Neutron-diffraction studies of Tb2C and Dy2C in the temperature range 4–296 K

Neutron power-diffraction data of the trigonal Tb2C have been obtained and compared with our previous results (given in parentheses) for a Tb-rich Tb2C. Significant differences were observed in the c spacing and the ferromagnetic moment, e.g., the saturation value of 7.6(8.6) Bohr magnetons, which is 84(96)% of the free-ion moment, indicating a considerable crystal-field effect. The Curie temperature (266 K) and an unusual magnetostriction along c were unchanged. The ordered-moment direction (parallel to c) has now been established unambiguously using a magnetically induced, preferential crystallite orientation in Tb2C. A short-range ferromagnetic ordering, which coexists with the long-range ordering in Tb2C, was analyzed anew. Dy2C becomes ferromagnetic below 168 K, and the saturation ordered moment is 6.8 Bohr magnetons, which is 68% of the free-ion moment. A magnetically induced, preferential crystallite orientation in Dy2C indicated that the ordered-moment direction is parallel to the [104] axis, which corresponds to the [100] axis of the high-temperature cubic modification.