Microstructure and magnetic properties of FePt-Al-O granular thin films

We have investigated the microstructures and magnetic properties of L1(0) ordered FePt granular thin films prepared by ion beam sputtering and subsequent annealing. As-deposited FePt-Al-O films are composed of fine spherical FePt particles of similar to 2 nm diameter with disordered face-centered-cubic structure. These particles are embedded in the amorphous aluminum oxide matrix with average spacing of similar to 1.3 nm, and the film exhibits superparamagnetism. By annealing above 650 degrees C, the nanoparticles transform to the L1(0) ordered phase and the grains are coarsened to similar to 20 nm, which results in a high coercivity up to 10 kOe. In the films with a high Al content, most of the particles are isolated by the amorphous aluminum oxide matrix, while the grains are interconnected in the films with a low Al content. The changes in magnetic properties are discussed based on the microstructural observation results. (C) 2000 American Institute of Physics. [S0003-6951(00)05126-3].