Structural and magnetic properties of CoFeSiB amorphous wire GMI element

Abstract

In this study, the amorphous soft magnetic Co68.15Fe4.35Si12.5B15 wires prepared by the conventional inrotating water melt-spinning technique were investigated. The XRD pattern of the as-cast wire sample exhibits a very weak diffusive peak that reveals the amorphous structure. The DTA thermogram shows one exothermic process, which results from crystallization with a peak temperature of 566 °C. The XRD pattern of the sample annealed at 700 °C shows the presence of two diffraction peaks: the first could be ascribed to the crystal phase e-CoSi (structure of P2 order), and the second could belong to crystal phases Co2B and e-CoSi (P2 order). The giant magnetoimpedance (GMI) frequency behavior (ranging from 50 Hz to 5 MHz) was monitored as a function of an external dc magnetic field applied parallel to the wire sample. The critical frequency of about 5 kHz - 7 kHz was observed with the initial increase of MI. In the medium frequency range (which usually starts at about 1 MHz) the skin effect and the magnetization vector rotation mechanism are dominant in the process of circular magnetization (the movement of the magnetic domain walls is blocked). Therefore, the shape of dependence of the MI-ratio on the external DC magnetic field changes significantly and the appearance of a peak is recorded. The attained peak value of the impedance modulus of about 35 Ω was registered at the highest frequency of 5 MHz. The maximum GMI ratio of 334% was recorded at a frequency of 0.95 MHz (@ 7.72 kA/m).