We theoretically investigate the angular and spin dependent transport in normal-metal/helical-multiferroic/ferromagnetic heterojunctions. We find a tunneling anisotropic magnetoresistance (TAMR) effect due to the spiral magnetic order in the tunnel junction and to an effective spin-orbit coupling induced by the topology of the localized magnetic moments in the multiferroic spacer.
The predicted TAMR effect is efficiently controllable by an external electric field due to the magnetoelectric coupling.
We study the tunneling magnetoresistance in the ensembles of ferromagnetic granules with random easy axes of magnetic anisotropy taking into account the exchange interaction between granules. It is shown that due to the exchange interaction magnetoresistance is effectively decoupled from magnetization, i.e. the strongest negative magnetoresistance can be observed at the field where magnetization is almost saturated. Under some conditions, the sign of magnetoresistance can be reversed and tunneling magnetoresistance can become positive at certain magnetic fields. Our theory agrees with measurem…
We investigate the tunneling magnetoresistance in magnetic tunnel junctions (MTJs) comprised of Weyl semimetal contacts. We show that chirality-magnetization locking leads to a gigantic tunneling magnetoresistance ratio, an effect that does not rely on spin filtering by the tunnel barrier. Our results indicate that the conductance in the anti-parallel configuration is more sensitive to magnetization fluctuations than in MTJs with normal ferromagnets, and predicts a TMR as large as 10^4 % when realistic magnetization fluctuations are accounted for. In addition, we show that the Fermi arc states…
Using a simple quantum-mechanical model, we explore a tunneling anisotropic magnetoresistance (TAMR) effect in ferroelectric tunnel junctions (FTJs) with a ferromagnetic electrode and a ferroelectric barrier layer, which spontaneous polarization gives rise to the Rashba and Dresselhaus spin-orbit coupling (SOC). For realistic parameters of the model, we predict sizable TAMR measurable experimentally. For asymmetric FTJs, which electrodes have different work functions, the built-in electric field affects the SOC parameters and leads to TAMR dependent on ferroelectric polarization direction. The…
We have studied the influence of the transverse size of a magnetic tunnel nanojunction on the magnitude of the magnetoresistance. During modeling, the size of the right contact was fixed, while the size of the left one gradually changed until they coincided. We found a sharp drop in the tunneling magnetoresistance (TMR) in nanocontacts with mismatched cross section. This can be explained by the peculiarities of the spatial distribution of the electron density, which is different for majority and minority-spin states. The discovered effect must be taken into account in the design of TMR-based n…
We investigated the tunneling anisotropic magnetoresistance (TAMR) in thick hcp Co films at cryogenic temperatures using scanning tunneling microscopy. At around -350 mV, a strong TAMR up to 30\% is found with a characteristic voltage dependence and a reversal of sign. With the help of \textit{ab initio} calculations the TAMR can be traced back to a spin-polarized occupied surface states that experience a strong spin-orbit interaction leading to a magnetization direction depending hybridization with bulk states.
We report on the importance of resonant-tunneling processes on quantum transport through interacting quantum-dot spin valves. To include Coulomb interaction in the calculation of the tunneling magnetoresistance (TMR), we reformulate and generalize the recently-developed, numerically-exact method of iterative summation of path integrals (ISPI) to account for spin-dependent tunneling. The ISPI scheme allows us to investigate weak to intermediate Coulomb interaction in a wide range of gate and bias voltage and down to temperatures at which a perturbative treatment of tunneling severely fails.
