CUBIC MAGNETIC-ANISOTROPY OF NONSTOICHIOMETRIC MAGNETITE

The cubic magnetic anisotropy constants of Fe3(1-delta)O4 single crystals (with 0.000 < delta < 0.006), obtained by curve fitting of the respective magnetization curves, are reported between room temperature and the isotropic point (approximately 130 K), where the easy axis changes from [111] to [100] . Two distinct temperature dependences are observed for nonstoichiometries above and below delta(C) = 0.0039, in samples with second- and first-order Verwey transitions, respectively. The characteristic temperatures for the first-derivative curves are consistent with mean-field parameters for nearest-neighbor-interaction models.