On the growth and magnetic properties of flower-like nanostructures formed on diffusion of FePt with Si substrate

Nearly equi-atomic FePt films were deposited on a silicon substrate with a native SiO₂ layer by co-sputtering technique. Structural and magnetic properties of the films are influenced by the growth temperature. The native SiO₂ layer acts as a diffusion barrier for the FePt film on Si. In the absence of diffusion of Fe and Pt with Si substrate, a high coercivity (∼8.2 kOe) L1₀ Fe₅₀Pt₅₀ phase is formed. Depending on the growth temperature and the thickness/quality (continuously or containing some pinholes) of SiO₂ layer, diffusion of FePt film with Si substrate is observed. Diffusion results in the change in film composition, and formation of various Fe- and Pt-silicide phases along with the flower-like surface morphology. Growth of flower like nano-structures are shown to be governed by the accelerated diffusion of Fe on a dimpled surface of Si substrate. The detailed structural and magnetic characterization revealed that the flower-like patterns are composed of chemically ordered antiferromagnetic FePt₃ phase (Q₂-type). The Neel's temperature for these flowers-like nano-structures is ∼80 K and they are surrounded by a ferromagnetic matrix. Growth mechanism of flower-like patterns is identified. Site specific growth of antiferromagnetic nano-structures in a ferromagnetic matrix is also demonstrated.