No abstract

The crystalline structure, chemical composition, and bonding states across epitaxial Fe/MgO/Fe͑001͒ magnetic tunnel junctions grown by molecular-beam epitaxy have been investigated down to the atomic scale by spatially resolved electron energy-loss spectroscopy. Both metal-insulator interfaces exhibit significant roughness, which can be attributed to Fe and MgO terraces overlapping one another. These terraces extend over typical widths of 6-10 nm parallel to the interface and over typical heights below 1 nm, and a structural asymmetry of the roughness is revealed. These features could be responsible for the nonsymmetrical transport properties measured when reversing the applied voltage.

Despite several attempts, the intimate electronic structure of two-dimensional electron systems buried at the interface between LaAlO 3 and SrTiO 3 still remains to be experimentally revealed. Here, we investigate the transport properties of a high-mobility quasi-two-dimensional electron gas at this interface under high magnetic field (55 T) and provide new insights for electronic band structure by analyzing the Shubnikov-de Haas oscillations. Interestingly, the quantum oscillations are not 1∕B-periodic and produce a highly non-linear Landau plot (Landau level index versus 1/B). We explore different scenarios leading to 1/B-aperiodic oscillations where the charge and the chemical potential vary as the magnetic field increases. Overall, the magneto-transport data are discussed in light of high-resolution scanning transmission electron microscopy (HRSTEM) analysis of the interface as well as calculations from density functional theory.