Nirmala R, Jang Kwang-Hyun, Sim Hasung, Cho Hwanbeom, Lee Junghwan, Yang Nam-Geun, Lee Seongsu, Ibberson R M, Kakurai K, Matsuda M, Cheong S-W, Gapontsev V V, Streltsov S V, Park Je-Geun
Center for Strongly Correlated Materials Research, Seoul National University, Seoul 08826, Korea. Department of Physics, Indian Institute of Technology Madras, Chennai 600 036, India. Department of Physics, Sungkyunkwan University, Suwon 16419, Korea.
J Phys Condens Matter. 2017 Apr 5;29(13):13LT01. doi: 10.1088/1361-648X/aa5c72. Epub 2017 Jan 31.
CuAlO is a normal spinel oxide having quantum spin, S = 1/2 for Cu. It is a rather unique feature that the Cu ions of CuAlO sit at a tetrahedral position, not like the usual octahedral position for many oxides. At low temperatures, it exhibits all the thermodynamic evidence of a quantum spin glass. For example, the polycrystalline CuAlO shows a cusp centered at ~2 K in the low-field dc magnetization data and a clear frequency dependence in the ac magnetic susceptibility while it displays logarithmic relaxation behavior in a time dependence of the magnetization. At the same time, there is a peak at ~2.3 K in the heat capacity, which shifts towards a higher temperature with magnetic fields. On the other hand, there is no evidence of new superlattice peaks in the high-resolution neutron powder diffraction data when cooled from 40 to 0.4 K. This implies that there is no long-ranged magnetic order down to 0.4 K, thus confirming a spin glass-like ground state for CuAlO. Interestingly, there is no sign of structural distortion either although Cu is a Jahn-Teller active ion. Thus, we claim that an orbital liquid state is the most likely ground state in CuAlO. Of further interest, it also exhibits a large frustration parameter, f = |θ /T | ~ 67, one of the largest values reported for spinel oxides. Our observations suggest that CuAlO should be a rare example of a frustrated quantum spin glass with a good candidate for an orbital liquid state.
CuAlO是一种具有量子自旋的正常尖晶石氧化物，其中铜的自旋S = 1/2。CuAlO的一个相当独特的特征是，铜离子处于四面体位置，这与许多氧化物中常见的八面体位置不同。在低温下，它呈现出量子自旋玻璃的所有热力学证据。例如，多晶CuAlO在低场直流磁化数据中显示出一个以约2K为中心的尖点，在交流磁化率中显示出明显的频率依赖性，同时在磁化强度的时间依赖性中表现出对数弛豫行为。同时，在热容量中约2.3K处有一个峰值，该峰值随磁场向更高温度移动。另一方面，当从40K冷却到0.4K时，高分辨率中子粉末衍射数据中没有新的超晶格峰的证据。这意味着在0.4K以下没有长程磁序，从而证实了CuAlO的自旋玻璃状基态。有趣的是，尽管铜是 Jahn-Teller 活性离子，但也没有结构畸变的迹象。因此，我们认为轨道液态是CuAlO中最可能的基态。更有趣的是，它还表现出一个大的失配参数，f = |θ /T | ~ 67，这是尖晶石氧化物报道的最大值之一。我们的观察表明，CuAlO应该是具有轨道液态良好候选者的受挫量子自旋玻璃的罕见例子。
