Stimulated by our new approach of a fully integrable ΔE-effect magnetic field sensor [Gojdka et al., APL 99 (2011) 223502, Nature 480 (2011) 155], we present a comprehensive description of the origin of the ΔE-effect in magnetostrictive thin films and their application for magnetic field sensors.
The ΔE-effect describes the nonlinearity of stress-strain behavior in magnetic materials. It originates from magnetoelastic coupling and results in a change of elastic modulus upon application of a magnetic field. This is modeled using an extended Stoner-Wohlfarth approach including anisotropy distributions and thin film geometry. The model is then expanded to correctly describe the properties of a MEMS cantilever resonance shift with magnetic field and stress. Such high Q cantilevers have been studied intensely for the application as magnetic field sensors. To operate the sensor, it is externally excited using an additional piezoelectric layer of AlN. The impedance change of this magnetically detuned electromechanical resonator is used for high sensitivity sensors able to detect magnetic fields well below 1 nT.