Effect of P addition on nanocrystallization and high temperature magnetic properties of low B and Nb containing FeCo nanocomposites

The P content dependencies of the nanocrystallization behaviors and high temperature magnetic properties of the Fe 54.6 Co 29.4 Si 2.8 (B 0.8ÀY P Y) 14 Nb 1 Cu 1 (Y ¼ 0, 0.2, and 0.3) alloys have been investigated. Alloys were prepared by melt spinning and subsequently annealed in an argon atmosphere to induce nanocrystallization. P addition increases primary crystallization temperature (Tx 1), thermal stability (DTx), and activation energy (Q JMA) for secondary crystallization in as-cast alloys. The saturation induction (B s) of 1.68 T for as-cast P free alloy decreases continuously with the addition of P. However, the soft magnetic properties are enhanced for P added alloys. The XRD pattern reveals that grain refinement increases with increasing P contents. Alloys annealed at 430 C confirm primary nanocrystallization of a-FeCo in the amorphous matrix, while annealing at 550 C causes secondary crystallization of other non-magnetic phases as well. The magnetic moment of as-cast and annealed alloys, measured by vibrating sample magnetometry (VSM), has minimum values at two temperatures, labeled Tc 1 , Tc 2 , prior to secondary crystallization, corresponding to the ferromagnetic transitions of as-quenched amorphous and residual amorphous phase, respectively. The stabilization of amorphous phase delays primary crystallization, resulting in increase of Tc 1 for P-rich as-cast alloys.