Wawrzyńczak R, Tanaka Y, Yoshida M, Okamoto Y, Manuel P, Casati N, Hiroi Z, Takigawa M, Nilsen G J
Institut Laue-Langevin, 6 rue Jules Horowitz, 38042 Grenoble, France.
Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan.
Phys Rev Lett. 2017 Aug 25;119(8):087201. doi: 10.1103/PhysRevLett.119.087201. Epub 2017 Aug 22.
We present the results of a combined ^{7}Li-NMR and diffraction study on LiGa_{0.95}In_{0.05}Cr_{4}O_{8}, a member of the LiGa_{1-x}In_{x}Cr_{4}O_{8} "breathing" pyrochlore family. Via specific heat and NMR measurements, we find that the complex sequence of first-order transitions observed for LiGaCr_{4}O_{8} is replaced by a single second-order transition at T_{f}=11 K. Neutron and x-ray diffraction rule out both structural symmetry lowering and magnetic long-range order as the origin of this transition. Instead, reverse Monte Carlo fitting of the magnetic diffuse scattering indicates that the low-temperature phase may be described as a collinear spin nematic state, characterized by a quadrupolar order parameter. This state also shows signs of short-range order between collinear spin arrangements on tetrahedra, revealed by mapping the reverse Monte Carlo spin configurations onto a three-state color model.
我们展示了对LiGa₀.₉₅In₀.₀₅Cr₄O₈（LiGa₁₋ₓInₓCr₄O₈“呼吸”焦绿石家族的一员）进行的⁷Li-NMR和衍射联合研究的结果。通过比热和NMR测量，我们发现，LiGaCr₄O₈中观察到的一级转变的复杂序列被Tf = 11 K时的单一二级转变所取代。中子和X射线衍射排除了结构对称性降低和磁长程序作为该转变起源的可能性。相反，磁漫散射的反向蒙特卡罗拟合表明，低温相可描述为共线自旋向列相，其特征是具有四极序参量。通过将反向蒙特卡罗自旋构型映射到三态颜色模型上，该状态还显示出四面体上共线自旋排列之间的短程序迹象。
