Giant magneto-impedance in heterogeneous microwires
Recent results concerning the giant magneto-impedance effect, GMI, in magnetic microwires having diameter in the range of a few micrometers and heterogeneous character are introduced in this work. Two types of microwires have been studied, namely, (i) magnetic microwires covered by insulating Pyrex glass coating and (ii) copper wires covered by electrodeposited magnetic microtubes. The magnetic anisotropy distribution in each type of microwire is correlated with giant magneto-impedance. While the main source of anisotropy in glass coated microwires is of magnetoelastic origin created by the stresses induced during quenching and by the coating, in the case of the microtubes the origin is the columnar growth during the electrodeposition. The influence on GMI of various treatments that modify the anisotropy is analyzed. Heterogeneous microwires with different thicknesses of insulating coating and of magnetic tube are analyzed.
Determination of closure domain penetration in electrodeposited microtubes by combined magnetic force microscopy and giant magneto-impedance techniques
The domain structure of electrodeposited Co90P10 microtubes exhibiting radial magnetic anisotropy and giant magneto-impedance effect has been characterized by combined magnetic force microscopy imaging and impedance measurements. It has been shown that the size of the closure domains increases with the CoP layer thickness. Furthermore, the depth of the closure domains has been quantitatively determined from the high frequency behavior.
The magnetization reversal process in amorphous wires
The most outstanding property of amorphous wires is their capability to magnetized through a single Barkhausen jump giving rise to squared hysteresis loop. This phenomenon is spontaneously shown in large magnetostriction wires in the as-quenched state. According to the previous model, such a Barkhausen jump arises from the magnetization reversal inside core having axial easy magnetization axis. In this work, we review some recent results leading to a refinement of the previous model paying particular attention to the domain structure close to wires having different lengths. The existence of "closure" domains in such regions and the ends of existence of their variation when applied fields up to a critical value for magnetization reversal process. To deepen the knowledge of the dynamics of the wall responsible for the magnetization two experimental studies were performed namely, the conventional Sixtus-Tonks experiment and the magnetization reversal under homogeneous applied field along the sample. The main conclusions are: (a) the reversal process is spontaneously initiated close to the end of the wire where the wall is depinned and propagates along the entire wire, (b) the starting end alternates in each reversal or remains the same depending on an additional external applied field, and (c) the wall during the reversal approaches a planar shape. >