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, such a symmetry is generally absent from the system itself and only appears for certain parameter values. Without resonant behavior in the topological surface states of a proximitized three-dimensional topological insulator (TI), TAMR measurements can readily distinguish them from often misinterpreted trivial Rashba-like states inherent to many TIs.
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 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 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 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…
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 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…
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…
Injection of spins into semiconductors is essential for the integration of the spin functionality into conventional electronics. Insulating layers are often inserted between ferromagnetic metals and semiconductors for obtaining an efficient spin injection, and it is therefore crucial to distinguish between signatures of electrical spin injection and impurity-driven effects in the tunnel barrier. Here we demonstrate an impurity-assisted tunneling magnetoresistance effect in nonmagnetic-insulator-nonmagnetic and ferromagnetic-insulator-nonmagnetic tunnel barriers. In both cases, the effect refle…
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…
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…
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…
We investigate the effect of the interlayer spin-flip tunneling for the interlayer magnetoresistance under magnetic fields in alpha-(BEDT-TTF)2I3, which is a multilayer massless Dirac fermion system under pressure. The mean field of the spin-flip correlation associated with the interlayer Coulomb interaction enables the interlayer spin-flip tunneling. Assuming the non-vertical interlayer spin-flip tunneling, we calculate the interlayer magnetoresistance using the Kubo formula. The crossover magnetic field, at which the interlayer magnetoresistance changes from positive to negative is shifted b…
Impact of current paths on measurement of tunneling magnetoresistance and spin torque critical current densities in GaMnAs-based magnetic tunnel junctions
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…
Tunneling Magnetoresistance between two ferrromagnets is an issue of fundamental importance in spintronics. In this work, we show that tunneling magnetoresistance can also emerge in junctions composed of ferromagnets and time-reversal invariant topological superconductors without spin-rotation symmetry. Here the physical origin is that when the spin-polarization direction of injected electron from the ferromagnet lying in the same plane of the spin-polarization direction of Majorana zero modes, the electron will undergo a perfect spin-equal Andreev reflection, while injected electrons with oth…
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…
Quantum-well (QW) devices have been extensively investigated in semiconductor structures. More recently, spin-polarized QWs were integrated into magnetic tunnel junctions (MTJs). In this work, we demonstrate the spin-based control of the quantized states in iron $3d$-band QWs, as observed in experiments and theoretical calculations. We find that the magnetization rotation in the Fe QWs significantly shifts the QW quantization levels, which modulate the resonant-tunneling current in MTJs, resulting in a tunneling anisotropic magnetoresistance (TAMR) effect of QWs. This QW-TAMR effect is sizable…
Magnetic silicene superlattices (MSSLs) are versatile structures with spin-valley polarization and tunneling magnetoresistance (TMR) capabilities. However, the oscillating transport properties related to the superlattice periodicity impede stable spin-valley polarization states reachable by reversing the magnetization direction. Here, we show that aperiodicity can be used to improve the spin-valley polarization and TMR by reducing the characteristic conductance oscillations of periodic MSSLs (P-MSSLs). Using the Landauer-Büttiker formalism and the transfer matrix method, we investigate the spi…
By exploiting proximity coupling, we probe the spin state of the surface layers of CrI3, a van der Waals magnetic semiconductor, by measuring the induced magnetoresistance (MR) of Pt in Pt/CrI3 nano-devices. We fabricate the devices with clean and stable interfaces by placing freshly exfoliated CrI3 flake atop pre-patterned thin Pt strip and encapsulating the Pt/CrI3 heterostructure with hexagonal boron nitride (hBN) in a protected environment. In devices consisting of a wide range of CrI3 thicknesses (30 to 150 nm), we observe that an abrupt upward jump in Pt MR emerge at a 2 T magnetic field…
We study the anomalous Hall-like effect (AHLE) and the effective anisotropic magnetoresistance (EAMR) in antiferromagnetic γ -IrMn3/Y3Fe5O12(YIG) and Pt/YIG heterostructures. For γ -IrMn3/YIG, the EAMR and the AHLE resistivity change sign with temperature due to the competition between the spin Hall magnetoresistance (SMR) and the magnetic proximity effect (MPE) induced by the interfacial antiferromagnetic uncompensated magnetic moment. In contrast, for Pt/YIG the AHLE resistivity changes sign with temperature whereas no sign change is observed in the EAMR. This is because the MPE and the SMR …
We theoretically investigate tunneling magnetoresistance (TMR) devices, which are probing the spin-momentum coupled nature of surface states of the three-dimensional topological insulator Bi$_{2}$Se$_{3}$. Theoretical calculations are performed based on a realistic tight-binding model for Bi$_{2}$Se$_{3}$. We study both three dimensional devices, which exploit the surface states of Bi$_{2}$Se$_{3}$, as well as two-dimensional devices, which exploit the edge states of thin Bi$_{2}$Se$_{3}$ strips. We demonstrate that the material properties of Bi$_{2}$Se$_{3}$ allow a TMR ratio at room temperat…
A first-principles study of tunneling magnetoresistance in Fe/MgAl2O4/Fe(001) magnetic tunnel junctions
利用第一性原理计算研究了Fe/MgAl 2 O 4/Fe（001）磁性隧道结的电子结构和弹道电导随自旋的变化.计算得到的Fe/MgAl 2 O 4/Fe（001）MTJ的隧道磁电阻（TMR）比约为160%，远小于相同势垒厚度的Fe/MgO/Fe（001）MTJ的TMR比（1600%）。而在正常尖晶石MgAl 2 O 4的费米能级附近的能隙中存在δ 1对称的倏逝态，表明Fe/MgAl 2 O 4/Fe（001）MTJ中可能存在大的TMR. Fe/MgAl 2 O 4/Fe（001）MTJ的小TMR比是由于Fe电极的面内波矢量（k//）的二维（2-D）布里渊区中的带折叠效应导致的少数自旋态中的新导电沟道。由于MgAl 2 O 4的面内晶胞尺寸是bcc Fe的原始面内晶胞尺寸的两倍，边界边缘的能带被折叠，并且在MgAl 2 O 4势垒中与δ 1倏逝态耦合的少数自旋态出现在k//=0处，这显著降低了MTJ的TMR比。
