Emergence of a “devil’s staircase” in a spin-valve system
Hexagonal single crystal of SrCo6O11, with a sample diameter of approximately 0,2 millimetres.
The material exhibits distinct magnetization plateau connected with different spin configurations.
A Japanese-German team observes at BESSY II how spins form unusual magnetic structures in a complex cobalt oxide single crystal. Such a material offers new perspectives for spintronic applications.
While classical GMR systems are composed of metallic layers, complex oxides often intrinsically provide layered structures with alternating magnetic configurations that can act as spin valves. Cobalt oxides are a class of materials that can exhibit complex magnetic order that changes with increasing magnetic field, as for example indicated by distinct plateaux in the magnetization curve.
Magnetic structures mapped
A Japanese team of researchers led by the group of Associate Professor Hiroki Wadati at the University of Tokyo has been successful in characterizing the magnetic structures of the complex cobalt oxide SrCo6O11 using the high-field diffractometer of BESSY II. Synthesis of new materials often results in tiny samples, and the crystals studied here had a diameter of only 0.2 mm. With the very high sensitivity of resonant diffraction, a core competence at the UE46_PGM1 beamline of BESSY II, they managed to observe a fascinating type of spin order in the samples that are hardly visible by the bare eye. This order is called devil’s staircase, characterizing a phenomenon, where a pletora, in principle even an infinite number, of so-called commensurate superstructures - magnetic configurations in the present case - can be realized by tuning an external parameter, e.g., a magnetic field.
New options with a Devil's staircase
This exceeds the characteristic of a spin valve and may open new paths in spintronics. The research was carried out in close cooperation with German scientists from the Institut für Festkörper-und Werkstoffforschung Dresden and HZB. The results are now published in Physical Review Letters.
Reference: T. Matsuda, S. Partzsch, T. Tsuyama, E. Schierle, E. Weschke, J. Geck, T. Saito, S. Ishiwata, Y. Tokura, and H. Wadati, "Observation of a Devil’s Staircase in the Novel Spin-Valve System SrCo6O11", Physical Review Letters 114 (236403-1-5):
doi:10.1103/PhysRevLett.114.236403.
- The future of corals – what X-rays can tell usThis summer, it was all over the media. Driven by the climate crisis, the oceans have now also passed a critical point, the absorption of CO2 is making the oceans increasingly acidic. The shells of certain sea snails are already showing the first signs of damage. But also the skeleton structures of coral reefs are deteriorating in more acidic conditions. This is especially concerning given that corals are already suffering from marine heatwaves and pollution, which are leading to bleaching and finally to the death of entire reefs worldwide. But how exactly does ocean acidification affect reef structures?
Prof. Dr. Tali Mass, a marine biologist from the University of Haifa, Israel, is an expert on stony corals. Together with Prof. Dr. Paul Zaslansky, X-ray imaging expert from Charité Berlin, she investigated at BESSY II the skeleton formation in baby corals, raised under different pH conditions. Antonia Rötger spoke online with the two experts about the results of their recent study and the future of coral reefs.
- Susanne Nies appointed to EU advisory group on Green DealDr. Susanne Nies heads the Green Deal Ukraina project at HZB, which aims to support the development of a sustainable energy system in Ukraine. The energy expert has now also been appointed to the European Commission's scientific advisory group to comment on regulatory burdens in connection with the net-zero target (DG GROW).
- Long-term stability for perovskite solar cells: a big step forwardPerovskite solar cells are inexpensive to produce and generate a high amount of electric power per surface area. However, they are not yet stable enough, losing efficiency more rapidly than the silicon market standard. Now, an international team led by Prof. Dr. Antonio Abate has dramatically increased their stability by applying a novel coating to the interface between the surface of the perovskite and the top contact layer. This has even boosted efficiency to almost 27%, which represents the state-of-the-art. After 1,200 hours of continuous operation under standard illumination, no decrease in efficiency was observed. The study involved research teams from China, Italy, Switzerland and Germany and has been published in Nature Photonics.