Magnetic ordering of Gd3+ and Sm3+ in the T and T* copper oxides and oxychlorides

The magnetic ordering of Sm3+ and Gd3+ moments in some T and T* copper oxides and oxychlorides has been studied. The temperature-dependent magnetic susceptibility of CaGdCuO3Cl and Sr0.1La0.9Gd0.9CuO4, both with T* structure, showed anomalies at 275 K and 150275 K, respectively, which are attributed to the antiferromagnetic ordering of the copper spins in each system. A comparison between the magnetic ordering of Gd3+ and Sm3+ in the oxychlorides revealed that the Gd3+ moments order at 6.1 K, while those of Sm3+ do not order down to 2 K. In contrast, both the parent T oxides Gd2CuO4 and Sm2CuO4 order at 6.66 and 5.95 K, respectively. A mechanism for superexchange involving the rare-earth f orbitals and the surrounding oxygen or copper orbitals is proposed based on crystal-field arguments to explain the observed differences in the magnetic ordering of the Gd3+ and Sm3+ moments.