In yttrium‐iron garnet, iron may be entirely replaced by aluminum and gallium; chromium, scandium, and indium may be substituted for iron to a limited extent. Substitution proceeds on a steric basis for the nonmagnetic ions: Al3+and Ga3+, which are smaller than Fe3+, preferentially occupy the smaller, tetrahedrally coordinated positions, 24(d); the Sc3+and In3+ions, which are larger than Fe3+, preferentially occupy the larger, octahedrally coordinated positions, 16(a). The Cr3+ion, though smaller than Fe3+, preferentially occupies the octahedral position, presumably because of its electronic configuration. The magnetic moment initially increases with octahedral substitution and decreases with tetrahedral substitution. The Curie temperature is decreased by the substitution of nonmagnetic ions for iron as a consequence of the decrease in the number of Fe3+&sngbnd;O2−&sngbnd;Fe3+interactions.