Contributors to fluxgate magnetic noise in permalloy foils including a potential new copper alloy regime

• Published in: Geoscientific instrumentation, methods and data systems Vol. 11; no. 1; pp. 111 - 126
• Main Authors: Miles, David M, Dvorsky, Richard, Greene, Kenton, Hansen, Christian T, Narod, B. Barry, Webb, Michael D
• Format: Journal Article
• Language: English
• Published: Gottingen Copernicus GmbH 03-03-2022; Copernicus Publications
• Subjects: Alloys; Copper; Copper base alloys; Diameters; Ferromagnetic materials; Ferromagnetism; Ferrous alloys; Fluxgate magnetometers; Foils; Geometry; Grain size; Heat; Heat treatment; Heat treatments; Magnetic alloys; Magnetic field; Magnetic fields; Magnetic measurement; Magnetometers; Manufacturing; Molybdenum; Molybdenum base alloys; Noise; Permeability; Physical properties; Racetracks; Specialty metals industry
• ISSN: 2193-0864; 2193-0856; 2193-0864
• DOI: 10.5194/gi-11-111-2022

Fluxgate magnetometers provide sensitive and stable measurements of the static and low-frequency vector magnetic field. Fluxgates form a magnetic
field measurement by periodically saturating a ferromagnetic core and the intrinsic magnetic noise of this material can determine the noise floor of
the instrument. We present the results of an empirical experiment to understand the physical parameters that influence the intrinsic magnetic noise
of fluxgate cores. We compare two permalloy alloys – the historical standard 6 % molybdenum alloy and a new 28 % copper alloy. We examine
the influence of geometry using the historical standard 1 in. diameter spiral-wound ring core and a new stacked washer racetrack
design. We evaluate the influence of material thickness by comparing 100 and 50 µm foils. Finally, we investigate heat treatments in
terms of temperature and ramp rate and their role in both grain size and magnetic noise. The results of these experiments suggest that thinner
foils, potentially comprising the copper alloy, manufactured into continuous racetrack geometry washers may provide excellent performance in
fluxgate sensors.