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

BaFe 12 O 19 (BaM) thin films with thickness ranging from 15-200 nm were deposited on Al 2 O 3 (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 perpendicular orientation BaM thin film grows on the buffer layer. Atomic force microscope 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 the optimum magnetic properties with Ms =319 emu/cm 3 and Hc =1546 Oe.