Interactions between a ferromagnet, cobalt, and a ferroelectric copolymer, poly(vinylidene fluoride with trifluoroethylene) in thin film heterostructures result in a 5% change in the ferroelectric polarization on application of a perpendicular 6 kG magnetic field corresponding to a magnetoelectric coupling coefficient of . The effect disappears on magnetic saturation, ruling out conventional strain coupling. A simple model posits that the ferroelectric film develops in-plane strain gradients, a consequence of the coupling to strain gradients present at the domain walls in the multidomain Co layer, resulting in the measured polarization change via the flexoelectric effect.
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We assume that over the width of a ferromagnetic domain wall, the ferroelectric consists of a single crystal, with a unique direction of polarization. Domain walls in Co, approximately 30 nm are comparable to the ferroelectric crystallites, 30 nm to 50 nm (Ref. 12). The presence of multiple ferroelectric crystallites within a magnetic domain wall will reduce the effect.
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