Atomic-Scale Mechanism of Grain Boundary Effects on the Magnetic and Transport Properties of Fe₃O₄ Bicrystal Films

Abstract

In strongly correlated materials, change of the local lattice configuration is expected to tune or even generate new properties otherwise in the ideal bulk materials. For highly spinpolarized materials, the spin-dependent transport is sensitive to the local magnetic structure. Here, the artificial grain boundaries (GBs) with different tilt angles are produced in Fe 3 O 4 films using SrTiO 3 bicrystal substrates. The saturation magnetization of Fe 3 O 4 bicrystal films is enhanced. The detailed atomic structural results combining with density functional theory calculations reveal that the elongated Fe A -O bond length at GBs resulting in the reduction of charge transfer reduces the Fe A magnetic moments, which enhances the total magnetic moments of Fe 3 O 4 . The in-plane rotation of the Fe 3 O 4 lattice on bicrystal substrates alters the magnetization processes. Especially, the Fe 3 O 4 bicrystal film with a tilt angle of 22.6°shows strong in-plane magnetic anisotropy due to the zigzag GBs. The altered magnetic anisotropy of Fe 3 O 4 bicrystal films enhances the anisotropic magnetoresistance. The findings reveal the mechanism of GBs on the magnetic and transport properties and manifest that the strategy of utilizing GBs can tune the physical properties in highly spin-polarized materials.

Effect of Film Thickness on Microstructural and Magnetic Properties of Lithium Ferrite Films Prepared on SrTiO₃ (001) Substrates

“…Additionally, the appearance of a high density of antiferromagnetic TBs [26] in the 30-nm-thick film can lower the Ms of the film. In contrast, the oriented GBs are dominant in the 7.5-nm-thick film, which may enhance the Ms of the film owing to the magnetic coupling at the interfaces [9,17]. Overall, varying thicknesses of the LiFe5O8 films on SrTiO3(001) substrate can effectively modify the microstructural and magnetic properties of the film.…”

“…Compared to the bulk material, spinel thin films exhibit microstructural variations such as the presence of planar defects, which can alter the electrical and magnetic structures of the films [6,7]. Thus, research efforts concentrating on the growth, structure, property, and applications of the spinel thin films have proliferated over the last decades [8][9][10].…”

Atomic-Scale Structural and Magnetic Coupling Properties of Twin Boundaries in LiFe5O8 Film

“…For instance, antiphase boundaries (APBs) have been frequently observed in spinel ferrite films, e.g., Fe3O4, NiFe2O4, and LFO [2][3][4]. Atomic models and magnetic coupling across APBs have been extensively determined using high resolution scanning transmission electron microscopy (STEM) and density function theory in spinel-type materials [5][6][7]. Antiferromagnetic coupling occurs across the APBs, leading to non-saturation of magnetization and larger magnetoresistance of the ferromagnetic film, which can be harmful for applications [8][9][10].…”

Effect of Film Thickness on Microstructural and Magnetic Properties of Lithium Ferrite Films Prepared on Strontium Titanate (001) Substrates

“…Compared to the bulk material, spinel thin films exhibit microstructural variations such as the presence of planar defects, which can alter the electrical and magnetic structures of the films [6,7]. Thus, research efforts concentrating on the growth, structure, properties, and applications of spinel thin films have proliferated over the last few decades [8][9][10].…”