Magneto-electric effects in functionally stepped magnetic nanobilayers on ferroelectric substrates: Observation and theory on the influence of interlayer exchange coupling

Abstract

The strain mediated magnetoelectric (ME) coupling is studied in composites of functionally stepped ferromagnetic thin films on ferroelectric lead magnesium niobate-lead titanate substrates. Nanometer thick layers of nickel with negative piezomagnetic coefficient q and Fe0.81Ga0.19 (Galfenol) with positive q were deposited by pulsed laser deposition to achieve the desired step in q for the ferromagnetic phase. The measured maximum ME voltage coefficient (MEVC) ranges from 4.2 to 5.05 mV/(cm Oe) and shows a general increase with increasing Ni-to-Galfenol thickness ratio. Data on MEVC as a function of static field H show a large zero-bias ME coefficient. A model is developed for the ME effect that considers (i) the step in q in the magnetic layers of the ME composite and (ii) influence of the interlayer exchange interaction between Ni and Galfenol. Estimated bias magnetic field dependence of MEVC is in qualitative agreement with the experimental data. © 2014 AIP Publishing LLC.