Generation of second harmonic in off-diagonal magneto-impedance in Co-based amorphous ribbons

Abstract

The off-diagonal magneto-impedance in Co-based amorphous ribbons was measured using a pick-up coil wound around the sample. The ribbons were annealed in air or in vacuum in the presence of a weak magnetic field. The evolution of the first and second harmonics in the pick-up coil voltage as a function of the current amplitude was studied. At low current amplitudes, the first harmonic dominates in the frequency spectrum of the voltage, and at sufficiently high current amplitudes, the amplitude of the second harmonic becomes higher than that of the first harmonic. For air-annealed ribbons, the asymmetric two-peak behaviour of the field dependences of the harmonic amplitudes was observed, which is related to the coupling between the amorphous phase and surface crystalline layers appearing after annealing. For vacuum-annealed samples, the first harmonic has a maximum at zero external field, and the field dependence of the second harmonic exhibits symmetric two-peak behaviour. The experimental results are interpreted in terms of a quasi-static rotational model.It is shown that the appearance of the second harmonic in the pick-up coil voltage is related to the anti-symmetrical distribution of the transverse field induced by the current. The calculated dependences are in a qualitative agreement with the experimental data.Recently, the generation of the second harmonic in the off-diagonal magnetoimpedance in Co-based amorphous ribbons annealed in air in the presence of a weak magnetic field has been reported [24]. In this paper, we present the results of the study of the nonlinear off-diagonal magneto-impedance in Co-based amorphous ribbons annealed in air or in vacuum. The evolution of the first and second harmonics in the pick-up coil voltage with an increase of the current amplitude is analysed. It is demonstrated that formation of the surface crystalline layers in air-annealed samples changes drastically the behaviour of the harmonics. The experimental results are described in the framework of a quasi-static rotational model.

Influence of current amplitude on the nonlinear asymmetric ac volt–ampere characteristics in amorphous ribbons with GMI effect

“…However, at a sufficiently high I a2 , the (V 2 /V 0 )$t curve changes the frequency to twice that of I a2 , indicating that the second harmonic dominates in the ac voltage frequency spectrum for the high current amplitude. This agrees well with experimental results of published papers [5]. Experiments found that the contribution of the second harmonic to the voltage response increases with the growth of the current amplitude.…”

“…Experiments found that the contribution of the second harmonic to the voltage response increases with the growth of the current amplitude. The reason may be that the anti-symmetrical transverse magnetic-field distribution originating from the ac current has different magnetic variations over the upper and lower layers; the difference increases with the current amplitude and then the second harmonic contribution to the pick-up coil voltage increases [5].…”

“…Usually, GMI is measured as the field dependence of the voltage drop across a sample or as the voltage in the pick-up coil wound around a conductor [4]. The latter is referable for sensor applications since it generates a linear voltage response with enhanced field sensitivity [5].…”

Asymmetric off-diagonal magnetoimpedance in field-annealed amorphous ribbons: Analysis of bias current effect

“…Recently, the off-diagonal magnetoimpedance in fieldannealed Co-based amorphous ribbons has been reported [16][17][18]. The asymmetric two-peak behavior of the field dependence of the off-diagonal impedance has been observed.…”

“…The field annealing produces asymmetric hysteresis loops in the ribbons [22][23][24] due to the exchange coupling between the amorphous bulk and the magnetically harder surface crystalline layers. The coupling between two phases results in the asymmetry in the DC magnetization in the amorphous bulk that is responsible for the asymmetric GMI [19][20][21] and the asymmetric offdiagonal magnetoimpedance [16][17][18] in Co-based amorphous ribbons. Another method of producing the asymmetric field dependence of the impedance consists in applying DC bias current to the sample [8][9][10][11][12]25,26].…”