The generation of magnetic bistability in annealed Fe-Si-B fibre by hydrogenation

Abstract

The magnetically bistable nature of as-quenched Fe77.5Si7.5B15 amorphous fibre disappeared when the material underwent stress-relief annealing at 400 degrees C for 30 min. A reduction of internal stress leading to a lowering of the magnetoelastic anisotropy was the cause of such a change from bistable to normal ferromagnetic behaviour. Cathodic hydrogen impregnation caused the re-appearance of magnetic bistability, the magnitude of which was dependent on the duration of hydrogen charging (and hence on the hydrogen concentration). Perfect bistability was restored when the annealed Fe77.5Si7.5B15 fibre was charged for 120 min at the charging current density of 120 mA cm(-2). Owing to the positive molar volume of hydrogen, internal stresses were generated by hydrogenation, which increased the size of the longitudinal anisotropy region. When this longitudinal anisotropy region was big enough to act as a monodomain at the core of the fibre, bistability with a large switching field (H* = 17.5 A m(-1)) was observed.