Initial Permeability Characteristics of Mixed Yttrium-Gadolinium Iron Garnets

Abstract

Complex initial permeability measurements have been made on polycrystalline garnet toroids of the form $\text{(3−x)}{\mathrm{Y}}_2{\mathrm{O}}_3\mathrm{·x}{\mathrm{Gd}}_2{\mathrm{O}}_3\text{·5}{\mathrm{Fe}}_2{\mathrm{O}}_3$ where $x$ ranged from zero (yttrium iron garnet) to three (gadolinium iron garnet). Both the real initial permeability $\mathrm{\mu \prime }$ and the imaginary initial permeability $\mathrm{\mu \prime \prime }$ were measured at 23°C, −78°C and −196°C over a frequency range of 1 kc to 2000 Mc. At room temperature, the low frequency value of $\mathrm{\mu \prime }$ was found to decrease with increasing gadolinium content. At lower temperatures the low frequency value of $\mathrm{\mu \prime }$ exhibits a minimum in $x$ caused by the temperature dependent behavior of the two different magnetic sublattices. The frequency at which the maximum value of $\mathrm{\mu \prime \prime }$ occurs was found to increase with the addition of gadolinium. No thermal relaxation was observed in these garnets, but rather the peaks in the curves shifted to slightly higher frequencies with decreasing temperature.