Correlation between microstructure and magnetic properties of amorphous and nanocrystalline Fe73.5Cu1Nb3Si16.5B6

The correlation between microstructure, saturation magnetostriction constant lambda(s), coercive field H-c and remanence of nanocrystallizing Fe73.5Cu1Nb3Si16.5B6 amorphous alloy after 1 h annealing at 400-800 degrees C was studied. The amorphous ribbons (4 mm wide and 20 mu m thick) were prepared in air by the single-roller chill-block melt-spinning method. The structure of partially crystallized alloys was investigated using differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The saturation magnetostriction constant lambda(s) was measured at room temperature using two methods: the three-terminal capacitance (TTC) method and the strain-modulated ferromagnetic resonance (SMFMR) method. Quasi-static hysteresis loop was measured in order to determine H-c and lambda(s). Very soft magnetic behavior (H-c = 0.7-0.9 A m(-1)) was observed for two-phase nanocrystalline material composed of amorphous matrix and alpha-Fe(Si) crystallites 12-15 nm in diameter obtained after annealing at 480-520 degrees C. The observed effect of the almost constant value of H-c when a substantial decrease of lambda(s) was measured is ascribed to the compensation of the decrease of magnetoelastic anisotropy by the increase of effective magnetocrystalline anisotropy related to the observed increase of average grain diameter. The observed differences in lambda(c) measured using TTC and SMFMR methods suggest a higher volume fraction of crystallites at the surface than inside the ribbon. (C) 1997 Elsevier Science S.A.