Neutron diffraction investigation of the crystal and magnetic structure of the new ThCo4Bcompound

Abstract

The crystal and magnetic structures of a new ternary phase in the Th–Co–B system havebeen investigated by high resolution neutron diffraction. The spontaneous magnetizationand Curie temperature were determined by magnetic measurements. The ThCo4Bphase crystallizes in a hexagonal crystal structure, space groupP6/mmm with a = 5.088 Å and c = 7.003 Å.ThCo4Borders ferromagnetically at 303 K, a temperature much smaller than that of the isotypic RCo4Bwhere R is a rare-earth element or yttrium. The Co magnetic moments are found to be alignedalong the c-axisof the hexagonal structure in the whole ordered temperature region. Thetwo inequivalent Co crystal sites are found to exhibit different magneticbehaviours. At 2 K a substantial magnetic moment of 1.8 ± 0.1μBis observed on the Co 2c site whereas a nearly zero magnetic moment is found on theCo 6i site. A similar behaviour was also found at room temperature, 1.2 ± 0.2μB on the Co 2c siteand zero μBon the Co 6i site. The influence of the local environmenton the magnitude of the Co moments in ThCo4Bis discussed. The magnetic properties of ThCo4Bare compared to that of isotypic YCo4B.