A. A. R. Fernandes

Crystallization of the amorphous alloy Fe40Ni40B20: a ferromagnetic resonance study

The ferromagnetic resonance (FMR) technique was used to study the crystallization of the metallic glass Fe40Ni40B20 (Vitrovac 0040). The line intensity of the amorphous phase was measured for several isothermal annealing times in the temperature range 360 to 375° C. The transformed fraction, as derived from FMR data, satisfies the Johnson-Mehl-Avrami equation with the exponentn between 1.49 and 1.70. The activation energy for crystallization is estimated from the times to 25% to 75% transformation to be 364 kJ mol−1.

Influence of vanadium concentration on the ESR linewidth of V4+ in rutile

Abstract Electron spin resonance spectra of vanadium-doped rutile have been studied at 77 K for V concentrations between 0.01 and 1.00 mol%. The results suggest that the range of the exchange interaction between V 4+ ions is about 0.81 nm.

FMR study of crystallization in the metglas 2826 amorphous alloy

Abstract The ferromagnetic resonance technique was used to study the annealing behavior of the metallic glass Fe40Ni40P14B6 (Metglas 2826). The peak-to-peak FMR linewidth, ΔHpp, was measured at room temperature and 9.5 GHz for several times of isothermal annealing in the temperature range 350–375°C. After an initial decrease, attributed to structural relaxation, the linewidth increases with annealing time for all temperatures investigated. The activation energy for crystallization, Ec, is estimated from the times to ΔHpp = 20 to 80 mT as (412±23) kJ/mol. The results suggest that, for sufficiently long annealing times, there is a well-defined relation between ΔH and the volume fraction of the transformed phase. If this relation is assumed to be linear, the transformed fraction, as derived from linewidth data, satisfies the Johnson-Mehl-Avrami equation with the exponent n equal to 1.67±0.13.

Crystallization of the metallic glass Metglas 2605S-3A: Comparative study between ferromagnetic resonance and electrical resistivity measurements

Electrical resistivity and ferromagnetic measurements were performed on as-received and partially crystallized samples of a commercial metallic glass, Metglas 2605S-3A. As the measurements were performed on the same set of samples, the influence of sample preparation can be discarded and any difference in the results attributed to intrinsic differences between the two methods. The results of the present investigation suggest that both techniques lead essentially to the same results.

X-ray induced valence changes in the V2O5MgO system

Abstract The properties of radiation-induced V2+ centers in MgO were investigated using the electron spin resonance (ESR) technique. The experimenta results suggest that the solid solubility limit of V3+ in magnesium oxide is about 0·01 cation % and that the decay of V2+ centers is a thermally activated process that can be attributed to two different first-order processes. A model for the formation and decay of V2+ centers in MgO is proposed.