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The exact perovskite structure has simple cubic symmetry and composition ABO 3 , where A is a relatively large cation and B a smaller one. The choices of A and B cations, and the substitutions possible on either site, generate a large variety of materials sharing the same base, with relatively small distortions of the size and shape of the cube. In addition, these oxides often allow oxygen non-stoichiometry with or without order to the amount of several percent. They form a vast set of technologically important materials due to their conducting, insulating, ferroelectric, magnetic, superconducting, etc., properties. Heteroepitaxy of perovskite oxides allows one to construct atomically sharp interfaces between these materials and therefore to envisage a set of useful heterojunctions. The epitaxy has side effects that may also prove useful: (1) it forces a chemical neighbouring that would not occur naturally, creating a two-dimensional third material, and (2) it imposes a lateral strain. Both of these effects allow one to explore novel, sometimes unforeseen, properties with a strong two-dimensional character. This paper first reviews some of the knowledge that has been accumulated on {100} surfaces and interfaces of perovskites, with an emphasis on properties that could be used in future all-oxide microelectronics. It then exposes the case of the interface between the half-metal La 2/3 Sr 1/3 MnO 3 and the insulator SrTiO 3 , which plays a key role in the magnetoresistance of magnetic tunnel junctions. It particularly presents thorough electron energy loss spectroscopy measurements that uncover the atomic scale structural and electronic properties of these objects. [ABSTRACT FROM AUTHOR]

Co/Al[sub 2]O[sub 3]/NiFe tunnel junctions were deposited on misoriented silicon substrates. A thermal treatment activates a step bunching mechanism on the silicon surface leading to a modulated topology with a nanometric lateral period. The bottom magnetic electrode and the barrier follow this topology. Such junctions present good magnetotransport characteristics with a magnetoresistance about 14% at room temperature. Due to the uniaxial anisotropy induced by the topological modulation, the antiparallel configuration of the magnetization is well defined leading to perfect square magnetoresistance cycles at all temperatures. The magnetic behavior of patterned junctions has been investigated by transport measurements and Kerr microscopy. More than inducing a strong uniaxial anisotropy, the modulated topology is shown to strongly influence the switching mechanism of the magnetization. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have investigated the magnetic behavior and the structural properties of ferromagnetic–antiferromagnetic systems (NiFe–IrMn and Co–IrMn) deposited directly on a thin tantalum buffer layer (bottom configuration) or above a thin Al2O3 tunnel barrier layer (top configuration). In the bottom configuration, the bilayer system exhibits higher magnetic performances than in the top configuration in terms of thermal stability. We have performed a detailed structural study by X-ray diffraction and high-resolution transmission electron microscopy which allow us to establish a clear correlation between the situation of the bilayer with respect to the tunnel barrier, its texture and its magnetic properties. [Copyright &y& Elsevier]