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arXiv 1902.06407cond-mat.str-el
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均匀三角晶格Li2AMo3O8(A = In,Sc)中的量子磁性

Quantum magnetisms in uniform triangular lattices Li2AMo3O8 (A = In, Sc)

K. Iida, H. Yoshida, H. Okabe, N. Katayama, Y. Ishii, A. Koda, Y. Inamura, N. Murai, M. Ishikado, R. Kadono, R. Kajimoto

摘要:

基于分子的自旋为1/2的三角晶格系统如LiZn $_2$ Mo $_3$ O $_8$引起了研究兴趣。扭曲,缺陷,和intersite无序抑制在这样的分子基磁体,和内在的几何挫折引起非常规和意想不到的基态。Li $_2$ $A$ Mo $_3$ O $_8$($A$ = In或Sc)是这样一种化合物,其中自旋为1/2的Mo $_3$ O $_{13}$簇代替Mo离子形成均匀的三角形晶格。它们的基态根据$A$位点而不同。Li $_2$ InMo $_3$ O $_8$在低于$T_\text{N}=12$ ~K时经历常规的$120^\circ$长程磁序,而同晶Li $_2$ ScMo $_3$ O $_8$在低于0.5~K时没有长程磁序.在这里,我们报告奇异的磁性在Li $_2$ InMo $_3$ O $_8$和Li $_2$ ScMo $_3$ O $_8$调查的μ子自旋旋转($μ$ SR)和非弹性中子散射(INS)光谱使用多晶样品。Li $_2$ InMo $_3$ O $_8$和Li $_2$ ScMo $_3$ O $_8$显示在$μ$ SR和INS测量中观察到的完全不同的行为,代表它们不同的基态。Li $_2$ InMo $_3$ O $_8$表现出自旋波激发,其由基于$120^\circ$自旋结构的最近邻各向异性海森堡模型定量描述。相反,Li $_2$ ScMo $_3$ O $_8$在低于4 K的温度下经历短程磁序,并在低于基温时具有类似量子自旋液体的磁涨落。从晶体结构的各向异性和磁相互作用的角度讨论了不同基态的起源。

英文摘要:

Molecular based spin-1/2 triangular lattice systems such as LiZn$_2$Mo$_3$O$_8$ have attracted research interest. Distortions, defects, and intersite disorder are suppressed in such molecular-based magnets, and intrinsic geometrical frustration gives rise to unconventional and unexpected ground states. Li$_2$$A$Mo$_3$O$_8$ ($A$ = In or Sc) is such a compound where spin-1/2 Mo$_3$O$_{13}$ clusters in place of Mo ions form the uniform triangular lattice. Their ground states are different according to the $A$ site. Li$_2$InMo$_3$O$_8$ undergoes conventional $120^\circ$ long-range magnetic order below $T_\text{N}=12$~K whereas isomorphic Li$_2$ScMo$_3$O$_8$ exhibits no long-range magnetic order down to 0.5~K. Here, we report exotic magnetisms in Li$_2$InMo$_3$O$_8$ and Li$_2$ScMo$_3$O$_8$ investigated by muon spin rotation ($μ$SR) and inelastic neutron scattering (INS) spectroscopies using polycrystalline samples. Li$_2$InMo$_3$O$_8$ and Li$_2$ScMo$_3$O$_8$ show completely different behaviors observed in both $μ$SR and INS measurements, representing their different ground states. Li$_2$InMo$_3$O$_8$ exhibits spin wave excitation which is quantitatively described by the nearest neighbor anisotropic Heisenberg model based on the $120^\circ$ spin structure. In contrast, Li$_2$ScMo$_3$O$_8$ undergoes short-range magnetic order below 4~K with quantum-spin-liquid-like magnetic fluctuations down to the base temperature. Origin of the different ground states is discussed in terms of anisotropies of crystal structures and magnetic interactions.

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