Frequency-tunable nickel-titanium substrates for magnetoelectric sensors

Abstract

We show the use of nickel-titanium (NiTi) metal thin films as functional substrates of magnetoelectric composites allowing the composites’ mechanical resonance to be tuned towards the frequency range of interest by employing the gradual change of the Young’s modulus during the martensite-austenite phase transformation. Such composites are successfully fabricated by layering functional piezoelectric aluminum nitride and highly magnetostrictive FeCoSiB on sputtered NiTi-films. Subsequent characterizations reveal high magnetoelectric response. Applied as magnetic field sensors a high sensitivity (with a magnetoelectric coefficient αME=290 V/cm Oe) and low limit of detection of approximately 110 pT/Hz1/2 is observed for AC magnetic fields matching the mechanical resonance frequency. This mechanical resonance of the sensor can be altered with a Δf of 12% in the temperature interval between room temperature and 130 °C. This offers the possibility to adjust the sensor’s mechanical resonance frequency featuring the highest sensitivity to the magnetic field frequency to be measured.