Abstract
The magnetic and structural properties of Fe–Pt nanocomposites and relatedidealized structures have been investigated by a combination of experimental andtheoretical techniques. The dependence of magnetocrystalline anisotropy (MCA) ofL10 FePt on the ratio of the tetragonal lattice parameters,c/a, has been calculated with a relativistic version of the full potential local orbitalmethod, assuming complete chemical order and fixed unit-cell volume. It hasbeen found that the well known tetragonal lattice distortion in this phase has arelatively small influence on the MCA (compared to the influence of chemicalordering) and even reduces the MCA. The calculated in-plane anisotropy is negligible.The structure, magnetic properties and magnetization reversal processes ofFe100−xPtx (x = 40,45, and 50) powders produced by mechanical milling and subsequent annealing have beeninvestigated. Structural studies reveal that upon annealing of the as-milled powders consisting of fineFe/FePt(A1)/Pt lamellae, chemicallyhighly ordered L10 FePt and, in the case of the Fe-rich compositions,L12 Fe3Pt areformed. The nanometre scale multilayer structure preserved after annealing gives rise to large effectsof exchange interactions between the crystallites of the phases. With decreasing Pt concentrationx, the remanence enhancement increases, due to the increase of theFe3Pt fraction, whereas the coercivity and the switching fields for irreversible magnetizationreversal are reduced.
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