Composition-dependent spin reorientations in silicon-substituted yttrium iron garnets

The spin reorientations in silicon-substituted yttrium iron garnets with 0.12 to 0.40 ${\mathrm{Si}}^{4+}$ per formula unit, prepared by solid-state reaction or flux grown have been investigated with Mössbauer spectroscopy. There is no spin reorientation for less than 0.18 ${\mathrm{Si}}^{4+}$ per formula unit. For ${\mathrm{Si}}^{4+}$ content greater than 0.18 per formula unit, the temperature of the onset of the spin reorientation increases with ${\mathrm{Si}}^{4+}$ content to 0.3 per formula unit, after which the effect saturates at approximately 260 K. Chemical analyses indicate that the ${\mathrm{Fe}}^{2+}$ contents are about two-thirds of the ${\mathrm{Si}}^{4+}$ contents and are consistent with the results obtained on the spin reorientations. A semiquantitative model is given which accounts for the broad spin reorientations and the composition dependence including the saturation of the effect.