Control of spin current by a magnetic YIG substrate in NiFe/Al nonlocal spin valves

Abstract

We study the effect of a magnetic insulator (Yttrium Iron Garnet -YIG ) substrate on the spin transport properties of Ni80Fe20/Al nonlocal spin valve (NLSV) devices. The NLSV signal on the YIG substrate is about 2 to 3 times lower than that on a non magnetic SiO2 substrate, indicating that a significant fraction of the spin-current is absorbed at the Al/YIG interface. By measuring the NLSV signal for varying injector-to-detector distance and using a three dimensional spin-transport model that takes spin current absorption at the Al/YIG interface into account we obtain an effective spin-mixing conductance G ↑↓ 5 − 8 × 1013 Ω −1 m −2 . We also observe a small but clear modulation of the NLSV signal when rotating the YIG magnetization direction with respect to the fixed spin polarization of the spin accumulation in the Al. Spin relaxation due to thermal magnons or roughness of the YIG surface may be responsible for the observed small modulation of the NLSV signal.The coupled transport of spin, charge and heat in nonmagnetic (N) metals deposited on the magnetic insulator Y 3 Fe 5 O 12 (YIG) has led to new spin caloritronic device concepts such as thermally driven spin currents, the generation of spin angular momentum via the spin Seebeck effect (SSE) [1], spin pumping from YIG to metals [2], spin-orbit coupling (SOC) induced magnetoresistance effects [3,4] and the spin Peltier effect, i.e., the inverse of the SSE that describes cooling/heating by spin currents [5]. In these spin caloritronic phenomena, the spinmixing conductance G ↑↓ of the N/YIG interface controls the transfer of spins from the conduction electrons in N to the magnetic excitations (magnons) in the YIG, or vice versa [6][7][8][9][10]. The interconversion of spin current to a voltage employs the (inverse) spin Hall effect in heavymetals such as Pt or Pd. The possible presence of proximity induced magnetism in these metals is reported to introduce spurious magnetothermoelectric effects [11,12] or enhance G ↑↓ [7]. Owing to the short spin-diffusion length λ in these large SOC metals, the applicability of the diffusive spin-transport model is also questionable. Experimental measurements that alleviate these concerns are however scarce and hence are highly required.In this article, we investigate the interaction of spin current (in the absence of a charge current) with the YIG magnetization using the NLSV geometry [13][14][15]. Using a metal with low SOC and long spin-diffusion length allows to treat our experiment using the diffusive spin-transport model. We find that the NLSV signal on the YIG substrate is two to three times lower than that on the SiO 2 substrate, indicating significant spincurrent absorption at the Al/YIG interface. By varying the angle between the induced spin accumulation and the YIG magnetization direction we observe a small but clear modulation of the NLSV signal. We also find that modifying the quality of the Al/YIG interface, using different thin-film deposition methods [4], influences G ↑↓ and hence the size of the spin current...

Competing effects at Pt/YIG interfaces: Spin Hall magnetoresistance, magnon excitations, and magnetic frustration

“…However, the MR expected from magnon excitations is much smaller than from the SMR for the range of temperatures explored here. It has been estimated to be ~16 % at room temperature with respect to the SMR [19,21,25], and that it should vanish at zero temperature [29]. Therefore, this rules out the excitation of magnons as responsible for the unexpected MR measured in Pt/YIG + at low temperatures [see Fig.…”

“…The advantage of using FMIs against metallic ones is that the flow of charge currents is avoided, thus preventing ohmic losses or the emergence of undesired spurious effects. Some phenomena explored in insulating spintronics include the spin pumping [2][3][4][5], the spin Hall magnetoresistance (SMR) [5][6][7][8][9][10][11][12][13][14][15], the spin Seebeck effect [5,[16][17][18], the spin Peltier effect [19], the magnetic gating of pure spin currents [20,21] or the magnon spin transport (MST) [2,[22][23][24][25][26][27][28][29][30].…”

Spin Hall Magnetoresistance as a Probe for Surface Magnetization inPt/CoFe2O4Bilayers

“…Given the interfacial origin of the effect, controlling the quality of the NM/FMI interface is crucial to get an enhanced magnetoresistance effect [27,28]. Although only recently discovered, the SMR has already proven to be a successful approach to quantify the spin-mixing interfacial conductance of NM/FMI bilayers [24,25,27,28], a concept at the base of this and other spin-dependent phenomena such as the spin Seebeck effect [29][30][31][32], the spin pumping [29,[33][34][35] or the magnetic gating of pure spin currents [36,37].…”

Spin injection and detection via the anomalous spin Hall effect of a ferromagnetic metal

“…1(c). The coercive field of our YIG film is approximately 1 mT [15] and any B greater than this value will cause the YIG magnetization (M YIG ) to align parallel to B. On the other hand, the Py strips have a shape anisotropy, which leads to a higher saturation field and to the Py magnetization (M Py ) fully aligning along B only above 50 mT.…”