Microstructure and hard magnetic properties of directly synthesized L1 ₀(Fe _1-xPt _x) ₇₈Zr ₄B ₁₈ nanocrystalline alloys by melt spinning

The microstructure and the hard magnetic properties of the melt-spun (Fe1-x Ptx) 78 Zr4 B18 (x=0.385, 0.45, 0.50, and 0.55) nanocrystalline alloys have been investigated. The ordered L 10 - FePt phase with a grain size smaller than the critical single domain size is directly formed by rapidly quenching of the alloy melt with x=0.45 and 0.50. The alloys have a mixed microstructure composed of the L 10 -FePt and fcc phases, and exhibit high coercivity (Hc) of 649 and 688 kAm, respectively, in an as-quenched state. On the other hand, the alloys with x=0.385 and 0.55 are found to composed of two fcc phases and fcc+L 12 - FePt3 +L 10 -FePt, respectively, and exhibit Hc values lower than 70 kAm in an as-quenched state. The rapidly quenching of the melt of the (Fe1-x Ptx) 78 Zr4 B18 alloys with x=0.45-0.50 is useful to realize the good hard magnetic properties through the grain size refinement of the near equiatomic FePt alloys.