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(a) AFM image of BaTiO3 surface topography showing terraces and periodic steps with a unit-cell height. (b) Schematic illustration of non-contact macroscopic poling method: a large needle held at a dc bias of ±800 V and at ∼100 μm above sample surface scans the sample surface (∼5 × 5mm2) in high vacuum conditions. The step increment during scanning was 50 μm. (c) PFM phase image of the polydomain structure of the as-grown BTO film. (d) PFM phase image of the uniformly polarized BTO film after noncontact poling. (e), (f) PFM amplitude (e) and phase (f) images showing comparison between the macroscopic non-contact poling and poling by PFM. Central 2 × 2 μm2 and 0.5 × 0.5 μm2 squares have been produced by scanning with an AFM tip under +4 V/−4 V dc bias in contact mode, while an outer region shows the result of macroscopic non-contact poling. Saturated polarization has been obtained for both poling methods. Scan size is the same for all AFM/PFM images.
(a) In-plane M-H curves of BTO/LSMO(25 nm) heterostructure measured by SQUID at room temperature for upward and downward polarization directions in BTO. (b) In-plane M-H curve of BTO/LSMO (10 nm) heterostructure measured by MOKE at room temperature for upward and downward polarization directions in BTO showing the same trend as in (a). (c) Dependence of the relative change of magnetization ΔM on the LSMO layer thickness t. The open circle indicates a normalized data point. The solid curve is a fit to the 1/t function. (d) Temperature dependence of saturation magnetization of BTO/LSMO (25 nm) heterostructure for upward and downward BTO polarizations measured at 2500 Oe. The inset shows temperature dependence of the relative magnetization change ΔM.
(a) Temperature-composition phase diagram of LSMO showing ferromagnetic metal (FM), paramagnetic insulator (PI), ferromagnetic insulator (FI), and paramagnetic metal (PM) phases. (Reprinted with permission from E. Dagotto, T. Hotta, and A. Moreo, Phys. Rep. 344, 1 (2001). Copyright 2001, American Institute of Physics.) Also shown are calculations of the shift of the phase boundary between insulating and metallic states for two possible BaTiO3 polarization values. Polarization screening shifts the effective charge concentration x at the interface: the leftward shift leads to metal-insulator transition while the rightward shift keeps the system in the metallic state. (b) Schematic illustration of the metal-insulator phase transition in LSMO due to accumulation of screening charges at the BTO/LSMO interface. (c) Temperature dependence of the thickness of the magnetically modulated layer in LSMO.
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