Observation of longitudinal spin seebeck voltage in YIG films chemically prepared by co-precipitation and spin coating

Longitudinal spin Seebeck effect (LSSE) of Y₃Fe₅O₁₂ (YIG) thin films chemically prepared on a Si substrate with a SiO₂ surface layer has been investigated with a particular focus on its dependence on the metal (Pt or W) for the capping layer used to carry out the measurements. The YIG films are prepared by a combination of co-precipitation, spin coating, and annealing processes. The structural characterization by X-ray diffraction proves that the films are polycrystalline in a garnet phase with an average crystallite size of 34 nm. The microstructural analyses of the film surface by scanning electron microscopy and scanning probe microscopy show that the roughness R_a of the film is 31 nm. The magnetic easy axis of the YIG films is in the direction parallel to the films. We have found that the polarity of the LSSE voltage V_LSSE measured with a Pt capping layer apparently differs from that observed when a W capping layer is used. The value of V_LSSE increases almost linearly with increasing temperature difference Δ T independent of the choice of metal for the capping layer. The observed LSSE for the polycrystalline YIG films is one order of magnitude smaller than that reported for YIG and Bi:YIG single-crystal samples grown by metal-organic decomposition.