Surface magnetic anisotropy-mediated spin Hall magnetoresistance and spin Seebeck effects in a YIG/Pt heterostructure

•Spin Seebeck effect (SSE), Spin Hall magnetoresistance (SMR), and transverse susceptibility (TS) have been studied in YIG/Pt system.•A similar temperature dependence with a peak at ∼ 80 K is observed in SSE, SMR, and surface anisotropy field.•The low-temperature behavior of these effects is related to a non-collinear alignment of bulk and surface spin states in YIG.•Temperature, Field, and thickness dependence of the low-temperature peak is explained through surface anisotropy change. The role of magnon-phonon coupling in the low-temperature behavior of the spin Seebeck effect (SSE) in YIG/Pt has been puzzling for more than a decade. To elucidate the origin of the anomalous peak around 80 K, we investigate the temperature evolution of SSE, spin Hall magnetoresistance (SMR), and magnetic anisotropy in the same YIG/Pt heterostructure. We find that these effects, along with magnetic damping, show the peaks at the same temperature (∼80 K). This simultaneous occurrence, where no heat is applied in the case of SMR, rules out the phonon-magnon drag related origin of SSE in the YIG/Pt system. We further show that the intrinsic surface anisotropy behavior in YIG is responsible for controlling the SSE, SMR, and magnetic damping in the YIG/Pt structure. Our findings not only help to understand these effects fundamentally but also provide an effective way for improving them by manipulating the surface magnetic anisotropy for spin caloritronic applications.