The thermal, magnetic, and structural characterization of the crystallization kinetics of amorphous soft magnetic materials

Abstract

Summary form only given. The characterization of the crystallization kinetics of amorphous soft magnetic materials, namely NANOPERM/spl trade/, an Fe/sub 88/Zr/sub 7/B/sub 4/Cu/sub 1/ amorphous soft magnetic alloy, and its derivatives, is presented. Crystallization kinetics are observed isothermally and non-isothermally by differential scanning calorimetry (DSC), synchrotron x-ray diffraction (XRD) and vibrating sample magnetometry (VSM). Vibrating sample magnetometry and x-ray diffractometry, used concurrently with differential scanning calorimetry in observing crystallization kinetics, is a novel concept that takes advantage of the magnetic property that the Curie temperature of the amorphous phase of the NANOPERM/spl trade/ alloy is below its primary crystallization temperature. This property allows for crystallization kinetics, i.e. the volume of nanocrystals transformed in the 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 non-isothermal crystallization kinetics using data gathered from the three characterization methods. Linear regression and non-linear regression analysis of the mechanisms of crystallization in NANOPERM/spl trade/ 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/spl trade/ 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. Extension of the isothermal model for crystallization kinetics to non-isothermal cases is also presented.