Merons which are topologically equivalent to one-half of skyrmions can exist only in pairs or groups in two-dimensional (2D) ferromagnetic (FM) systems. The recent discovery of meron lattice in chiral magnet Co8Zn9Mn3 raises the immediate challenging question that whether a single meron pair, which is the most fundamental topological structure in any 2D meron systems, can be created and stabilized in a continuous FM film? Utilizing winding number conservation, we develop a new method to create and stabilize a single pair of merons in a continuous Py film by local vortex imprinting from a Co disk. By observing the created meron pair directly within a magnetic field, we determine its topological structure unambiguously and explore the topological effect in its creation and annihilation processes. Our work opens a pathway towards developing and controlling topological structures in general magnetic systems without the restriction of perpendicular anisotropy and Dzyaloshinskii–Moriya interaction.

Magnetic skyrmions are topological spin textures, which usually exist in noncentrosymmetric materials where the crystal inversion symmetry breaking generates the so-called Dzyaloshinskii-Moriya interaction. This requirement unfortunately excludes many important magnetic material classes, including the recently found two-dimensional van der Waals (vdW) magnetic materials, which offer unprecedented opportunities for spintronic technology. Using photoemission electron microscopy and Lorentz transmission electron microscopy, we investigated and stabilized Néel-type magnetic skyrmion in vdW ferromagnetic Fe3GeTe2 on top of (Co/Pd)n in which the Fe3GeTe2 has a centrosymmetric crystal structure. We demonstrate that the magnetic coupling between the Fe3GeTe2 and the (Co/Pd)n could create skyrmions in Fe3GeTe2 without the need of an external magnetic field. Our results open exciting opportunities in spintronic research and the engineering of topologically protected nanoscale features by expanding the group of skyrmion host materials to include these previously unknown vdW magnets.

Significance and Impact of the Study: Colistin has been reported to be effective in selective digestive decontamination (SDD), which is an infection prevention measure used in the treatment of certain patients in intensive care. We are the first to report that colistin-induced intestinal dysbacteriosis can injure intestinal mucosal barrier function and increase bacterial translocation, whereas a high dose of colistin does not damage the intestinal mucosal barrier in germ-free (GF) mice raised in a GF environment. These results may indicate that prolonged use of a high dose of a SDD medication should be carefully considered. AbstractThe purpose of this study was to determine the effect of colistin-induced intestinal dysbacteriosis on intestinal mucosal barrier function and bacterial translocation in a mouse model. Colistin or saline was administered orally for 7 days, and populations of viable organisms from the caecal mucosa and its content, the ileal segments, the mesenteric lymph nodes (MLNs) and the internal organs were prepared for examination. In the intestinal dysbacteriosis model, intestinal barrier dysfunction was observed and associated with increased bacterial translocation to extraintestinal sites. The extent of bacterial translocation to the MLNs and internal organs in the colistin group was significantly higher than in the saline group. Colistin-induced intestinal dysbacteriosis was shown to injure the intestinal mucosa barrier function and increase bacterial dislocation.

The recent discovery of spin current transmission through antiferromagnetic insulating materials opens up vast opportunities for fundamental physics and spintronics applications. The question currently surrounding this topic is: whether and how could THz antiferromagnetic magnons mediate a GHz spin current? This mismatch of frequencies becomes particularly critical for the case of coherent ac spin current, raising the fundamental question of whether a GHz ac spin current can ever keep its coherence inside an antiferromagnetic insulator and so drive the spin precession of another ferromagnet layer coherently? Utilizing element- and time-resolved x-ray pump-probe measurements on Py/Ag/CoO/Ag/Fe75Co25/MgO(001) heterostructures, here we demonstrate that a coherent GHz ac spin current pumped by the Py ferromagnetic resonance can transmit coherently across an antiferromagnetic CoO insulating layer to drive a coherent spin precession of the Fe75Co25 layer. Further measurement results favor thermal magnons rather than evanescent spin waves as the mediator of the coherent ac spin current in CoO.

Meron is a special topological object that carries only one-half of the topological charge unit. In condensed matter physics, a spin meron corresponds to one-half of a spin skyrmion. As compared to the many fascinating topological properties of skyrmion materials, little is known of the properties of spin merons especially on their formations. It was confirmed only recently that hedgehog merons could exist in pairs via a spin flux closure with opposite helicities. However, it is unclear on whether a single hedgehog meron could ever exist by pairing with another type of meron. Using element-resolved magnetic imaging measurement on epitaxial trilayer disks, we show that a spin meron with a full range of helicity, including the hedgehog meron, can be stabilized by pairing with another vortex meron with a fine tuning of the magnetic coupling between the two merons. Furthermore, the meron divergence is fully controlled by the polarity of the vortex meron, independent of the vortex helicity.

Co films and micron sized disks were grown on top of piezoelectric PMN-PT(011) and Cu/PMN-PT(001) substrates and investigated by the Magneto-Optic Kerr Effect and Photoemission Electron Microscopy. By applying an electric field in the surface normal direction, we find that the strain of the ferroelectric PMN-PT(011) substrate induces an in-plane uniaxial magnetic anisotropy in the Co overlayer. Under specific conditions, the Co magnetic vortex could be switched between clockwise and counterclockwise circulations. The variations of the Co vortex switching were attributed to the variations of the ferroelectric domains under the Co disks. We speculate that the switching of the magnetic vortex circulation is a dynamical process which may involve pulses of appropriate magnitude and duration of the uniaxial magnetic anisotropy delivered to the magnetic vortex.

The High Granularity Timing Detector (HGTD) will be installed in the ATLAS detector to mitigate pile-up effects during the High Luminosity (HL) upgrade of the Large Hadron Collider (LHC) at CERN. The design of the HGTD is based on the use of Low Gain Avalanche Detectors (LGADs), with an active thickness of 50 μm, that allow to measure with high-precision the time of arrival of particles. The HGTD will improve the particle-vertex assignment by measuring the track time with a resolution ranging from approximately 30 ps at the beginning of the HL-LHC operations to 50 ps at the end. Performances of several unirradiated, as well as neutron- and proton-irradiated, LGAD sensors from different vendors have been measured in beam test campaigns during the years 2018 and 2019 at CERN SPS and DESY. This paper presents the results obtained with data recorded by an oscilloscope synchronized with a beam telescope which provides particle position information within a resolution of a few μm. Collected charge, time resolution and hit efficiency are presented. In addition to these properties, the charge uniformity is also studied as a function of the position of the incident particle inside the sensor pad.

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