Effect of current annealing on magnetic anisotropy in glass-coated amorphous microwires with positive magnetostriction

The magnetoimpedance (MI) effect is known as a large and sensitive change in a voltage measured across a magnetic conductor carrying a high frequency current. In the present paper, we propose current annealing with the aim to establish a specific magnetic anisotropy of a helical type, which is important to enhance the MI sensitivity at microwave frequencies, or to realize pulsed MI for such applications as Magnetoresistive Random Access Memory (MRAM). Co-rich amorphous wires may have a small positive magnetostriction and almost bistable type of magnetization behavior. Our work concerns hysteresis loop and MI measurements before and after passing dc current in the wires under the study for 15, 30, 45, 60 and 75 minutes. The used current was passed in Co-based microwires with a total diameter of 29.5 μm and a core diameter of 23.9 μm and fixed at 26 mA in this study. In Figure 1 we present hysteresis loop variation without and with current annealing at different times, 15 minutes and 75 minutes. One can see that the magnetization behavior changed from bistable type which is typical for axial anisotropy to that occurring for helical anisotropy. As a result, the impedance at MHz frequencies may show a hysteresis of a bistable type, and at GHz frequencies the impedance remains sensitive to applied magnetic field and tensile stress. Yet, we can conclude that the dc current treatment is interesting enough for enhancing magnetic properties and for the development of magnetic-field sensors which is prominent in soft magnetic materials.