Magnetoimpedance aftereffect in a soft magnetic amorphous wire

Abstract

A slow relaxation of the high-frequency impedance is observed in a Co 68.25 Fe 4.5 Si 12.25 B 15 amorphous wire after nucleation of a new domain pattern in a previously saturated sample. The observed impedance decay follows quasilogarithmic kinetics, and it is probably associated with the low-field ac magnetic permeability aftereffect of the circular domain walls. The impedance drop achieves relative amplitudes up to 1%, 16 s after the removal of the saturating external field. The effect is studied under typical magnetoimpedance experimental conditions, varying both the ac current amplitude and frequency. Although completely undesirable for many technical applications, the unique kinetic features of the impedance aftereffect may be explored to study circular magnetization processes under extreme domain-wall velocities. ͓S0163-1829͑97͒50410-3͔Although amorphous magnetic materials have been known for more than thirty years, their basic and applied interest has been constantly renewed, owing to the discovery of new and attractive properties. Recently, the observation of large field-induced changes in the high-frequency impedance of soft magnetic amorphous wires 1-3 and ribbons 4,5 opened enormous perspectives in the use of amorphous materials as cheap and sensitive magnetic-field sensors. When a highfrequency ( f Ͼ100 kHz͒ and low-intensity (iϽ15 mA͒ electrical current flows through a soft magnetic material, its impedance suffers a strong variation if an external magnetic field is applied to the sample. This effect, known as giant magnetoimpedance ͑GMI͒, can be qualitatively understood in terms of field-induced changes in the magnetic penetrationwhere is the electrical resistivity, is the transversal permeability ͑in the case of wires, it is the circular permeabil-ity͒, and f is the field ͑current͒ frequency. In a naive view, the application of a longitudinal dc magnetic field causes a strong variation in the transversal permeability, which is directly related to the imaginary component of the impedance ͑the reactance X͒, 3 causing a strong change in the penetration depth, and therefore influencing also the real part of the impedance ͑the resistance R͒. 3 Although rooted in classical electrodynamics, there are several aspects of GMI that remain to be understood, in particular, the role of induced anisotropies and the effect of different magnetization mechanisms in the observed phenomena. [2][3][4][5] On the other hand, it is well known that after a sudden rearrangement of the magnetic domain structure in amorphous ferromagnetic materials, a relaxing behavior of the low-field permeability is observed at any temperature ͑up to T c ͒, being characterized by quasilogarithmic relaxation kinetics. 7,8 This relaxation, also known as magnetic permeability aftereffect ͑MAE͒, or simply disaccommodation, has been explained in terms of directional ordering mechanisms of specific atoms, or atom pairs, interacting with the local magnetization vector. 7,8 The time relaxation of the magnetic permeability is thought to be an intrins...

Relationship between the giant magnetoimpedance effect and the relaxation of magnetic permeability

“…4(b). The presence of magnetic after effect in amorphous wires has been previously reported in ribbons [4,5]. The Presence of MAE is usually ascribed to the rearrangement of the magnetic moments in the magnetically coupled grains [8].…”

“…According to the bibliography [2], typical values of parameters involved in such a dynamics goes to relaxation/resonance frequencies corresponding to a few MHz, reason because of this analysis can not be omitted in GMI experiences. In fact, there is in the bibliography a bit of information concerning to magnetic relaxation in amorphous samples, but the results are not conveniently related to GMI relaxation [3][4][5].…”

Magnetic After-effect in Amorphous Co-Fe-Si-B Wire

“…Magnetoimpedance after-effect in amorphous wire was reported in [3,4]. They observed 1-1.5 % change of impedance at room temperature.…”

Magnetic after-effect of the giant magnetoimpedance in cobalt-based amorphous wires

“…In this work we study the time dependence of the complex impedance after a sudden change in the magnetic field. The existing number of works dealing with the time dependence of GMI in this materials are very reduced [4][5][6] although the consequences can be important. From the theoretical point of view MAE gives information about the dynamics of the material but also reveals a useful information about the stability and accuracy of these materials for technical applications in the field of sensors.…”