Magnetotransport properties of Fe3O4 epitaxial thin films: Thickness effects driven by antiphase boundaries

Abstract

Effect of metallic buffer layers on the antiphase boundary density of epitaxial Fe 3 O 4Enhancement of the magnetization saturation in magnetite (100) epitaxial films by thermo-chemical treatment J. Appl. Phys. 95, 7357 (2004); 10.1063/1.1687632 Domain structures in epitaxial (110) Fe 3 O 4 particles studied by magnetic force microscopyWe present an in-depth study of the magnetotransport properties of epitaxial Fe 3 O 4 films as a function of film thickness. The films, grown on ␣-Al 2 O 3 ͑0001͒ single crystals by atomic-oxygen assisted molecular beam epitaxy, exhibit high structural order and abrupt interfaces. These films contain antiphase boundaries ͑APBs͒, the density of which is strongly dependent on film thickness. A series of resistivity and magnetoresistance measurements demonstrate a systematic evolution of these properties with decreasing film thickness, revealing the impact of APBs on the transport properties in the films. We present a model based on the spin-polarized transport across an antiferromagnetically coupled APB in order to successfully reproduce our experimental data over a large range of applied magnetic fields. The comparison of this model with experimental results further clarifies the mechanism of the anomalous magnetotransport behavior in Fe 3 O 4 .

Origin of the giant magnetic moment in epitaxialFe3O4thin films

“…Therefore, the APB density decreases significantly with the increase in film thickness ͑t͒. 6 Finally, APBs have been observed in Fe 3 O 4 films grown on MgAl 2 O 4 and related to the absence of epitaxial strain relaxation, 24 as if the APBs network leads to the formation of areas with opposite sign of stress, compensating and reducing the effective stress experienced by the films. Thus, APBs can be considered as a strain relaxation mechanism.…”

“…2͒ and its characteristic metal-insulator transition at 120 K ͑Verwey transition͒. [3][4][5] Differences between some properties of bulk magnetite and epitaxial thin films have been observed, such as an increased resistivity with decreasing film thickness, [6][7][8] negative magnetoresistance, [9][10][11] decreased and broadened Verwey transition temperature ͑T V ͒, 7,12,13 superparamagnetism in ultrathin films, 14,15 decreased saturation magnetization, [16][17][18][19] and anomalous, planar, and ordinary Hall effects. [20][21][22] This anomalous behavior has often been associated to the film microstructure and the presence of structural growth defects called antiphase boundaries ͑APBs͒.…”

Epitaxial growth and ferrimagnetic behavior of MnFe2O4(111) ultrathin layers for room-temperature spin filtering

“…APBs are stacking defects of the atomic planes in the spinel lattice corresponding to a half-lattice translation of the cationic sublattice, whereas the oxygen sublattice remains unchanged. In the case of Fe 3 O 4 , these APBs have been widely studied due to their important effect on the magnetic 17,27 and magnetotransport [28][29][30] properties of this material. In the case of MnFe 2 O 4 , much less is known.…”

Nanoparticles charge response from electrostatic force microscopy

“…For magnetite thin films, the transition is broad 12,13 and only a crossover between a high temperature metallic phase and a low temperature insulating phase is observed. In NPs, size effects are expected to broaden the Verwey transition even more.…”