Nanocrystalline grain size control for Ni80Fe20/Cu micro-composite wires by different electrodeposition methods

Abstract

In the development of high sensitivity bio-magnetic field sensors, extremely high permeability magnetic materials are essential as sensing elements. Materials composition, nanocrystalline grain size, uniformity and thickness are the key factors affecting the permeability of the magnetic materials. According to the random anisotropy model (RAM), magnetic properties can be drastically improved when the grain size is decreased below the critical magnetic interaction exchange length, which was calculated to be 270 nm for Ni 80 Fe 20 . Pulse-reverse electrodeposited and pulse electrodeposited Ni 80 Fe 20 have been reported to possess extremely good magnetic properties. Pulse-reversed specimens were predicted to possess much better magnetic properties due to improved uniformity, arising from the presence of an anodic current. In this study, a layer of Ni 80 Fe 20 was deposited onto 20 μm diameter Cu wires using pulse-reverse electrodeposition. The composition of the deposited layer was fixed constant by the manipulation of Ni 2+ and Fe 2+ ions while the thickness was controlled to be similar by the manipulation of the deposition time. The nanocrystalline grain sizes of the specimens were characterized using XRD and compared to those from dc electrodeposition and pulse electrodeposition. Results showed that the nanocrystalline grain sizes of specimens produced by pulse-reverse electrodeposition was the largest, followed by those from dc electrodeposition and then pulse electrodeposition. However, with the introduction of an off-time period to the pulse-reverse current waveform, the average grain size of the resulting deposited material was found to decrease. The magneto-impedance effect of the specimens from pulse reverse electrodeposition with off-time was found to be higher than those from pulse reverse electrodeposition without off-time.