Effects of Layer Repetition and Cu Spacer Thickness on the Magnetoimpedance of Electrodeposited Permalloy Multilayers at 100 kHz and Its Application as a Magnetic Nanoparticle Sensor

Optimizing multilayer structures is essential for improving magnetoimpedance (MI) responses in low-frequency magnetic sensing applications. This study investigates the effects of layer repetition number (N) and Cu spacer thickness (x) on the magnetoimpedance (MI) response of [NiFe(600 nm)/Cu(x)/NiFe(600 nm)]N/Cu(200 nm)/[NiFe(600 nm)/Cu(x)/NiFe(600 nm)]N multilayer structures electrodeposited onto Cu printed circuit board substrates with meander patterns. The MI response was systematically evaluated at an operating frequency of 100 kHz to determine the optimal multilayer configuration. The results reveal that both layer repetition and Cu spacer thickness significantly influence the MI ratio. The highest MI ratio of 2.07% was achieved at N = 3 and x = 100 nm, suggesting an optimal balance between magnetic permeability and electrical conductivity. The sensing capability of the optimized multilayer structure was further evaluated using cobalt ferrite nanoparticles. Changes in the MI ratio of 0.32 and 0.64 were observed for nanoparticle masses of 0.1 and 0.3 g, respectively, indicating a mass-dependent sensor response. These findings demonstrate the potential of electrodeposited NiFe/Cu multilayer structures as low-frequency magnetoimpedance sensing platforms for magnetic nanoparticle detection.