Hall Effect Of Polycrystalline And Epitaxial Fe₃o₄ Films

The anomalous Hall effect (AHE) has been discovered for almost a century, however, its origin is still undecided now. Fe3O4, whose conductivity stems from the hopping of electrons, is one of the magnetic half-metallic materials. Therefore, it becomes a significant media for investigating the effect of localization on AHE.We have prepared Fe₃O₄ and Fe3?δO4 films by facing–target reactive sputtering, and their microstructure, transport and magnetic properties were studied systematically.Structure analyses show that all the samples have inverse spinel structure. Whenρxx<4×105μ? cm, the anomalous Hall conductivity,σxAyHE, of the epitaxial Fe₃O₄ films follow the scaling law of the universal theory. While theσxAyHEof the samples deviates from the universal theory whenρxx>4×105μ? cm, due to the cancellation of theσASJHE andσABHerEry generated by side jump and Berry phase respectively. The AHE of the epitaxial Fe₃O₄ films with different orientations is isotropic while theσASJHE of the sample is relatively small.The universal theory is invalid for the polycrystalline Fe₃O₄ films with small grain size, because the depletion layers near the grain boundaries modify the Fe₃O₄ band structure significantly. TheσxAyHE of the Fe3?δO4 films containing Fe grains does not follow the scaling law of universal theory, and even experiences a sign reversal near the Verwey transitional temperature. The reason is that the sign of theσAFeHE generated by Fe grains is different from that of the Fe₃O₄ matrix, and the cancellation of theσAFeHE and Fe3O4σAHE leads to the alternation of the power law. The universal theory is only valid for the Fe3?δO4 film withγ?Fe₂O₃ phase whenρxx<4×105μ? cm, becauseγ?Fe₂O₃ does not generate AHE.