Magnetoimpedance properties of CoNbZr, multilayer CoNbZr/Au and multilayer NiFe/Au thin films

Thin-film magnetic sensors using the giant magnetoimpedance (GMI) effect show great promise for sensitive low-field magnetic measurements. Optimising sensor performance requires a thorough understanding of the properties of various soft magnetic materials. This study examines the electric, magnetic, and GMI properties of sputtered single-layer amorphous CoNbZr, multilayer amorphous CoNbZr/Au, and crystalline NiFe/Au thin films. GMI measurements reveal distinct ferromagnetic resonance (FMR) frequencies: 1.4 GHz for CoNbZr, 0.7 GHz for CoNbZr/Au, and 0.5 GHz for NiFe/Au. Au interlayers improve the GMI response, increasing the GMI ratio by 50% and reducing FMR frequency compared to single-layer CoNbZr. The highest GMI ratio of 300% occurs in a 20 $\mu$m x 5000 $\mu$m CoNbZr/Au strip at 1.8 GHz under 2 mT, while NiFe/Au exhibits 280% at 4 mT. These differences are linked to variations in in-plane demagnetising factors and saturation magnetisations, emphasising the role of material and geometry in GMI sensor performance.