Investigation of dipolar interaction in FINEMET ribbons through longitudinally driven magneto-impedance effect

The magnetic dipolar interactions among multiple FINEMET ribbons have been studied by longitudinally driven magneto-impedance effect (LDMI) and hysteresis loops in this paper. The effect of dipolar fields on LDMI apparently expands the “bell” magneto-impedance profiles and raises its characteristic frequency. This is essentially correlated with the domain nucleation process under the combined effect of ac driving field and dc external field. A theoretical model was utilized to explicate the LDMI variation with the number of ribbons N. Basically, the nucleation field varied linearly with N. The influence of the frequency of ac current causes the increase of the nucleation field by adding a term H_e∼f^0.38 before 4 MHz, but the dipolar field barely decreases with ac current. At frequency of 10 kHz, the dipolar field is fitted to be about 0.69 Oe, and the geometric factor can be estimated to be 5.60 × 10⁻⁵. Additionally the nucleation field reduces slightly due to the compensation of the alternating field, while the LDMI ratio changes obviously. The results indicate that LDMI can be employed as a sensitive tool to reveal the dipolar interaction in FINEMET ribbons and facilitate the design of the materials for magnetic devices.