Impact of the interface quality on the spin Hall magnetoresistance in Pt/YIG hybrids

For the generation and detection of pure spin currents via the (inverse) spin Hall effect, a combination of a non-ferromagnetic metal and an insulating magnet is required. In this context platinum (Pt) thin films grown on yttrium iron garnet (Y3Fe5O12, YIG) serve as prototype structures [1-3]. Recently, the influence of the Pt/YIG interface quality on the spin Hall effect came into focus and the importance of improving the surface quality of YIG was discussed [4-6].We present a systematic study of Pt thin film growth on YIG single crystals correlating the interface quality of the Pt/YIG bilayers to spin Hall magnetoresistance (SMR) measurements. Prior to the Pt deposition, which was carried out by thermal evaporation under UHV conditions, YIG crystals were exposed to different surface treatments. The sample quality was controlled in-situ by Auger-electron- spectroscopy, reflection high/low energy electron diffraction as well as ex-situ by X- ray reflectivity and atomic force microscopy.Best Pt thin films were achieved using YIG crystals treated with Piranha solution followed by annealing in oxygen prior to the thin film growth. In these samples a SMR value of about 4·10-4 was achieved, which is close to the SMR effect of respective Pt/YIG samples with in-situ interfaces [3]. Growing Pt thin films at higher temperature increases the thin film roughness as well as the interdiffusion of Pt and YIG. However, by utilizing X-ray magnetic circular dichroism, no induced magnetic moment could be detected neither in Pt thin films on YIG substrates fabricated at room temperature nor at 500°C. This result is in agreement with earlier measurements on Pt/YIG thin films [7].References[1] H. Nakayama et al., Phys. Rev. Lett. 110, 206601 (2013)[2] Y. Sun et al., Phys. Rev. Lett. 111, 106601 (2013)[3] M. Althammer et al., Phys. Rev. B 87, 224401 (2013)[4] M. B. Jungfleisch et al., Appl. Phys. Lett. 103, 022411 (2013)[5] Z. Qiu, et al., Appl. Phys. Lett. 103, 09404 (2013)[6] A. Aqeel et al., J. Appl. Phys. 116, 15703 (2014).[7] S. Geprägs, et al., Appl. Phys. Lett. 101, 262407 (2012)