Abstract
A clear understanding of the temperature evolution of the longitudinal spin Seebeck effect (LSSE) in the classic Pt/yttrium iron garnet (YIG) system and its association with magnetic anisotropy is essential towards optimization of its spin-caloric functionality for spintronics applications. We report here for the first time the temperature dependences of LSSE voltage (VLSSE), magnetocrystalline anisotropy field (HK) and surface perpendicular magnetic anisotropy field (HKS) in the same Pt/YIG system. We show that on lowering temperature, the sharp drop in VLSSE and the sudden increases in HK and HKS at ~175 K are associated with the spin reorientation due to single ion anisotropy of Fe2+ ions. The VLSSE peak at ~75 K is attributed to the HKS and MS (saturation magnetization) whose peaks also occur at the same temperature. The effects of surface and bulk magnetic anisotropies are corroborated with those of thermally excited magnon number and magnon propagation length to satisfactorily explain the temperature dependence of LSSE in the Pt/YIG system. Our study also emphasizes the important roles of bulk and surface anisotropies in the LSSE in YIG and paves a new pathway for developing novel spin-caloric materials.
Highlights
Spin caloritronics based on the spin-Seebeck effect (SSE) is an emerging area of research owing to its potential use in advanced spintronics devices[1,2]
A maximum in VLSSE around 75 K has been reported in both bulk and thin films of YIG9. While this enhancement was explained by the magnon-phonon drag model[8,16], a recent study on the temperature dependences of thermal conductivity (σ) and VLSSE of Yttrium Iron garnet (YIG) has revealed a maximum in σ(T) around 25 K17, which is about 50 K below the VLSSE(T) peak (~75 K)[8,9], questioning about the validity of the existing magnon-phonon drag model
Coupled with the temperature evolution of VLSSE, we show that on lowering temperature, a sudden decrease in VLSSE at ~175 K corresponds to the sudden increases in HK and HKS, arising from the spin reorientation that occurs at the same temperature
Summary
The same sample (single crystal: Y3Fe5O12 or YIG) was used for LSSE and TS measurements. The VLSSE peak at ~75 K is attributed to the surface PMA (HKS) and the MS whose peaks occur in the same temperature range These effects of surface and bulk magnetic anisotropies are corroborated with those of thermally excited magnon number and magnon propagation length to explain the temperature dependence of LSSE in the Pt/YIG system. Our study emphasizes the important role of magnetic anisotropy in the LSSE in YIG and validates the recent theoretical predictions about anisotropic SSE in magnetic materials providing a new pathway for developing novel spin-caloric materials through desired tuning of the magnetic anisotropy
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