First-order-reversal-curve analysis of Pr-Fe-B-based nanocomposites

Ribbons of nominal composition (Pr9.5Fe84.5B6)0.96Cr0.01(TiC)0.03 were produced by arc-melting and melt-spinning the alloys on a Cu wheel. X-ray diffraction reveals two main phases, one based upon α-Fe and the other upon Pr2Fe14B. The ribbons show exchange spring behavior with Hc=12.5 kOe and (BH)max=13.6 MGOe when these two phases are well coupled. Transmission electron microscopy revealed that the coupled behavior is observed when the microstructure consists predominantly of α-Fe grains (diameter ∼100 nm.) surrounded by hard material containing Pr2Fe14B. A first-order-reversal-curve (FORC) analysis was performed for both a well-coupled sample and a partially-coupled sample. The FORC diagrams show two strong peaks for both the partially-coupled sample and for the well-coupled material. In both cases, the localization of the FORC probability suggests demagnetizing interactions between particles. Switching field distributions were calculated and are consistent with the sample microstructure.