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 , T_N=32±2 K; Nd₂ReC₂ , T_N=42±2 K; Gd₂ReC₂ , T_N=100±5 K and Tm₂ReC₂ , T_N=5±3 K.