Publication of this remarkable effect shortly follows previous results, presented in Physical Review Letters, in which scientist of Twente and Stanford explain why the same materials, being insulators as well, show current conductivity at their interface. Magnetism in nanoscale materials is a hot topic, as is also shown in the June issue of Physics Today. Magnetic layers in semiconductor structures are particularly interesting for new information carriers.
Atomic layering of the materials SrTiO3 and LaAlO3 results in a charge transfer to the interface. The electrons form localised magnetic momenta in materials that aren’t magnetic by themselves.
The materials showing these unexpected properties are so-called perovskites. The Inorganic Materials and Low Temperatures sections of the MESA+ Institute for Nanotechnology have examined the properties of these materials for some time now. They are oxidic materials showing other surprising features like high-temperature superconductivity and ferroelectricity. Combinations of materials, made by layering them on top of each other, yield interface properties totally differing from those of the bulk material. The interface between strontium-titanate (SrTiO3) and lanthane-aluminate (LaAlO3), both insulators, shows high current conductivity. Joint research at Twente and Stanford University show that, apart from charge that is intrinsically built up, oxygen vacancies play a major role. The research now presented in Nature Materials shows that the layers aren’t just highly conductive: the interface is magnetic as well.
Layer for layer
For studying the interface, precise control of the growth of materials on the atomic scale is vital. Using laser pulses, the scientists can ‘build’ a material unit cell for unit cell, on a carrying crystal. The unit cell is the smallest basic structure of a crystal. Growth can be monitored to the extreme detail. Looking at separate atoms within a unit cell, layers with different charges can occur. Whenever a layer with a net positive charge is placed above a layer with a negative charge, and so on, configurations are possible with an extra positive layer. These layers provide electrons, and take care for conductivity and magnetism.
Inzicht in grensvlakmagnetisme
Through tests in the High Field Magnet Laboratory of the Radboud University of Nijmegen, The Netherlands, holding one of the largest magnets in the world, the researchers gained more insight into the magnetism at the interface between strontium-titanate and lanthane-aluminate. They found out that the electrical resistance is a function of the external magnetic field. In a strong field of 30 Tesla, the resistance is 30% lower than without a magnetic field. This implies that at the intergace local magnetic momenta are present, of which the alignment has an effect upon the resistance. Apart from that, resistance and temperature are logarithmically related, which points in the direction of the so-called Kondo effect. This quantummechanical effect describes localized magnetic momenta shielded by free electrons. At extremely low temperatures (300 millikelvin) hysteresis appears in the resistance: this is a strong indication for magnetic ordening at larger distances.
Magnetism within thin layers, especially in semiconductor structures, forms a hot topic within physics. The new results open the way to a fully new model system for fundamental research on magnetic interaction in materials. Broadening the scope, other phenomena not appearing within the bulk, but present at the interface can be investigated.
The research has been made possible by the Dutch Foundation for Fundamental Research on Matter (FOM) and the Dutch Organisation for Scientific Research NWO.
Wiebe van der Veen | alfa
A 100-year-old physics problem has been solved at EPFL
23.06.2017 | Ecole Polytechnique Fédérale de Lausanne
Quantum thermometer or optical refrigerator?
23.06.2017 | National Institute of Standards and Technology (NIST)
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
23.06.2017 | Physics and Astronomy
23.06.2017 | Physics and Astronomy
23.06.2017 | Information Technology