Strain relaxation inFe3O4/MgAl2O4heterostructures: Mechanism for formation of antiphase boundaries in

Abstract

Strain relaxation studies in epitaxial magnetite, Fe 3 O 4 , thin films grown on MgAl 2 O 4 ͑100͒ substrates are reported. The study shows that the films were relaxed in line with the theoretical model prediction with a critical thickness, t c = 5 nm. Antiphase boundaries ͑APBs͒ are not expected to form in Fe 3 O 4 films grown on MgAl 2 O 4 substrates because both film and substrate have the same crystal symmetry. In contrast, our study reveals the formation of APBs within the Fe 3 O 4 films. Our analysis shows that the APBs in a Fe 3 O 4 / MgAl 2 O 4 heteroepitaxial system are formed by partial dislocations, which accommodate the misfit. This formation mechanism of APBs is fundamentally different from the one found in the Fe 3 O 4 / MgO system, where APBs are formed as a consequence of equivalent nucleation sites on the MgO substrate separated by nontranslational vectors of the Fe 3 O 4 lattice. The mechanism for the formation of antiphase boundaries through partial dislocations should be applicable to a wide range of epitaxial systems having identical symmetries of the film and the substrate and significant lattice mismatch.

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.…”

“…Thus, APBs can be considered as a strain relaxation mechanism. 24,25 In bulk magnetite the dominating magnetic coupling is the antiferromagnetic superexchange between neighboring tetrahedral and octahedral cation sites, the coupling between octahedral site cations being effectively ferromagnetic. However, in Fe 3 O 4 thin films, these magnetic interactions are altered at the antiphase boundaries, 15,17 across which the intrasublattice exchange interactions dominate, reversing the spin coupling.…”

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

“…[11][12][13][14][15][16][17][18][19][20] The interest is partly due to the great application potential of this material in spintronics. Fe 3 O 4 is one of the most important half-metallic oxides with the highest Curie temperature (T C = 858 K).…”

“…21 There are many reports on the growth of Fe 3 O 4 thin films on different types of substrates like MgO, MgAl 2 O 4 , sapphire, Si, or GaAs using a variety of deposition techniques. 11,12,[22][23][24][25][26][27] MgO (lattice constant 0.4212 nm), which has a rock salt crystal structure, is a widely used substrate for epitaxy of magnetite (lattice constant 0.83987 nm) due to the small lattice mismatch of only 0.33%. 9 Antiphase boundaries (APB) are structural defects occurring in thin films during epitaxial growth and are observed in Fe 3 O 4 films when grown on a variety of substrates like MgO, MgAl 2 O 4 , and α-Al 2 O 3 .…”

Anomalous magnetization reversal due to proximity effect of antiphase boundaries

“…[1][2][3][4] Antiphase boundaries (APB) are natural growth defects occurring due to the symmetry difference between the thin film and the substrate crystal structures. [5][6][7] Studies of epitaxial thin films and heterostructures containing APBs have attracted considerable attention during the last decade as APBs can significantly alter the physical properties of thin films, which is advantageous for the development of spintronic devices. [8][9][10][11] One of the important epitaxial heterostructures for these studies is Fe 3 O 4 thin films grown on MgO substrates.…”