Effect of length and annealing conditions on magnetoimpedance of Co68Fe5Si12B15 amorphous ribbons

Abstract

The effect of conventional annealing and Joule annealing on magnetoimpedance (MI) of Co68Fe5Si12B15 ribbons was studied. The ribbons used for the MI measurements were 1 and 5 cm long. The as cast 5-cm-long ribbons exhibit a larger MI compared with the 1-cm-long ribbons, at all frequencies. The maximum MI of the as cast ribbons of 5 cm length is 17% at 600 kHz whereas for the 1-cm-long ribbons it is 3% at 500 kHz. Conventional annealing carried out at 200 and 300 °C for 1 h results in the decrease of the MI in both the 5 and 1-cm-long ribbons, respectively. The Joule annealing of the 5-cm-long ribbons employing a current of 500 mA for 5 min. causes the increase of the MI to 26% at 800 kHz. For the 1 cm Joule-annealed ribbon, employing a current of 500 mA for 5 min., the maximum MI observed is 6% at 500 kHz.

Critical length and giant magnetoimpedance in Co69Fe4.5Ni1.5Si10B15 amorphous ribbons

“…Vazquez et al [11] reported that the GMI effect decreased in Fe-based nanocrystalline wires as the wire length decreased from 8 to 1 cm. A similar trend was also observed for the case of Co-based amorphous ribbons [12][13][14], Febased nanocrystalline ribbons [15,16] and CoSiB/Cu/CoSiB layered thin films [5]. However, Phan et al [17] reported that the decrease of length of a Co-based microwire from 4 to 1 mm resulted in a strong increase of the GMI effect.…”

“…For samples with L < L 0 , the decrease of GMI results mainly from the strong decrease of T due to the demagnetization effect. This explains why the GMI effect decreased with decreasing L in Co-based amorphous ribbons [12][13][14], Fe-based nanocrystalline ribbons [15,16] and CoSiB/Cu/CoSiB layered thin films [5]. Actually, the magnitude of L 0 depends on the type of domain structure [11,17,18], and it has been found that the critical length is shorter for Co-based wires than for Fe-based wires [18].…”

“…Actually, the magnitude of L 0 depends on the type of domain structure [11,17,18], and it has been found that the critical length is shorter for Co-based wires than for Fe-based wires [18]. A final note is that while the observed GMI effect largely varied with changing L for the case of magnetic wires and ribbons [11][12][13][14][15][16], it was almost independent of L for the case of a La 0.7 Sr 0.3 MnO 3 manganite [26]. This could arise from the fact that the demagnetization effect played less important role in the bulk and thick manganite sample [26].…”

“…However, Phan et al [17] reported that the decrease of length of a Co-based microwire from 4 to 1 mm resulted in a strong increase of the GMI effect. These varied observations lead to a general expectation that for each type of material there exists a critical length (L 0 ), below which the GMI effect decreases with decreasing sample length [11][12][13][14][15] and above which it increases with decrease of sample length [17]. This hypothesis has been supported by the previous observation of the effect of L 0 on the magnetization process in Co-based and Fe-based amorphous wires [18].…”

“…Such modification in the domain structure near the extremities of the sample can result in variation in GMI features with respect to change in sample length. The decrease of GMI with decreasing L for the cases of Fe-based nanocrystalline wires [11] and Co-based amorphous ribbons [12][13][14] can be attributed to the formation of closure domain structures due to the demagnetization effect, when the measured sample length is less than the critical length, L < L 0 . On the other hand, the increase of GMI effect with decreasing L for the case of Co-based microwires reported by Phan et al [17] can be reconciled with the fact that the measured sample length is larger than the critical length, L > L 0 .…”