Effect of a high magnetic field on hard magnetic multilayered Fe-Pt alloys

Abstract Fe-50 vol%Pt multilayers that were prepared by accumulative roll-bonding were annealed in vacuum for 2 h at various temperatures between 723 K and 823 K. Some samples were annealed without any high magnetic field (HMF). Others were subjected HMF up to 31.2 T, applied in either in-plane or out-of-plane directions. The annealing partially transformed the original multilayered structure into a polycrystalline hard-magnetic FePt magnetic phase with ordered L10 structure. Textured FePt/Fe nanocomposite foils were formed under HMF. Magnetic anisotropic behavior was observed in the annealed FePt/Fe composite because of the textured nanostructure. HMF annealing decreased grain size and increased the (0 0 1) texture along the HMF direction. In the sample annealed with out-of-plane HMF, both coercivity and maximum energy product were enhanced because of higher (0 0 1) out-of-plane texture and finer nanoscaled grain sizes compared to other samples. An in-plane HMF appeared to strongly inhibit phase transformation. This inhibition likely resulted from a change in Gibbs free energy and the diffusion inhibition caused by HMF.