Optimizing the spin-pumping induced inverse spin Hall voltage by crystal growth in Fe/Pt bilayers

Abstract

We examine the influence of crystal growth on the spin-pumping induced inverse spin Hall effect in Fe/Pt bilayers. The morphology of the Fe/Pt interface influences the effective spin mixing conductance. The increase of growth temperature leads to smoother and larger grains at the interface that enhance the effective spin mixing conductance. The spin current injection efficiency into Pt, measured by the inverse spin Hall effect, is maximized by optimizing the epitaxy of Pt on Fe. In magnetic field dependent measurements, the presence of a strong magnetic anisotropy gives rise to two distinct inverse spin Hall effect voltage peaks.Magnon spintronics -an emerging sub-field of spintronics in which magnons, the quasi-particles of the magnetization dynamics, are used as information carriershas attracted considerable attention in the last years. 1,2 A powerful method to detect magnons is the combination of spin pumping and the inverse spin Hall effect. The spin-pumping effect allows for the injection of a spin current from a ferromagnetic (FM) layer into an attached non-magnetic metal (NM) layer. 3 This spin current is subsequently transformed into a charge current by the inverse spin Hall effect (ISHE). 1,4 Many aspects of magnetization dynamics in FM/NM bilayers have been investigated by means of spin pumping and ISHE in various kinds of materials. 5 A prominent material combination is Ni 80 Fe 20 (Py) and Pt bilayers. 6,7 In these kind of metallic heterosystems, the dependencies of the spin-pumping induced ISHE voltage on the saturation magnetization and the damping constant, 8 on the geometry 6 and on the thicknesses of the individual layers 9 have been investigated. Recently, it has been shown that the spin-pumping mechanism is even applicable in insulating FM/NM bilayers like YIG/Pt (YIG:yttrium iron garnet). 2,10-18 Investigations on standing 18 as well as propagating 17 magnons in a wide range of wavelengths 15,16 by a combination of spin pumping and ISHE have been performed. Furthermore, the YIG and Pt thickness dependence on the ISHE-voltage from spin pumping 12-14 and nonlinear spin pumping 11 has been observed.Although spin pumping is an interfacial effect, the manner in which it, and therefore the ISHE signal strength, is affected by the structural parameters of the interface have so far not been investigated in detail. Recently, the role of the cleanliness of the YIG suface, 10 and the crystal perfection of YIG 19 in the YIG /Pt system proved the great importance of the interface properties. However in metallic systems the study of the influence of a) FIG. 1. (left) Schematic diagram of the sample structure with the corresponding thicknesses. Ferromagnetic resonance is excited by a microwave magnetic field induced by a Cu microstrip antenna and a tunable magnetic external field (Hext) while a silicon oxide plate isolates the Pt from the Cu antenna. (right) Scheme of the geometry used for FMR and ISHE measurements.the growth modes is limited. For example, it is not clear to what extend the polycrystalline n...

Control of the spin to charge conversion using the inverse Rashba-Edelstein effect

“…The obtained dispersion relation of epitaxial Fe films is in very good agreement with the one previously determined by ISH measurements in Fe/Pt stacks. 12 The estimation of the spin Hall angle in bismuth can be extracted from the Bi thickness dependence of the ISH voltage in the stacks Fe(10 nm)/FeO X (%2 nm)/Bi(t). This is plotted in Figure 3(a) where ISH voltages were measured at 9.46 GHz and 15 dBm for Bi thickness between 7 and 24 nm.…”

Inverse spin-Hall effect voltage generation by nonlinear spin-wave excitation

“…It is known from the literature that the perpendicular orientation between the static magnetic field that is parallel to the easy axis of the permalloy rectangles and the high-frequency field in combination with the position of the voltage contacts allow for an optimum ratio between symmetric and asymmetric voltage contributions [9,11,13,14,16,17]. Exemplary transport measurements can be seen in Figs for the extrema of the voltage are matching very well.…”

“…An evaluation of the voltage maxima revealed no qualitative changes, only a slight shift of the voltage surge towards smaller high-frequency fields for the sample with the increased width and towards larger high-frequency fields for the sample with nonperpendicularly oriented edges occurs. Indeed, ISHE voltages up to a few microvolts have been reported before [9][10][11][12][13][14][15][16][17]. However, the lateral dimensions of the bilayers used there are typically one or two orders of magnitude larger than the ones used here.…”

“…Similar transport measurements have been reported before, e.g., in Refs. [9][10][11][12][13][14][15][16][17]. In these publications a linear (quadratic) relation between the excitation power (field amplitude) and the measured voltage was found.…”

“…This effect can be linked with our measurements via micromagnetic simulations and our FMR measurements. In the strong excitation regime, the current density reached in our mesoscopic device is two orders of magnitude larger than the ones in the conventional millimeter-sized ISHE experiments [9][10][11][12][13][14][15][16][17].…”