Magnetic Properties of Nd-Fe-B/α-Fe Nanocomposite Thin Films

Abstract

Thin films consisting of randomly distributed Nd₂Fe₁₄B and α-Fe phases were fabricated on glass substrates by rf sputtering. Although the existence of both Nd₂Fe₁₄B and α-Fe phases were confirmed by X-ray diffraction, the magnetization curves showed a single-phase-like behavior. This result indicates exchange coupling between the Nd₂Fe₁₄B and Fe phases. On the basis of Rietveld analysis of the X-ray diffraction profiles, the volume fractions of the Nd₂Fe₁₄B and Fe phases were estimated. With an increase in the volume fraction of Fe (V_Fe) from 5% to 76%, H_c decreased from 12.3 to 0.8 kOe, while M_r/M_s increased from 0.54 to 0.83. The mean grain size, which was estimated from the widths of the X-ray diffraction peaks, decreased with increasing V_Fe. Micromagnetic calculations of magnetization curves suggested that the effective exchange coupling between the soft and hard phases becomes larger with increasing V_Fe, because of the decreasing grain sizes.