Magnetic properties of S = 1/2 quasi-triangular lattice materials: Cu _(2(1-x))Zn_(2x)(OH)_3NO_3/(C _7H_(15)COO). mH_2O

摘要

We have investigated the structural and magnetic properties of two classes of spin S = 1/2 antiferromagnetic quasi-triangular lattice materials: Cu _(2(1-x))Zn_(2x)(OH)_3NO_3 (0 ≤ x ≤ 0.65) and its long chain organic derivatives Cu_(2(1-x))Zn _(2x)(OH)_3/(C_7H_(15)COO)·mH _2O (0 ≤ x ≤ 0.29). The series of layered structure compounds constitute a substitutional magnetic system, in which spin S = 1/2Cu ~(2+) ions and nonmagnetic Zn~(2+) ions are arranged on a two-dimensional quasi-triangular lattice. For the nitrate compounds we found that the substitution of Zn~(2+) ions can continuously decrease the Néel temperature, T_N, but never completely remove the magnetic order. In addition, the frustration effect in these materials is suppressed by a three-dimensional interlayer interaction. On the other hand, the corresponding long chain alkyl carboxylic acid group of intercalated materials, Cu _(2(1-x)Xn_(2x)(OH)_3(C_7H _(15)COO)·mH_2O, show spin-glass-like behavior, which is caused by the interplay of geometric frustration and mixed sign interactions. A tentative explanation for these findings is proposed in terms of a cluster-glass picture.