Not everything is ferromagnetic in high magnetic fields
Bei 25,8 Tesla findet in dem Urankristall ein Phasenübergang statt und ein komplexes magnetisches Muster etabliert sich. © HZB
High magnetic fields have a potential to modify the microscopic arrangement of magnetic moments because they overcome interactions existing in zero field. Usually, high fields exceeding a certain critical value force the moments to align in the same direction as the field leading to ferromagnetic arrangement. However, a recent study showed that this is not always the case. The experiments took place at the high-field magnet at HZB's neutron source BER II, which generates a constant magnetic field of up to 26 Tesla. This is about 500,000 times stronger than the Earth's magnetic field. Further experiments with pulsed magnetic fields up to 45 Tesla were performed at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR).
The physicists examined crystals of U2Pd2In, which form a special class of solids (Shastry-Sutherland system). The interactions between the magnetically active uranium atoms are quite complex in this structure, mainly due to the extended 5f orbitals of the outermost electrons of uranium in a solid. These 5f electrons are also carriers of the magnetic moment in the material.
Using neutron diffraction in strong fields they found that an unusually complicated non-collinear modulated magnetic structure above a critical magnetic field. The magnetic unit cell is twenty times larger than the crystallographic unit, containing 80 magnetic moments. Such a structure is a consequence of competition between different strong interactions and the applied field. “Our results are important from two reasons”, Dr. Karel Prokes (HZB) says. “First, they show that the field induced phase is not ferromagnetic and the magnetization increase at high fields is probably due to a gradual rotation of U moments towards the field direction, a finding that might be of relevance for many other systems and second, they may help to develop more precise theories dealing with 5f electron systems”.
Phys. Rev. Research (2020): Noncollinear magnetic structure in U2Pd2In at high magnetic fields.
K. Prokeš, M. Bartkowiak, D. I. Gorbunov, O. Prokhnenko, O. Rivin, and P. Smeibidl
DOI: 10.1103/PhysRevResearch.2.013137
- 3D magnetic field experiment at BESSY II takes spintronics a step further(Fe0.63Ni0.3Pd0.07)3P or FNPP is a magnetic material that exhibits complex magnetic structures even at room temperature. This makes the material of interest for spintronics, a field that could enable data processing with significantly lower energy consumption. One potential application is novel magnetic memory devices. However, generating and modifying the desired structures in a controlled manner remains a challenge to date. A new study led by HZB has now taken a step forward in this regard. They demonstrated at the worldwide unique VEKMAG-Station at BESSY II, that a tiny external B-field in the plane of the magnetic patterns is sufficient to change them.
- Thin nickel films boost green hydrogen productionUltra-thin nickel oxide coatings can significantly improve the performance of anion exchange membrane (AEM) water electrolysers, a promising technology for producing green hydrogen. This was demonstrated by a team led by HZB scientist Dr. Michelle Browne. The results show that a nickel oxide film only 10 nanometres thick outperformed conventional nickel oxide powder electrodes while using less than 1% of the catalyst material. The study is published in the Journal of Materials Chemistry A,
- Detailed insights at BESSY II into the oxidation processes of copperBefore pure copper oxide builds up, complex superstructures such as ‘29’CuxO, are formed. The new results on the '29' CuxO superstructure have relevance for catalyst research and corrosion protection in the development of safe copper containers for nuclear waste repositories.