Spin-phonon coupling across a magnetic quantum critical point in Mn1-xFexSi

Mn1-xFexSi 中磁量子临界点的自旋声子耦合

• 批准号: 419331252
• 负责人: Dr. Frank Weber
• 金额: --
• 依托单位: Institut für Festkörperphysik (IFP)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/419331252?language=en
• 关键词: Spin; phonon; coupling; across; magnetic

This proposal addresses the presence and implications of spin-phonon coupling in Mn1-xFexSi where helimagnetic order is suppressed by increasing Fe concentration to a quantum critical point at x = 0.17. The parent compound at x = 0, MnSi, is a seminal compound for competing magnetic interactions resulting in a complex phase diagram with novel crystalline orders. On the other end at x = 1, FeSi is a narrow-gap and non-magnetic insulator at low temperatures but exhibits temperature-activated paramagnetism at elevated temperatures puzzling the scientific community for nearly 50 years. The noncentrosymmetric crystal structure present for the whole doping series results in a finite spin-orbit interaction providing a natural coupling between magnetic moments and the crystal lattice. Recent investigations of lattice dynamical properties – including our own work – revealed a close but unexpected link between magnetic and lattice degrees of freedom in FeSi: (1) Electronic states mediating conventional electron-phonon coupling are only activated in the presence of strong magnetic fluctuations. (2) Furthermore, phonons entailing strongly varying Fe-Fe distances are damped via dynamic coupling to the temperature-induced magnetic moments, highlighting FeSi as a material with direct spin-phonon coupling and multiple interaction paths. We propose a work program to investigate the energy, momentum and compositional dependence of spin-phonon coupling in Mn1-xFexSi via phonon spectroscopy. Based on the results for FeSi and preliminary data on MnSi, we will focus on the evolution of longitudinal phonons at the R point, i.e., the zone boundary along the [111] direction in momentum space, which exhibit strongly varying Mn/Fe – Mn/Fe distances. Ab-initio lattice-dynamical calculations predict spectacular phonon renormalization at the R point with increasing Fe concentration but closely linked to a magnetically ordered ground state. The suppression of magnetic order at x = 0.17 may have a critical impact on this behavior and could result in a strong lattice dynamical response to the alleged magnetic quantum critical point. Experimentally, we already have 10 well-characterized samples with doping levels 0.03 ≤ x ≤ 0.32. We will employ Raman scattering to obtain a full x dependence of zone center optical phonons and then investigate the most interesting samples via momentum and energy resolved high resolution inelastic x-ray scattering and inelastic neutron spectroscopy in order to measure the evolution of the above discussed phonons at the R point.Our investigation will scrutinize the so far overlooked interaction between spin and lattice degrees of freedom in a seminal material family with potential applications in spintronic devices. Here, understanding the ways in which such materials respond to extrinsic parameters such as doping is a key challenge for developing and functionalizing new materials.

该提案解决了MN1-XFEXSI Helimagnetic Order的存在，通过将Fe NTration增加到X = 0.17时的量子临界点，是在X = 0，MNSI时，是用于在X = 0的量子上。在低温屁股上具有磁性绝缘体的复杂相图在升高的温度下表现出近50年的sciecun速度。矩和晶格。 - 磁矩，将FESI作为一种直接自旋和多个离子路径的材料在MNSI上的FESI和预启示数据，沿[111]方向的区域边界在动量空间中表现出较差的Mn /Fe-Mn /Fe距离与磁性的磁序紧密相关，X = 0.17可能会对这种行为和批判点有关键的影响采用拉曼散射以通过动量和能量分辨率的X射线散射和非弹性中子光谱法获得全部X区域中央电话和最有趣的样品的完整X依赖性，以便在r点上讨论的手机的演变。到目前为止，忽略了与potheratial applicatials的旋转和晶格自由度之间的相互作用。