Characterization of antiphase boundary network in Fe_3O_4(111) epitaxial thin films: Effect on anomalous magnetic behavior

摘要

We report on the antiphase boundaries network of Fe_3O_4(111) thin films. 5- to 50-nm-thick samples were epitaxially grown by molecular beam epitaxy onto α-Al_2O_3(0001) substrates. The magnetic properties of the samples have been interpreted within the framework of a one-dimensional model of antiphase boundary (APB), which predicts that the magnetization is given by M_∞(1-b/H~(1/2)) in the approach to saturation regime. Transmission electron micrographs of several samples were used to extract the statistical parameters of the APB network, particular emphasis being put on the relevance and statistical significance of the studied parameters. The mean antiphase domain size D, as the antiphase boundaries characteristic length l_0 extracted from a fractal analysis, vary as the square root of film thickness/deposition time and are within the 10 nm range. The APB density was found to vary as 1/l_0 as expected from the fractal dimensions of the network. The dependency of the b parameter of the magnetic model on the APB density is finally analyzed in the light of micromagnetic simulations of chains including finite size antiphase domains and two APBs.