Anisotropic magnetoresistance across Verwey transition in charge ordered Fe 3 O 4 epitaxial films

Abstract

The anisotropic magnetoresistance (AMR) near the Verwey temperature (TV) is investigated in charge ordered Fe 3 O 4 epitaxial films. When the temperature continuously decreases below TV, the symmetry of AMR in Fe 3 O 4 (100) film evolves from twofold to fourfold at a magnetic field of 50 kOe, where the magnetic field is parallel to the film surface, whereas AMR in Fe 3 O 4 (111) film maintains twofold symmetry. By analyzing AMR below TV, it is found that the Verwey transition contains two steps, including a fast charge ordering process and a continuous formation process of trimeron, which is comfirmed by the temperature-dependent Raman spectra. Just below TV, the twofold AMR in Fe 3 O 4 (100) film originates from uniaxial magnetic anisotropy. The fourfold AMR at a lower temperature can be ascribed to the in-plane trimerons. By comparing the AMR in the films with two orientations, it is found that the trimeron shows a smaller resistivity in a parallel magnetic field. The field-dependent AMR results show that the trimeron-sensitive field has a minimum threshold of about 2 kOe.