A. Chizhik

Manipulation of domain wall dynamics in amorphous microwires through the magnetoelastic anisotropy

We studied the effect of magnetoelastic anisotropy on domain wall (DW) dynamics and remagnetization process of magnetically bistable Fe-Co-rich microwires with metallic nucleus diameters (from 1.4 to 22 μm). We manipulated the magnetoelastic anisotropy applying the tensile stresses and changing the magnetostriction constant and strength of the internal stresses. Microwires of the same composition of metallic nucleus but with different geometries exhibit different magnetic field dependence of DW velocity with different slopes. Application of stresses resulted in decrease of the DW velocity, v, and DW mobility, S. Quite fast DW propagation (v until 2,500 m/s at H about 30 A/m) has been observed in low magnetostrictive magnetically bistable Co56Fe8Ni10Si10B16 microwires. Consequently, we observed certain correlation between the magnetoelastic energy and DW dynamics in microwires: decreasing the magnetoelastic energy, Kme, DW velocity increases.

Interaction between Fe-rich ferromagnetic glass-coated microwires

Abstract Hysteresis loop measurements of several Fe-rich glass-coated amorphous microwires of Fe 65 Si 15 B 15 C 5 composition have been performed using the conventional fluxmetric and SQUID magnetometers and magneto-optical Kerr effect technique. The number of the wires used in the measurements has been varied from 1 to 10. The hysteresis loops exhibit large Barkhausen jumps (LBJ) between two remanent states for all number of the wires involved in the measurements. The number of jumps is correlated with the number of wires. The lowest switching field decreases as the number of wires increases. The shape of the hysteresis loop and the switching field values depend on the sweeping rate, d H /d t , and on the distance between wires. The obtained results have been analyzed considering the mutual influence of the wires due to stray field effects. The superposition of external and stray fields creates some spatial distribution of the magnetic field to produce successive magnetization reversals in the multi-wire system.

Correlation of surface domain structure and magneto-impedance in amorphous microwires

The correlation between surface domain structure (SDS) and high frequency magneto-impedance (MI) in amorphous microwires has been systematically studied. First, we applied the magneto-optical polarizing microscopy to determine the SDS and found that it is considerably different in unstressed microwire and in microwires to which tensile and torsional stress were applied. Then, we measured the longitudinal and off-diagonal MI in these microwires and also observed quite different MI dependencies. We analyzed the experimental MI curves and their dependence on the SDS with the help of a simple model that nevertheless yields good qualitative agreement with experiment. We have demonstrated that the analysis of the MI dependencies, especially the off-diagonal one, can reveal the SDS in the microwires. The obtained results can also be useful for magnetic and stress sensing applications.

Direct imaging of the magnetization reversal in microwires using all-MOKE microscopy

We report a method of imaging of the magnetization reversal process using analysis of real-time images of magnetic domain structures in cylindrically shaped microwires. This method uses wide-field polarizing optical microscopy and is based on the magneto-optical Kerr effect (MOKE). The aperture diaphragm in MOKE microscope was used to control the incident angles of the light rays that reached the non-planar surface of the microwire and also determined the MOKE geometries. The movement of the non-central position of the hole in this diaphragm leads to a change in the orientation of the plane of incidence of the light along the perpendicular or the parallel direction to the axial direction of the wire. The visualization of the surface magnetic domain structures is obtained using polar and longitudinal MOKE geometries. The hysteresis loops were obtained by plotting the averaged image contrast as a function of the external magnetic field. The separation of the all-magnetization components is performed using different MOKE geometries in a microscope. We demonstrate the use of vector magnetometry to analyze the orientation of the magnetization in a cylindrically shaped microwire under the influence of an external magnetic field.

Magnetization reversal of Co-rich wires in circular magnetic field

The process of magnetization reversal of Co-rich amorphous wires in circular magnetic field has been studied by Kerr effect. The transverse Kerr loops had features, related to circular domains nucleation and domain wall propagation. A correlation between the switching field and wire length has been found. A remarkable change of the magnetization reversal under the application of axial dc magnetic field was observed. This could be explained by the presence of an interaction between the axial inner core and circular outer shell of Co-rich wires.

Circular magnetic bistability induced by tensile stress in glass-covered amorphous microwires

Investigations of magnetic reversal in Co-rich glass covered amorphous microwires were performed using the magneto-optical Kerr-effect technique. The appearance of circular magnetic bistability was found in the presence of external tensile stress. A tensile-induced large Barkhausen jump of circular magnetization is associated with a change of the value of the magnetostriction constant induced by stress and by rearrangement of domain structure in the outer shell of the microwire.

Vortex-type domain structure in Co-rich amorphous wires

Investigation of the surface magnetic domain structure has been performed in Co-rich, nearly zero magnetostrictive, amorphous wires using magneto-optical Kerr effect magnetometry and microscopy. The formation and motion of a multidomain vortex-type structure with curved domain walls have been observed in amorphous wires. The possible origins of the existence of the vortex-type structures in these amorphous wires are discussed.

Manipulation of domain wall dynamics in amorphous microwires through domain wall collision

Experimental results of the magnetic field driven domain walls dynamics in magnetically bistable Fe-rich microwires are reported. We have observed that under certain conditions a controllable domain wall (DW) collision can be realized in different parts of the wire, and that it is possible to manipulate the DW dynamics in a field-driven regime. The DW collisions obtained in this way can be used to release pinned domain walls. We have also found a correlation between the local nucleation field distribution and field dependence of DW velocity: the magnetic field value corresponding to the minimum nucleation field determines a threshold between single and multiple domain wall propagation regimes.

Circular magnetic bistability in Co-rich amorphous microwires

Circular magnetic bistability associated with a large Barkhausen jump between two states with opposite directions of circular magnetization have been observed by magneto-optical Kerr effect in nearly-zero magnetostrictive glass covered Co-rich amorphous microwire. The influence of external axial tensile stress on the circular switching field has been studied. Observed results have been related with a circular magneto-elastic anisotropy induced by a tensile stress in the outer transversally magnetized shell of the microwire.

Direct observation of giant Barkhausen jumps in magnetic microwires

Magnetization reversal induced by a circular magnetic field has been studied using the magneto-optical Kerr effect in magnetic microwires. The visualization of the classical effect of a giant Barkhausen jump is reported in a magnetic microwire. It was directly confirmed that the surface giant Barkhausen jump consists of the nucleation of a single circular domain followed by the long distance quick motion of the solitary circular domain walls.