We present a comprehensive neutron scattering study of the breathing pyrochlore magnet ${\mathrm{LiGaCr}}_4{\mathrm{S}}_8$. We observe an unconventional magnetic excitation spectrum with a separation of high- and low-energy spin dynamics in the correlated paramagnetic regime above a spin-freezing transition at 12(2) K. By fitting to magnetic diffuse-scattering data, we parametrize the spin Hamiltonian. We find that interactions are ferromagnetic within the large and small tetrahedra of the breathing pyrochlore lattice, but antiferromagnetic further-neighbor interactions are also essential to explain our data, in qualitative agreement with density-functional-theory predictions [Ghosh et al., npj Quantum Mater. 4, 63 (2019)]. We explain the origin of geometrical frustration in ${\mathrm{LiGaCr}}_4{\mathrm{S}}_8$ in terms of net antiferromagnetic coupling between emergent tetrahedral spin clusters that occupy a face-centered-cubic lattice. Our results provide insight into the emergence of frustration in the presence of strong further-neighbor couplings, and a blueprint for the determination of magnetic interactions in classical spin liquids.

中文翻译：

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呼吸性烧绿石磁体中的团簇受挫LiGaCr4S8

我们对呼吸性烧绿石磁体进行了全面的中子散射研究 ${\mathrm{锂镓铬}}_4{\mathrm{小号}}_8$。我们在12（2）K处自旋冻结转变以上的相关顺磁态中观察到了具有高能和低能自旋动力学分离的非常规磁激发光谱。通过拟合磁扩散散射数据，我们对自旋进行了参数化哈密​​尔顿 我们发现，在呼吸性烧绿石晶格的大小四面体中相互作用是铁磁性的，但是反铁磁性的近邻相互作用对于解释我们的数据也是必不可少的，与密度泛函理论的预测在质量上是一致的[Ghosh等。，npj Quantum Mater。 4，63（2019）]。我们解释了几何挫折的起源${\mathrm{锂镓铬}}_4{\mathrm{小号}}_8$就占据面心立方晶格的新兴四面体自旋簇之间的净反铁磁耦合而言。我们的结果提供了在存在强邻耦合的情况下挫折感出现的见解，以及确定经典自旋液体中磁性相互作用的蓝图。