Electronically Driven Major-Reversal with No Major Field-Dr Massimo Ghidini (Materials Sciences)

The electrical reversal of magnetization is one of the key goals in the study of multiferroic and magnetoelectric materials, and was recently demonstrated in ferromagnetic films using strain1 or exchange bias2 from multiferroic single-crystal substrates. However, each reversal event required the reversal of an applied magnetic field, and so repeatable magnetic reversal under purely electrical control remains an outstanding goal. Here we perform microscopic investigations of commercially manufactured multilayer capacitors (MLCs) which serendipitously display strain-mediated magnetoelectric coupling between magnetostrictive Nielectrodes and piezoelectric BaTiO3 (BTO) dielectric layers. Magnetic force microscopy
(MFM) reveals perpendicularly magnetized features in the electrode layers that exhibit electrically driven repeatable magnetization reversals with no applied magnetic field. Micromagnetic modelling supports our interpretation that this non-volatile magnetization reversal may be achieved via a dynamic process that is associated with a temporary reduction in perpendicular uniaxial magnetic anisotropy driven by strain from fast and reversible voltage-driven ferroelectric-domain switching.

I will also report on the reversible control of perpendicular magnetic anisotropy in polycrystalline nickel films evaporated on single-crystal ferroelectric BTO substrates via thermal and electrical treatments. We have employed both MFM and photoemission electron microscopy with magnetic contrast from x-ray magnetic circular dichroism (XMCD-PEEM), to study the effects of thermally and electrically driven changes in the BTO substrate on the magnetic domain structure of the nickel films. I will show that the perpendicular component of the magnetization can be erased and reset by thermally cycling through the structural transitions of the substrate and more importantly, it can be reversibly electrically controlled at room temperature.