Neutron-diffraction study of Ho2C at 4–296 K

By neutron powder diffraction, trigonal Ho2C has been shown to become ferromagnetic below 100 K. The paramagnetic scattering indicates the free Ho3+-ion moment, while the saturation moment in the ferromagnetic phase is 7.16 Bohr magnetons (72% of the free-ion moment), showing a sizeable crystal-field effect. The preferential crystallite orientation induced by the applied magnetic field has shown that the ordered moments are aligned parallel to the [104] axis which corresponds to the [100] axis of the high-temperature cubic modification. The previously proposed HoN-type magnetic ordering is not compatible with our results. The residual, disordered moments exhibit a ferromagnetic short-range order superposing on the ferromagnetic long-range order. Crystallographic-structure data at 296 and 4 K are also presented.