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Interconversion between charge and spin through spin-orbit coupling lies at the heart of condensed-matter physics. In normal metal/ferromagnet bilayers, a concerted action of the interconversions, the spin Hall effect and its inverse effect of normal metals, results in spin Hall magnetoresistance, whose sign is always positive regardless of the sig...
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... The MR in the yz-plane is more complicated: beside the SMR effect discussed previously, the geometry size effect (GSE) [38][39][40] in the FM layer also contribute to the MR effect in the yz-plane. However, the GSE-induced MR has the character of R z , R y for the NiFe film, 41 which is different from the situation of R y , R z in this work. Therefore, we believe that the GSE is not the origin of the observed MR in the yz-plane, and it should be ascribed to the SMR effect. ...
Spin–orbit torque provides an efficient strategy for electric manipulation of magnetization. However, Joule heat accompanying with electron motion in the electron-mediated spin current result in unavoidable power dissipation. Moreover, the spin diffusion length in electron-mediated spin current is relatively short, preventing the transmission of spin information over long distances. Magnon-mediated spin current, without moving electrons, can be an excellent alternative to the conventional spin current. Magnon-mediated transfer torque effect has been reported in several previous works. Here, we report the magnon-mediated spin Hall magnetoresistance (SMR) and unidirectional magnetoresistance (UMR) in Pt/NiO/NiFe structures. The significant SMR and UMR were observed in the samples with the NiO thickness up to 60 nm, demonstrating the efficient transmission of magnon-mediated spin current over long distances in the NiO layer. In addition, we observed current-induced in-plane magnetization switching in the NiFe layer via the UMR measurement. These results demonstrated the possibility for developing the efficient spintronic devices operated by magnons.
... 1,2 These include sensors that exploit anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), and tunnel magnetoresistance (TMR). Lately, a spin Hall magnetoresistance (SMR) sensor is demonstrated using spin-orbit torque (SOT) induced field-like effective field as the built-in linearization mechanism, [3][4][5][6][7][8][9][10] which has approximately zero DC offset, negligible hysteresis, and a detectivity of around 1 nT at 1 Hz. 2,10 Pt/NiFe (Py) heterostructures are the core components of SMR sensors, which are substantially facilitated by the use of SOT biasing. ...
... 22 In contrast to the SHE (or the Rashba) effect, the interfacial spin-orbit coupling-induced J s production and its reciprocal impact leads to another negative SMR contribution, which is observed in Ta/Py heterostructures. 9 Moreover, recent theoretical work has shown that the intrinsic SHE is accompanied by a complementary process involving the orbital angular momentum, the so-called orbital Hall effect (OHE), 23 which consists in a flow of orbital momentum perpendicular to the charge current. The theoretical orbital Hall conductivity of light elements is comparable to or even larger than the spin Hall conductivity of Ta, W, and Pt, which provides a strong SHE. ...
... The SHE (or Rashba-induced) effect in HM (HM/FM interface), the geometrical size effect (GSE) of the FM layer, and the anomalous Hall effect (AHE) in FM layers are the known mechanisms that lead to the magneto-transport effect. 9 The GSE is the only one out of them that can produce a negative Δρ xx =ρ xx ; the effect of others are invariably positive. Determining whether the GSE of single Py layers is sufficient to cause the negative Δρ xx =ρ xx of the heterostructures or if an additional as of yet undiscovered mechanism is required is, therefore, necessary. ...
The recent discovery of inherently stable two-dimensional (2D) transition-metal dichalcogenides (TMDs) provides a unique platform for spintronic devices. However, its efficacy for electric detection by spin Hall magnetoresistance (SMR) has not been established yet. In this work, we report on SMR in 2D TMDs/ferromagnet heterostructures, i.e., PtSe2/NiFe (Py), whose magnitude reaches the maximum with bilayer PtSe2. Notably, the SMR value in bilayer PtSe2/Py heterostructures undergoes a sign change with increasing Py thickness. For thinner Py samples, the SMR rapidly decreases with increasing Py thickness, eventually changing from positive to negative. In the case of intermediate Py thicknesses, the SMR consistently exhibits negative behavior. However, for thicker Py samples, the negative SMR values gradually decrease. This complex behavior is attributed to the dominant and competing mechanisms that contribute to SMR, including the spin Hall effect (or Rashba-induced effect) and its inverse effect, the orbital Hall effect and its inverse effect, as well as interfacial spin–orbit-coupling-induced spin-current-to-charge-current conversion. These findings would expand the arsenal for advanced spintronic applications based on 2D TMDs.
... For example, in the nonlocal AHE, charge current transforms to a spin polarized current along the z-polarized direction by spin-dependent interfacial scattering at AlO x /CuO x interface, then it is turned into a transverse charge current by interfacial spin orbital coupling [36]. In SHAHE, interfacial spin or orbital current and their inverse effects lead to negative R AH , which is similar to the recently proposed negative spin Hall magnetoresistance [45]. To intensive understanding the microscopic mechanism of the negative AHE encourages us to set up particularly perspective experiments. ...
