INFLUENCE OF THE SAMPLE LENGTH ON THE SWITCHING PROCESS OF MAGNETOSTRICTIVE AMORPHOUS WIRE

Bistable behavior occurs in highly magnetostrictive amorphous wires due to the presence of an inner core where magnetization is roughly aligned with the wire axis. In this work, the squareness ratio that gives information about the radius of such an inner core and the switching field for bistability have been studied as a function of applied tensile stress for a series of Fe77.5Si7.5B15 wires with different lengths. Experimental results have been obtained in as-cast wires as well as after different thermal treatments. The switching field increases with the length of the wire up to a saturation value, while a minimum length of about 6 cm is needed to observe bistability. For applied tensile stresses larger than the internal ones, switching fields follow a sigma-1/2 law. Thermal treatments, that reduce internal stresses, decrease the switching field and bistabilitY can even disappear for well relaxed samples. It is concluded that the axial demagnetizing field which depends on the inner core dimensions and the strength of internal and applied stresses play a decisive role in determining the switching process.