Gd2OsC2, a soft ferromagnet with a surprisingly high Curie temperature and other rare-earth osmium and rhenium carbides with Pr2ReC2 type structure

Abstract

The six new carbides Ln2OsC2 (Ln=Y, Gd–Er) have been prepared by arc-melting cold-pressed pellets of the elemental components with subsequent annealing. They crystallize in the orthorhombic Pr2ReC2 structure (Pnma, Z=4), which was refined from powder diffractometer data of Tb2OsC2 . Chemical bonding in these carbides is discussed. The magnetic susceptibilities of the compounds Ln2OsC2 (Ln=Y, Gd and Tb) have been investigated with a SQUID magnetometer between 2 and 400 K with magnetic flux densities up to 5.5 T. The magnetic susceptibility of Y2OsC2 is low and almost temperature independent, suggesting Pauli paramagnetism. Gd2OsC2 and Tb2OsC2 are ferromagnetic with the relatively high Curie temperatures of 320±5 and 210±5 K, respectively. The gadolinium compound has the rather low coercivity of 23.8±0.4 A cm–1 at room temperature and 31.8±0.8 A cm–1 at 5 K. The magnetic properties of the corresponding rhenium carbides Ln2ReC2 (Ln=Ce, Pr, Nd, Gd, Tm) were also determined, thus completing the magnetic characterization of the rhenium series. The cerium atoms in Ce2ReC2 show mixed-valence behaviour. Antiferromagnetic order was observed for the moments of the rare-earth atoms in Pr2ReC2 , TN=32±2 K; Nd2ReC2 , TN=42±2 K; Gd2ReC2 , TN=100±5 K and Tm2ReC2 , TN=5±3 K.