Characterization of antiphase boundary network inFe3O4(111)epitaxial thin films: Effect on anomalous magnetic behavior

Abstract

We report on the antiphase boundaries network of Fe 3 O 4 ͑111͒ thin films. 5-to 50-nm-thick samples were epitaxially grown by molecular beam epitaxy onto ␣-Al 2 O 3 ͑0001͒ substrates. The magnetic properties of the samples have been interpreted within the framework of a one-dimensional model of antiphase boundary ͑APB͒, which predicts that the magnetization is given by M ϱ ͑1−b / ͱ H͒ 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.

Positive antiphase boundary domain wall magnetoresistance in Fe3O4(110) heteroepitaxial films

“…34,41 This could be because of the differences in the APB network geometry, the fraction of APBs exhibiting AF couplings, and the difference in the APB density. …”

“…28 Micro magnetic simulations reported by Bataille et al show that APBs can no longer be considered independent when the distance between them is less than 40 nm and the blocking field H B increases as film thickness decreases. 34 This is due to the reason that, when two AF-APBs come closer the spins within the boundary can be pinned, which allows for less rotational freedom compared to spins in larger domains. This could be the reason for the dependency of DWMR APB on film thickness.…”

“…Exchange interactions occurring across some of the APBs must be antiferromagnetic (AF), and experimental evidence suggests that these AF-APBs dominate the magnetic and magnetotransport properties of Fe 3 O 4 thin films. 20,32,34 It was shown that if the spins on neighboring ions are not parallel but, instead, form an angle ϕ nn , the transfer integral is reduced tot = t o cos ϕ nn /2. 32 Therefore, the transfer of the conduction electrons between ions with antiparallel spins at an AF-coupled APB is blocked and, according to the model, the conductivity reduces to zero.…”

Field-dependent anisotropic magnetoresistance and planar Hall effect in epitaxial magnetite thin films

“…The combination of all these factors makes a correct identification of the dominant scattering processes in play challenging. We do note, however, that the difference between bulk compounds and thin films grown on MgO (particulary, lack of high field saturation) has been attributed to the presence of antiphase boundaries (APB) [15,18,[21][22][23]. The APB disturb the magnetic configuration even at high magnetic fields, particularly close to the boundary, as illustrated in the inset of Fig.…”

Anomalous magnetization reversal due to proximity effect of antiphase boundaries

“…The domain sizes calculated for our (110) oriented films are found to be on average 9.7% smaller than the corresponding domain sizes reported in the case of (100) oriented films for the same film thickness. 19 By considering that around 20-30% of APBs are AF-APBs 11,25 and the mean domain size of our (110) oriented films is significantly smaller than in the case of (100) oriented films, we can consider the possibility of exchange coupling of neighboring magnetic domains through AF-APBs. For a greater understanding let us consider a simplified situation, where two magnetic domains of different size, large domain (L), and small domain (S) are exchange coupled through the in-plane AF-APBs.…”