Magnetic and crystalline microstructures of Fe–B/FePt-type Nanocomposite ribbons with high permanent properties

We present a magnetic force microscopy and atomic force microscopy study of magnetic and crystalline microstructures of melt-spun binary Fe50+xPt50−x (x=0−20) and ternary (Fe0.5+yPt0.5−y)82B18(y=0−0.2) nanocomposite ribbons. It was confirmed that an ordered magnetically hard γ1-FePt phase could be fully formed at x⩽10 in Fe50+xPt50−x ribbons. From the topographic images of the Fe50+xPt50−x and (Fe0.5+yPt0.5−y)82B18 ribbons, it was found that the average crystal size D¯ is large (∼1.1–3.9 μm) for the Fe50+xPt50−y ribbons without B, but that of the (Fe0.5+yPt0.5−y)82B18 ribbons with invariable B content is much small (∼57–65 nm). Moreover, the magnetic force images with distinct contrast could be detected by MFM only in the ribbons with strong exchange-coupling interaction. Finally, it was found that for exchange-coupling nanocomposite ribbons, the strength of the exchange-coupling interaction can be reflected roughly by the root-mean-square roughness of phase shift, (Δφ)rms(Δφ)rms, of magnetic force images and the ratio of the average domain width w¯ to the average crystal size D¯.