Magnets often harbour intricate magnetization textures, some of which are at the heart of modern technologies such as hard disk drives. Now, an international team of scientists report the discovery of unexpected magnetic structures inside a GdCo₂ micropillar. In ptychography experiments at SLS, they observed sub-micrometre loop-shaped configurations, which they identified as magnetic vortex rings. The existence of such structures had been predicted theoretically, but as transient phenomenon. In the experiments now reported, however, the vortex rings turned out to be surprisingly stable. Far beyond their aesthetic appeal, these textures might point the way to further complex three-dimensional structures arising in the bulk of magnets, and could one day form the basis for novel technological applications, for instance energy-efficient 3D data storage and processing.

Topological point defects in the 3D Heisenberg model known as spin hedgehogs have the intriguing property that they can behave as emergent magnetic monopoles, and hence couple strongly to conduction electrons in suitable materials. A team led by scientists from the University of Tokyo demonstrated that beyond static properties, the dynamics of the emergent monopoles also noticeably affects charge transport. Combining small-angle neutron scattering (SANS) experiments at SINQ and magnetotransport measurements, they studied the ‘melting’ transformation of a spin-hedgehog crystal in the chiral magnet MnGe. These experiments establish that by monitoring changes in the Hall effect and the SANS-peak patterns, the roles of static and dynamic emergent monopoles on magnetotransport can be both clearly distinguished and disentangled.

In the prototypical cuprate superconductor La_2–xBa_xCuO₄, an intriguing competition takes place between uniform 3D and spatially modulated 2D ‘striped’ superconducting orders. An international team led by PSI scientists now provides fresh insight into the relationship between the two distinct orders. In muon spin rotation experiments, they showed that an extremely low stress of ∼0.1 GPa applied within the CuO₂ planes of La_1.885Ba_0.115CuO₄ induces a dramatic rise in the onset of 3D superconductivity. However, its 2D counterpart reacts much less sensitively to stress, showing that the variation in onset temperatures of superconductivity is quite modest as stress shifts the balance from 2D to 3D superconducting order. This suggests that the underlying pairing mechanisms are essentially the same in the alternative superconducting states with and without spin stripe order. What evolves, instead, is the degree to which fluctuations have a role and the way bulk coherence is established.

In September, the new soft X-ray beamline Athos of SwissFEL has been operated for the first time in parallel with the hard X-ray beamline Aramis, which is in user operation since the end of 2017. This marks a further milestone for SwissFEL in general and the new Athos beamline in particular. Athos produced its first laser beam in December 2019, and passed the beam for the first time to the Maloja endstation in June this year. Now, the SwissFEL team has taken the important step of optimising the Athos and Aramis beamlines in parallel — with both beamlines delivering new record values in pulse energy. This provides a bright outlook for the first experiments at Athos, which are planned for 2021.

In principle, the short wavelengths of X-rays should provide direct access to physical phenomena in the single-digit nanometre regime. In practice, soft X-ray microscopy with a 2D resolution beyond ten nanometres has long remained a challenge for both scanning and full-field X-ray microscopy. Now, PSI researchers together with an international team of collaborators demonstrate imaging with a resolution of seven nanometres, a record for direct X-ray imaging. This achievement has been made possible by a combination of lithography-based diffractive optics developed at PSI — enabling the production of Fresnel zone plate lenses with structural sizes as small as 6.4 nm — with stability and precision improvements for the PolLux and HERMES scanning X-ray microscopes at SLS.
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In November and December the two submission deadlines for SINQ and SμS beam time requests have passed. In both cases the User Office received extraordinary large numbers of new proposals. 
For SINQ 254 beamtime requests were submitted for the nine instruments that were already open for new proposals after the upgrade programme. Together with the previous deadline that constitutes a new record for the annual submission — with more than 450 new proposals in 2020. In particular, HRPT (50), SANS-I (42) and ICON (38) are heavily booked for the next cycle and it will be a major task for the external review panels to distribute the available beam time among the submitted requests.
There is also an enormous demand for beam time at the Swiss Muon Source. In total the user community submitted 216 new proposals for beam time in cycle I-2021. The instruments GPS (74 proposals) and DOLLY (66) are the most requested but also GPD, HAL-9500 and LEM received many new proposals. The high overbooking factors are increased additionally by a certain backlog caused by the Corona pandemic.
The review panels will gather by the end of January (SINQ) and beginning of February (SμS) and we aim at informing the users soon after that about the results.

The muCool Collaboration has accomplished an important step toward their goal of producing high-brightness, low-energy muon beams for novel precision experiments with muons and muonium atoms at PSI. They demonstrated efficient transverse phase-space compression of a 12.5-MeV/c muon beam stopped in a helium gas target, reducing the vertical muon stop distribution from 14 to 0.25 mm within 3.5 µs. Combining such transverse compression with previously demonstrated longitudinal compression should enable a 10¹⁰-fold improvement in the phase-space density of a muon beam, with
10^-3 efficiency.
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The PSI Facility Newsletter addresses the users of the PSI large facilities and appears quarterly in English. Any feedback is highly welcome! More information. 

Contact: PSI User Office, Phone: +41-56-310-4666, Email: useroffice@psi.ch