MAGNETIC-PROPERTIES OF THE URANIUM TRANSITION-METAL CARBIDES U2TC2 (T=RU, OS, RH, IR AND PT)

The magnetic susceptibilities of the title compounds were investigated with a SQUID magnetometer with magnetic flux densities up to 5.5 T in the temperature range between 2 and 300 K. The carbides U2RuC2 and U2 OsC2 show strong, weakly temperature-dependent paramagnetism, suggesti ng an intermediate valence for the uranium atoms, while the ruthenium and osmium atoms do not seem to carry magnetic moments. In contrast, t he two carbides U2RhC2 and U2IrC2 display temperature-dependent parama gnetism, which is compatible with one unpaired electron per transition metal site, while the magnetic susceptibility data of U2PtC2 indicate two unpaired electrons per formula unit. U2RhC2 exhibits complex magn etic behaviour below the Neel temperature of T-N = 18(+/-1) K, while t he temperature dependence of the susceptibility of U2IrC2 resembles th at of a normal antiferromagnet with T-N = 7(+/-3) K. The presence of t wo unpaired spins per formula unit in U2PtC2 is remarkable, because th is carbide is known as a ''nearly-heavy-fermion'' compound, which beco mes superconducting below 1.5 K.