Relating surface roughness and magnetic domain structure to giant magneto-impedance of Co-rich melt-extracted microwires.

Understanding the relationship between the surface conditions and giant magneto-impedance (GMI) in Co-rich melt-extracted microwires is key to optimizing their magnetic responses for magnetic sensor applications. The surface magnetic domain structure (SMDS) parameters of ~45 μm diameter Co69.25 Fe4.25 Si13 B13.5-x Zrx (x = 0, 1, 2, 3) microwires, including the magnetic domain period (d) and surface roughness (Rq ) as extracted from the magnetic force microscopy (MFM) images, have been correlated with GMI in the range 1-1000 MHz. It was found that substitution of B with 1 at. % Zr increased d of the base alloy from 729 to 740 nm while retaining Rq from ~1 nm to ~3 nm. A tremendous impact on the GMI ratio was found, increasing the ratio from ~360% to ~490% at an operating frequency of 40 MHz. Further substitution with Zr decreased the high frequency GMI ratio, which can be understood by the significant increase in surface roughness evident by force microscopy. This study demonstrates the application of the domain period and surface roughness found by force microscopy to the interpretation of the GMI in Co-rich microwires.