Here, we report experimental observations in the Dirac semimetal Cd3As2 of giant anisotropic magnetoresistance and its transverse version, called the planar Hall effect. The relative anisotropic magnetoresistance is negative and up to -68% at 2 K and 10 T. The high anisotropy and the minus sign in this isotropic and nonmagnetic material are attributed to a field-dependent current along the magnetic field, which may be induced by the…
Spacer thickness and electrical conditioning have their own influence in enhancing giant magnetoresistance (GMR) ratio. At some condition one factor can override the other as reported by experiment results. An empiric model about competition about these two factors is discussed in this work. Comparison from experiment results to validate the model are also shown and explained. A formulation is proposed to extend the existing one that now accommodates both spacer thickness and electrical conditioning in one form.
We predict a magnetoresistance induced by the interfacial Rashba spin-orbit coupling in normal metal|ferromagnetic insulator bilayer. It depends on the angle between current and magnetization directions identically to the "spin Hall magnetoresistance" mechanism caused by a combined action of spin Hall and inverse spin Hall effects. Due to the identical phenomenology it is not obvious whether the magnetoresistance reported by Nakayama et al. is a bulk metal or interface effect. The interfacial Rashba induced magnetoresistance may be distinguished from the bulk metal spin Hall magnetoresistance …
We demonstrate giant magnetoresistance in Fe/MoS$_2$/Fe junctions by means of \textit{ab-initio} transport calculations. We show that junctions incorporating either a mono- or a bi-layer of MoS$_2$ are metallic and that Fe acts as an efficient spin injector into MoS$_2$ with an efficiency of about 45\%. This is the result of the strong coupling between the Fe and S atoms at the interface. For junctions of greater thickness a maximum magnetoresistance of $\sim$300\% is obtained, which remains robust with the applied bias as long as transport is in the tunneling limit. A general recipe for impro…
We report on a giant negative magnetoresistance in very high mobility GaAs/AlGaAs heterostructures and quantum wells. The effect is the strongest at $B \simeq 1$ kG, where the magnetoresistivity develops a minimum emerging at $T \lesssim 2$ K. Unlike the zero-field resistivity which saturates at $T \simeq 2 $ K, the resistivity at this minimum continues to drop at an accelerated rate to much lower temperatures and becomes several times smaller than the zero-field resistivity. Unexpectedly, we also find that the effect is destroyed not only by increasing temperature but also by modest in-plane …
We study the spin Hall magnetoresistance effect in ferrimagnet/normal metal bilayers, comparing the response in collinear and canted magnetic phases. In the collinear magnetic phase, in which the sublattice magnetic moments are all aligned along the same axis, we observe the conventional spin Hall magnetoresistance. In contrast, in the canted phase, the magnetoresistance changes sign. Using atomistic spin model calculations of the magnetic configuration, we show that the electric transport for the different magnetic phases can be rationalized considering the individual sublattice moment orient…
We study theoretically the resistance at the interface between the two planar systems with different lattice constants a and b. The resistance and the effect of the magnetic field depends sensitively on the ratio a/b. The size of the enlarged unit cell $λ= n_Aa = n_Bb$ ($n_A$, $n_B$: integers) is the crucial quantity, and the magnetic flux penetrating this enlarged unit cell determines the oscillation of the resistance. Therefore, the magnetoresistance is very much enhanced at (nearly) incommensurate relation between a and b.
A spin-thermo-electronic valve with the free layer of exchange-spring type and inverse magnetoresistance is investigated. The structure has S-shaped current-voltage characteristics and can exhibit spontaneous oscillations when integrated with a conventional capacitor within a resonator circuit. The frequency of the oscillations can be controlled from essentially dc to the GHz range by the circuit capacitance.
