Influence of Magnetostriction of NiFe Electroplated Film on the Noise of Fluxgate

One of the sources of fluxgate noise is the noise originating in the magnetic core. Several parameters, such as anisotropy and shape, are traditionally studied and optimized to reduce the noise. In this paper, we show how the magnetostriction influences the noise of the fluxgate. We electroplated NiFe thin-film over a copper layer using different current density. By energy-dispersive X-ray spectroscopy we show that the mutual percentage of Fe and Ni in the film depends on the current density. As a result the magnetostriction is changed from negative to positive values, with minimum magnetostriction found at around Fe₁₉Ni₈₁ composition. When we used these ring cores as base for a fluxgate we observed that the noise rapidly rises as the absolute value of magnetostriction increases, while the minimum noise is achieved at lowest value of magnetostriction. An increase of one order of magnitude of the magnetostriction causes and increment of almost two orders of magnitude in the noise. Therefore, we conclude that it is vital to employ alloys with the lowest possible magnetostriction as core for fluxgates.