Ferromagnetism in rare-earth group VA and VIA compounds with Th ₃P₄ structure

Abstract

The bcc structure I4̄3d-Td6(Th3P 4) occurs as a defect structure in 2:3 compounds of rare-earth elements with S, Se, and Te, or as an inverted structure in 4:3 compounds with group VA elements. The structural, electric, and magnetic properties of the metallic 4:3 compounds and the 2:3 rare-earth semiconductors have been investigated with specific reference to gadolinium, for which the S ground state gives the minimum crystal field effect. Gd4Bi3 and Gd4Sb3 are both ferromagnetic with a saturation magnetization obeying the spin-wave T32 law up to 0.8 of the Curie temperature. The Curie temperature Tc varies in the solid solution system Gd4Sb3Single Bond sign Gd4Bi3 with composition from 260°to 340°K. The semiconducting compound Gd 2Se3(ρRT=3 Ω cm) has been found to be antiferromagnetic below TN=6°K. Solution of Gd in the holes of the defect Th3P4 structure decreases the electrical resistivity without a measurable variation of lattice constant (a 0=8.718 Å). With increasing conductivity the material changes from antiferromagnetic to ferromagnetic. At the composition Gd 2.1Se2.9 the Curie temperature is Tc=80°K with ρRT=1.4×10-3 Ω cm. The relation between Curie temperature and electrical resistivity has been examined by introducing the same spin concentration into Gd2Se3 by Eu2+ doping. The semiconductor Eu0.5Gd 1.6Se2.9 is paramagnetic. However, Y0.5Gd 1.6Se2.9 has low resistivity and is ferromagnetic below Tc=47°K. © 1964 The American Institute of Physics.