We predict a spin anomalous-Hall unidirectional magnetoresistance (AH-UMR) in conducting bilayers composed of a ferromagnetic layer and a nonmagnetic layer, which does $\textit{not}$ rely on the spin Hall effect in the normal metal layer$-$in stark contrast to the well-studied unidirectional spin-Hall magnetoresistance$-$but, instead, arises from the spin anomalous Hall effect in the ferromagnetic layer. Physically, it is the charge-spin conversion induced by the spin anomalous Hall effect that conspires with the structural inversion asymmetry to generate a net nonequilibrium spin density in t…
Strong magnetoresistance effects are often observed in ferromagnet-nonmagnet multilayers, which are exploited in state-of-the-art magnetic field sensing and data storage technologies. In this work we report a novel current-perpendicular-to-plane magnetoresistance effect in multilayer graphene as grown on a catalytic nickel surface by chemical vapor deposition. A negative magnetoresistance effect of 10^4% has been observed, which persists even at room temperature. This effect is correlated with the shape of the 2D peak as well as with the occurrence of D peak in the Raman spectrum of the as-gro…
Coherent spin transport through bilayer graphene (BLG) nanoflakes sandwiched between two electrodes made of single-layer zigzag graphene nanoribbon was investigated by means of Landauer-Buttiker formalism. Application of a magnetic field only on BLG structure as a channel produces a perfect spin polarization in a large energy region. Moreover, the conductance could be strongly modulated by magnetization of the zigzag edge of AB-stacked BLG, and the junction, entirely made of carbon, produces a giant magnetoresistance (GMR) up to $10^6\%$. Intestinally, GMR and spin polarization could be tuned …
We study the temperature dependence of the spin Hall magnetoresistance (SMR) in yttrium iron garnet/platinum hybrid structures via magnetization orientation dependent magnetoresistance measurements. Our experiments show a decrease of the SMR magnitude with decreasing temperature. Using the sensitivity of the SMR to the spin transport properties of the normal metal, we interpret our data in terms of a decrease of the spin Hall angle in platinum from 0.11 at room temperature to 0.075 at 10K, while the spin diffusion length and the spin mixing conductance of the ferrimagnetic insulator/normal met…
We present a formalism that simultaneously incorporates the effect of quantum tunneling and spin diffusion on spin Hall magnetoresistance observed in normal metal/ferromagnetic insulator bilayers (such as Pt/YIG) and normal metal/ferromagnetic metal bilayers (such as Pt/Co), in which the angle of magnetization influences the magnetoresistance of the normal metal. In the normal metal side the spin diffusion is known to affect the landscape of the spin accumulation caused by spin Hall effect and subsequently the magnetoresistance, while on the ferromagnet side the quantum tunneling effect is det…
We study the temperature dependence of spin Hall magnetoresistance (SMR) in antiferromagnetic insulator (AFI)/metal bilayer systems. We calculate the amplitude of the SMR signal by using a quantum Monte Carlo simulation and examine how the SMR depends on the amplitude of the spin, thickness of the AFI layer, and randomness of the exchange interactions. Our results for simple quantum spin models provide a useful starting point for understanding SMR measurements on atomic layers of magnetic compounds.
We show how a dc current can be generated in a Hall bar without applying a bias voltage. The Hall resistance $R_H$ that corresponds to this pumped current is quantized, just as in the usual integer quantum Hall effect (IQHE). In contrast with the IQHE, however, the longitudinal resistance $R_{xx}$ does not vanish on the plateaus, but equals the Hall resistance. We propose an experimental geometry to measure the pumped current and verify the predicted behavior of $R_H$ and $R_{xx}$.
In this work, the investigation of magnetic proximity effect was extended to Ta which has been reported to have a negative spin Hall angle. Magnetoresistance and Hall measurements for in-plane and out-of-plane applied magnetic field sweeps were carried out at room temperature. The size of the MR ratio observed (~10-5) and its magnetization direction dependence are similar to that reported in Pt/YIG, both of which can be explained by the spin Hall magnetoresistance theory. Additionally, a flip of magnetoresistance polarity is observed at 4 K in the temperature dependent measurements, which can …
By computing spin-polarized electronic transport across a finite zigzag graphene ribbon bridging two metallic graphene electrodes, we demonstrate, as a proof of principle, that devices featuring 100% magnetoresistance can be built entirely out of carbon. In the ground state a short zig-zag ribbon is an antiferromagnetic insulator which, when connecting two metallic electrodes, acts as a tunnel barrier that suppresses the conductance. Application of a magnetic field turns the ribbon ferromagnetic and conducting, increasing dramatically the current between electrodes. We predict large magnetores…
A giant asymmetry in the magnetoresistance was revealed in high-mobility, two-dimensional electron gas on a cylindrical surface. The longitudinal resistance along the magnetic-field gradient impressed by the surface curvature was found to vanish if measured along one of the edges of the curved Hall bar. If the external magnetic field is reversed, then the longitudinal resistance vanishes at the opposite edge of the Hall bar. This asymmetry is analyzed quantitatively in terms of the Landauer-Buettiker formalism.
