Hall Effect of Polycrystalline and Epitaxial Fe3O4 Films
|Course||Materials Physics and Chemistry|
|Keywords||Fe3O4 films transport properties anomalous Hall effect universal theory side jump Berry phase|
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.