Research On Microstructure And Properties Of FePt Alloy Fabricated By Accumulative Roll Bonding

Nano-magnetic material is widely used in the field of information technology and have growing importance.Ultra-fine grained FePt nano-magnetic material exhibits excellent intrinsic magneto-crystalline anisotropy,strong corrosion resistance and good thermal stability.FePt nano-magnetic material with ideal organization is expected to be a suitable candidate for permanent magnet applications and ultrahigh-density magnetic recording media.This paper focuses on the research of microstructure and magnetic performance of multilayer nanostructured FePt alloy fabricated by accumulative roll bonding,and annealed under high magnetic field.Relationship between the performance of FePt alloy and the parameters of accumulative roll bonding process has been analyzed.The effect of annealing temperature and strength of magnetic field on the microstructure and performance has been studied.FePt magnetic layers have been prepared by accumulative roll bonding and subsequent magnetic annealing.The Fe and Pt layers were rolled down to nm scale.In the Fe-50vol%Pt alloy,the L10-FePt grains were well distributed and varied from 40 nm to 100 nm.The phenomenon of twinning was observed in the L10-FePt grains.In Fe-33vol%Pt alloy,L10-FePt phase and Fe3Pt phase were found to coexist.There were residual α-Fe and Pt existed in both alloys.In the scale of 100 nm to 200 nm,α-Fe acted as a single crystal.There were twinning and dislocations observed in the L10-FePt and Fe3Pt grains.With increasing annealing temperatures,the solid-state phase transformation(Fe+Pt→face centered tetragonal FePt)tended to be more sufficient,accompanied by grain growth.In the Fe-50vol%Pt alloy,the relative content of L10-FePt increased with increasing annealing temperature.In the Fe-33vol%Pt alloy,the relative content of soft magnetic phase-Fe3Pt increased with increasing annealing temperature.Thus the magnetic properties decreased with the increasing relative content of Fe3Pt.A combination of higher intensity of(001)texture,finer nanoscaled grain size and more sufficient solid-state phase transformation resulted in higher values of maximum energy product(BH)max in the Fe-50vol%Pt nanocomposites annealed under a magnetic field perpendicular to the layer surface.In both Fe-50vol%Pt and Fe-33vol%Pt nanocomposites,magnetic anisotropy behavior was observed due to the textured nanostructure.The solid-state phase transformation was suppressed by a high magnetic field parallel to the foil surface.