GD2OSC2, A SOFT FERROMAGNET WITH A SURPRISINGLY HIGH CURIE-TEMPERATURE AND OTHER RARE-EARTH OSMIUM AND RHENIUM CARBIDES WITH PR2REC2 TYPE-STRUCTURE

The six new carbides Ln(2)OsC(2) (Ln=Y, Gd-Er) have been prepared by a re-melting cold-pressed pellets of the elemental components with subse quent annealing. They crystallize in the orthorhombic Pr2ReC2 structur e (Pnma, Z=4), which was refined from powder diffractometer data of Tb 2OsC2. Chemical bonding in these carbides is discussed. The magnetic s usceptibilities of the compounds Ln(2)Os(2) (Ln=Y, Gd and Tb) have bee n investigated with a SQUID magnetometer between 2 and 400 K with magn etic flux densities up to 5.5 T. The magnetic susceptibility of Y2OsC2 is low and almost temperature independent, suggesting Pauli paramagne tism. Gd2OsC2 and Tb2OsC2 are ferromagnetic with the relatively high C urie temperatures of 320 +/- 5 and 210 +/- 5 K, respectively. The gado linium 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 pro perties of the corresponding rhenium carbides Ln(2)ReC(2) (Ln = Ce, Pr , Nd, Gd, Tm) were also determined, thus completing the magnetic chara cterization of the rhenium series. The cerium atoms in Ce2ReC2 show mi xed-valence behaviour. Antiferromagnetic order was observed for the mo ments of the rare-earth atoms in Pr2ReC2, T-N=32+/-2K; Nd2ReC2, T-N=42 +/-2 K; Gd2ReC2, T-N=100+/-5K and Tm2ReC2, T-N=5+/-3K.