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 ${\text{7.3\hspace{0.17em}±\hspace{0.17em}0.2 μ}}_B$ which is considerably smaller than the free He³⁺ value of ${\text{10 μ}}_B$ . The temperature dependency of the spontaneous magnetization is approximated by the Brillouin function with $\text{S\hspace{0.17em}=\hspace{0.17em}1\hspace{0.17em}±\hspace{0.17em}}\frac{1}{2}$ but departs significantly from the free ion function with $\text{J(g\hspace{0.17em}−\hspace{0.17em}1)\hspace{0.17em}=\hspace{0.17em}2}$ . 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.