DETECTION OF SHORT RANGE ORDER FROM THE ULTRASONIC AND MAGNETIC PROPERTIES OF ANNEALED AMORPHOUS METALS

Using non-contact techniques for generation and detection, the velocity and attenuation of acoustic waves have been measured in samples of isothermally annealed amorphous Fe81, B13.5, Si3.5, C2 (Metglas 2605SC). Apart from an abrupt change due to the onset of crystallisation, the velocity increases with anneal temperature, Ta, due to the development of chemical short range order (CSRO). Attenuation is shown to follow the same dependence on Ta as the magnetic permeability and is attributed to the magnetoelastic coupling which changes with stress relief. Neither the magnetic properties, being dependent on other factors as well as CSRO, nor the electrical resistivity which is too insensitive, are clear indicators of structural ordering. However, the velocity of ultrasound, being related to the elastic modulus, is a better monitor of the growth in short range order before any crystallisation can be detected with X-ray diffraction.