Scientific Highlights

Niéli’s paper is accepted in the Journal of Physical Chemistry Letters! We use X-ray absorption spectroscopy and X-ray magnetic circular dichroism to watch directly how the Co and Fe ions in a molecular cube change their oxidation states and turn from diamagnetic into paramagnetic units upon light irradiation.

Scientists have demonstrated in a combined theoretical and experimental effort that the new ligand-field density functional theory method (LF-DFT) can be used to calculate the X-ray absorption spectra (XAS) and X-ray magnetic circular dichroism (XMCD) of lanthanide compounds from purely structural input.

Understanding how and how fast we can drive atoms to create a structural phase transition is of fundamental interest as it directly relates to many processes in nature. Here we show that a photoexcitation can drive a purely structural phase transition before the energy is relaxed in the material that corresponds to a “warmer” equilibrated state.

A peculiar magnetic “dead layer” is detected at the surface of thin films of DyTiO3, a ferrimagnetic Mott insulator. Depth dependent X-ray absorption measurements performed at the X-Treme beamline in the Swiss Light Source indicate that this layer is associated with a deviation of the Ti valence from 3+ toward 4+ at the film surface, suppressing the magnetic coupling between Ti ions and unleashing a strong paramagnetic response from uncoupled Dy ions.

In the week of March 18-23 PSI welcomes 20 PhD students and postdocs taking part in the HERCULES 2018 school on Neutron and Synchrotron Radiation. They will attend lectures and perform two days of practical courses at several beam lines of the Swiss Light Source.

Using the FEMTO slicing source at SLS, we have studied the structural response during the photoinduced transition in a charge-ordered Pr_1-xCa_xMnO₃ thin films. By investigating the dynamics of both superlattice reflections and regular Bragg peaks, we disentangle the different structural contributions and analyze their relevant time-scales. Comparing these results with studies of the charge order and magnetic dynamics, a comprehensive picture of the phase transition linked to a single critical fluence f_c is proposed.

The unexpected finding that in an ‘artificial spin ice’ magnetostatic energy can be transformed into directed rotation of magnetization provides fresh insights into such nano-patterned magnetic structures — and might enable novel applications in nanoscale devices.

The advent of x-ray free electron lasers has extended the unique capabilities of resonant x-ray spectroscopy techniques to ultrafast time scales. Here, in collaboration between researchers from PSI, Sorbonne Universités, HASYLAB/DESY, Synchrotron SOLEIL, CNRS, and Uppsala University, we report on a novel experimental method that allows retrieving with a single x-ray pulse the time evolution of an ultrafast process, not only at a few discrete time delays, but continuously over an extended time window.

Controlled motions of atoms using ultrashort electric field pulses allow to manipulated the properties of a material on ultrafast timescales. Here we show how metallic structures can be used to enhance a THz electric field pulse and track the induced atomic motions with ultrashort x-ray pulses emitted by a X-ray free electron laser.

We employ time-resolved resonant x-ray diffraction to study the insulator-to-metal transition that is launched via resonant excitation of an infrared-active optical phonon mode in a half doped manganite. We find that the charge order reduces promptly with a highly nonlinear (quartic) dependence on excitation fluence.

SIM beamline scientist Carlos Vaz was recognized as outstanding referee for providing high quality peer review for the journals of the American Physical Society (APS).

On 7th February Dr. Christian Papp from University Erlangen (Germany) is visiting the SIM beamline and will give a Photon Science Seminar talk with the title: "In-situ Studies of the Reactivity of Model Catalysts: Surface Chemistry from flat surfaces to nanoparticles"

The Magnetism and Microscopy group has met for its annual retreat meeting in Lungern 11- 15.1.2017 (in the central mountain region of Switzerland) for extensive discussions on its science program. As for other years, after some general introductory lecture into the techniques used, current and future projects have been presented by the PhD students, postdocs, and scientists as well as from guests who collaborate with the group. Discussion went into the time where dinner has been prepared together, followed by some leisure activities on Saturday.