In ferromagnet/normal-metal bilayers, the sensitivity of the spin Hall magnetoresistance and the spin Nernst magnetothermopower to the boundary conditions at the interface is of central importance. In general, such boundary conditions can be substantially affected by current-induced spin polarizations. In order to quantify the role of the latter, we consider a Rashba two-dimensional electron gas with a ferromagnet attached to one side of the system. The geometry of such a system maximizes the effect of current-induced spin polarization on the boundary conditions, and the spin Hall magnetoresis…
We present a theory of the spin Hall magnetoresistance (SMR) in multilayers made from an insulating ferromagnet F, such as yttrium iron garnet (YIG), and a normal metal N with spin-orbit interactions, such as platinum (Pt). The SMR is induced by the simultaneous action of spin Hall and inverse spin Hall effects and therefore a non-equilibrium proximity phenomenon. We compute the SMR in F$|$N and F$|$N$|$F layered systems, treating N by spin-diffusion theory with quantum mechanical boundary conditions at the interfaces in terms of the spin-mixing conductance. Our results explain the experimenta…
We report on the angular and field dependence of the magnetoresistance (MR) in bilayers of Pt/EuO_{1-x} thin films, measured in both in-plane and out-of-plane geometries at different temperatures (T). Presence of oxygen vacancies manifested by a metal-insulator transition as well as a high-T ferromagnet to paramagnet transition (T_P) were observed in the bilayers. The Anisotropic Magnetoresistance (AMR) could be extracted in the entire T-range, even above T_P, exhibiting two sign crossovers. We attribute its T-evolution to the rotation of easy axis direction from a high-T out-of-plane to a low…
We investigated spin Hall magnetoresistance in FeMn/Pt bilayers, which was found to be one order of magnitude larger than that of heavy metal and insulating ferromagnet or antiferromagnet bilayer systems, and comparable to that of NiFe/Pt bilayers. The spin Hall magnetoresistance shows a non-monotonic dependence on the thicknesses of both FeMn and Pt. The former can be accounted for by the thickness dependence of net magnetization in FeMn thin films, whereas the latter is mainly due to spin accumulation and diffusion in Pt. Through analysis of the Pt thickness dependence, the spin Hall angle, …
We perform electronic measurements of unidirectional spin Hall magnetoresistance (USMR) in a Permalloy/Pt bilayer, in conjunction with magneto-optical Brillouin light spectroscopy of spin current-driven magnon population. We show that the current dependence of USMR closely follows the dipolar magnon density, and that both dependencies exhibit the same scaling over a large temperature range of 80-400 K. These findings demonstrate a close relationship between spin current-driven magnon generation and USMR, and indicate that the latter is likely dominated by the dipolar magnons.
