High frequency magnetic properties of an amorphous Fe78B13Si9 ribbon improved by a.c. Joule heating

A straight specimen of amorphous Fe78B13Si9 ribbon was heated by passing an a.c. current through the specimen. In addition to the Joule effect, the current-induced magnetic field was combined with a high d.c. applied magnetic field along the longitudinal direction of the specimen to improve the magnetic properties. Under the applied testing magnetic field Ha = 2 Oe, the magnetic induction Bm ≅14.5 kG for the heat-treated specimen is much better than the magnetic induction Bm ≅8.7 kG for the as-cast specimen. The remanence ratio of the heat-treated specimen ranges from Br/Bm = 0.55 at f = 20 Hz to Br/Bm = 0.89 at f = 20 kHz, while the remanence ratio of the as-cast specimen is from Br/Bm = 0.23 at f = 20 Hz to Br/Bm = 0.46 at f = 20 kHz. This shows that the heat-treated specimen has the desired squareness of the B-H loop for some applications at high frequencies.