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
- Only at BESSY II worldwide: IR nanoscopy at very long THz wavelengthsThe team at the IRIS beamline at BESSY II has created a new experimental option: They achieved infrared nanoscopy with a spatial resolution of around 50 nm at very long THz wavelengths. This was possible thanks to a temporal pattern of light pulses known as the low-alpha operating mode at BESSY II. Worldwide, BESSY II is the only synchrotron light source at which users could perform nanoscopy in a single setup from 25 to 4000 cm-1, a unique opportunity for ultra-broadband characterisation of complex materials at the nanoscale in both the life sciences and materials sciences.
- Ultrafast demagnetisation - Thinner iron, stronger effectThe thinner an iron film, the more easily it can be demagnetised by a laser pulse. Researchers at the University of Duisburg-Essen, working with Helmholtz-Zentrum Berlin and other partners, have discovered why: the key lies in the magnetic order at the material's interfaces. In the long term, these findings could contribute to the development of new technologies for magnetic data storage. The results have been published in the scientific journal Advanced Science.
- Patterns of polar vortices in lead-free superlattices on siliconA team at HZB has, for the first time, reported polar vortices in (BaTiO3/SrTiO3)10 superlattices on silicon. These results expand the range of materials and substrates on which polar topological textures can occur and open up new options for incorporating complex ferroelectric states into silicon-based technologies.