Spin transport properties of BixY3-xFe5O12thin films prepared by spin coating

Yttrium iron garnet (YIG), as a room temperature ferrimagnetic insulator with low damping and narrow ferromagnetic resonance linewidth, has always been the research hotspot of spintronics due to its spin transport properties. Bi is one of the most common doping elements used in YIG, and some works have proved that it can tune the magnetic properties of YIG. Previous studies on Bi<sub>x</sub>Y<sub>3-x</sub>Fe<sub>5</sub>O<sub>12</sub> thin films have focused on the evolution of structure, morphology, and magnetic characteristics. Yet, the effect of Bi<sup>3+</sup>substitution of Y<sup>3+</sup> on spin transport in YIG thin films has not been systematically studied. The regulation of YIG spin transport by doping is expected to provide a new idea for the spintronics exploration of Pt/YIG system. In this work, we prepared a series of Bi<sub>x</sub>Y<sub>3-x</sub>Fe<sub>5</sub>O<sub>12</sub> films with different doping ratios by spin coating. And we investigated the effect of Bi<sup>3+</sup> on morphology, structure and spin transport properties of YIG films. The results show that Bi doping does not change the crystal structure of YIG. Absorption of the films increases and the bandgap decreases with the increase of doping ratio. XPS indicates the co-existence of Bi<sup>3+</sup> and Bi<sup>2+</sup>. The regulation of Bi doping on spin transport is reflected in the fact that the magnon diffusion length of Bi<sub>x</sub>Y<sub>3-x</sub>Fe<sub>5</sub>O<sub>12</sub> films is significantly smaller than that of pure YIG films. Meanwhile, we found that the obvious spin Hall magnetoresistance can still be detected in the Pt/Bi<sub>x</sub>Y<sub>3-x</sub>Fe<sub>5</sub>O<sub>12</sub> heterostructure, and the amplitude is the largest when x=0.3.