Magnetic Macrostructural Study of L1₀ Nanocrystalline FePt Alloys by Means of Electron Holography

Abstract

L1₀ nanocrystalline FePt alloy is directly formed by rapid quenching the melt with simultaneous addition of Zr and B and high coercivity can be obtained in the composition range of (Fe_0.55Pt_0.45)₇₈Zr_2–4B_18–20. Single domain characteristic of the nanocrytalline FePt grains is clarified by Lorentz micorosocpy. Through the measurement of original magnetization curve and hysteresis loop, it is proposed that the mechanism of coercivity belongs to nucleation type. Distributions of lines of magnetic flux at demagnetized state and remanent state for two samples of (Fe_0.55Pt_0.45)₇₈Zr₄B₁₈ and (Fe_0.55Pt_0.45)₇₈Zr₂B₂₀ are observed by electron holography through ex situ experiment by applying a magnetic field. Obvious differences in the reconstructed phase images indicate the difference of the coercivities of the two samples.