Surface oxidation and magnetic properties of (Cu sub(60)Co sub(40)) sub(68)Zr sub(32) glassy ribbons

The evolution of local Co density during thermal annealing of (Cu sub(60)Co sub(40)) sub(68)Zr sub(32) glassy ribbons was intended to be probed by in situ and ex situ magnetization measurements. However, even when the as-quenched sample is exposed to air at room temperature for several hours, Zr becomes strongly enriched at the surface due to selective oxidation and material in the adjacent sample volume subsequently separates into Co-rich and Cu-rich phases and the magnetic properties are decisively affected by these processes taking place within the first 20 nm from the surface. In this paper we report on the characterization of the oxidation and separation processes at the (Cu sub(60)Co sub(40)) sub(68)Zr sub(32) glassy ribbons' surface by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), magnetization measurements and X-ray photoelectron spectroscopy (XPS) and point out why the results of magnetization measurements, especially for this type of materials, i.e. metallic ribbons with a high ratio of surface to volume, have to be considered critically in general.