Short range spin ice type correlations of HoAgGe by diffuse neutron scattering

Spin ices are exotic phases of matter characterized by frustrated spins obeying local “ice rules” that minimize the number of spatially isolated magnetic monopoles, in analogy with the electric dipoles in water ice. In two dimensions, one can similarly define ice rules for in-plane Ising-like spins arranged on a kagome lattice, which could lead to a variety of unique orders and excitations. Based on single-crystal neutron diffraction results, we determine the magnetic structures of HoAgGe both at 10K and 4K, consistent with classical kagome spin ice predicted theoretically before. As far as we know this is the first time that such an order is observed in a naturally existing material. According to this scenario, above the long range magnetic order, there should be a short-range order satisfying the ice rule. To further verify such correlations, we plan to do diffuse neutron scattering.

自旋冰（spin ice）是一类奇异的物相，其核心特征为阻挫自旋（frustrated spins）遵循局域冰规则（ice rules）——该规则通过约束自旋排布以最小化空间孤立磁单极子（magnetic monopoles）的数量，其物理机制类比于水冰中的电偶极子（electric dipoles）排布规律。在二维体系中，我们同样可以为排布于笼目晶格（kagome lattice）上的面内类伊辛自旋（Ising-like spins）定义冰规则，这类体系有望呈现多种独特的有序态与激发模式。基于单晶中子衍射（single-crystal neutron diffraction）实验结果，我们确定了HoAgGe在10K与4K下的磁结构（magnetic structures），该结果与此前理论预言的经典笼目自旋冰模型相符。据我们所知，这是首次在天然存在的材料中观测到此类有序态。根据该理论框架，在长程磁有序（long-range magnetic order）的临界温度以上，应当存在满足冰规则的短程有序（short-range order）。为进一步验证此类关联效应，我们计划开展漫散中子散射（diffuse neutron scattering）实验。