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arXiv 0901.2791cond-mat.str-el
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S=1/2 Kagome反铁磁体族的磁化率

Magnetic susceptibilities in a family of S=1/2 Kagome antiferromagnet

T. Ono, K. Morita, M. Yano, H. Tanaka, K. Fujii, H. Uekusa, Y. Narumi, K. Kindo

摘要:

半方反铁磁体Cs $_2$ Cu $_3$ MF $_{12}$(M = Zr,Hf,Sn)具有均匀的Cu $^{2+}$ Kagome晶格,S = 1/2,而Rb $_2$ Cu $_3$ SnF $_{12}$与均匀的Kagome晶格相比具有2 α × 2 α的扩大晶胞.报道了首次合成的Cs $_2$ Cu $_3$ SnF $_{12}$的晶体数据。我们使用单晶对这个家族的可果美反铁磁体进行了磁化率测量。在Cs-$_2$-Cu-$_3$-MF-$_{12}$体系中,当M = Zr,Hf和Sn时,分别在$T_t = 225$ K,172 K和185 K观察到结构相变。对24位Kagome团簇分别用$J/k_B = 244$ K、266 K和240 K精确对角化得到的理论结果几乎完美地描述了对$T > T_t$观测到的磁化率。在$T_N = 23.5$ K、24.5 K和20.0 K下,磁有序化伴随着弱铁磁矩。弱铁磁矩的起源应归因于晶格畸变,这种畸变破坏了$T < T_t$和Dzyaloshinsky-Moriya相互作用的交换网络的六角对称性。Rb $_2$ Cu $_3$ SnF $_{12}$在磁性上被描述为具有四种相邻交换相互作用的改进的可果美反铁磁体。在Rb $_2$ Cu $_3$ SnF $_{12}$中没有观察到结构和磁性相变。它的磁性基态被发现是一个自旋单重态与三重态间隙。使用精确对角化的12个站点的可果美集群,我们分析了磁化率和评估个人的交换相互作用。讨论了Cs $_2$ Cu $_3$ SnF $_{12}$和Rb $_2$ Cu $_3$ SnF $_{12}$基态不同的原因。

英文摘要:

Hexagonal antiferromagnets Cs$_2$Cu$_3$MF$_{12}$ (M = Zr, Hf and Sn) have uniform Kagome lattices of Cu$^{2+}$ with S = 1/2, whereas Rb$_2$Cu$_3$SnF$_{12}$ has a 2a by 2a enlarged cell as compared with the uniform Kagome lattice. The crystal data of Cs$_2$Cu$_3$SnF$_{12}$ synthesized first in the present work are reported. We performed magnetic susceptibility measurements on this family of Kagome antiferromagnet using single crystals. In the Cs$_2$Cu$_3$MF$_{12}$ systems, structural phase transitions were observed at $T_t = 225$ K, 172 K and 185 K for M = Zr, Hf and Sn, respectively. The magnetic susceptibilities observed for $T > T_t$ are almost perfectly described using theoretical results obtained by exact diagonalization for the 24-site Kagome cluster with $J/k_B = 244$ K, 266 K and 240 K, respectively. Magnetic ordering accompanied by the weak ferromagnetic moment occurs at $T_N = 23.5$ K, 24.5 K and 20.0 K, respectively. The origins of the weak ferromagnetic moment should be ascribed to the lattice distortion that breaks the hexagonal symmetry of the exchange network for $T < T_t$ and the Dzyaloshinsky-Moriya interaction. Rb$_2$Cu$_3$SnF$_{12}$ is magnetically described as a modified Kagome antiferromagnet with four types of neighboring exchange interaction. Neither structural nor magnetic phase transition was observed in Rb$_2$Cu$_3$SnF$_{12}$. Its magnetic ground state was found to be a spin singlet with a triplet gap. Using exact diagonalization for a 12-site Kagome cluster, we analyzed the magnetic susceptibility and evaluated individual exchange interactions. The causes leading to the different ground states in Cs$_2$Cu$_3$SnF$_{12}$ and Rb$_2$Cu$_3$SnF$_{12}$ are discussed.

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