The crystal structure and ferrimagnetism of yttrium-iron garnet, Y 3Fe 2(FeO 4) 3

Abstract

A refinement of the crystal structure of yttrium-iron garnet (cubic space group— Ia3 d) has been carried out by application of the least-squares method of calculation to single-crystal X-ray data. The oxygen parameters are x = −0.027 4, y = 0.057 2, z = 0.149 2; the tetrahedral iron-oxygen distance is 1.88 Å, the octahedral iron-oxygen distance is 2.00 Å and the yttrium-oxygen distances are 2.37 and 2.43 Å. None of the oxygen polyhedra is regular even though the space group would allow the tetrahedra and octahedra to be regular simultaneously. Interionic distances and angles which are important to the interaction between magnetic ions have been calculated. The strongest interactions probably occur between Fe 3+ in 16( a) and 24( d) positions and between Fe 3+, 24( d), and M 3+, a magnetic rare-earth ion substituted for yttrium, in the 24( c) positions. Interactions between crystallographically equivalent ions are all small. The number of interactions per Fe 3+ ion per formula unit is 3 5 that in a spinel “ferrite” and, correspondingly, the Curie temperature observed is 0.64 that of magnetite. No change of symmetry is observed up to 900°C, and the behavior of the lattice constant, a 0 vs. T is consistent with the presence of a Curie transition.