Crystallization process of a rapidly quenched Fe–B–Nd nanocomposite magnet

Superior magnetic properties of Nd–Fe–B nanocomposite magnets rely on their nanoscaled structure composed of hard-magnetic Nd2Fe14B and soft-magnetic Fe3B phases, which results from a glassy state upon subsequent annealing. It has been known from X-ray diffraction (XRD) analysis that for this system, an addition of Cr is critical to control the crystallization route to produce the desired mixture of Nd2Fe14B and Fe3B phases. We have investigated the partitioning of Cr in a Nd5Fe74.5B18Cr2.5 alloy throughout its crystallization process using atom probe field ion microscopy (APFIM). Cr is found to be enriched in Fe3B, up to 4.7 at.%, and the Cr concentration in Nd2Fe14B is determined to be 0.70 at.%. Together with the results of XRD, we have discussed the effect of Cr, based on the idea that Cr alters the phase decomposition route by stabilizing the Fe3B phase.