Interlayer exchange interactions in perovskite oxide heterostructures

Magnetism in systems of reduced dimension has been an extremely dynamic research area in condensed matter physics. Among the major advances are the discovery of giant magnetoresistance and oscillatory exchange coupling in magnetic metallic multilayers. Over a bit more than a decade, this activity has progressed from being a fundamental scientific issue to a matter of important technological applications.; Doped lanthanum manganese oxides, the materials that exhibit colossal magnetoresistance in large magnetic fields, have been yet another topic of intensive research lately. Their high degree of carrier spin polarization makes these compounds very attractive for applications in spintronics.; Touching upon both issues, this thesis focuses on the investigation of magnetism and transport in a new class of magnetic multilayers—artificially layered films combining colossal magnetoresistive ferromagnetic manganites with structurally compatible paramagnetic or antiferromagnetic perovskite oxides. Single-crystal atomically-defined heterostructures, with nanometer scale periodicity have been fabricated by ozone-assisted molecular beam epitaxy and characterized by a number of techniques.; In this work, in particular, the phenomena of oscillatory interlayer exchange coupling and magnetoresistance have been studied in heterostructures of two metallic oxides: ferromagnetic La_2/3Ba_1/3MnO ₃ and paramagnetic LaNiO₃. The experimental data have been interpreted within a conventional Ruderman-Kittel-Kasuya-Yosida model employing an ab initio calculated band structure of LaNiO₃, taking into account strong electron scattering in the nickelate spacer.; In another development, unidirectional magnetotransport anisotropy has been studied in ultrathin films of exchange-biased manganites. The effect is attributed to the influence of the exchange-induced anisotropy on transport in magnetoresistance ferromagnets.; The results obtained are evaluated in the context of current research in this field, and the possibilities and challenges that lie ahead are outlined.