An unexpectedly larger current-induced spin-orbit torque in oxidized Cu (CuOx)/Ferromagnet (FM) than heavy-metal/FM has recently attracted intense attention in spintronic studies. Although the two mechanisms, interfacial Rashba Edelstein effect and spin-vorticity coupling, have been put forward based on the two different conductive features of CuOx, i.e., electrical insulator and gradient of electrical mobility, the detailed investigation of transport of CuOx is still lacking. Here we experimentally report the positive and negative anomalous Hall effect in naturally oxidized normal-metal Al/Cu double films. We found that the onset temperature of anomalous Hall effect corresponds to magnetic transition temperature of CuOx. Furthermore, by comparing Hall resistance of the crystalline and amorphous Cu/Al double films, we identify that the positive anomalous Hall resistance attributes to magnetic moment of CuOx itself, while the negative anomalous Hall resistance can originate from the spin or orbital currents generated at the CuOx/AlOx interface interact with magnetization of CuOx and its inverse process.
... They arise due to the influence of SOC on the scattering of electrons in the bulk FM and at its interface(s) [3,30,31]. Therefore, despite the fact that the SMR contribution to MR of the HM/FM bilayers has been reliably proven [32][33][34][35][36], the SOT efficiency estimated in this way can be erroneous [25], since it is difficult to separate out a pure SMR effect [24]. ...
... In spite of the various developed approaches to adapt and extend the theory describing the SMR mechanism to all-metallic bilayers and multilayers (MLs) [32][33][34][35][36][37][38][39][40], heated debate about the origin of the observed MR effects has not subsided for a decade. In general, the SMR mechanism can be distinguished from the AMR one, which is a fundamental magneto-transport property of FMs, by their different angular dependences, since the out-of-plane rotation of magnetization perpendicular to the current changes the resistance according to the SMR mechanism, but does not 4 change it according to the AMR mechanism. ...
... Alternatively, methods such as the Spin Hall Magnetoresistance [133] rely on the anisotropy of the spin current relaxation in a ferromagnet. However, the need for a spin-charge interconversion material strongly complexifies the analysis, while the presence of a charge current flowing in the active part of the device generates strong parasitic signals unrelated to the spin current transport [134]. Finally, the main method used for the measurement of the non-collinear spin transport parameters are FMR based methods such as spin-pumping [135], however without possibility to compare the spin relaxation efficiency in the collinear and non-collinear situations, and strong spin-backflow effects which make impossible the measurement of the spin mixing conductance at the interface between 3d-ferromagnets and low spin conductance materials such as copper. ...
Spin-to-charge current interconversion in non-magnetic systems is based on the spin-orbit coupling. During the past ten years, spintronics has been deeply transformed by the use of this effect. While the spin-to-charge interconversion in conventional spintronics relies on the exchange interaction, this can also be achieved using the strong spin-orbit coupling present in some ferromagnetic materials. The effect of the interplay between the exchange interaction and spin-orbit coupling on the spin transport and interconversion is however not well understood, which for now limits the use of the new functionalities offered by these materials. In addition to the study of the spin-to-charge interconversion in metals, other type of materials such as topological insulators, Rashba interfaces and ferroelectric semi-conductors are being investigated. These systems are appealing for novel spin-logic concepts due to their large spin-orbit-driven spin-to-charge interconversion and multifunctional properties. This thesis focuses on the exploration of spin-to-charge interconversion effects in these materials using various techniques and devices. The first chapter presents the concepts used and developed throughout this thesis, which are the spin transport in metals with the magnetization collinear and transverse to the spin polarization, as well as the conversion of a spin current into a charge current into metals, Rashba interfaces and topological insulators. In the second chapter, the collinear and transverse spin transport properties are measured using lateral spin valves, setting the groundwork for a quantitative characterization of the spin-to-charge interconversion effects in the aforementioned systems. In the third chapter, the effect of the competition between the exchange interaction and the spin-orbit coupling on the spin-to-charge interconversion is evaluated. This is done by measuring the inverse spin Hall effect in ferromagnetic materials across their transition temperature using a spin-pumping ferromagnetic resonance technique, and by rotating the ferromagnet ISHE-material magnetization with respect to the spin current polarization using a novel design of lateral spin valve. The fourth chapter studies the spin-to-charge interconversion in two-dimensional electron gas at interfaces between SrTiO3 and various metals, and in the newly discovered two-dimensional electron gas at the metal-KTaO3 interface using spin-pumping measurements. Finally, the fifth chapter discuss the local detection of the interconversion in the context of recently proposed spin-logic devices. In the first part of this last chapter, the optimization of the interconversion voltage output required for magnetoelectric spin-orbit devices is studied in platinum, through interface engineering and by performing local detection of the interconversion in the topological insulator Sb2Te3. In the second part, the patterning of such local interconversion devices using the ferroelectric Rashba semiconductor GeTe and the two-dimensional electron gas present at the metal-SrTiO3 interfaces is performed, with an opening toward their use for the recently proposed ferroelectric spin-orbit device.
