Tantalum clustering in the A1 to L1o iron-platinum-tantalum chemical ordering phase transformation

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A series of Fe₅₂Pt₄₈, Fe₅₂․₃Pt₄₆․₃Ta₁․₄ and Fe₅₂Pt₄₀․₇Ta₇․₃ thin films were sputter- deposited and subsequently annealed at 550°C and 750°C for 30 min. The as-deposited films adopted the A1 phase. The addition of Ta resulted in the change in the {111} to {200} fiber texture for these films. This has been explained in terms of the competition between surface energy and strain energy. The Fe₅₂Pt₄₈ and Fe₅₂․₃Pt₄₆․₃Ta₁․₄ films ordered into L1₀ at 550°C but the Fe₅₂Pt₄₀․₇Ta₇․₃ did not. Upon annealing at 750°C all three films phase transformed to the L1₀ phase. As the Ta concentration increased, the grain size was refined and hindered grain growth. Atom probe tomography revealed nano-scale clustering upon annealing for films that contained Ta. For the lower 1.4 at.% Ta concentration film, these clusters were predominately within the grains. For the 7.3 at.% Ta film, the clusters formed predominately in the grain boundaries. The formation of clusters appears to be a necessary initial step to allow the short range A1 to L1₀ ordering processes in FePt to occur.

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Engineering, Materials Science, Engineering, Metallurgy