We show that a surface acoustic wave (SAW) applied across the terminals of a magnetic tunnel junction (MTJ) decreases both the (time-averaged) parallel and antiparallel resistances of the MTJ, with the latter decreasing much more than the former. This results in a decrease of the tunneling magnetoresistance (TMR) ratio. The coercivities of the free and fixed layer of the MTJ, however, are not affected significantly, suggesting that the SAW does not cause large-angle magnetization rotation in the magnetic layers through the inverse magnetostriction (Villari) effect at the power levels used. Thi…
We investigate magnetoresistance in spin valves involving CoPd-contacted carbon nanotubes. Both temperature and bias voltage dependence clearly indicate tunneling magnetoresistance as the origin. We show that this effect is significantly affected by the tunnel barrier strength, which appears to be one reason for the variation between devices previously detected in similar structures. Modeling the data by means of the scattering matrix approach, we find a non-trivial dependence of the magnetoresistance on the barrier strength. Furthermore, analysis of the spin precession observed in a nonlocal …
Temperature dependence of the tunnel magnetoresistance (TMR) was calculated in range of the quantum-ballistic model in the magnetic tunnel junctions (MTJs) with embedded nanoparticles (NPs). The electron tunnel transport through NP was simulated in range of double barrier approach, which was integrated into the model of the magnetic point-like contact. The resonant TMR conditions and temperature impact were explored in detail. Moreover, the possible reasons of the temperature induced resonant conditions were discussed in the range of the lead-tunneling cell-lead model near Kondo temperature. W…
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…
Nanoscale multifunctional perpendicular organic spin valves have been fabricated. The devices based on an La$_{0.7}$Sr$_{0.3}$MnO$_3$/Alq$_3$/Co trilayer show resistive switching of up to 4-5 orders of magnitude and magnetoresistance as high as -70% the latter even changing sign when voltage pulses are applied. This combination of phenomena is typically observed in multiferroic tunnel junctions where it is attributed to magnetoelectric coupling between a ferromagnet and a ferroelectric material. Modeling indicates that here the switching originates from a modification of the La$_{0.7}$Sr$_{0.3…
Large magnetoresistance effect controlled by electric field rather than magnetic field or electric current is a preferable routine for designing low power consumption magnetoresistance-based spintronic devices. Here we propose an electric-field controlled antiferromagnetic (AFM) tunnel junction with structure of piezoelectric substrate/Mn3Pt/SrTiO3/Pt operating by the magnetic phase transition (MPT) of antiferromagnet Mn3Pt through its magneto-volume effect. The transport properties of the proposed AFM tunnel junction have been investigated by employing first-principles calculations. Our resul…
Resistive and magnetoresistive properties of two samples of compacted powders of ferromagnetic half-metal CrO_{2} with shape anisotropy of nanoparticles were studied. The powders were prepared by the method of hydrothermal synthesis and consisted of needle-like particles with average diameters 24-34 nm and mean length of 300 nm. One of the samples has been made of compacted powder of pure CrO_{2}, while another sample has been prepared from a substitution solid solution Cr_{1-x}Fe_{x}O_{2}. The aim of this work was to study the effect of Fe impurity on the value of tunnel resistance and tunnel…
We experimentally investigate the structural, magnetic and electrical transport properties of La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ based magnetic tunnel junctions with a SrSnO$_3$ barrier. Our results show that despite the large number of defects in the strontium stannate barrier, due to the large lattice mismatch, the observed tunnel magnetoresistance is comparable to tunnel junctions with a better lattice matched STiO$_3$ barrier, reaching values of up to 350% at T=5 K. Further analysis of the current-voltage characteristics of the junction and the bias voltage dependence of the observed tunnel m…
Quantum Oscillations of Tunnel Magnetoresistance Induced by Spin-Wave Excitations in Ferromagnet-Ferromagnet-Ferromagnet Double Barrier Tunnel Junctions
Impact of current paths on measurement of tunneling magnetoresistance and spin torque critical current densities in GaMnAs-based magnetic tunnel junctions
We reveal that the interplay between Rashba spin-orbit coupling and proximity-induced magnetization in a two-dimensional electron gas leads to peculiar transport properties and large anisotropy of magnetoresistance. While the related tunneling anisotropic magnetoresistance (TAMR) has been extensively studied before, we predict an effect with a different origin arising from the evolution of a resonant condition with the in-plane rotation of magnetization and having a much larger magnitude. The resonances in the tunneling emerge from a spin-parity-time symmetry of the scattering states. However,…
We report the precise control of tunneling magnetoresistance (TMR) in devices of self-assembled core/shell Fe$_3$O$_4$/Co$_{1-x}$Zn$_x$Fe$_2$O$_4$ nanoparticles ($0\leq x\leq 1$). Adjusting the magnetic anisotropy through the content of Co$^{2+}$ in the shell, provides an accurate tool to control the switching field between the bistable states of the TMR. In this way, different combinations of soft/hard and hard/soft core/shell configurations can be envisaged for optimizing devices with the required magnetotransport response.
Magnetic multilayer devices that exploit magnetoresistance are the backbone of magnetic sensing and data storage technologies. Here we report novel multiple-spin-filter magnetic tunnel junctions (sf-MTJs) based on van der Waals (vdW) heterostructures in which atomically thin chromium triiodide (CrI3) acts as a spin-filter tunnel barrier sandwiched between graphene contacts. We demonstrate tunneling magnetoresistance which is drastically enhanced with increasing CrI3 layer thickness, reaching a record 19,000% for magnetic multilayer structures using four-layer sf-MTJs at low temperatures. These…
We investigate the thickness and temperature dependence of a series of Ni0:8Fe0:2/Ir0:2Mn0:8 bilayer samples with varying thickness ratio of the ferromagnet/antiferromagnet (tFM/tAFM) in order to explore the exchange coupling strengths in tunneling anisotropic magnetoresistance (TAMR) devices. Specific values of tFM/tAFM lead to four distinct scenarios with specific electric responses to moderate magnetic fields. The characteristic dependence of the measured TAMR signal on applied voltage allows us to confirm its persistence up to room temperature despite an overlapped contribution by a therma…
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…
