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
Astronomers find unexpected, dust-obscured star formation in distant galaxy
24.03.2017 | University of Massachusetts at Amherst
Gravitational wave kicks monster black hole out of galactic core
24.03.2017 | NASA/Goddard Space Flight Center
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
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