Bismuth composition, thickness, and annealing temperature dependence of the spin Seebeck voltage in Bi-YIG films prepared using sol–gel solution and spin-coating method

Abstract

We investigated the Bi composition, film thickness, and annealing temperature (Ta) dependence of the magnitude of the longitudinal spin Seebeck effect (LSSE) voltage in BixY3-x Fe5O12 (0 ≤ x ≤ 1.2) (Bi-YIG) films on a Si substrate, prepared using sol–gel solution and spin-coating methods. The Bi-YIG garnet films exhibited a polycrystalline structure, and the thickness of the film formed by the agglomeration of nanoparticles was approximately 50 nm. The LSSE coefficient (S) of the Bi-YIG/Pt (5 nm) films tends to increase with increasing Bi composition (0 ≤ x ≤ 0.8), and the value of the S at x = 0.8 is 1.7 times larger than that at x = 0. When the Bi composition is 0 ≤ x ≤ 0.8, the values of the saturation magnetization and resistivity are almost constant regardless of x, and the value of the Gilbert damping constant increases with increasing x, while the values of the spin mixing conductance and maximum Kerr rotation angle are tended to increase with increasing x. This result indicates that the increasing tendency of the S occurs because of the induced of effective spin current conversion in the Pt layer thorough Bi-YIG due to the enhancement of interface effect between the Pt and Bi-YIG by Bi substitution. In addition, a large S is obtained in Bi-YIG films annealed at Ta = 973 K because the films contained few cracks and smooth surface conditions.