MAGNETIC AFTEREFFECTS IN SINGLE AND POLYCRYSTALLINE YTTRIUM-IRON-GARNET

Magnetic aftereffect (MAE) measurements on single and polycrystalline yttrium iron garnet, Y3Fe5O12, have been carried out from 4.4 to 450 K by means of an LC-oscillator technique. In nonoriented and oriented s ingle crystal samples three processes around 60, 130 and 250 K are obs erved. Similar peaks appear in polycrystalline samples which had been sintered in air or CO2 atmospheres. Following CO2 sintering, a negativ e MAE is observed at low temperatures (T < 100 K) which is affected by the conditions of sample demagnetization. The processes have been app roximated using least squares fitting techniques and are discussed in terms of a model based on the presence of oxygen vacancies and Fe2+ io ns in tetrahedral and octahedral positions.