Guus Rijnders MESA+ Institute for nanotechnology, Fac. of Science & Technology, University of Twente, Enschede, the Netherlands
omplex oxides have attracted great interest since they exhibit a rich spectrum of physical properties such as ferromagnetism, antiferromagnetism, colossal magnetoresistance, ferroelectricity, dielectricity, and superconductivity. Novel heteroepitaxial devices based on these complex oxides, like spin-polarized ferromagnetic tunnel junctions, superconducting devices and piezoelectric devices, have great potential and are currently under investigation in many groups. The nature of the above-mentioned physical properties in complex oxides is determined by very small characteristic length scales, comparable to the unit cell lattice parameters of complex oxide. Because of these small characteristic length scales, growth control on an atomic level is essential in epitaxial heterostructures. Furthermore, the terminating atomic layer of each complex oxide thin film in these structures influences the interface properties and, consequently, the device performance. Interfaces therefore play an important role in the physical and electrical properties of the complex oxide devices and growth control on an atomic level is essential. Recently, a new “degree of freedom” has been recognized. By atomic control of interfaces between oxide materials, i.e., the chemical composition and crystalline structure, new phenomena are observed. A heterointerface between perovskites (ABO3) introduces polarity discontinuities when both elements A and B on either side of the interface have different valence states. Recently, a different electronic behavior for thin LaAlO3 films on either SrO- or TiO2-terminated SrTiO3 substrates was foundi.ii, the former interface being insulating and the latter interface being an n-type conductor. The discovery of conduction caused by electronic reconstruction at oxide interfaces has attracted a lot of interest. In this contribution, I will show how, in analogy to this remarkable interface-induced conductivity, magnetism can be inducediii at the interface between the otherwise non-magnetic insulating perovskites SrTiO3 and LaAlO3. A large negative magnetoresistance of the interface is found, together with a logarithmic temperature dependence of the sheet resistance. At low temperatures, the sheet resistance reveals magnetic hysteresis. The conducting oxide interface now provides a versatile system to induce and manipulate magnetic moments in otherwise non-magnetic materials. In this presentation I will address the recent developments as well as future challenges of heterointerfaces between perovskite oxides.