Abstract
We have studied spin transport and magnetoresistance in yttrium iron garnet (YIG)/NiO/Pt trilayers with varied NiO thickness. To characterize the spin transport through NiO we excite ferromagnetic resonance in YIG with a microwave frequency magnetic field and detect the voltage associated with the inverse spin-Hall effect (ISHE) in the Pt layer. The ISHE signal is found to decay exponentially with the NiO thickness with a characteristic decay length of 3.9 nm. This is contrasted with the magnetoresistance in these same structures. The symmetry of the magnetoresistive response is consistent with spin-Hall magnetoresistance (SMR). However, in contrast to the ISHE response, as the NiO thickness increases the SMR signal goes towards zero abruptly at a NiO thickness of ≃ 4 nm, highlighting the different length scales associated with the spin-transport in NiO and SMR in such trilayers.
Highlights
We investigate spin transport through NiO layers with varied thickness at room temperature by exciting ferromagnetic resonance (FMR) in yttrium iron garnet (YIG) and detecting the voltage signal across the Pt film associated with the inverse spin Hall effect (ISHE)
A comparison of these results shows that the ISHE signal decreases monotonically as a function of NiO thickness, while the spin-Hall magnetoresistance (SMR) vanishes abruptly at a thickness of about 4 nm
A peak in the ISHE voltage signal is seen at the resonance field of the YIG. (The FMR absorption data is not shown.) There is a minor peak which is most likely due to inhomogneity in our extend film samples
Summary
Antiferromagnets have attracted a great deal of attention in spintronics because of their unique properties, such as a low magnetic susceptibility and terahertz spin dynamics.[1,2] In metallic antiferromagnet-based spintronics, electrical switching of the antiferromagnetic domains in CuMnAs was successfully performed[3] and spin pumping studies have demonstrated spin injection into IrMn.[4,5] In oxide spintronics, ferromagnet (FM)/antiferromagnet (AFM)/heavy metal trilayer structures have been used to study spin-transport in insulating antiferromagnets.[6,7,8,9,10,11,12,13] Experimental techniques include microwave-field-induced magnetization precession in the FM to generate a spin-current in the AFM and the inverse spin Hall effect (ISHE) in the heavy metal to convert the spin-current transmitted through the AFM into a voltage.[6,7,8,14] Such experimental studies have shown that NiO can be an efficient spin-conductor. A theoretical model has been proposed that explains these experimental results by spin-currents conducted by evanescent spin-waves in NiO.[15,16] In similar structures, YIG/NiO/Pt, the spin-Hall magnetoresistance (SMR) has been measured as a function of temperature. Results suggest that NiO can suppress the magnetic proximity effect measured in a 3 nm thick Pt layer and were further interpreted to indicate spin-transport between Pt and YIG through NiO layers.[14]. These two types of experiments have not been conducted on the same samples as a function of the NiO thickness.
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