A magnetic study of melt-spun Nd₁₀Fe₈₅B₅ ribbons

The structural and magnetic properties of Nd₁₀Fe₈₅B₅ ribbons produced by melt-spinning and subsequent annealing have been studied in this work. A mixture of Nd₂Fe₁₄B and 13 vol.% of Fe was found in the ribbon melt-spun at 30 m s^-1 and in samples subsequently annealed. ⁵⁷Fe-Mössbauer spectroscopy was used for phase analysis and for study of remanence enhancement. Remanence enhancement was found in ribbons after optimized treatment, after which ribbons consisted of 20-30 nm grains of Nd₂Fe₁₄B and Fe phases. The remanence enhancement effect was attributed to both the soft and hard phases. Demagnetization processes have been studied. All samples exhibited single-phase behaviour, i.e. irreversible demagnetization processes of the hard and soft phases were synchronous even for samples consisting of sub-micron grains. No significant evidence of exchange-spring magnet behaviour was found for samples after optimum treatment. The exchange-spring magnet behaviour was observed in samples annealed at higher temperatures, at which the mean grain sizes were significantly larger than the domain wall thickness of Fe. The magnetic properties of Nd₁₀Fe₈₅B₅ ribbons in this work were associated with separation of soft Fe grains by Nd₂Fe₁₄B grains because of a low fraction of Fe.