The cation distribution and magnetic structure of Y 3Fe (5− x) Al xO 12

Abstract

The samples of Y 3Fe (5− x) Al x O 12 ( x=1, 2, 3, 4, 5) were sintered from corresponding mixed hydroxides that were obtained by coprecipitation of mixed nitrates. The neutron diffraction experiments were done, for all the samples, at 295 and 10 K. All the samples crystallize in the garnet structure type. The iron and aluminum ions occupy tetrahedral and octahedral positions. The preferential distribution of these cations is found. The iron ions preferentially occupy octahedral positions, the smaller aluminum ions preferentially occupy the smaller tetrahedral positions. The samples with x=1, 2 are collinear ferrimagnetics, with antiparallel moments in tetrahedral and octahedral positions, at 10 K. The sample with x=1 retains this magnetic order at 295 K. The magnetically ordered phases were refined in the cubic space group Ia3d and in the rhombohedral space group R-3c. In the rhombohedral space group the magnetic moments of the iron ions at 10 K are −3.94(6) and −3.6(1) μ B in the tetrahedral position and 4.28(5) and 3.75(7) μ B in the octahedral position, for samples with x=1, 2, respectively. In the R-3c the total magnetic moment, per formula unit, agrees with the results of the classical magnetic measurements. Both samples ( x=1, 2) are rhombohedral at low temperatures and the symmetry of x=1 sample approaches the cubic with the increase of temperature.