Nanocomposite R2Fe14B/Fe exchange coupled magnets

Abstract
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.