The relationship between structure and magnetic properties in nanostructured FePd ferromagnets

FePd L1(0), ferromagnets with ultra-fine microstructures (submicron/nanoscale) have been studied. The powders and thin films with nanoscale microstructure were produced using high energy ball, milling and vacuum sputtering, respectively. These ultra-fine grained materials were characterized using TEM, SEM, and X-ray diffraction. The line broadening method was used to estimate the crystallite size and lattice strain of the ball-milled powders with the aid of TEM observation. The magnetic properties of the epoxy-bonded powders, isostatically pressed pellets and the thin films were measured using a vibrating sample magnetometer (VSM). The enhanced coercivities exhibited by these ferromagnets compared to bulk materials are discussed in terms of the mechanism of magnetization reversal operating in these fine-particle aggregates and thin films in the grain size range of D<Dc but well above the superparamagnetic regime. Micromagnetic analysis is applied to discuss the mechanism of coercivity, and a "pinning" model is proposed in these so-called "interaction" domain ferromagnets.