Single holmium atoms adsorbed on few monolayers of magnesium oxide are extraordinarily stable magnets. They retain a significant fraction of their magnetization when the external magnetic field is switched off. This has been shown recently in a study combining x-ray magnetic circular dichroism performed at the Swiss Light Source (SLS) and at the European Synchrotron Radiation Facility (ESRF) as well as scanning tunneling microscopy. The results open perspectives of storing and processing information at ultrahigh density.

Researchers from PSI and EPFL have demonstrated that the magnetization hysteresis and remanence of TbPc₂ single-molecule magnets drastically depends on the substrate on which they are deposited. If a few atomic layers thick magnesium oxide film grown on a silver substrate is used, a record wide hysteresis and record large remanence can be obtained. Single-molecule magnets are attractive for molecular spintronics applications such as information processing or storage.

X-ray magnetic circular dichroism at the Co L_3,2 edges measured at the X-Treme beamline, SLS and at the Advanced Light Source, evidence that three distinct electric field driven remanent magnetization states can be set in the Co film at room temperature. Ab initio density functional theory calculations unravel the relative contributions of both strain and charge to the observed magnetic anisotropy changes illustrating magnetoelectroelastic coupling at artificial multiferroic interfaces.

Resonant magnetic scattering performed at the x-ray free electron laser facility LCLS (USA) has been used to investigate the magnetization dynamics of elemental Holmium. It is found that the demagnetization of conduction electrons and localized 4f magnetic moments have the same temporal evolution showing a strong coupling between the different magnetic moments.

A new kind of 2DEG is found by inserting two atomic layers of the antiferromagnetic and insulating compound EuTiO₃ between LaAlO₃ and SrTiO₃. The 2DEG is found to exhibit besides a superconducting ground state, a strong spin-polarization. The magnetism of Eu and Ti was studied by XMCD at the X-Treme beamline in SLS.

At the PEARL beamline, metal-supported ultrathin oxide films have been studied which are a class of materials of technological importance in various research fields such as catalysis, spintronics, or nanoelectronics.

Using a X-ray magnetic circular dichroism measured at the X-Treme beamline, SLS, in conjunction with X-ray reflectivity measured at the SEXTANTS beamline, SOLEIL, the authors show that the degree of intermixing at the monolayer scale allows interface-driven properties such as charge transfer and the induced magnetic moment in the nickelate layer to be controlled.

The surface-induced changes of the oxidation state and magnetic properties of Mn ion clusters have been probed by X-ray absorption spectroscopy and X-ray magnetic circular dichroism.

A research team led by scientists from the Swiss Light Source has for the first time established three-dimensional (3D) electronic structure of the perovskite compound La1−xSrxMnO3 connected with its colossal magnetoresistance. Instrumental for this study has been the use of the new experimental technique of soft-x-ray ARPES, available at the ADRESS beamline, with its intrinsically sharp definition of 3D electron momentum.

Understanding the interplay of the various degrees of freedom such as the electrons, spins and lattice is essential for many complex materials, including the high-temperature superconductors.

Ultrafast magnetization reversal driven by femtosecond laser pulses has been shown to be a promising way to write information. Seeking to improve the recording density has raised intriguing fundamental questions about the feasibility of combining ultrafast temporal resolution with sub-wavelength spatial resolution for magnetic recording. Here we report on the experimental demonstration of nanoscale sub-100 ps all-optical magnetization switching, providing a path to sub-wavelength magnetic recording.

X-ray magnetic circular dichroism measurements evidence a 10K shift of the magnetic Curie temperature for La_0.7Sr_0.3MnO₃ deposited on the piezoelectric substrate [Pb(Mg_1/3Nb_2/3)O₃]_0.68−[PbTiO₃]_0.32 (011) for two different remanent piezostrain states.