Magnetic Structure of α-Ho2C3

The antiferromagnetic structure of α-Ho2C3 as revealed by neutron powder diffraction is stabilized below 19 ± 1°K and is markedly different from the ordered spin structure of the isostructural α-Tb2C3 (the cubic body-centered Pu2C3 type). Two out of four body diagonally linked arrays of Ho atoms become the ferromagnetically ordered chains and the remaining two arrays show one-dimensional antiferromagnetic alignment. Among three nearest Ho–Ho neighbors bridging between the different body-diagonal arrays are two antiferromagnetic pairs and one ferromagnetic pair. The moment direction is most likely parallel to one of the ferromagnetic linear arrays. The maximum spontaneous moment is 7.3 ± 0.2 μB which is considerably smaller than the free He3+ value of 10 μB. The temperature dependency of the spontaneous magnetization is approximated by the Brillouin function with S = 1 ± 12 but departs significantly from the free ion function with J(g − 1) = 2. The magnetically ordered phase exhibits a sizeable magnetic diffuse scattering having the characteristics of a ferromagnetic short-range order and this persists down to near 0°K.