Microstructure refinement and magnetic property enhancement of nanocomposite Pr2Fe14B/α-Fe magnets by small substitution of M for Fe (M=Cr, Nb, Ti and Zr)

A comprehensive study on the effect of various substitutions of M on the magnetic and structural properties of melt-spun nanocomposite Pr8Fe84M2B6 (M=Cr, Nb, Ti and Zr) magnets has been performed with the aim of refining the microstructure and therefore enhancing the hard magnetic properties. It has been found that magnetic properties are improved by all the substitutions. The largest enhancement is obtained in Nb substituted Pr8Fe84Nb2B6 magnets where a coercivity of 6.5 kOe and a maximum energy product of 17.9 MGOe have been obtained, as compared to the coercivity of 4.3 kOe and the energy product of 9.1 MGOe in the Pr8Fe86B6 magnet. Microstructure studies revealed a finer and more uniform 2:14:1/α-Fe nanoscale microstructure with M substitutions. The most uniform microstructure with the smallest average grain size of 10–20 nm is developed in the Nb substituted magnets. The enhancement of magnetic properties by M substitution is believed to be due to the microstructure refinement which leads to an enhanced exchange coupling between Pr2Fe14B and α-Fe.