CRYSTALLOGRAPHIC DISTORTION AND MAGNETIC-STRUCTURE OF TERBIUM IRON-GARNET AT LOW-TEMPERATURES

The crystallographic and magnetic structures of terbium iron garnet were refined simultaneously from neutron powder patterns at four temperatures, 290, 39, 13, and 5 K, by the Rietveld method. The distortion from the cubic room-temperature structure (space group Ia3d, a = 12.4339(1)Å) leads to rhombohedral symmetry. R3 is compatible with both the crystallographic and magnetic structure at low temperatures. The lattice constants are arh = 10.7442(1)Å and α = 109.412(1)° at 5 K. Precise values for the shifts of atomic parameters were derived and the evolution of the magnetic structure at low temperatures is given. No deviation from the collinearity has been observed for the iron spin sublattices. The results are compared with previous work. © 1990.