Magnetic Behavior of Substituted Ferrimagnetic Garnets

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Abstract
The results of magnetic measurements on a large number of substituted yttrium iron garnets may be interpreted in terms of solid solutions between the ideal ferrimagnet and antiferromagnet. It is proposed that when substitution of diamagnetic ions is made exclusively in one Fe3+ ion sublattice, the moments of the Fe3+ ions in that sublattice remain parallel, while the weakened average a—d interactions and the intrasublattice interactions lead to random canting of the Fe3+ ion moments of the other. This tendency occurs as soon as substitution begins. On continued substitution a point is reached beyond which canting increases more rapidly with increasing substitution; in this region the intrasublattice interactions dominate the a—d interactions, but it is probable that the canting continues to be random. The model accounts for the results of simultaneous substitution of diamagnetic for Fe3+ ions in both sublattices. It has been found that different diamagnetic ion substituents may produce different magnetic behavior. Usually this is especially noticeable when the interactions are weak. However, in the case of V5+ ion substitution, dramatic effects are observed even for small substitution. It is suggested that these effects result from chemical bonding subtleties. The 0°K magnetic behavior of substituted gadolinium iron garnets may also be explained in terms of the model derived for the substituted YIG's. In particular, the behavior of the Gd3+ ion moments is linked directly with that of the tetrahedral Fe3+ ion moments. The model also leads to an explanation of the behavior of paramagnetic ion substituted YIG's.