Dynamic Squareness in Polycrystalline Garnets

Abstract

Certain samples of polycrystalline yttrium iron garnet and lutetium iron garnet have previously been found to acquire a square 60-cps hysteresis loop when cooled to 78°K in a magnetic field. It is found that these are not normal square-loop materials, for at sufficiently slow excitation (ca. 0.5 cps for yttrium iron garnet, one cycle per hour for lutetium iron garnet) they revert to normal, but strongly frequency-dependent loops. At 78°K, for proper amplitude step excitation, the response of these cores is a delayed pulse. For lutetium iron garnet this delay can be several hundred μsec in duration. The behavior of these materials can be qualitatively explained by domain wall instability produced by a diffusion after-effect mechanism.