A solid solution of yttrium-iron garnet with yttrium-gallium or yttrium-aluminum garnet is formed over the entire range of composition; the lattice constant variation is nearly linear. The trivalent ions, ${\mathrm{Sc}}^{3+}$, ${\mathrm{In}}^{3+}$, and ${\mathrm{Cr}}^{3+}$, may be substituted for ${\mathrm{Fe}}^{3+}$ to a limited extent. Substitution proceeds on a steric basis for nonmagnetic ions: those smaller than ${\mathrm{Fe}}^{3+}$, namely ${\mathrm{Al}}^{3+}$ and ${\mathrm{Ga}}^{3+}$, preferentially occupy the smaller, tetrahedrally coordinated sites, 24(d); larger ions, ${\mathrm{In}}^{3+}$ and ${\mathrm{Sc}}^{3+}$, preferentially occupy larger, octahedrally coordinated sites, 16(a). The ${\mathrm{Cr}}^{3+}$ ion, though smaller than ${\mathrm{Fe}}^{3+}$, preferentially occupies the octahedral site, presumably because of its electronic configuration. The magnetic moment initially rises with octahedral substitution of nonmagnetic ions and falls with tetrahedral substitution because the moment corresponds to the difference in the moments of the ${\mathrm{Fe}}^{3+}$ ions in the two octahedral sites and the three tetrahedral sites per formula unit, ${\mathrm{Y}}_3$${\mathrm{Fe}}_2$${\left(\mathrm{F}\mathrm{e}{\mathrm{O}}_4\right)}_3$. The Curie temperature is decreased by the substitution of nonmagnetic ions for iron on account of the decrease in the number of ${\mathrm{Fe}}^{3+}$-${\mathrm{O}}^{2-}$-${\mathrm{Fe}}^{3+}$ interactions.

• Received 9 December 1957

DOI:https://doi.org/10.1103/PhysRev.110.73