The two-dimensional van der Waals (vdW) magnets retaining magnetic order in atomically thin limit demonstrate challenging physical phenomena and they are considered as prospective building blocks for construction of advanced spintronics and nanoelectronics devices. Here, we present experimental evidence for negative thermal expansion of lattice volume and vdW layers and strong spin–phonon coupling effects, caused by formation of the long-range ferromagnetic order in the vdW material CrBr₃. The neutron and X-ray diffraction measurements revealed anomalous temperature variation of lattice parameters and interatomic distances and angles in the vicinity of Curie temperature (T_C). A pronounced rise of the frequencies of the most of the observed vibrational modes and unusual reversal broadening of their full widths at half maximum below T_C was found from Raman spectroscopy measurements.

二维范德华（vdW）磁体在原子上薄薄的限度内保持磁序，显示出具有挑战性的物理现象，它们被认为是构建高级自旋电子学和纳米电子器件的潜在基础。在这里，我们提供了实验证据，表明在vdW材料CrBr _3中形成了远距离铁磁有序，从而导致了晶格体积和vdW层的负热膨胀以及强烈的自旋声子耦合效应。中子和X射线衍射测量显示出居里温度（T _C）。从拉曼光谱测量中发现，观察到的大多数振动模式的频率均显着上升，并且其半峰宽低于T _C时，其整个宽度出现了异常的逆向展宽。