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Spin currents probed by magnetic circular dichroism in X-ray absorption spectroscopy (XMCD) - a theoretical study

X 射线吸收光谱 (XMCD) 中磁圆二色性探测自旋电流 - 理论研究

基本信息

批准号：
327501276
负责人：
Professor Dr. Hubert Ebert
金额：
--
依托单位：
Department Chemie
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2016
资助国家：
德国
起止时间：
2015-12-31 至 2020-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/327501276?language=en
关键词：
Spin currents probed magnetic circular

项目摘要

The theory project aims to supply an ab-initio description of XMCD (X-ray magnetic circular dichroism in X-ray absorption) experiments used to monitor dynamical magnetic properties in the field of spintronics. The focus will be on experiments that monitor spin currents induced by an electric field (EFI-XMCD) or ferromagnetic resonance (FMR-XMCD) as well as the motivation of new experiments. All numerical work will be based on local spin density functional theory (LSDA) and its extensions with the electronic structure represented in terms of Green functions evaluated using the fully relativistic multiple scattering formalism.A first simplified description of the EFI-XMCD in FM/NM (FM and NM: ferromagnetic and normal metals, respectively) layered systems will be given by combining Kubo's linear response formalism with the theory on XMCD. Corresponding numerical work allow for a first comparison with experiments on systems in a steady state (SS). In the next step a more reliable description of the EFI-XMCD will be achieved by adopting the steady state non-equilibrium Green function (SS-NEGF) formalism. Corresponding calculations will clarify the applicability of linear-response theory and provide a detailed interpretation for on-going experiments meant to probe spin currents in the NM as well as FM part of FM/NM layered systems. This work will in particular reveal the mechanism giving rise to the observed XMCD together with its connection to the spin current. To describe recent FMR-XMCD experiments for which spin currents are stimulated by spin-pumping via FMR the adiabatic approximation will be used in a first step. This allows in particular to discuss the relation of the induced spin current and the XMCD spectra. Within further work the general Keldysh NEGF formalism will be used, making use of developments done by the applicant when dealing with pump-probe experiments in photo emission.Further work is meant to investigate the use of the EFI-XMCD to probe and verify new magneto-transport properties and to stimulate corresponding experiments. The Edelstein effect, i.e. the occurrence of a magnetization induced by an electric field in systems without inversion symmetry, will be investigated for NM bulk and NM/NM layered systems. The resulting spectra will be interpreted in terms of the magneto-electric susceptibility by adapting the XMCD sum rules. In addition calculations of EFI-XMCD spectra will be done to motivate experiments that verify the occurrence of induced longitudinal spin currents in low-dimensional solids predicted by the applicant. For this purpose NM/NM layered systems will be investigated that should show a pronounced effect that can be clearly distinguished from the Edelstein effect by symmetry considerations.

该理论项目旨在提供 XMCD（X 射线吸收中的 X 射线磁圆二色性）实验的从头开始描述，该实验用于监测自旋电子学领域的动态磁特性。重点将放在监测由电场 (EFI-XMCD) 或铁磁共振 (FMR-XMCD) 引起的自旋电流的实验以及新实验的动机。所有数值工作都将基于局域自旋密度泛函理论 (LSDA) 及其扩展，其中使用完全相对论多重散射形式主义评估的格林函数表示的电子结构。通过将 Kubo 的线性响应形式主义与 XMCD。相应的数值工作可以与稳态（SS）系统的实验进行首次比较。下一步，将通过采用稳态非平衡格林函数 (SS-NEGF) 形式来实现对 EFI-XMCD 的更可靠的描述。相应的计算将阐明线性响应理论的适用性，并为正在进行的旨在探测 NM 以及 FM/NM 分层系统的 FM 部分中的自旋电流的实验提供详细的解释。这项工作将特别揭示产生所观察到的 XMCD 的机制及其与自旋电流的联系。为了描述最近的 FMR-XMCD 实验，其中通过 FMR 通过自旋泵浦来激发自旋电流，第一步将使用绝热近似。这尤其允许讨论感应自旋电流和 XMCD 光谱的关系。在进一步的工作中，将使用通用的 Keldysh NEGF 形式主义，利用申请人在处理光发射中的泵浦探测实验时所做的开发。进一步的工作旨在研究使用 EFI-XMCD 来探测和验证新的磁输运特性并刺激相应的实验。 Edelstein 效应，即在没有反演对称性的系统中由电场引起的磁化的发生，将针对 NM 体和 NM/NM 层状系统进行研究。通过采用 XMCD 求和规则，将根据磁电磁化率来解释所得光谱。此外，还将进行 EFI-XMCD 谱的计算，以激发验证申请人预测的低维固体中感应纵向自旋流的发生的实验。为此目的，将研究 NM/NM 分层系统，该系统应表现出明显的效应，通过对称性考虑可以将其与 Edelstein 效应清楚地区分开来。