Influence of Nd Substitution on the Phase Constitution in (Zr,Ce)Fe₁₀Si₂ Alloys with the ThMn₁₂ Structure

Iron-based compounds with a ThMn₁₂-type structure have the potential to bridge the gap between ferrites and high performance Nd₂Fe₁₄B magnets. From the point of view of possible applications, the main advantage is their composition, with about 10 wt.% less rare earth elements in comparison with the 2:14:1 phase. On the other hand, the main issue delaying the development of Fe-rich alloys with a ThMn₁₂-type structure is their structural stability. Therefore, various synthesis methods and stabilizing elements have been proposed to stabilize the structure. In this work, the influence of increasing Nd substitution on the phase constitution of Zr_0.4-xNd_xCe_0.6Fe₁₀Si₂ (0 ≤ x ≤ 0.3) alloys was analyzed. X-ray diffraction and ⁵⁷Fe Mössbauer spectrometry were used as the main methods to derive the stability range and destabilization routes of the 1:12 structure. For the arc-melted samples, an increase in the lattice parameters of the ThMn₁₂-type structure was observed with the simultaneous growth of bcc-(Fe,Si) content with increasing Nd substitution. After isothermal annealing, the ThMn₁₂-type structure (and the coexisting bcc-(Fe,Si)) were stable over the whole composition range. While the formation of a 1:12 phase was totally suppressed in the as-cast state for x = 0.3, further heat treatment resulted in the growth of about 45% of the ThMn₁₂-type phase. The results confirmed that the stability range of ThMn₁₂-type structure in the Nd-containing alloys was well improved by other substitutions and the heat treatment, which in turn, is also needed to homogenize the ThMn₁₂-type phase. After further characterization of the magnetic properties and optimization of microstructure, such hard/soft magnetic composites can show their potential by exploiting the exchange spring mechanism.