Silicene, germanene and stanene are two-dimensional topological insulators exhibiting helical edge states. We investigate global and local manipulations at the edges by exposing them to (i) a charge-density-wave order, (ii) a superconductor, (iii) an out-of-plane antiferromagnetic, and (iv) an in-plane antiferromagnetic field. We show that these perturbations affect the helical edge states in a different fashion. As a consequence one can realize quantum spin-Hall effect without edge states. In addition, these edge manipulations lead to very promising applications: a giant magnetoresistance and…
We present a versatile method for detecting the presence and motion of a trapped domain wall in a narrow ferromagnetic layer using current-perpendicular-to-plane (CPP) giant magnetoresistance (MR). The CPP-MR response to small motions of the trapped domain wall is enhanced because the CPP current is restricted to the region of wall trapping. We use a Permalloy/Cu/Permalloy spin valve in the shape of a long, ~500-nm-wide wire with a constriction (notch) near its middle that acts as a trapping site for a head-to-head domain wall. Two different notch shapes were studied, mostly at 4.2 K but also …
We calculate the spin-polarized electronic transport through a molecular bilayer spin valve from first principles, and establish the link between the magnetoresistance and the spin-dependent inter- actions at the metal-molecule interfaces. The magnetoresistance of a Fe|bilayer-C70|Fe spin valve attains a high value of 70% in the linear response regime, but it drops sharply as a function of the applied bias. The current polarization has a value of 80% in linear response, and also decreases as a function of bias. Both these trends can be modelled in terms of prominent spin-dependent Fe|C70 inter…
Giant or tunneling magnetoresistance are physical phenomena used for reading information in commercial spintronic devices. The effects rely on a conserved spin current passing between a reference and a sensing ferromagnetic electrode in a multilayer structure. Recently, we have proposed that these fundamental spintronic effects can be realized in collinear antiferromagnets with staggered spin-momentum exchange interaction, which generates conserved spin currents in the absence of a net equilibrium magnetization. Here we elaborate on the proposal by presenting archetype model mechanisms for the…
Transverse magnetoresistance in a ferromagnetic/nonmagnetic/ferromagnetic trilayer originated from charge-spin conversion by anomalous Hall effect is investigated theoretically. Solving the spin diffusion equation in bulk and using the spin-dependent Landauer formula at the ferromagnetic/nonmagnetic interface, an analytical formula of the transverse resistivity is obtained. The charge-spin conversion by the anomalous Hall effect contributes to the magnetoresistance in a manner proportional to the square of the spin anomalous Hall angle. The angular dependence of the magnetoresistance is basica…
In this paper, we report the observation of spin-orbit magnetoresistance (SOMR) in ferromagnetic metal/heavy metal/MgO system. We measure the magnetoresistance as the function of the thickness of heavy metal (HM) for CoFeB/HM/MgO and CoFeB/HM films where HM = Pt and Ta. Besides the conventional spin Hall magnetoresistance (SMR) peak, the evidence of the SOMR is indicated by another peak of the MR ratio when the thickness of HM is around 1 ~ 2 nm for CoFeB/HM/MgO films, which is absent for CoFeB/HM films. We speculate the SOMR observed in our experiment originates from the spin-orbit coupling a…
We present a theory of the spin Hall magnetoresistance of metals in contact with magnetic insulators. We express the spin-mixing conductances, which govern the phenomenology of the effect, in terms of the microscopic parameters of the interface and the spin-spin correlation functions of the local moments on the surface of the magnetic insulator. The magnetic field and temperature dependence of the spin-mixing conductances leads to a rich behaviour of the resistance due to an interplay between the Hanle effect and spin mixing at the interface. Our theory provides a useful tool for understanding…
Quantum dynamics and kinetics of electrically gated graphene ribbons with lateral n-p and e-n-p junctions under magnetic field are investigated. It is shown that the snake-like states of quasiparticles skipping along the n-p interface do not manifest themselve in the main semiclassical part of the ribbon conductance. Giant oscillations of the conductance of a ribbon with an n-p-n junction are predicted and analytically calculated. Depending on the number of junctions inside the ribbon its magnetoresistance may be controllably changed by 50% - 90% by an extremely small change of the magnetic fi…
We experimentally investigate and quantitatively analyze the spin Hall magnetoresistance effect in ferromagnetic insulator/platinum and ferromagnetic insulator/nonferromagnetic metal/platinum hybrid structures. For the ferromagnetic insulator we use either yttrium iron garnet, nickel ferrite or magnetite and for the nonferromagnet copper or gold. The spin Hall magnetoresistance effect is theoretically ascribed to the combined action of spin Hall and inverse spin Hall effect in the platinum metal top layer. It therefore should characteristically depend upon the orientation of the magnetization …
