The role of sub-micron grain size in the development of rare earth hard magnetic alloys

The magnetic properties of nanocrystalline melt spun rare earth–iron–boron alloys based on Nd or Pr and on Nd–Pr mixtures are compared for a wide range of RE:Fe ratio. Their magnetic properties are compared with those of corresponding alloy ribbons based on Nd. The Pr containing alloys have generally higher coercivity than their Nd counterparts because of the higher anisotropy constant of the Pr2Fe14B phase. Co substitution for Fe increases the Curie temperature and thermal stability for the nanophase alloys. Excellent magnetic property combinations were achieved for single phase Pr12(Fe100−xCox)82B6 (x=0–20) alloys, processed by overquenching and devitrification annealing. In contrast, in the case of nanocomposite Pr10(Fe100−xCox)84B6 alloys, based on Pr2Fe14B/α-Fe mixtures, only for 30% substitution of Fe by Co could useful enhancement of (BH)max be achieved, due to generally rather coarse α-Fe crystallites.