Small Angle X-ray Scattering Studies of Fe-Si-Cu-B Melt-Spun Ribbons

Nanocrystalline ribbons of Fe-Cu-Si-B ([Fe] = 76.5-80.7 at%) were produced by rapid quenching and subsequent annealing to obtain higher saturation magnetization. To control the thickness of the ribbons, different quenching rates were applied. The magnetic properties, even after annealing, show clear differences depending on the thickness. To understand the origin of these differences, small angle X-ray scattering (SAXS) measurements were acquired to investigate and quantify changes in the microstructures of samples of different thicknesses, with and without annealing. Since crystallization kinetics were strongly affected by sample thickness (e.g., quenching rate), the volume fraction in samples with different thickness but the same composition were varied in addition to the average size of the bcc crystals. Balancing the average size and the volume fraction gives the optimum sample thickness for obtaining the best soft magnetic properties in the Fe-Cu-Si-B ribbons.