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

The correlation between microstructure, saturation magnetostriction constant λs, coercive field Hc and remanence of nanocrystallizing Fe73.5Cu1Nb3Si16.5B6 amorphous alloy after 1 h annealing at 400–800 °C was studied. The amorphous ribbons (4 mm wide and 20 μm 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 λs 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 Hc and λs. Very soft magnetic behavior (Hc = 0.7–0.9 A m−1) was observed for two-phase nanocrystalline material composed of amorphous matrix and α-Fe(Si) crystallites 12–15 nm in diameter obtained after annealing at 480–520 °C. The observed effect of the almost constant value of Hc when a substantial decrease of λs was measured is ascribed to the compensation of the decrease of magnetoelastic anisotropy by the increase of effective magnetocrys-talline anisotropy related to the observed increase of average grain diameter. The observed differences in λs measured using TTC and SMFMR methods suggest a higher volume fraction of crystallites at the surface than inside the ribbon.