MnCoGe磁相变材料中自旋-晶格耦合的中子散射研究

MnCoGe基合金化合物是一种多功能磁相变材料，具有磁卡、压卡、磁致伸缩、负热膨胀等物理效应。这些通过外场驱动的物理效应与材料复杂的一级磁相变相关。本项目拟针对该材料体系中存在的三个问题——各种相关磁效应的弱磁场响应能力、复杂磁结构之间相互转换的主导因素、以及晶格熵与磁熵在磁卡效应中的贡献比例，对其展开一级磁相变相关微观机理的研究。本项目将从价电子浓度、温度和磁场对磁性性能、晶体结构和磁结构的调控入手，结合声子与磁振子的中子散射测量，从微观层面深入探究自旋-晶格之间的耦合行为，系统分析一级磁相变与各种磁性物理效应之间的内在联系，从而揭示各种相关效应的微观起源及其弱磁场响应能力的原因；同时通过分析声子与磁振子态密度，直接评估晶格熵与磁熵在热卡效应中的贡献。本项目的实施将为一级磁相变材料中各种相关磁效应性能的优化提供实验方面的指导，也为建立自旋-晶格耦合的理论模型提供可参照的对象。

MnCoGe-based compounds are a group of multifunctional magnetic materials, which can be used for magnetocaloric effect, barocaloric effect, magnetostriction and negative thermal expansion. These physical effects driven by external fields stem from the complex magnetic structure and magneto-structural coupling. However, the dominant factors for the conversion between complex magnetic structures are not well understood, the weak response of the magnetic phase transition to external magnetic field limited its practical application, and the exact magnetic and lattice contribution to the total entropy change is also not clear. In this project, we will try to tune the magnetic properties, crystal and magnetic structures by varying the valence electron concentration, temperature or magnetic field. In addition, inelastic neutron scattering technique will be used to study the variation of phonon and magnon across the magnetic phase transition. All these information will be used to analyze the spin-lattice coupling behavior, underlying reason for the weak response capability of magnetic effects to external magnetic field, as well as the correlations between magnetic-structural phase transition and magnetic effects. In addition, the contribution of lattice entropy and magnetic entropy will be directly evaluated from the measurements of phonon and magnon density of states. The implementation of this project will provide useful guides to tune and/or enhance the magnetic-related physical effects, and also provide experimental reference for the theoretical study of spin-lattice coupling.