Lab News & Scientific Highlights

Plenary Session Featuring The Fred Kavli Distinguished Lectureship in Materials Science:

Tuesday, April 23

8:15 am – 9:30 am

PCC North, 100 Level, Ballroom 120 D

SIM beamline scientist Carlos Vaz was recognized as outstanding referee for providing high quality peer review for the Journal of Materials Chemistry C (Royal Society of Chemistry).

Lithography‐like writing of conducting regions at the interface between SrTiO₃ and amorphous Si using X‐ray irradiation opens ways for spatially controlled functionalities in oxide heterostructures.

Direct manipulation of the atomic lattice using intense long-wavelength laser pulses has become a viable approach to create new states of matter in complex materials. Conventionally, a high-frequency vibrational mode is driven resonantly by a mid-infrared laser pulse and the lattice structure is modified through indirect coupling of this infrared-active phonon to other, lower-frequency lattice modulations.

In the week of April 1-5 PSI welcomes 20 PhD students and postdocs taking part in the European HERCULES 2019 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.

The Einstein–de Haas effect, first demonstrated more than a century ago, provides an intriguing link between magnetism and rotation in ferromagnetic materials. An international team led by ETH physicist Steven Johnson now established that the effect has also a central role in ultrafast processes that happen at the sub-picosecond timescale — and thus deliver fresh insight into materials that might form the basis for novel devices.

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.

In recent years, electronic data processing has been evolving in one direction only: The industry has downsized its components to the nanometer range. But this process is now reaching its physical limits. Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the Paul Scherrer Institut (PSI) are therefore exploring spin waves or so-called magnons – a promising alternative for transporting information in more compact microchips. Cooperating with international partners, they have successfully generated and controlled extremely short-wavelength spin waves. The physicists achieved this feat by harnessing a natural magnetic phenomenon, as they explain in the journal Nature Nanotechnology.

Additive manufacturing of high-entropy alloys combines the mechanical properties of this novel family of alloys with the geometrical freedom and complexity required by modern designs. An approach to additive manufacturing of high-entropy alloys has been developed based on 3D extrusion of inks containing a blend of oxide nanopowders (Co₃O₄ + Cr₂O₃ + Fe₂O₃ + NiO), followed by co-reduction to metals, inter-diffusion and sintering to near-full density CoCrFeNi in H₂. A complex phase evolution path is observed by in-situ X-ray diffraction in extruded filaments: the oxide phases undergo reduction and the resulting metals inter-diffuse, ultimately forming the desired fcc-CoCrFeNi alloy (see figure). Linked to this phase evolution is a complex micro-structural one, from loosely packed oxide particles to fully-annealed, metallic CoCrFeNi with 99.6 ± 0.1% relative density. CoCrFeNi micro-lattices are created with strut diameters as low as 100 μm and excellent mechanical properties at ambient and cryogenic temperatures.

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.

The effect of diameter reduction on the mechanical properties of cold-drawn nickel microwires has been analyzed by a combination of in situ X-ray diffraction and electron backscatter diffraction observations.

Magnetic domain walls can be reliably displaced by electrical currents, allowing for the fabrication of retentive magnetic memory elements without mechanically moving parts, such as e.g. the magnetic racetrack memory. Researchers in a joint collaboration between the PolLux endstation of the Swiss Light Source and the University of Leeds were able to investigate the dynamics of magnetic domain wall motion with a sub-ns time step, providing a substantial step forward towards the unraveling of the physical processes behind the current- and magnetic field-induced motion of magnetic domains.

We have developed a new cruciform geometry with reduced thickness at the center, which allows reaching high plastic strain under equibiaxial loading. The novel thinning method results in excellent surface quality, suitable for electron backscatter diffraction (EBSD) and high-resolution digital image correlation (HRDIC) investigations. We performed an in-situ HRDIC study on a 304 austenitic stainless steel using the new cruciform geometry to follow the slip activity under uniaxial and equibiaxial loadings.

The mechanical behavior of cold-rolled Mg AZ31B is studied during in-plane multiaxial loading and tension-tension strain path changes using in situ neutron diffraction and electron backscatter diffracion.

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The reliable electrical detection of magnetic skyrmions is of fundamental importance for the application of such topological magnetic quasi-particles for data storage devices. Researchers in a joint collaboration between the University of Leeds and the PolLux endstation have investigated the electrical detection of isolated magnetic skyrmions in applications-relevant nanostructured devices, observing the presence of a strong skyrmion-dependent contribution to the Hall resistivity.

The summer shutdown was used to install more missing hardware. With the new components the Bernina instrument will be already very close to the full design capabilities when the exciting time of user experiments will begin in 2019.

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.

In March 2018, the nine-week MOOC “Introduction to synchrotrons and x-ray free-electron lasers” (abbreviated to “SYNCHROTRONx”) came online via the edX provider of the École Polytechnique Fédérale de Lausanne (EPFL), created by Phil Willmott of the Swiss Light Source, Paul Scherrer Institute. “MOOC” is an acronym for “massive open online course”, a teaching platform started in the first decade of this century, which has become increasingly popular in the last five to six years. MOOCs have no limits to participation and are free. Some of the most popular MOOCs can attract many tens of thousands of participants. Even the most specialized subjects may have an initial enrollment of over a thousand, more than an order of magnitude larger than that typically found in traditional higher education. There were over 70 million MOOC enrollments covering nearly 10’000 subjects offered by the top five providers in 2017 alone!

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 this work, we have enhanced our originally proposed experiment-modeling synergy in Upadhyay et al. Acta Mat. 2016, to capture the stress evolution in the complex cruciform geometry during arbitrary multi-axial load path changes. We perform cruciform simulations using the implementation of the visco-plastic self-consistent (VPSC) model as a user material (UMAT) into the ABAQUS finite element (FE) solver. We also use the Elasto-viscoplastic fast Fourier transform (EVP-FFT) approach to compute yield surfaces. This experiment-modeling synergy is exploited to understand the mechanical response (including the elastic response, Bauschinger effect and hardening) of 316L stainless steel following biaxial load path changes.

The writing and deletion of magnetic Skyrmions is a fundamental step towards the fabrication of memory devices based on this promising spin configuration. Researchers at the Korea Institute of Technology have demonstrated the writing and deleting of isolated magnetic Skyrmions at room temperature in ferrimagnetic multilayer superlattice stacks using electrical currents.

X-ray Free Electron Lasers (XFELs) combine the properties of synchrotron radiation (short wavelengths) and laser radiation (high lateral coherence, ultrashort pulse durations). These outstanding machines allow to study ultra-fast phenomena at an atomic level with unprecedented temporal resolution for answering the most intriguing open questions in biology, chemistry and physics.

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.

In-situ neutron diffraction studies performed on metastable 201 stainless steel combined with EBSD measurements confirm that ε-martensite is a precursor for α′-martensite during uniaxial and equibiaxial deformation at the same loading rate. In both loading states, the grains that contain martensite belong to orientations for which the leading partial dislocations have higher Schmid factor than the trailing partial dislocations. The martensitic transformation is suppressed during equibiaxial loading as a consequence of the different textures formed during deformation.

Researchers at PSI have established a link between the martensitic transformation, microstructural evolution and the mechanical behavior under multiaxial deformation in a NiTi alloy by using a unique combination of in situ high-resolution Digital Image Correlation (DIC), in situ X-ray diffraction and electron microscopy characterization.