Electronic and magnetic properties of sub-unit cell Fe2O3 (0001) films with variant thicknesses (N = 1 ~ 6, the number of Fe-O octahedral slabs) on the Al2O3 (0001) substrate are investigated by first-principles calculations. Five different magnetic configurations are comparatively studied:(i) Type I (++|- - ) with spins parallel within each Fe-O octahedral slab and antiparallel between two neighboring Fe-O octahedral slabs; (ii) Type II (+- |+- ) with spins antiparallel within each Fe-O octahedral slab and between two neighboring Fe-O octahedral slabs; (iii) Type III (++|++) with spins parallel for all Fe; (iv) Type IV (++|+- ) with spins parallel and antiparallel within each Fe bilayer but parallel between two neighboring Fe-O octahedral slabs; and (v) Type V (- +|+- ) with spins antiparallel within each Fe-O octahedral slab but parallel between two neighboring Fe-O octahedral slabs. It is found that ferromagnetic configuration (++) is stabilized for monolayer (N = 1) Fe2O3 with the lowest formation energy. The magnetic property of sub-unit cell Fe2O3 (0001) films depends on the film thickness. The Fe2O3 thin films comprising of odd number (N = 1, 3, 5) of Fe-O octahedral slabs are ferromagnetic, while those of even number (N = 2, 4, 6) of Fe-O octahedral slabs are antiferromagnetic. The band gap of sub-unit cell Fe2O3 films is obviously lower than that of the bulk. These findings can not only reveal the magnetic coupling nature in subunit cell antiferromagnetic crystals, but also promote the applications of Fe2O3 ultrathin films in magnetic and electronic devices.
Key words
Electron states at interfaces/Magnetic properties of interface/First-principles calculations/Metallic oxide/ALPHA-FE2O3/THIN/SURFACE/NANOPARTICLES/ALPHA-AL2O3/HEMATITE
NSTL
Elsevier