Single crystals of Cr$_2$Ge$_2$Te$_6$ were studied by high-resolution capacitance dilatometry to obtain in-plane ($B\parallel ab$) and out-of-plane ($B\parallel c$) thermal expansion and magnetostriction at temperatures between 2 and 300 K and in magnetic fields up to 15 T. The anomalies in both response functions lead to the 'magnetoelastic' phase diagrams and separate the paramagnetic (PM), ferromagnetic low-temperature/low-field (LTF) and aligned ferromagnetic (FM) phases. The presence of two distinct thermal expansion anomalies at small fields $B\parallel ab$ of different magnetic field dependence clearly supports the scenario of an intermediate region separating PM and LTF phases and is indicative of a tricritical point. Simulations of the magnetostriction using the Stoner-Wohlfarth model for uniaxial anisotropy demonstrate that the observed quadratic-in-field behavior in the LTF phase is in line with a rotation of the spins from the preferred $c$ direction into the $ab$ plane. Both the LTF and the PM phase close to T$_{\rm C}$ exhibit very strong pressure dependencies of the magnetization, ${\partial}\ln{M_{\rm ab}}/{\partial}p_{\rm ab}$, of several hundred %/GPa and also the transition from the LTF to the FM phase strongly depends on $p_{\rm ab}$ ($\sim -$280%/GPa), indicating a strong decrease of the uniaxial anisotropy under applied in-plane pressure. Our data clearly demonstrate the relevance of critical fluctuations and magnetoelastic coupling in Cr$_2$Ge$_2$Te$_6$.
Magnetic anisotropy in the near-stoichiometric van der Waals ferromagnet Fe$_3$GeTe$_2$
Leibniz Institute for Solid State and Materials Research（莱布尼茨固体与材料研究所）；Institute for Solid State and Materials Physics, TU Dresden（德累斯顿工业大学固体与材料物理研究所）；Department of Condensed Matter and Materials Physics, S. N. Bose National Centre for Basic Sciences（S.N. 玻色基础科学国家中心凝聚态与材料物理系）；School of Physical Sciences, Indian Association for the Cultivation of Science（印度科学促进协会物理科学学院）
Magnetic Excitations in the Multiferroic Néel-type Skyrmion Host GaV$_4$S$_8$
对GaV单晶$_4$ S $_8$进行了宽带微波光谱研究，该单晶在13 K以下呈现出复杂的磁相图，包括摆线、Néel型skyrmion晶格以及场极化铁磁相.在零和小磁场两个集体模式被发现在5和15 GHz，这是在这个易轴磁铁的摆线状态的特点。在有限场中，进入skyrmion晶格相，光谱转变成多模模式，吸收峰接近4，8和15 GHz。发现GaV $_4$ S $_8$中的自旋激发谱及其场依赖性与在具有布洛赫型skyrmions的材料中观察到的自旋激发谱密切相关。明显的差异产生于强单轴磁各向异性的GaV4S8不存在于迄今已知的skyrmion主机。
Crystal-Field--Driven Magnetoelectric Coupling in the Non-Kramers Hexaaluminate PrMgAl11O19
Charles University（查理大学）；Adam Mickiewicz University（亚当·密茨凯维奇大学）；Institute of Physics, Czech Academy of Sciences（捷克科学院物理研究所）；Institute of Molecular Physics, Polish Academy of Sciences（波兰科学院分子物理研究所）
