Nanostructured Fe-Pt-B alloys consisting of hard and soft magnetic phases have revealed excellent hard magnetic properties with a potential for fabrication of efficient exchange-coupled spring magnets. In these alloys the ordered tetragonal γ₁-FePt serves as the hard magnetic phase whereas the Fe₂B phase is magnetically soft.

In the present work we compare structural and magnetic properties of two Fe₆₀Pt_25-xB_15+x (x=0 or 10) alloys. Both alloys were prepared in the form of ribbons by the melt spinning technique. Thermally induced phase transformations in the alloys were studied by differential scanning calorimetry (DSC) measurements. Structural properties of the as-quenched and annealed alloys were characterised by X-ray diffraction and Mössbauer spectroscopy techniques. Magnetic properties of the samples were investigated by using a vibrating sample magnetometer and a Faraday balance equipment.

The as-quenched Fe₆₀Pt₁₅B₂₅ ribbon was fully amorphous whereas the Fe₆₀Pt₂₅B₁₅ alloy was partially crystalline with major contribution of the γ-FePt disordered solid solution. Both alloys crystallize revealing a single exothermal peak at the DSC curves with the maximal effect at 847 K and 880 K for x=0 and 10, respectively. The ordered tetragonal γ₁-FePt and Fe₂B phases were formed after the DSC exposure of the ribbons. Magnetic properties of the annealed alloys, studied by hysteresis loop measurements, were related to differences in relative volume fractions of the hard and soft magnetic phases calculated from the Mössbauer spectra. The as-quenched alloys were magnetically soft while the annealed samples exhibited hard magnetic properties. Temperature dependence of magnetization reflected structural transformations of the samples induced by annealing.

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