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Register a new userQuantitative study of the spin Hall magnetoresistance in ferromagnetic insulator/normal metal hybrids
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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 in the adjacent ferromagnet, and prevail even if an additional, nonferromagnetic metal layer is inserted between Pt and the ferromagnet. Our experimental data corroborate these theoretical conjectures. Using the spin Hall magnetoresistance theory to analyze our data, we extract the spin Hall angle and the spin diffusion length in platinum. For a spin mixing conductance of $4times10^{14};mathrm{Omega^{-1}m^{-2}}$ we obtain a spin Hall angle of $0.11pm0.08$ and a spin diffusion length of $(1.5pm0.5);mathrm{nm}$ for Pt in our thin film samples.
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Spin-dependent transport at heavy metal/magnetic insulator interfaces is at the origin of many phenomena at the forefront of spintronics research. A proper quantification of the different interfacial spin conductances is crucial for many applications. Here, we report the first measurement of the spin Hall magnetoresistance (SMR) of Pt on a purely ferromagnetic insulator (EuS). We perform SMR measurements in a wide range of temperatures and fit the results by using a microscopic model. From this fitting procedure we obtain the temperature dependence of the spin conductances ($G_s$, $G_r$ and $G_i$), disentangling the contribution of field-like torque ($G_i$), damping-like torque ($G_r$), and spin-flip scattering ($G_s$). An interfacial exchange field of the order of 1 meV acting upon the conduction electrons of Pt can be estimated from $G_i$, which is at least three times larger than $G_r$ below the Curie temperature. Our work provides an easy method to quantify this interfacial spin-splitting field, which play a key role in emerging fields such as superconducting spintronics and caloritronics, and topological quantum computation.
We measure electrically detected ferromagnetic resonance in microdevices patterned from ultra-thin Co/Pt bilayers. Spin pumping and rectification voltages are observed and distinguished via their angular dependence. The spin-pumping voltage shows an unexpected increase as the cobalt thickness is reduced below 2 nm. This enhancement allows more efficient conversion of spin to charge current and motivates a theory modelling the dependence of impurity scattering on surface roughness.
We observe an unusual behavior of the spin Hall magnetoresistance (SMR) measured in a Pt ultra-thin film deposited on a ferromagnetic insulator, which is a tensile-strained LaCoO3 (LCO) thin film with the Curie temperature Tc=85K. The SMR displays a strong magnetic-field dependence below Tc, with the SMR amplitude continuing to increase (linearly) with increasing the field far beyond the saturation value of the ferromagnet. The SMR amplitude decreases gradually with raising the temperature across Tc and remains measurable even above Tc. Moreover, no hysteresis is observed in the field dependence of the SMR. These results indicate that a novel low-dimensional magnetic system forms on the surface of LCO and that the Pt/LCO interface decouples magnetically from the rest of the LCO thin film. To explain the experiment, we revisit the derivation of the SMR corrections and relate the spin-mixing conductances to the microscopic quantities describing the magnetism at the interface. Our results can be used as a technique to probe quantum magnetism on the surface of a magnetic insulator.
We theoretically examine the spin-transfer torque in the presence of spin-orbit interaction (SOI) at impurities in a ferromagnetic metal on the basis of linear response theory. We obtained, in addition to the usual spin-transfer torque, a new contributioin $sim {bm j}_{rm SH}^{phantom{dagger}} cdot abla {bm n}$ in the first order in SOI, where ${bm j}_{rm SH}^{phantom{dagger}}$ is the spin Hall current driven by an external electric field. This is a reaction to inverse spin Hall effect driven by spin motive force in a ferromagnet.
Pure spin currents, i.e. the transport of angular momentum without an accompanying charge current, represent a new, promising avenue in modern spintronics from both a fundamental and an application point of view. Such pure spin currents can not only flow in electrical conductors via mobile charge carriers, but also in magnetically ordered electrical insulators as a flow of spin excitation quanta. Over the course of the last years remarkable results have been obtained in heterostructures consisting of magnetically ordered insulators interfaced with a normal metal, where a pure spin current flows across the interface. This topical review article deals with the fundamental principles, experimental findings and recent developments in the field of pure spin currents in magnetically ordered insulators. We here put our focus onto four different manifestations of pure spin currents in such heterostructures: The spin pumping effect, the longitudinal spin Seebeck effect, the spin Hall magnetoresistance and the all-electrical detection of magnon transport in non-local device concepts. In this article, we utilize a common theoretical framework to explain all four effects and explain important material systems (especially rare-earth iron garnets) used in the experiments. For each effect we introduce basic measurement techniques and detection schemes and discuss their application in the experiment. We account for the remarkable progress achieved in each field by reporting the recent progress in each field and by discussing research highlights obtained in our group. Finally, we conclude the review article with an outlook on future challenges and obstacles in the field of pure spin currents in magnetically ordered insulator / normal metal heterostructures.
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