... The blue and red lines represent the dampinglike and fieldlike SOTs, which are given by the real and imaginary parts of t F T , respectively. The parameters used [72][73][74][75] are as follows: ...
We theoretically investigate spin-orbit torques in insulator/ferromagnet/normal-metal structures with a focus on interfacial spin-orbit coupling effect at an insulator/ferromagnet interface. Based on the spin drift-diffusion formalism generalized to consider transverse spin currents in a ferromagnet and the boundary condition to consider transverse spin currents leaving from a ferromagnet, we find that interfacial spin-orbit coupling at the insulator/ferromagnet interface contributes to dampinglike spin-orbit torque, which is important for current-driven magnetization dynamics, even when the interfacial spin-orbit coupling generates the only fieldlike component. We also calculate spin-orbit torques in a single ferromagnet sandwiched by two dissimilar insulators, which provides additional information about interfacial spin-orbit interaction at insulator/ferromagnet interfaces.
... On the other hand, the smaller AMR 0 or C 2 of Pt(3 nm)/c 0 -Fe 4 N(t Fe4N 6 nm) bilayers may be related to the MPE-induced interfacial Pt local moments, which has been reported in other HM/FM bilayers, such as W/YIG, 35 Pt/Co, 36 and Ta/NiFe. 9 Assuming that "the smaller AMR 0 is related to the interfacial Pt local moments" is true, the AMR 0 -T behavior of Pt(3 nm)/ c 0 -Fe 4 N(t Fe4N 6 nm) bilayers should be consistent with that of single c 0 -Fe 4 N films. 32 According to Eq. (4), the C 2h and C 4h of the single c 0 -Fe 4 N film are tightly associated with the magnetization components of the c 0 -Fe 4 N layer, where the AMR 0 -T behavior is consistent with that of the M S -T dependence. ...
The conversion between charge and spin through spin–orbit coupling (SOC) is critical in heavy nonmagnetic metal/ferromagnetic metal systems. Here, both the single γ′-Fe4N films and the epitaxial Pt/γ′-Fe4N bilayers were fabricated by facing-target sputtering. In the Pt(3 nm)/γ′-Fe4N(tFe4N ≤ 6 nm) bilayers, the anisotropy magnetoresistance (AMR) exhibits an “M” shape, which is opposite to that of the single γ′-Fe4N film with a “W” shape. Meanwhile, the planar Hall resistivity (PHR) reversal also appears. The inversion of AMR and PHR after capping a 3-nm-thick Pt layer on the γ′-Fe4N layer is mainly determined by the interfacial effect, in which the magnetic-proximity-effect induced the interface Pt local moments and the inverse-spin-Hall-effect caused the reflected spin-current to charge-current conversion. Our work helps to understand the interfacial SOC effects and has potential application in the field of magnetic sensors.
Unidirectional magnetoresistance (UMR) has garnered extensive attention for its rich physics and potential applications. The prevailing belief is that indispensable ferromagnetic films serve as scattering sources of polarized electrons or that noncentrosymmetric systems cause spin band splitting, driving most research toward ferromagnet/normal-metal bilayer films or nonmagnetic Rashba systems. However, our observations reveal a significant UMR in bilayer films consisting solely of the oxidized light metal Al/Cu. Remarkably, the UMR signal of 0.073% is approximately one order of magnitude larger than that of most structures. Such a UMR is attributed to the dual functionality of copper oxide, which not only generates polarized electrons—a recognized function—but also scatters these electrons in a weak magnetization manner. Our findings provide a fresh strategy to generate the UMR, facilitating its application through the use of more readily available materials.
The electrical detection of spin and orbital angular momentum usually requires the utilization of a ferromagnetic metal (FM). When an angular momentum is generated in a light metal (LM), for example, through the orbital Hall effect, a bilayer system that consists of the LM/FM is commonly used to study the effect. In this work, by studying the magnetoresistance in the zirconium/nickel bilayer, a typical LM/FM bilayer structure, we observe a negative angular dependent magnetoresistance (ADMR) in the β scan direction. Through analysis, we exclude the contributions from the bulk effects and their combinations, such as the spin Hall effect and orbital Hall effect in zirconium, and the anomalous Hall effect in nickel. Instead, we attribute the negative ADMR to the interfacial spin-orbit coupling, which is caused by the imbalanced spin transmission and reflection at the interface. Our observation highlights the nontrivial contribution from the spin transport at the interface, which has often been overlooked in the study of the bulk effects in LM/FM bilayers.
