Bromine NMR Study of Cupric Compounds (C_<i>n</i>H_2<i>n</i>+1NH₃)₂CuBr₄(<i>n</i>=1, 2)

Abstract

The spin structure of (C n H 2 n +1 NH 3 ) 2 CuBr 4 ( n =1, 2) is studied by Br NMR at 1.7 K. In (C 2 H 5 NH 3 ) 2 CuBr 4 , the magnetic space group is P b ' c ' a type and the moment direction inclines at an angle of 49.5° with the c -axis. A weak ferromagnetic moment appears along to the c -axis. The anisotropic exchange field is estimated to be 2.5 kOe. The inter-layer exchange field and the out-of-layer anisotropy field are much smaller than previously reported values. The parameters of Br nuclear spin Hamiltonian are also obtained. In (CH 3 NH 3 ) 2 CuBr 4 , the moment direction inclines at 27° with the c -axis. It is difficult to interpret the NMR results by the two-sublattice model. A model of the four-sublattice antiferromagnet is developped.