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

We have investigated the microstructures and magnetic properties of L1(0) o rdered FePt granular thin films prepared by ion beam sputtering and subsequ ent annealing. As-deposited FePt-Al-O films are composed of fine spherical FePt particles of similar to 2 nm diameter with disordered face-centered-cu bic structure. These particles are embedded in the amorphous aluminum oxide matrix with average spacing of similar to 1.3 nm, and the film exhibits su perparamagnetism. By annealing above 650 degrees C, the nanoparticles trans form 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 alumi num oxide matrix, while the grains are interconnected in the films with a l ow Al content. The changes in magnetic properties are discussed based on th e microstructural observation results. (C) 2000 American Institute of Physi cs. [S0003-6951(00)05126-3].