Structure and properties of nanoporous FePt fabricated by dealloying a melt-spun Fe₆₀Pt₂₀B₂₀ alloy and subsequent annealing

A nanoporous FePt alloy has been fabricated by dealloying a melt-spun Fe₆₀Pt₂₀B₂₀ alloy composed of nanoscale amorphous and face-centered-cubic FePt (fcc-FePt) phases in H₂SO₄ aqueous solution. The nanoporous alloy consists of single fcc-FePt phase with an Fe/Pt atomic ratio of about 55.3/44.7, and possesses a uniform interpenetrating ligament-channel structure with average ligament and pore sizes of 27 nm and 12 nm, respectively. The nanoporous fcc-FePt alloy shows soft magnetic characteristics with a saturation magnetization of 37.9 emu/g and better electrocatalytic activity for methanol oxidation than commercial Pt/C in acidic environment. The phase transformation from disordered fcc-FePt into ordered face-centered-tetragonal FePt (L1₀-FePt) in the nanoporous alloy has been realized after annealing at 823–943 K for 600 s. The volume fraction of the L1₀-FePt phase in the alloy increases with the rise of annealing temperature, which results in the enhancements of coercivity and saturation magnetization from 0.14 kOe and 38.5 emu/g to 8.42 kOe and 51.4 emu/g, respectively. The ligament size of the samples is increased after annealing.