Effect of magnetic field on the magnetic structure of nanocrystalline electroplated NiFe layers

In order to develop high sensitivity micro sensors for bio-magnetic field using NiFe electroplated composite sensing elements, it is important to study how different plating processes can affect the magnetic properties in terms of the chemical composition and magnetic structure of the plated layer. In this study, to study the effect of the magnetic field on the magnetic structure of the electroplated NiFe layers, magnetic controlled plating in which a longitudinal magnetic field ranging from 0 to 400 Oe is applied during nanocrystalline electroplating of permalloy Ni₈₀Fe₂₀ layer of 2 μm thick onto a 20 μm diameter Cu wire. The magnetic structure of the plated layers is studied by investigating the Giant magneto-impedance (GMI) effect of the plated layer. GMI has been measured from a frequency range of 100 kHz to 50 MHz. It is observed that under conventional electroplating without an external magnetic controlling field, the anisotropy of the plated layer is generally circumferential as indicted by the double peaks of the MI curves in testing at high frequency. When a longitudinal magnetic field is applied during electroplating, the plated layer shows single peak MI curves, suggesting that the anisotropy is changed from circumferential to longitudinal. The results also show that the sensitivity and resolution of a magnetic field sensor is improved greatly by changing the anisotropy of the plated layer from circumferential to longitudinal.