Structure and thermomagnetic properties of new FeCo-based nanocrystalline ferromagnets

FeCo-based ferromagnetic alloys (HIT-PERM variants) of composition Fe44.5Co 44.5Zr7B4, Fe44Co44Zr5.7B3.3Ta2Cu1, Fe44Co44Zr5.7B3.3Mo2Cu1, and Fe37.2Co30 .8Zr7B4Cu1 were prepared by melt-spinning amorphous precursors, followed by nanocrystallization. Samples were characterized using vibrating sample mag netometry (VSM), x-ray diffraction (XRD), and differential scanning calorim etry (DSC). VSM was used to measure magnetization vs. temperature from 370- 1260 K. Magnetic data showed structural and magnetic phase transitions incl uding primary and secondary crystallization events and the to a structural phase transition in FeCo nanocrystals. Th and Mo were observed to suppress the to a transition temperature of FeCo. The Fe : Co 65 : 35 alloy exhibits significant curvature in M(T) indicating proximity of the ferromagnetic to paramagnetic transition and the alpha to gamma transition. XRD phase analy sis identified crystallized phases as alpha -FeCo, (Fe,Co)(3)Zr, in agreeme nt with previous reports for unmodified HITPERM alloys. DSC data, analyzed using the Kissinger technique, indicated that the removal of Cu from the or iginal HITPERM composition increased the activation energy for primary crys tallization, whereas Th and Mo substitutions decrease the activation energy .