The spin Seebeck effect (SSE) refers to a direct energy conversion of heat to electricity that exploits magnon current in a ferromagnet (FM)/normal metal (NM) heterostructure. Since SSE is a transverse thermoelectric effect, it can be employed to realize transverse thermoelectric devices, which could potentially overcome the inherent limitations of conventional Seebeck effect-based devices. Yet, the widespread use of SSE is currently hindered by its low conversion efficiency. The thermoelectric efficiency of SSE can be improved through an optimization of bulk FM as well as FM/NM interface. A bulk FM can enhance the thermoelectric efficiency by introducing a ‘phonon-glass magnon-crystal’ concept, wherein scattering centers selectively scatter the heat-carrying phonons while not affecting the magnons that contribute to SSE. A high-quality FM/NM interface can boost the spin pumping across the interface as well as the electrical transport in NM. Here, by adopting polycrystalline nickel-ferrite (NFO)/Pt as a platform, we demonstrate the successful optimization of bulk FM together with FM/NM interface via a simple heat treatment scheme. The phase separation of NFO via such heat treatment results in a distinctive hierarchical microstructure of nano-sized NFO embedded in micro-sized NiO precipitates; this structure selectively scatters phonons while barely affecting magnons, leading to reduced thermal conductivity without variation of spin Seebeck coefficient. The simultaneous formation of a clean and smooth NFO/Pt interface provides efficient spin pumping at the interface and high electrical conductivity of Pt. As a result, the energy conversion efficiency of SSE in NFO/Pt system can be significantly improved. The proposed facile approach can be applied to design highly efficient oxide-based SSE devices.

中文翻译：

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通过同时优化体积和界面特性来设计基于自旋塞贝克的热电器件

自旋塞贝克效应（SSE）指的是将热量直接转化为电能的过程，该过程利用铁磁体（FM）/普通金属（NM）异质结构中的磁振电流。由于SSE是横向热电效应，因此可以用来实现横向热电器件，这可以潜在地克服常规基于Seebeck效应的器件的固有局限性。然而，SSE的低转换效率目前阻碍了SSE的广泛使用。通过优化整体FM以及FM / NM接口，可以提高SSE的热电效率。块状FM可以通过引入“声子-玻璃马格诺晶体”概念来提高热电效率，其中散射中心选择性地散射载热的声子，而不会影响构成SSE的马格诺斯。高质量的FM / NM接口可以促进自旋泵通过接口以及NM中的电传输。在这里，通过采用多晶镍铁氧体（NFO）/ Pt作为平台，我们展示了成功优化块体FM和FM / NM接口通过简单的热处理方案。通过这样的热处理，NFO发生相分离，从而形成嵌入微米级NiO沉淀物中的纳米级NFO独特的分层微观结构。这种结构在不影响磁振子的情况下选择性地散射声子，从而导致热导率降低而自旋塞贝克系数不变。同时形成干净，光滑的NFO / Pt界面可在界面处提供有效的自旋泵浦，并提供Pt的高电导率。结果，可以显着提高NFO / Pt系统中SSE的能量转换效率。所提出的简便方法可用于设计高效的基于氧化物的SSE器件。