Cooling rate controlled microstructure and magnetic properties of metastable Fe20Nd80 alloys

The microstructures and magnetic properties of as-cast and annealed Fe20Nd80 (hypereutectic) alloys were studied. Depending on the cooling rate the Fe20Nd80 alloys solidify into various metastable eutectic-like structures, which present a wide range of coercivity values varying from 0.2 to 0.48 T measured at room temperature. The alloys cooled at rates faster than 50 K/s display fine eutectic-like regions of Nd+A1 and are hard magnetic. The TEM studies clearly show that the hard magnetic A1 regions are microscopically inhomogeneous. The alloys cooled slower than 25 K/s show a discontinuous rod-type eutectic of Nd+Fe17Nd2 and, consequently, exhibit a soft magnetic behaviour. The correlations between the cooling rate, microstructure, and coercivity of the Fe20Nd80 alloys are discussed.