Effect of boron on the magnetic properties and exchange-coupling effect of FePtB-type nanocomposite ribbons.

Phase evolution and magnetic properties of melt-spun (Fe0.675Pt0.325)100-xBx (x=12-20) nanocomposite ribbons are investigated. For those ribbons spun at 45 m/s, followed with a 500 °C isothermal annealing for 1-6 h, the boron addition not only promotes disorder to order (γ!γ1) transformation but also leads to the formation of different kinds of Fe-borides. Pt exhibits a strong affinity to Fe during thermal processes in forming magnetically hard γ1(FePt) phase, leaving excess Fe to interact with B in forming Fe2B, Fe3B, or FeB. For x=12-18, all ribbons are composed of one hard phase, γ1-FePt, and three soft phases, γ-FePt, Fe2B, and Fe3B. But FeB also coexists for x =20. Through the exchange-coupling interaction between nanoscale γ1-FePt and multiple soft phases, record of magnetic properties of Br=9.4 kG, iHc=7.5 kOe, and (BH)max=14.0 MGOe has been successfully developed in isotropic (Fe0.675Pt0.325)84B16 ribbons, where the reduced remanence ratio (σr/σ12 kOe) is as high as 0.86. [ABSTRACT FROM AUTHOR]