LSMO/Pt双层体系中意外弱吉尔伯特阻尼的起源
Origin of unexpected weak Gilbert damping in the LSMO/Pt bilayer system
AI总结：
本文通过第一性原理与半经典分析揭示LSMO/Pt双层阻尼低于单层LSMO的成因，指出Pt分流抑制自诱导逆自旋霍尔效应，并提出通过调控自旋霍尔电导率比和自旋扩散长度来设计低损耗自旋轨道电子学异质结构的策略。
摘要：
本研究对La$_{0.7}$Sr$_{0.3}$MnO$_3$（LSMO）薄膜的吉尔伯特阻尼大于LSMO/Pt双层这一令人困惑的现象进行了第一性原理和半经典分析，该现象与传统的自旋泵浦预期相反。采用Wannier插值的密度泛函理论得到LSMO的本征阻尼为$α_{\mathrm{int}}^{\mathrm{LSMO}}\\!\approx\\!1.4\times10^{-3}$，支持高实验值来源于外禀机制。基于LSMO中已证实的自诱导逆自旋霍尔效应（ISHE）[Gupta et al., Phys. Rev. B 109, 014437 (2024)]，我们认为LSMO的大自旋霍尔角$|θ_{\mathrm{SH}}|\simeq 0.093$和低纵向电导率使得自旋流到电荷流的高效转换成为可能，从而增强了有效阻尼。在LSMO/Pt异质结构中，Pt覆盖层对电荷流产生分流作用，提高了$σ_{xx}$并将界面$|θ_{\mathrm{SH}}|$降低至约0.007。基于层分辨从头算自旋积累的Valet-Fert分析给出了Pt的自旋扩散长度和一个不可忽略的反阻尼自旋轨道矩（SOT）系数，定性地解释了在电流偏置下观测到的阻尼降低。因此，这一看似反常的阻尼层级关系无需引入额外的界面机制即可得到调和。在此背景下，决定自旋泵浦归一化的不同长度尺度至关重要，即单个LSMO薄膜中自泵浦所涉及的短吸收深度与适用于LSMO/Pt双层的完整磁性厚度。这一观察结果提出了一种实用的设计策略：通过同时调控自旋霍尔电导率与纵向电导率之比以及自旋扩散长度，可以设计出磁性损耗最小化的异质结构，用于自旋轨道电子学应用。
英文摘要：
This study presents a first-principles and semiclassical analysis of the puzzling observation that a La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) thin film exhibits larger Gilbert damping than an LSMO/Pt bilayer, contrary to conventional spin-pumping expectations. Density functional theory with Wannier interpolation yields an intrinsic damping of $α_{\mathrm{int}}^{\mathrm{LSMO}}\!\approx\!1.4\times10^{-3}$, supporting an extrinsic origin of the high experimental value. Guided by the self-induced inverse spin Hall effect (ISHE) demonstrated in LSMO [Gupta et al., Phys.Rev. B 109, 014437 (2024)], we argue that the large spin Hall angle $|θ_{\mathrm{SH}}|\simeq 0.093$ and low longitudinal conductivity of LSMO enable an efficient conversion of spin current to charge current boosting the effective damping. In the LSMO/Pt heterostructure the Pt cap shunts the charge current, raising $σ_{xx}$ and reducing the interfacial $|θ_{\mathrm{SH}}|$ to~0.007. A Valet-Fert analysis for layer-resolved ab-initio spin accumulation gives the Pt spin-diffusion length and a non-negligible antidamping SOT coefficient, qualitatively accounting for the observed damping reduction under current bias. The seemingly anomalous damping hierarchy is thus reconciled without invoking additional interfacial mechanisms. The distinct length scales governing spin-pumping normalization, namely, the short absorption depth relevant to self-pumping in a single LSMO film versus the full magnetic thickness applicable to an LSMO/Pt bilayer, are crucial in this context. This observation suggests a practical design strategy: by simultaneously tuning the spin Hall-to-longitudinal conductivity ratio and the spin-diffusion length, one can engineer heterostructures with minimized magnetic losses for spin-orbitronics applications.
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