Nanocomposite R2Fe14B/Fe exchange coupled magnets

We have studied the crystallization, crystal structure, microstructure and magnetic properties of R-Fe-B (R=Nd,Pr,Dy,Tb) based melt-spun ribbons consisting of a mixture of R2Fe14B and α-Fe phases. All the samples crystallize first to α-Fe and a metastable phase (Y3Fe62B14 for R=Nd,Pr,Dy and TbCu7 for R=Tb) before they finally transform to 2:14:1 and α-Fe. The highest values of coercivity and reduced remanence, 4.5 and 0.63 kOe, respectively, were obtained in a Nd3.85Tb2(Fe-Nb-B)94.15 sample. These properties are the result of a fine grain microstructure consisting of a mixture of α-Fe and 2:14:1 having an average grain size of 30 nm.