Thickness dependence of the magnetic properties of barium ferrite films prepared by pulsed laser deposition

BaFe₁₂O₁₉ (BaM) thin films with thicknesses ranging from 15 nm–200 nm were deposited on Al₂O₃(0001) substrates by pulsed laser deposition (PLD). X-ray diffraction patterns show that a buffer layer with a thickness of nearly 60 nm forms on the substrate, and then a c-axis perpendicularly oriented BaM thin film grows on the buffer layer. Atomic force microscopy results indicate that the BaM thin film exhibits a spiral island growth mode on the buffer layer. Magnetic hysteresis loop results confirm that the buffer layer exhibits no significant magnetic anisotropy, while the BaM thin film exhibits perpendicular magnetic anisotropy. The out-of-plane coercivity decreases with increasing BaM thin-film thickness due to the combined effect of grain size growth and lattice strain relaxation. The 200 nm thick film exhibits optimum magnetic properties with M_s = 319 emu/cm³ and H_c = 1546 Oe.