포논 부조화도 제어를 통한 고효율 스핀 열전 디바이스 제작

Abstract

The spin Seebeck effect (SSE) refers to a heat-to-electricity conversion via thermal spin current (or thermal magnon) in a ferromagnet (FM)/normal metal (NM) heterostructure1. As SSE-based thermoelectric (TE) devices offer various advantages due to their transverse geometry2, where the output electrical charge is perpendicular to input heat, they do not require n- and p-type materials pairs. This enables a much simplified device structure compared to conventional Seebeck-based TE devices. Despite their advantages, practical energy harvesting applications of SSE-based devices are challenging due to their low conversion efficiency . The efficiency of SSE is determined by the spin TE figure-of-merit zSSET=SSSE2T/FM, where SSSE is the spin Seebeck coefficient, is the electrical conductivity of NM, FM is the thermal conductivity of FM, and T is the absolute temperature. Therefore, both a high SSSE and FM could lead to a high zSSET. Previous studies have focused on increasing SSSE by improving the interface quality at FM/NM3 or by introducing a normal metal with high spin-to-charge conversion efficiency4. However, little attention has been payed to decreasing FM, as it is strongly entangled with SSSE and is hard to be controlled alone5. Here, we report the enhanced SSE in a multiple-elements-doped iron garnet system (Fig. 1, the SSE performance is evaluated by SSR=SSSE/FM). We propose an explanation for the enhanced signal, which involves the contribution of orbital angular momentum6 on SSSE and increased phonon anharmonicity leading to a decrease in FM7.