We present the magnetic properties of a quantum dimer magnet based on ${\mathrm{Co}}^{2+}$. The metal-organic framework compound ${\mathrm{Co}}_2{\left(\mathrm{BDC}\right)}_2{\left(\mathrm{DPTTZ}\right)}_2·\mathrm{DMF}$ features ${\mathrm{Co}}^{2+}$ dimers arranged nearly orthogonal to each other, similar to the Shastry-Sutherland lattice. Our assessment based on the magnetization and heat capacity experiments reveals that the magnetic properties at low temperatures can be described by pseudospin-1/2. The magnetic ground state of the material is found to be a singlet with a tiny spin gap. The thermodynamic properties are described by a model of isolated spin dimers with the anisotropic exchange couplings $J_{xy}\simeq 3.5$ K and $J_z\simeq 11$ K. Interestingly, no field-induced quantum phase transition is detected down to 100 mK around the critical field of gap closing, suggesting the absence of Bose-Einstein condensation of triplons and establishing isolated dimers with a negligible interdimer coupling.

中文翻译：

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具有正交自旋二聚体的自旋轨道耦合赝自旋12钴基金属有机骨架磁体中的无序基态

我们提出了基于量子二聚体磁体的磁特性${钴}^{2+}$。金属有机骨架化合物${钴}_2{（\mathrm{商业发展中心}）}_2{（\mathrm{DPTTZ}）}_2·\mathrm{二甲基甲酰胺}$特征${钴}^{2+}$二聚体彼此几乎正交排列，类似于沙斯特里-萨瑟兰晶格。我们基于磁化强度和热容实验的评估表明，低温下的磁特性可以用赝自旋1/2 来描述。发现材料的磁性基态是具有微小自旋间隙的单线态。热力学性质由具有各向异性交换耦合的孤立自旋二聚体模型描述$J_{Xy}\simeq 3.5$K 和$J_z\simeq 11$ K. 有趣的是，在间隙闭合临界场周围低至 100 mK 时，没有检测到场诱导的量子相变，这表明不存在三倍体的玻色-爱因斯坦凝聚，并建立了具有可忽略的中间二聚体耦合的孤立二聚体。