Relating the magnetic coercivity to the L1 0 ordered FePd phase in annealed Fe x Pd 100-x nanoparticles

Rare-earth-free or iron-based permanent nanomagnets are emerging as promising candidates for energy-conversion and information technologies. In this interest, Fe x Pd 100-x nanoparticles ( x = 50, 55, 60, and 63) were prepared from iron acetate and palladium acetate by sonoelectrodeposition. After annealing the nanoparticles at various temperatures from 450 to 700 °C for 1 h, structural changes were observed, and the samples exhibit hard magnetic properties that depend strongly on chemical composition and annealing temperature. The major phase in the as-prepared nanoparticles has a disordered face-centered cubic structure, which, upon annealing, transforms into a multi-phase material containing a L1 0 ordered FePd phase. The fractions of different phases present in the annealed samples, including that of the L1 0 phase as functions of chemical composition and annealing temperature, are quantified by means of X-ray diffraction and scanning transmission electron microscopy. Magnetic measurements show the desirable hard magnetic properties for the samples annealed at 550–600 °C. A correlation between the magnetic coercivity and the L1 0 ordered FePd phase fraction is established for the first time in the Fe x Pd 100-x nanoparticles.