In the field of magnetic nanomaterials our research activities focus on systems related to potential applications in spintronics and magnetoelectrics. Simultaneously, we work on the development and fundamental aspects of the methods and the instrumentation which we use in the soft x-ray range. These activities mainly involve experiments at beamline UE46-PGM1 at BESSY II.
In the following we present a few examples of research carried out within the last few years.
For a full list of publications of our institute click here.
Suppression of the Verwey Transition by Charge Trapping
The Verwey transition in Fe3O4 nanoparticles with a mean diameter of 6.3 nm is suppressed after capping the particles with a 3.5 nm thick shell of SiO2. By X‐ray absorption spectroscopy and its associated X‐ray magnetic circular dichroism this suppression can be correlated to localized Fe2+ states and a reduced double exchange visible in different site‐specific magnetization behavior in high magnetic fields. The results are discussed in terms of charge trapping at defects in the Fe3O4/ SiO2 interface and the consequent difficulties in the formation of the common phases of Fe3O4. By comparison to X‐ray absorption spectra of bare Fe3O4 nanoparticles in course of the Verwey transition, particular changes in the spectral shape could be correlated to changes in the number of unoccupied d states for Fe ions at different lattice sites. These findings are supported by density functional theory calculations.
C Schmitz-Antoniak, D Schmitz, A Warland, M Darbandi, S Haldar, S Bhandary, B Sanyal, O Eriksson, H Wende, Annalen der Physik 530 (2018) 1700363
Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces
At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from strong Coulomb interactions at and between transition metal and oxygen ions. Such electronic correlations offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. Here we show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metal–oxygen bond.
MN Grisolia, J Varignon, G Sanchez-Santolino, A Arora, S Valencia, M Varela, R Abrudan, E Weschke, E Schierle, JE Rault, J-P Rue, A Barthélémy, J Santamaria, M Bibes, Nature Physics 12, (
See also the associated highlight report