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

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Abstract
We have investigated the microstructures and magnetic properties of L10 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 ∼2 nm diameter with disordered face-centered-cubic structure. These particles are embedded in the amorphous aluminum oxide matrix with average spacing of ∼1.3 nm, and the film exhibits superparamagnetism. By annealing above 650 °C, the nanoparticles transform to the L10 ordered phase and the grains are coarsened 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.

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