Magnetic and Magnetodielectric Properties of Epitaxial Iron Vanadate Thin Films

Abstract

The magnetic and magnetodielectric behavior of epitaxial (001) transition metal oxide spinel iron vanadate (Fe1+xV2-xO4, FVO) thin films grown on (001) SrTiO3 substrates by pulsed laser deposition is reported. X-ray absorption spectroscopy studies confirm the trivalent and nominally divalent nature of V and Fe ions, respectively, while an excess of Fe3+ ions is also found. Aberration-corrected cross-sectional scanning transmission electron microscopy analysis suggests that the excess Fe3+ may be accommodated through Fe3O4 stacking faults along the {111} planes. Temperature-dependent X-ray magnetic circular dichroism spectra reveal an anti-parallel alignment of spins between the Fe2+ and V3+ cations. M-H loops acquired at 10 K, well below the noncollinear ferromagnetic phase transition temperature, show magnetic anisotropy and point to the existence of two distinct phases with different coercive fields. Visual evidence for magnetic domains and their switching is given by magnetic force microscopy, which finds a switching field of approximate to 3 T in agreement with the M-H loops. Magnetodielectric measurements for a Pd/FVO/Nb:STO heterostructure reveal a weak hysteresis in the magneto-capacitance loops at 10 K, thus confirming magneto-dielectric coupling. Detailed temperature and frequency-dependent dielectric studies find that Maxwell-Wagner-type relaxation dominates capacitance behavior above approximate to 40 K due to a FVO/Nb:SrTiO3 Schottky interface.