Institute for Solid State Physics , University of Tokyo , Kashiwa , Chiba 277-8581 , Japan.
Department of Physics, Faculty of Science , Hokkaido University , Sapporo 060-0810 , Japan.
Inorg Chem. 2019 Sep 16;58(18):11949-11960. doi: 10.1021/acs.inorgchem.9b01165. Epub 2019 Jun 18.
Volborthite CuVO(OH)·2HO is a copper mineral that materializes a two-dimensional quantum magnet comprising a kagome net of spin-/ Cu ions. We prepared single crystals of volborthite using hydrothermal conditions and investigated their crystal structures and magnetic properties. Unusual orbital "switching" and "flipping" transitions were observed: in the former type of transition (switching), the Cu 3d orbital occupied by an unpaired electron changes between the d(3-) and d(-) types, and in the latter type of transition (flipping), the d(-)-type orbitals change their directions. Their origin is ascribed to variations in the orientation of water molecules in the gap between the kagome layers and the accompanying changes of hydrogen bonding. These orbital transitions dramatically modify the magnetic interactions between Cu spins, from the anisotropic kagome type to the formation of spin trimers over the kagome net. The effective spin / generated on the trimers exhibits a frustrated magnetism, resulting in a rich phase diagram in the magnetic fields. Volborthite is a unique compound showing an exceptional interplay between the orbital and spin degrees of freedom.
羟氧铜矾（CuVO(OH)·2H₂O）是一种铜矿，它实现了一个由 kagome 网的自旋-/Cu 离子组成的二维量子磁体。我们使用水热条件制备了羟氧铜矾的单晶，并研究了它们的晶体结构和磁性。观察到了不寻常的轨道“开关”和“翻转”跃迁：在前一种跃迁（开关）中，未配对电子占据的 Cu 3d 轨道在 d(3-)和 d(-)之间变化，在后一种跃迁（翻转）中，d(-)型轨道改变它们的方向。它们的起源归因于 kagome 层之间间隙中水分子的取向变化以及氢键的伴随变化。这些轨道跃迁极大地改变了 Cu 自旋之间的磁相互作用，从各向异性的 kagome 型转变为在 kagome 网上形成自旋三聚体。在三聚体上产生的有效自旋 / 表现出受挫的磁性，导致在磁场中出现丰富的相图。羟氧铜矾是一种独特的化合物，它展示了轨道和自旋自由度之间的特殊相互作用。
