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(a) AFM topography images (tapping mode) of ultrathin 6T films vacuum-deposited on epitaxial Fe3O4(111) recorded at three successive stages of the film growth. Left:10 × 10 μm2; thickness = 2.5 nm (1ML); middle: 20 × 20 μm2; thickness = 3.75 nm (1.5ML); right: 10 × 10 μm2; thickness = 5.0 nm (2ML). The colour scale bars indicate the AFM contrast. The surface profiles shown below each AFM image have been recorded along the indicated horizontal lines. The narrow spike on the profile line of the 1ML image (Left) corresponds to a local second 6T monolayer. (b) Structural characterization of the α-Al2O3//CoFe2O4(5 nm)/Fe3O4(15 nm)/ 6T(5 nm)/Co(10 nm) heterostructure by X-ray reflectivity. Inset: associated fit table in good agreement with the nominal layer thicknesses. (c) Schematic drawing of the 6T-based organic-inorganic magnetic heterostructures.
Resistance map of 1ML of 6T (thickness = 2.5 nm) at room temperature deposited onto a Pt/CoFe2O4/Fe3O4 layer recorded by current-sensing AFM at a tip voltage of 1.5 V. High resistance spots (indicated by arrows) are due to adsorbates on the surface.
Room temperature in-plane magnetic hysteresis loops of CoFe2O4 (5 nm)/Fe3O4(15 nm)/6T/(LiF)/Co heterostructures (a) 6T(0.5ML), (b) 6T (1ML), (c) 6T(1ML) + LiF, and (d) 6T(2ML). Left column: VSM major and minor loops. Right column: VSM minor loops of the cobalt layer with extraction of the exchange field (μ0Hex). A negative exchange field around −6 mT is observed for 0.5ML of 6T while a positive exchange field around 30 mT is observed for 1ML of 6T.
(a) Magnification of the major hysteresis loop (inside the rectangle) at 50 K for a α-Al2O3//CoFe2O4/Fe3O4/6T(1ML)/Co/Au heterojunction revealing a cross-over, signature of AFC. (b) Temperature dependence of the exchange field (μ0Hex) and associated exchange constant (JAF) from minor loops in α-Al2O3//CoFe2O4/Fe3O4/6T(1ML)/(LiF)/Co/Au heterostructures. The square (blue) data point correspond to the JAF value extracted from the fit of the major loop.
(a) Polarized neutron reflectivity at T = 300 K as a function of the wave vector transfer (Q) of a CoFe2O4/Fe3O4/6T(1ML)/Co heterostructure measured in an in-plane saturation field (μ0Hsat) of 0.44 T and close to the remanence (5 mT) with associated fits (solid lines). Inset: neutron scattering length density (SLD) depth profiles along the z direction perpendicular to the surface corresponding to the fits at 0.44 T and 5 mT. (b) Top views of the evolution of the magnetic exchange coupling between Co (blue) and Fe3O4 (orange) with the applied magnetic field.
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