We use nanometer-sized point contacts to a Co/Cu spin valve to study the giant magnetoresistance (GMR) of only a few Co domains. The measured data show strong device-to-device differences of the GMR curve, which we attribute to the absence of averaging over many domains. The GMR ratio decreases with increasing bias current. For one particular device, this is accompanied by the development of two distinct GMR plateaus, the plateau level depending on bias polarity and sweep direction of the magnetic field. We attribute the observed behavior to current-induced changes of the magnetization, involv…
The large spin orbit coupling in topological insulators results in helical spin-textured Dirac surface states that are attractive for topological spintronics. These states generate an efficient spin-orbit torque on proximal magnetic moments at room temperature. However, memory or logic spin devices based upon such switching require a non-optimal three terminal geometry, with two terminals for the writing current and one for reading the state of the device. An alternative two terminal device geometry is now possible by exploiting the recent discovery of a unidirectional spin Hall magnetoresista…
We predict two spin-dependent transport phenomena in two-dimensional electron systems, which are induced by spatially fluctuating Rashba spin-orbit interaction. When the electron gas is magnetized, the random Rashba interaction leads to the anomalous Hall effect. An example of such a system is a narrow-gap magnetic semiconductor-based symmetric quantum well. We show that the anomalous Hall conductivity reveals a strongly nonlinear dependence on the magnetization, decreasing exponentially at large spin density. We also show that electron scattering from a fluctuating Rashba field in a two-dimen…
In a Dirac semimetal charges flow between two Weyl nodes when electric and magnetic fields (B||E) are parallel to each other manifesting interesting physical properties such as negative longitudinal magnetoresistance, planar Hall effect and anisotropic magnetoresistance. We observe a co-existence of weak antilocalization with large negative longitudinal magnetoresistance and an unusual Hall resistance with (B||E) configuration, at the conducting interface of LaVO$_3$ and KTaO$_3$. The depth of the conducting channel at the interface is estimated to be around 30 nm by using spectroscopy techniq…
Single-crystal inorganic halide perovskites are attracting interest for quantum device applications. Here we present low-temperature quantum magnetotransport measurements on thin film devices of epitaxial single-crystal CsSnBr$_{3}$, which exhibit two-dimensional Mott variable range hopping (VRH) and giant negative magnetoresistance. These findings are described by a model for quantum interference between different directed hopping paths and we extract the temperature-dependent hopping length of charge carriers, their localization length, and a lower bound for their phase coherence length of ~…
We study the influence of the interface quality of Pt/Y$_3$Fe$_5$O$_{12}$(111) hybrids on their spin Hall magnetoresistance. This is achieved by exposing Y$_3$Fe$_5$O$_{12}$(111) single crystal substrates to different well-defined surface treatments prior to the Pt deposition. The quality of the Y$_3$Fe$_5$O$_{12}$(YIG) surface, the Pt/YIG interface and the Pt layer is monitored \textit{in-situ} by reflection high-energy electron diffraction and Auger electron spectroscopy as well as \textit{ex-situ} by atomic force microscopy and x-ray diffraction. To identify the impact of the different surf…
The magnetotransport properties of disordered ferromagnetic kagome layers are investigated numerically. We show that a large domain-wall magnetoresistance or negative magnetoresistance can be realized in kagome layered materials (e.g. Fe$_3$Sn$_2$, Co$_3$Sn$_2$S$_2$, and Mn$_3$Sn), which show the quantum anomalous Hall effect. The kagome layers show a strong magnetic anisotropy and a large magnetoresistance depending on their magnetic texture. These domain-wall magnetoresistances are expected to be robust against disorder and observed irrespective of the domain-wall thickness, in contrast to c…
We report magnetoresistance measurements on thin Pt bars grown on epitaxial (001) and (111) CoFe2O4 (CFO) ferrimagnetic insulating films. The results can be described in terms of the recently discovered spin Hall magnetoresistance (SMR). The magnitude of the SMR depends on the interface preparation conditions, being optimal when Pt/CFO samples are prepared in situ, in a single process. The spin-mixing interface conductance, the key parameter governing SMR and other relevant spin-dependent phenomena such as spin pumping or spin Seebeck effect, is found to be different depending on the crystallo…
The dynamic coupling between spin and charge currents in non-magnetic conductors is considered. As a consequence of this coupling, the spin dynamics is directly reflected in the electrical impedance of the sample, with a relevant frequency scale defined by spin relaxation and spin diffusion. This allows the observation of the electron spin resonance by purely electrical measurements.
