Magnetization Process and GMI Effect in As-Cast Nanocrystalline Microwires

Results on the axial and circumferential magnetization processes in as-cast nanocrystalline glass-coated microwires are reported for the first time. Glass removal induces a peculiar change in the shape of the axial hysteresis loop. The initially rectangular axial hysteresis loop becomes almost anhysteretic after glass removal as a consequence of a change in the mechanism of axial magnetization, which has been explained by taking into account the changes induced by stress relief in the exchange length. Therefore, the nanosized crystalline grains can be coupled or uncoupled, depending on the presence of the glass coating. The change in the shape of the hysteresis loop is also observed on the circumferential direction. Results of giant magneto-impedance measurements support the explanation given, as the magneto-impedance response at 50 MHz increases about 9 times after glass removal due to both stress relief and to the phase consisting of coupled crystalline grains, which becomes the phase that preponderantly determines the magnetic behavior of the microwire after glass removal.