We have found evidence for a strong magnetoelectric (ME) coupling at room temperature between polycrystalline Co layers ($5$-${}40$ nm) and single-crystalline (001)-oriented BaTiO${}_{3}$ layers ($15$-${}17$ nm). We took advantage of the quasi-single polarization orientation, perpendicular to the film plane, of the ferroelectric BaTiO${}_{3}$ domains in the tetragonal phase. Using ferromagnetic resonance spectroscopy with the Co magnetization aligned either parallel or antiparallel to the BaTiO${}_{3}$ polarization, we assessed a strong anisotropy of about 0.14 T in the Co resonance field positions, indicating a coupling constant of 0.27 s/F. When sweeping the temperature through the phase transitions of BaTiO${}_{3}$, the two resonance positions are shifted in opposite directions. The ME coupling induces a notable magnetic anisotropy resulting in high values of the out-of-plane remanent magnetization. Our results are promising for future multiferroic devices.

In this work the thermal heating of tunnel junctions is investigated doing one-dimensional numerical simulations by solving the heat equation. The temperature increase is proportional to the power density $\mathrm{jV,}$ which is confirmed by transport measurements on patterned μm size junctions. The observed temperature increase was $\text{2.3\hspace{0.17em}}\mathrm{K}\mathrm{/(}\mathrm{mW}\mathrm{ \mu }{\mathrm{m}}^{\text{−2}})$ compared to a simulation result of $\text{0.9\hspace{0.17em}}\mathrm{K}\mathrm{/(}\mathrm{mW}\mathrm{ \mu }{\mathrm{m}}^{\text{−2}}\mathrm{).}$ Tunneling AFM measurements on 4, 5.4, and 6.7 Å barrier half-junctions, show hot spots with current densities up to 13 times the average density value. The current concentration could explain the higher heating observed experimentally compared to the simulated value. The hot spot density is $\text{600–900/μ}{\mathrm{m}}^2$ occupying roughly 5% of the barrier surface.

The growth, crystal and electronic structures, and photo-electrochemical properties of undoped and Ti doped hematite epitaxial films were studied. We evidence that Ti⁴⁺ substitutes Fe³⁺ in the hematite lattice inducing a slight modification of the oxygen octahedron. Ti doping is shown to induce a shift of the valence band toward higher binding energy due to a movement of the Fermi level toward the conduction band. The resulting modification of electrical conductivity appears as a possible origin of the improvement of photo-electrochemical properties in the doped sample.