The cation distribution and magnetic structure of Y3Fe((5-x))AlxO12

The samples of Y3Fe(5-x)AlxO12 (x = 1,2,3,4,5) were sintered from correspon ding mixed hydroxides that were obtained by coprecipitation of mixed nitrat es. 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 pr eferential distribution of these cations is found. The iron ions preferenti ally occupy octahedral positions, the smaller aluminum ions preferentially occupy the smaller tetrahedral positions. The samples with x = 1, 2 are col linear ferrimagnetics, with antiparallel moments in tetrahedral and octahed ral positions, at 10 K. The sample with x = 1 retains this magnetic order a t 295 K. The magnetically ordered phases were refined in the cubic space gr oup Ia3d and in the rhombohedral space group R-3c. In the rhombohedral spac e group the magnetic moments of the iron ions at 10 K are -3.94(6) and -3.6 (1)mu (B) in the tetrahedral position and 4.28(5) and 3.75(7)mu (B) in the octahedral position, for samples with x = 1,2, respectively. In the R-3c th e total magnetic moment, per formula unit, agrees with the results of the c lassical magnetic measurements. Both samples (x = 1,2) are rhombohedral at low temperatures and the symmetry of s = 1 sample approaches the cubic with the increase of temperature. (C) 2001 Elsevier Science B.V. All rights res erved.