Voltage Control of Perpendicular Magnetic Anisotropy in Multiferroic Composite Thin Films under Strong Electric Fields

Ferroelectric/ferromagnetic multiferroic composites with perpendicular magnetic anisotropy (PMA) are useful for developing power-efficient magnetic memories. Voltage control of PMA has been demonstrated in bulk multiferroic composites based on ferroelectric single crystals, but they are not compatible for integration. Multiferroic composite thin films are useful for developing integrated devices; however, voltage control of PMA in them has not been achieved yet at room temperature due to their low magnetoelectric (ME) coupling coefficient. Here, we demonstrate such functionality and propose to enhance their ME coupling effect under a strong electric field by taking full advantage of the large dielectric strength of ferroelectric thin films. First, the thickness-dependent breakdown of Pb(Zr-0.384 Ti0.576Nb0.04)O-3 (PNZT) thin films was studied, and the two-layer (similar to 200 nm) samples , exhibited the highest breakdown strength (3.68 MV/cm) and small surface roughness (<1 nm). Second, we fabricated PNZT/(Co/ Pt)(5) thin films with strong PMA whose breakdown strength is nearly independent of the top electrode materials. Finally, voltage-induced effective magnetic field (H-eff) in PNZT/(Co/Pt)(5) was studied. It is comparable to that achieved in bulk composites and will induce magnetization switching under strong electric fields. Multiferroic composite thin films with large breakdown strength will provide a useful platform for enabling integrated multiferroic devices.

Automated summary

Multiferroic composite thin films with large breakdown strength provide a useful platform for enabling integrated multiferroic devices. The two-layer PNZT thin films with a thickness of about 200 nm exhibit the highest breakdown strength and small surface roughness, while PNZT/(Co/Pt)5 thin films with strong PMA show voltage-induced effective magnetic field that can induce magnetization switching under strong electric fields.