Neutron diffraction investigation of the crystal and magnetic structure of the new ThCo4B compound

The crystal and magnetic structures of a new ternary phase in the Th-Co-B system have been investigated by high resolution neutron diffraction. The spontaneous magnetization and Curie temperature were determined by magnetic measurements. The ThCo4B phase crystallizes in a hexagonal crystal structure, space group P6/mmm with a=5.088 A and c=7.003 A. ThCo4B orders ferromagnetically at 303 K, a temperature much smaller than that of the isotypic RCo4B where R is a rare-earth element or yttrium. The Co magnetic moments are found to be aligned along the c-axis of the hexagonal structure in the whole ordered temperature region. The two inequivalent Co crystal sites are found to exhibit different magnetic behaviours. At 2 K a substantial magnetic moment of 1.8 ± 0.1μB is observed on the Co 2c site whereas a nearly zero magnetic moment is found on the Co 6i site. A similar behaviour was also found at room temperature, 1.2 ± 0.2μB on the Co 2c site and zero μB on the Co 6i site. The influence of the local environment on the magnitude of the Co moments in ThCo4B is discussed. The magnetic properties of ThCo4B are compared to that of isotypic YCo4B