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

Abstract

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 In3+ radii over that of Fe3+,the substitution of In3+ into the garnet structure is limited to the larger of the available Fe3+ sites. The general formula can be written Y3(Fe2−xInx)Fe3O12 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 x>0.6. For x<0.65 there is no “detectable” trace of a second phase and the lattice constants vary from 12.376±0.005 A (x = 0) to 12.445±0.005 A (x = 0.6). For x = 0.65 a small perovskitephase 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 x>0.65. However, repeated firings at various temperatures have so far failed to remove the perovskite phase. The relative initial complex permeability μ* was measured over a frequency range from 103 to 2×109 cps on high density toroids. Increases in μ0′, the low-frequency value of μ′, over that of YIG were found for all of the single-phased garnets in the series. A plot of μ0′ as a function of x shows an essentially linear increase from μ0′ = 112 for x = 0 (YIG) to μ0′ = 518 for x = 0.6. Measurements of μ0′ 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 Fe3+, the substitution of In3+ resulted in a decided decrease in the Curie temperature from 278±2°C for YIG to Tc = 148±2°C for x = 0.6. The room temperature moment is only slightly higher than that of YIG (6.8μB). On the basis of comparison of their thermal magnetic properties, it could be expected that Sc3+ substitution in small amounts would also produce a rise in μ0′. The increase in μ0′ is attributed to the lowering of the Curie temperature while the magnetic moment is held nearly constant or slightly increased.