Soft Magnetic Characteristics and Magnetoimpedance Phenomenon in Copper Wire Coated with Permalloy Film Electroplated from a Sodium Gluconate-Based Bath

Abstract

Nanocrystalline NiFe thin films of 11 μm thickness have been deposited on Cu wire using an electrochemical technique in galvanostatic mode with a sodium gluconate (SG) additive in the plating solution. The SG concentration is systematically varied from 0 g/L to 80 g/L, which results in a substantial enhancement in the soft magnetic characteristics and magnetoimpedance (MI) ratio of the plated wire across a broad frequency spectrum, specifically attributed to the optimal inclusion of SG at 55 g/L. The observed improvements in magnetic softness and MI ratio are linked to the reduction in crystalline size and surface roughness and modifications in the microstructure influenced by the SG additive in the electroplating bath. Furthermore, an equivalence between experimental impedance data and the theoretical framework based on the analytical model of circumferential permeability is outlined to extract the material parameters of the permalloy magnetic films. These extracted parameters play a pivotal role, enabling a comprehensive understanding of the variation in the MI ratio as well as circumferential permeability of the thin films as a function of the SG additive concentration in the plating bath. The intricate association observed between the MI ratio and circumferential permeability suggests that the amplification of the MI ratio resulting from the inclusion of SG is linked primarily to enhancements in circumferential permeability and the incorporation of magnetic softness. Thus, the present work offers both a theoretical and experimental framework for future research in advanced MI-based devices for magnetic sensing applications.