Title :
Structure and thermomagnetic properties of new FeCo-based nanocrystalline ferromagnets
Author :
Johnson, F. ; Hughes, P. ; Gallagher, R. ; Laughlin, D.E. ; McHenry, M.E. ; Willard, M.A. ; Harris, V.G.
Author_Institution :
Dept. of Mater. Sci. & Eng., Carnegie Mellon Univ., Pittsburgh, PA, USA
fDate :
7/1/2001 12:00:00 AM
Abstract :
FeCo-based ferromagnetic alloys (HITPERM variants) of composition Fe44.5Co44.5Zr7B4, Fe44 Co44Zr5.7B3.3Ta2Cu 1, Fe44Co44Zr5.7B3.3 Mo2Cu1, and Fe37.2Co30.8 Zr7B4Cu1 were prepared by melt-spinning amorphous precursors, followed by nanocrystallization. Samples were characterized using vibrating sample magnetometry (VSM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). VSM was used to measure magnetization vs. temperature from 370-1260 K. Magnetic data showed structural and magnetic phase transitions including primary and secondary crystallization events and the to a structural phase transition in FeCo nanocrystals. Ta 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 α to γ transition. XRD phase analysis identified crystallized phases as α-FeCo, (Fe, Co)3Zr, in agreement with previous reports for unmodified HITPERM alloys. DSC data, analyzed using the Kissinger technique, indicated that the removal of Cu from the original HITPERM composition increased the activation energy for primary crystallization, whereas Ta and Mo substitutions decrease the activation energy
Keywords :
X-ray diffraction; cobalt alloys; crystallisation; differential scanning calorimetry; ferromagnetic materials; ferromagnetic-paramagnetic transitions; iron alloys; magnetisation; nanostructured materials; soft magnetic materials; solid-state phase transformations; α-to-γ transition; 370 to 1260 K; Fe37.2Co30.8Zr7B4Cu 1; Fe44.5Co44.5Zr7B4; Fe44Co44Zr5.7B3.3Mo 2Cu1; Fe44Co44Zr5.7B3.3Ta 2Cu1; HITPERM; Kissinger technique; X-ray diffraction; activation energy; crystallization; differential scanning calorimetry; ferromagnetic-to-paramagnetic transition; magnetic phase transition; magnetization; melt spinning; nanocrystalline ferromagnetic alloy; soft magnetic properties; structural phase transition; thermomagnetic properties; vibrating sample magnetometry; Amorphous magnetic materials; Amorphous materials; Cobalt alloys; Copper alloys; Crystallization; Iron alloys; Temperature; X-ray diffraction; X-ray scattering; Zirconium;
Journal_Title :
Magnetics, IEEE Transactions on
