| In this work, we demonstrate a large charge-mediated magnetoelectric coupling in a PbZr0.2Ti0.8O3 / La0.8 Sr0.2MnO3 (PZT/LSMO) composite structure resulting from direct control of magnetism via charge carrier density. This approach has the advantage that its physical mechanism is transparent and the size of the effect can be quantified and understood qualitatively within the double-exchange model. Direct quantification of the charge-driven magnetic changes based on electronic, magnetic, and spectroscopic measurements show that both the spin state and spin configuration of LSMO are modulated.;Using a combination of advanced physical vapor deposition techniques, we have grown epitaxial PZT/LSMO bilayer heterostructures on (001) SrTiO 3 substrates with excellent crystallinity, atomically smooth surfaces, low leakage current density, and abrupt interfaces. Magneto-optic Kerr effect (MOKE) magnetometry was used to directly interrogate the local magnetic state of the LSMO as a function of the PZT polarization state. We show direct control of magnetism via applied electric fields, including modulation of the magnetotransport behavior and magnetic-ordering temperature, on/off switching of magnetism, and hysteretic magnetization versus electric field (M-E) characteristics. The magnetoelectric coupling strength, which relates the change in magnetization to the applied electric field, is found to vary strongly with temperature, reaching a low temperature saturation value of +6 Oe cm / kV, much larger than observed in single-phase magnetoelectrics and too large to be explained by a simple band-filling model. To clarify the origin of the magnetoelectric coupling, we carried out near edge x-ray absorption measurements that revealed a well defined change in the position of the Mn absorption edge with the ferroelectric polarization, giving a direct measure of the change in Mn valency in LSMO. We explain these results in terms of an interfacial magnetic reconstruction, whereby the spin coupling at the interface changes from ferromagnetic to antiferromagnetic.;This work opens new avenues for the development of novel nanoscale devices, such as spin-based technologies with large coupling between electric and magnetic degrees of freedom and Mott metal-insulator transition field effect memories and logic devices. Along these lines, we have demonstrated a non-volatile memory using an electric field induced metal-insulator transition. We characterized several key aspects of device performance, including on/off ratio, switching time, and retention, with an emphasis on lateral and vertical scaling and integration with mainstream semiconductor manufacturing. |
