Metal Oxide Sandwiches: New option to manipulate properties of interfaces

Sketch of the structure of both metal oxide layers. Interesting new properties can arise at the interface.

Sketch of the structure of both metal oxide layers. Interesting new properties can arise at the interface. © M.Bibes

A Franco-German cooperation has investigated a sandwich system of transition metal oxides at BESSY II. The scientists discovered a new option to control properties of the interface between the two layers, for instance the amount of charge transferred from one layer to the other or the emergence of ferromagnetism.  Their insights might help to create new properties at the interface, not present in the primary materials, maybe even novel forms of High Tc superconductivity.

Sandwich systems of thin film transition metal oxides display surprising properties at their interfaces. In case of the paradigmatic example of Lanthan-Aluminate ( LaAlO3) and Strontium-Titanate (SrTiO3) both materials are insulators and non-magnetic, while their interface has been observed to display ferromagnetism, high electrical conductivity and even superconductivity.

Now the team of Manuel Bibes, CNRS Thales at Palaiseau, France, in collaboration with scientists at HZB around Sergio Valencia and several European groups, devised a new approach to tailor interface properties. Together they designed a series of experiments at the synchrotron source BESSY II to shed more light on the emergence of such property changes, identifying a new “knob” for their control.

Rare-Earth Elements influence charge transfer

The samples, which the team of Manuel Bibes did produce, consisted of a sandwich of 2 nm  Gadolinium-Titanate (GdTiO3) and “R”-Nickelate (RNiO3) films, where R is a rare-earth element. “We have been able to combine two very different transition metal oxides: whereas in the titanate electrons in the chemical bonds are strongly localized around the ions, in the nickelate side these electrons are shared between Nickel- and Oxygen-ions, and thus highly covalent”, Manuel Bibes explains. When putting both materials together some charge is transferred from the titanate layer to the nickelate one. They investigated this charge transfer process for samples containing different rare-earth elements in the nickelate layer such as Lanthanum, Neodymium and Samarium at BESSY II.

Their results show that the charge transfer at the interface between the materials strongly depends on the rare earth element in the nickelate layer. Different rare-earth elements have different atomic radii (size).This modifies the interaction between the Ni and O atoms and the degree of “covalency” between Ni and O changes. This was already known, but now the scientists have observed that this also affects the charge transferred from the GdTiO3 to the Nickelate film. “This is the key result”, Sergio Valencia from HZB explains. “We have found a new “knob”. Covalency (which is controlled by changing R) controls the charge transfer between the titanate and the nickelate.”

Ferromagnetism observed, superconductivity still searched

Tuning the charge transfer in this way might allow to control the formation of new interfacial phases too. For example, the scientists observed a new ferromagnetic phase at the interface. “Our work may help in the ongoing quest for cuprate-like superconductivity in nickelate heterostructures”, Valencia says. “We hope that this study will help to design better interfaces for exploring new exciting new phases of matter at interfaces between covalent materials”, Bibes adds.

Published in Nature Physics: doi:10.1038/nphys3627
'Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces' . M. N. Grisolia, J. Varignon, G. Sanchez-Santolino, A. Arora, S. Valencia, M. Varela, R. Abrudan, E.Weschke, E. Schierle, J. E. Rault, J.-P. Rueff, A. Barthélémy, J. Santamaria and M. Bibes

arö

You might also be interested in

  • Humboldt Fellow Alexander Gray comes to HZB
    News
    12.08.2022
    Humboldt Fellow Alexander Gray comes to HZB
    Alexander Gray from Temple University in Philadelphia, USA, is working with HZB physicist Florian Kronast to investigate novel 2D quantum materials at BESSY II. With the fellowship from the Alexander von Humboldt Foundation, he can now deepen this cooperation. At BESSY II, he wants to further develop depth-resolved X-ray microscopic and spectroscopic methods in order to investigate 2D quantum materials and devices for new information technologies even more thoroughly.
  • Green hydrogen: Nanostructured nickel silicide shines as a catalyst
    Science Highlight
    11.08.2022
    Green hydrogen: Nanostructured nickel silicide shines as a catalyst
    Electrical energy from wind or sun can be stored as chemical energy in hydrogen, an excellent fuel and energy carrier. The prerequisite for this, however, is efficient electrolysis of water with inexpensive catalysts. For the oxygen evolution reaction at the anode, nanostructured nickel silicide now promises a significant increase in efficiency. This was demonstrated by a group from the HZB, Technical University of Berlin and the Freie Universität Berlin as part of the CatLab research platform with measurements among others at BESSY II.
  • RBB Abendschau on visit at CatLab
    News
    01.08.2022
    RBB Abendschau on visit at CatLab
    CatLab got a visit from the rbb Abendschau.
    Under the title "Der Weg weg vom Erdgas" (The way away from natural gas), the programme was broadcast on Sunday, 31st July in the rbb Abendschau and will be available in the rbb media library for 7 days.