The thermal, magnetic, and structural characterization of the crystallization kinetics of Fe/sub 88/Zr/sub 7/B/sub 4/Cu/sub 1/, an amorphous soft magnetic ribbon

Abstract

The characterization of the crystallization kinetics of an amorphous soft magnetic alloy, Fe/sub 88/Zr/sub 7/B/sub 4/Cu/sub 1/, called NANOPERM, is presented. Vibrating sample magnetometry (VSM), X-ray diffractometry, and differential scanning calorimetry have been used to observe crystallization kinetics. The VSM observations take advantage of the Curie temperature of the amorphous phase Tc-/sub amorphous/ of the NANOPERM alloy being below its primary crystallization temperature T/sub x1/. This allows for the volume of nanocrystals transformed in the crystallization process to be inferred magnetically, as well as thermally and structurally. The Johnson-Mehl-Avrami model for isothermal crystallization kinetics is compared with the Kissinger model for nonisothermal crystallization kinetics using data gathered from the three characterization methods. Linear regression and nonlinear regression analysis of crystallization data for NANOPERM ribbon and the significance of the values that describe them, namely, the activation energy Q and the morphology index n are investigated for isothermal and constant-heating crystallization. The activation energy for NANOPERM ribbon is presented here to be in the range of Q=2.8-3.4 eV, with the crystallization kinetics proceeding by three-dimensional diffusion and immediate nucleation, where the morphology index is n=1.5. A time constant to account for initial nonisothermal conditions during isothermal heating is introduced and determined to be T=120-200 s.