Effect of Indium Substitution in Yttrium Iron Garnet. High Permeability Garnets

Initial studies on the effect of small substitutions of indium for iron in polycrystalline yttrium iron garnet showed a substantial increase in the initial permeability over that of YIG. Since previous substitution of other ions has produced either little change or a decrease in the permeability, we have studied the effect of indium substitution on the garnet structure in more detail. Due to the size increase of ${\mathrm{In}}^{\text{3+}}$ radii over that of ${\mathrm{Fe}}^{\text{3+}}$ , the substitution of ${\mathrm{In}}^{\text{3+}}$ into the garnet structure is limited to the larger of the available ${\mathrm{Fe}}^{\text{3+}}$ sites. The general formula can be written ${\mathrm{Y}}_3({\mathrm{Fe}}_{\text{2−x}}{\mathrm{In}}_x){\mathrm{Fe}}_3{\mathrm{O}}_{12}$ where $x$ may take on values up to 2.0. X-ray determination of the lattice parameters for this series shows a linear dependence on $x$ with an apparent change in slope for $\text{x>0.6}$ . For $\text{x<0.65}$ there is no “detectable” trace of a second phase and the lattice constants vary from 12.376±0.005 A $\text{(x\hspace{0.17em}=\hspace{0.17em}0)}$ to 12.445±0.005 A $\text{(x\hspace{0.17em}=\hspace{0.17em}0.6)}$ . For $\text{x\hspace{0.17em}=\hspace{0.17em}0.65}$ a small perovskite phase is present, which becomes more apparent with larger $x$ . Since the lattice constant of the garnet phase in the two-phased samples does increase with $x$ , it appears that $x$ will enter the garnet structure for $\text{x>0.65}$ . However, repeated firings at various temperatures have so far failed to remove the perovskite phase. The relative initial complex permeability ${\mu }^{*}$ was measured over a frequency range from ${10}^3$ to ${\text{2×10}}^9\hspace{0.17em}\mathrm{cps}$ on high density toroids. Increases in ${\mu }_{\text{0′}}$ , the low-frequency value of $\mathrm{\mu \prime }$ , over that of YIG were found for all of the single-phased garnets in the series. A plot of ${\mu }_{\text{0′}}$ as a function of $x$ shows an essentially linear increase from ${\mu }_{\text{0′}}\text{\hspace{0.17em}=\hspace{0.17em}112}$ for $\text{x\hspace{0.17em}=\hspace{0.17em}0}$ (YIG) to ${\mu }_{\text{0′}}\text{\hspace{0.17em}=\hspace{0.17em}518}$ for $\text{x\hspace{0.17em}=\hspace{0.17em}0.6}$ . Measurements of ${\mu }_{\text{0′}}$ as a function of temperature up to the Curie point for this series are also presented. Magnetic moment measurements were made from −196°C to the Curie temperature for this series. As in the case of other substitutions for ${\mathrm{Fe}}^{\text{3+}}$ , the substitution of ${\mathrm{In}}^{\text{3+}}$ resulted in a decided decrease in the Curie temperature from 278±2°C for YIG to $\text{Tc\hspace{0.17em}=\hspace{0.17em}148±2°}\mathrm{C}$ for $\text{x\hspace{0.17em}=\hspace{0.17em}0.6}$ . The room temperature moment is only slightly higher than that of YIG ${\text{(6.8μ}}_B)$ . On the basis of comparison of their thermal magnetic properties, it could be expected that ${\mathrm{Sc}}^{\text{3+}}$ substitution in small amounts would also produce a rise in ${\mu }_{\text{0′}}$ . The increase in