Crstallographic and magnetic properties of barium ferrite thin films on various underlayers

In this work, both crystal orientation and microstructure of barium ferrite (BaM) thin films, deposited on Pt, Pd, and Pt-Pd underlayers have been manipulated. The thickness of underlayer is about 20 nm and the thickness of barium ferrite film is in the range from several nm to 20 nm. It is convinced by x-ray diffraction patterns that all of BaM films grown on the three kinds of underlayer show its c-axis orientation perpendicular to the films plane while underlayers have preferred (111) orientation. Magnetic hysteresis loops confirm the XRD results. All the films have a much higher coercivity in the perpendicular direction than that of in the parallel direction. And the squareness ratio of the perpendicular hysteresis is about 0.8 for the films prepared onto Pt underlayer. BaM Films grown on Pt and Pd underlayers have grains as large as 500 tim, while those grown on Pt-Pd alloy underlayers have grains as small as 5 nm. This is due to the small grain size of the Pt-Pd alloy underlayer. Our results indicate that the grain size of the underlayer strongly manipulate the grain size of the barium ferrite layer.