We report on the giant magnetoresistance (GMR) of multiwall carbon nanotubes with ultra small diameters. In particular, we consider the effect of the inter-wall interactions and the lead/nanotube coupling. Comparative studies have been performed to show that in the case when all walls are well coupled to the electrodes, the so-called inverse GMR can appear. The tendency towards a negative GMR depends on the inter-wall interaction and on the nanotube le ngth. If, however, the inner nanotubes are out of contact with one of the electrodes, the GMR remains positive even for relatively strong inter…
Motivated by recent experimental work, we consider spin transport between a normal metal and a gapped quantum paramagnet. We model the latter as the magnonic Mott-insulating phase of an easy-plane ferromagnetic insulator. We evaluate the spin current mediated by the interface exchange coupling between the ferromagnet and the adjacent normal metal. For the strongly interacting magnons that we consider, this spin current gives rise to a spin Hall magnetoresistance that strongly depends on the magnitude of the magnetic field, rather than its direction. This Letter may motivate electrical detectio…
The spin Hall magnetoresistance (SMR) allows to investigate the magnetic textures of magnetically ordered insulators in heterostructures with normal metals by magnetotransport experiments. We here report the observation of the SMR in in-situ prepared ferromagnetic EuO/W thin film bilayers with magnetically and chemically well-defined interfaces. We characterize the magnetoresistance effects utilizing angle-dependent and field-dependent magnetotransport measurements as a function of temperature. Applying the established SMR model, we derive and quantify the real and imaginary parts of the compl…
Electrical resistivities can be different for charge currents travelling parallel or perpendicular to the magnetization in magnetically ordered conductors or semiconductors, resulting in the well-known planar Hall effect and anisotropic magnetoresistance. Here, we study the analogous anisotropic magnetotransport behavior for magnons in a magnetic insulator Y$_{3}$Fe$_{5}$O$_{12}$. Electrical and thermal magnon injection, and electrical detection methods are used at room temperature with transverse and longitudinal geometries to measure the magnon planar Hall effect and anisotropic magnetoresis…
In bilayers consisting of a normal metal (N) with spin-orbit coupling and a ferromagnet (F), the combination of the spin-Hall effect, the spin-transfer torque, and the inverse spin-Hall effect gives a small correction to the in-plane conductivity of N, which is referred to as spin-Hall magnetoresistance (SMR). We here present a theory of the SMR and the associated off-diagonal conductivity corrections for frequencies up to the terahertz regime. We show that the SMR signal has pronounced singularities at the spin-wave frequencies of F, which identifies it as a potential tool for all-electric sp…
We develop a model of the nonlinear response to a DC electrical current of a two dimensional electron system(2DES) placed on a magnetic field. Based on the exact solution of the Schroedinger equation in arbitrarily strong electric and magnetic fields, and separating the relative and guiding center coordinates, a Kubo-like formula for the current is worked out as a response to the impurity scattering. Self-consistent expressions determine the longitudinal and Hall components of the electric field in terms of the DC current. The differential resistivity displays strong Hall field-induced oscilla…
Recent studies evidence the emergence of asymmetric electron transport in layered conductors owing to the interplay between electrical conductivity, magnetization, and the spin Hall or Rashba- Edelstein effects. Here, we investigate the unidirectional magnetoresistance (UMR) caused by the current-induced spin accumulation in Co/Pt and CoCr/Pt bilayers. We identify three competing mechanisms underpinning the resistance asymmetry, namely interface and bulk spin-dependent electron scattering and electron-magnon scattering. Our measurements provide a consistent description of the current, magnetic…
Snake orbits are trajectories of charge carriers curving back and forth which form at an interface where either the magnetic field direction or the charge carrier type are inverted. In ballistic samples their presence is manifested in the appearance of magnetoconductance oscillations at small magnetic fields. Here we show that signatures of snake orbits can also be found in the opposite diffusive transport regime. We illustrate this by studying the classical magnetotransport properties of carbon tubular structures subject to relatively weak transversal magnetic fields where snake trajectories …
Giant magnetoresistance (GMR) material has great potential as next generation magnetic field sensing devices, have magnetic properties and high electrical potential to be developed into various applications such as: magnetic field sensor measurements, current measurements, linear and rotational position sensor, data storage, head recording, and non-volatile magnetic random access memory (MRAM). Today, the new GMR materials based on organic material obtained after allowing for Organic Magnetoresistance (OMAR) was found in OLEDs (organic light-emitting diodes). This organic material is used as a…
