钒四氰乙烯（V[TCNE]$_x$，$x \sim 2$）中的磁振子扩散长度与纵向自旋塞贝克效应
Magnon Diffusion Length and Longitudinal Spin Seebeck Effect in Vanadium Tetracyanoethylene (V[TCNE]$_x$, $x \sim 2$)
AI总结：
本文扩展自旋塞贝克效应理论以纳入磁振子非守恒过程，并在分子基亚铁磁半导体V[TCNE]$_x$中观测到SSR，证实其具有室温下超长磁振子扩散长度与寿命。
摘要：
自旋电子学、自旋热电子学和磁振子学现象源于电荷、自旋和结构自由度之间的复杂相互作用，这些相互作用难以建模，更难以预测。具有相关功能的磁有序材料相对稀缺，使这一情况进一步复杂化，导致该领域严重局限于少数经过充分研究的体系，而这些体系并未涵盖基础理论所预言的全部现象学相空间。在此，我们展示了这一理论与实验耦合挑战中的一项重要进展：我们扩展了现有的自旋塞贝克效应（SSE）理论，以显式纳入磁振子非守恒过程的温度依赖性。这一扩展理论定量描述了此前在支柱材料钇铁石榴石（YIG）中测得的SSE信号的低温行为，并预言了具有低饱和磁化强度$M_S$和超低阻尼的磁振子与自旋电子材料的一个新区域。最后，我们通过在分子基亚铁磁半导体钒四氰乙烯（V[TCNE]$_x$，$x \sim 2$）中直接观测自旋塞贝克电阻（SSR）来验证这一预言。这些结果验证了扩展理论：所得SSR信号在幅值上与YIG相当，并且为V[TCNE]$_x$提取出的磁振子扩散长度（$λ_m>1$ μm）和磁振子寿命（$τ_{th}\approx 1-10$ μs）超过YIG（$τ_{th}\sim 10$ ns）。令人惊讶的是，尽管自旋波刚度（交换作用）相对较低，这些性质仍持续保持至室温。对高效SSE活性材料这一新区域的确认，为面向自旋电子学和磁振子学应用的一类新型磁性材料打开了大门。
英文摘要：
Spintronic, spin caloritronic, and magnonic phenomena arise from complex interactions between charge, spin, and structural degrees of freedom that are challenging to model and even more difficult to predict. This situation is compounded by the relative scarcity of magnetically-ordered materials with relevant functionality, leaving the field strongly constrained to work with a handful of well-studied systems that do not encompass the full phase space of phenomenology predicted by fundamental theory. Here we present an important advance in this coupled theory-experiment challenge, wherein we extend existing theories of the spin Seebeck effect (SSE) to explicitly include the temperature-dependence of magnon non-conserving processes. This expanded theory quantitatively describes the low-temperature behavior of SSE signals previously measured in the mainstay material yttrium iron garnet (YIG) and predicts a new regime for magnonic and spintronic materials that have low saturation magnetization, $M_S$, and ultra-low damping. Finally, we validate this prediction by directly observing the spin Seebeck resistance (SSR) in the molecule-based ferrimagnetic semiconductor vanadium tetracyanoethylene (V[TCNE]$_x$, $x \sim 2$). These results validate the expanded theory, yielding SSR signals comparable in magnitude to YIG and extracted magnon diffusion length ($λ_m>1$ $μ$ m) and magnon lifetime for V[TCNE]$_x$ ($τ_{th}\approx 1-10$ $μ$ s) exceeding YIG ($τ_{th}\sim 10$ ns). Surprisingly, these properties persist to room temperature despite relatively low spin wave stiffness (exchange). This identification of a new regime for highly efficient SSE-active materials opens the door to a new class of magnetic materials for spintronic and magnonic applications.
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