We investigate the impact of pinned antiferromagnetic order on the decoherence of spin current in polycrystalline IrMn. In NiFe/Cu/IrMn/CoFe multilayers, we coherently pump an electronic spin current from NiFe into IrMn, whose antiferromagnetic order is globally pinned by static exchangebias coupling with CoFe. We observe no anisotropic spin decoherence with respect to the orientation of the pinned antiferromagnetic order. We also observe no difference in spin decoherence for samples with and without pinned antiferromagnetic order. Moreover, although there is a pronounced resonance linewidth increase in NiFe that coincides with the switching of IrMn/CoFe, we show that this is not indicative of anisotropic spin decoherence in IrMn. Our results demonstrate that the decoherence of electron-mediated spin current is remarkably insensitive to the magnetization state of the antiferromagnetic IrMn spin sink.A spin current is said to be coherent when the spin polarization of its carriers, e.g., electrons, is locked in a uniform precessional phase. How a spin current loses its coherence, particularly as it interacts with magnetic order, is a crucial fundamental question in spintronics [1]. In a ferromagnetic metal (FM), an electronic spin current polarized transverse to the magnetization dephases quickly in the uniform ferromagnetic exchange field [2,3]. Experiments of ferromagnetic resonance (FMR) spin pumping [4][5][6], where a coherently excited spin current propagates from a FM spin source to a FM spin sink [7], show the transverse spin coherence length in FMs to be as short as ≈1 nm [8]. The dephasing of transverse spin polarization s also gives rise to a spin-transfer torque, ∝ m × s × m, acting on the magnetization m of the FM spin sink [2,3,9,10].For antiferromagnetic metals (AFMs) with staggered exchange fields, a fundamental understanding of spin transport has yet to be developed by experiment. Although the transverse spin coherence length can in principle be 1 nm [11][12][13], an electronic spin current polarized transverse to the antiferromagnetic order parameter (Néel vector l) is expected to dephase in the diffusive limit of transport [12,14]. Such spin dephasing in AFMs generates a spin-transfer torque, ∝ l × s × l [13-15], which may be crucial for emerging antiferromagnetic spintronic technologies [16][17][18][19][20].Furthermore, spin dephasing in an AFM with a uniform Néel vector may yield anisotropic decoherence, where spin absorption by the AFM is enhanced when l ⊥ s [21].By contrast, polycrystalline thin films of AFMs by themselves do not exhibit anisotropic spin decoherence on a macroscopic scale, since the grains contain a distribution of Néel vector orientations that averages out the anisotropy [22]. While polycrystalline AFMs have found commercial applications (i.e., pinning ferromagnetic layers in spin valves) [23] and been used as spin sinks [8,22,[24][25][26][27][28], their nonuniform, unpinned antiferromagnetic order poses a challenge for gaining fundamental insight into spin decoherence.To ali...
How spin-orbit torques emerge from materials with weak spin-orbit coupling (e.g., light metals) is an open question in spintronics. Here, we report on a field-like spin-orbit torque (i.e., in-plane spin-orbit field transverse to the current axis) in SiO2-sandwiched permalloy (Py), with the top Py-SiO2 interface incorporating ultrathin Ti or Cu. In both SiO2/Py/Ti/SiO2 and SiO2/Py/Cu/SiO2, this spin-orbit field opposes the classical Oersted field. While the magnitude of the spin-orbit field is at least a factor of 3 greater than the Oersted field, we do not observe evidence for a significant damping-like torque in SiO2/Py/Ti/SiO2 or SiO2/Py/Cu/SiO2. Our findings point to contributions from a Rashba-Edelstein effect or spin-orbit precession at the (Ti, Cu)-inserted interface.2 An electric current in a material with spin-orbit coupling generally gives rise to a non-equilibrium spin accumulation [1-6], which can then exert torquesi.e., spin-orbit torques (SOTs)on magnetization in an adjacent magnetic medium [7][8][9]. SOTs are often classified into two symmetries: damping-like SOT that either counters or enhances magnetic relaxation, and field-like SOT (or "spin-orbit field") that acts similarly to a magnetic field. Next generations of nanomagnetic computing devices may benefit from an improved understanding of mechanisms for SOTs and the discovery of new thin-film systems enabling large SOTs.While most efforts have focused on conductors known for strong spin-orbit coupling (e.g., 5d transition metals, topological insulators, etc.) [7,8], recent reports have shown SOTs in ferromagnets interfaced with materials that are not expected to exhibit significant spin-orbit coupling [10][11][12][13][14]. For example, a large damping-like SOT has been reported in ferromagnetic Ni80Fe20 (permalloy, Py) interfaced with partially oxidized Cu [10,11]; quantum-interference transport measurements have revealed that Cu with an oxidation gradient can, in fact, exhibit enhanced spin-orbit coupling comparable to that in heavier metals (e.g., Au) [15]. As another example of SOTs that emerge by incorporating seemingly weak spin-orbit materials, Py interfaced with a Ti seed layer and Al2O3 capping layer exhibits a sizable field-like SOT [12]. The key observed features of this spin-orbit field in Ti/Py/Al2O3 [12] are: (1) it points in-plane and transverse to the current axis, irrespective of the magnetization orientation in Py; (2) its magnitude scales inversely with the Py thickness, i.e., it is interfacial in origin; (3) it is modified significantly by the addition of an insertion layer (e.g., Cu) at the Py-Al2O3 interface. Ref. [12] claims that this spin-orbit field is governed by a Rashba-Edelstein effect (REE) [1,5,16,17] at the Py/Al2O3 and Cu/Al2O3 interfaces. However, the complicated stack structures of SiO2(substrate)/Ti/Py/(Cu/)Al2O3 with multiple dissimilar interfaces in Ref.[12] obscure the mechanisms of the spin-orbit field, particularly the roles played by the Ti and Cu layers.Here, by using simpler stack structures, we gain i...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.