Evidence for Different Ferromagnetic Phases in Amorphous Fe₄₀Ni₄₀B₂₀ Detected by EPR

Abstract

Amorphous ferromagnetic Fe^Ni^I^o (T C = 662 K) has been investigated by EPR in the temperature range from 110 to 510 K. From the temperature dependence of the magnetic field at resonance, the saturation magnetization could be evaluated. Around 470 K the line width of the resonance signal exhibits a pronounced minimum, and the EPR-intensity deviates at this temperature from pure ferromagnetic behaviour. Both effects can be explained by assuming the presence of a second ferromagnetic phase with a Curie temperature of r c '=470 K. Upon annealing of Fe4 0 Ni 40 B 2 o at temperatures slightly higher than 77 changes in physical properties, such as Curie temperature, density and relative strain at fracture are observable. It is proposed that the onset of the low temperature relaxation which is responsible for these changes in physical properties is related to the transition of the second ferromagnetic phase to the paramagnetic state.

Structural Evolution in Wet Mechanically Alloyed Co-Fe-(Ta,W)-B Alloys

“…The Curie temperature was determined from the inflection point using the derivative of magnetization with respect to temperature, i.e., dσ/dT. The Ta-100 shows the Curie temperature of the amorphous phase T C = 695(5) K. In case of the W-100, there are two transitions detected with Curie temperatures 700(5) K and 780(5) K. This may point to the inhomogeneities of an amorphous phase [41]. After reaching T C , the magnetization of the powder samples does not drop to zero and eventually increases due to the thermally activated structural changes (relaxation, crystallization) occurring at higher temperatures.…”