Eddy currents A misleading contribution when measuring magnetoelectric voltage coefficients of thin film devices
Résumé
Tb0.3Dy0.7Fe2/Pt/PbZr0.56Ti0.44O3 (Terfenol-D/Pt/PZT) magnetoelectric (ME) thin films were deposited on Pt/TiO2/SiO2/Si substrate. The ME voltage coefficient αH ME was determined at room temperature using a lock-in amplifier and by applying to the sample an alternating magnetic field of a few mT. Surprisingly, very similar responses were obtained from a simple commercial capacitor set in series with a small loop of wire. This allowed us first to accurately model and reproduce the frequency response of the ferroelectric PZT layer alone. We also observed that, at low frequency, the voltage across the ferroelectric capacitor and the current in the circuit did not decrease significantly when diminishing then removing, the area of the conductive loop. One major conclusion is that eddy currents in the lead wires, rather than the classical electromotive force across conductive loops, contribute significantly to the total voltage response, at least for thin film ME devices. A model taking into account eddy currents was then developed for the extraction of the true αH ME. A large αH ME of 4.6V/cm.Oe was thus obtained for the Terfenol-D/Pt/PZT thin film device, without DC magnetic field. © 2015 AIP Publishing LLC.