Crystal and magnetic structure of TbCo0.5Ni0.5C2

The pseudo-ternary intermetallic dicarbide TbCo0.5Ni0.5C2 has been investigated by powder neutron diffraction in the temperature range from 300 K to 2 K. The crystallographic space group is Amm2 with Tb on 2a (0, 0, 0), Co and Ni statistically distributed on 2b (1/2, 0, 0.608(5)) and C on 4e (1/2, 0.154(5), 0.305(4)); room temperature lattice parameters are a = 3.558(2) A, b = 4.501(1) A and c = 6.045(2) A. C - C distances are 1.39 A. Below 13 K the Tb-moments order magnetically in a two-component structure: (1) an incommensurate component along c with propagation vector [0.165(1), 0, 0] due to a sine-modulation of the moments (amplitude 6.82(2)μB) and (2) an additional commensurate ferromagnetic component of 2.5(2)μB along a. The magnetic order of Tb in TbCo0.5Ni0.5O2 appears to be a compromise between TbNiC2, antiferromagnetic along c, and TbCoC2, ferromagnetic along a. (orig.)