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Advanced vector imaging techniques provide us with 3D maps of magnetization fields in which topological concepts can be directly applied to describe real-space experimental textures in non-ideal geometries. Here, the 3D magnetization of a low symmetry permalloy microstructure is obtained by X-ray vector magnetic tomography and analysed in detail in terms of topological charges and emergent fields. A central asymmetric domain wall with a complex 3D structure is observed in which magnetization chirality transitions are mediated by Bloch points arranged in several dipoles and a triplet. The ideal spherical symmetry of the emergent field of an isolated monopole is severely modified due to shape effects of the permalloy microstructure. Emergent field lines aggregate into bundles that either connect adjacent Bloch points within a topological dipole or tend towards the surface. These bundles may present different textures such as helical vortices or half merons, depending on asymmetries and confinement, but are constrained by topological charge conservation in a given sample volume. This precise description of the singularities in realistic systems, enabled by the quantitative experimental information on magnetization vector fields, can significantly improve our understanding of topological constraints in 3D magnetic systems and provide advancements in the design of magnetic devices., Comment: 20 pages, 4 figures

The scientific and technological exploration of artificially designed three-dimensional magnetic nanostructures opens the path to exciting novel physical phenomena, originating from the increased complexity in spin textures, topology, and frustration in three dimensions. Theory predicts that the equilibrium magnetic ground state of two-dimensional systems which reflects the competition between symmetric (Heisenberg) and antisymmetric (Dzyaloshinskii-Moriya interaction (DMI)) exchange interaction is significantly modified on curved surfaces when the radius of local curvature becomes comparable to fundamental magnetic length scales. Here, we present an experimental study of the spin texture in an 8 nm thin magnetic multilayer with growth-induced in-plane anisotropy and DMI deposited onto the curved surface of a 1.8 {\mu}m long non-magnetic carbon nanowire with a 67 nm radius. Using magnetic soft x-ray tomography the three-dimensional spin configuration in this nanotube was retrieved with about 30nm spatial resolution. The transition between two vortex configurations on the two ends of the nanotube with opposite circulation occurs through a domain wall that is aligned at an inclined angle relative to the wire axis. Three-dimensional micromagnetic simulations support the experimental observations and represent a visualization of the curvature-mediated DMI. They also allow a quantitative estimate of the DMI value for the magnetic multilayered nanotube.

Magnetic skyrmions are topological spin textures holding great potential as nanoscale information carriers. Recently, skyrmions have been predicted in antiferromagnets, with key advantages in terms of stability, size and dynamical properties over their ferromagnetic analogs. However, their experimental demonstration is lacking. Here we show that skyrmions can be stabilized at zero field and room temperature at the interface of sputtered IrMn thin films exchange-coupled to a ferromagnetic layer. This was realised by replicating the skyrmionic spin texture of the ferromagnet in the antiferromagnet, via annealing above the blocking temperature of the ferromagnet/antiferromagnet bilayer. Using the high-spatial-resolution magnetic microscopy technique XMCD-PEEM, we observe the skyrmions within the IrMn interfacial layer from the XMCD signal of the uncompensated Mn spins at the interface. This result opens up a path for logic and memory devices based on skyrmion manipulation in antiferromagnets.

Spin Hall effect provides an efficient tool for the conversion of a charge current into a spin current, opening the possibility of producing pure spin currents in non-magnetic materials for the next generation of spintronics devices. In this sense, giant Spin Hall Effect has been recently reported in Cu doped with 0.5 % Bi grown by sputtering and larger values are expected for larger Bi doping, according to first principles calculations. In this work we demonstrate the possibility of doping Cu with up to 10 % of Bi atoms without evidences of Bi surface segregation or cluster formation, as studied by different microscopic and spectroscopic techniques. In addition, YIG/BiCu structures have been grown, showing a spin mixing conductance larger that the one shown by similar Pt/YIG structures. These results reflects the potentiality of these new materials in spintronics devices., 6 pages, 4 figures

The timing and synchronization system at the ALBA synchrotron facility is based on the well-established event-based model broadly used in the particle accelerator facilities built in the last decade. In previous systems, based on signal model architecture, the master frequency was distributed using a direct analog signal and delayed at each target where the triggers were required. However, such strategy has proven to be extremely expensive and non-scalable. In the event-based model, the data stream is generated at a continuous rate, synchronously with the master clock oscillator of the accelerator. This strategy improves the flexibility for tuning the trigger parameters remotely and reduces the costs related to maintenance tasks. On the other hand, the absence of the pure RF signal distributed in the experimental stations implies much more complexity in the performance of time-resolved experiments. Abstract here explain how these difficulties have been overcome in the ALBA timing system in order to allow the signal reconstruction of the RF master frequency at the CIRCE beamline., Proceedings of the 16th Int. Conf. on Accelerator and Large Experimental Control Systems, ICALEPCS2017, Barcelona, Spain

A new 6-DOF sample manipulator has been designed for the ALBA Synchrotron PhotoEmission Electron Microscopy (PEEM) experimental station, based on a commercial Elmitec LEEM 3. The new design includes full motorization of all 6 axes with position feedback, no backlash, and maximized stability, crucial to achieve the best spatial resolution of down to 8 nm (in so-called LEEM mode). The in-plane longitudinal and transversal motions with sub-micron resolution are based on high precision linear guides, while the pitch and roll stages (sample tilt), guided by angular guides, are actuated by a double-flexure system, which enhances the overall rigidity of the system. The vertical stage is composed by a high rigidity recirculating roller screw and cross roller guides. Finally, 360° yaw rotation is supplied by a differentially pumped commercial rotary stage. On top of the stage, the sample support is mounted on a customized DN63CF flange. This support keeps the original functionalities of the sample manipulator and holders, with 6 independent electrical contacts, and the possibility to heat the sample up to 2000 K and cool it to 100 K with an improved liquid nitrogen cooling system., Proceedings of the Mechanical Eng.~Design of Synchrotron Radiation Equipment and Instrumentation, MEDSI2018, Paris, France

Changes in strain can be used to modify electronic and magnetic properties in crystal structures, to manipulate nanoparticles and cells, or to control chemical reactions. The magneto-elastic (ME) effect--the change of magnetic properties caused by the elastic deformation (strain) of a magnetic material--has been proposed as an alternative approach to magnetic fields for the low power control of magnetization states of nanoelements since it avoids charge currents, which entail ohmic losses. Multiferroic heterostructures \cite{Zheng2004} and nanocomposites have exploited this effect in search of electric control of magnetic states, mostly in the static regime. Quantitative studies combining strain and magnetization dynamics are needed for practical applications and so far, a high resolution technique for this has been lacking. Here, we have studied the effect of the dynamic strain accompanying a surface acoustic wave on magnetic nanostructures. We have simultaneously imaged the temporal evolution of both strain waves and magnetization dynamics of nanostructures at the picosecond timescale. The newly developed experimental technique, based on X-ray microscopy, is versatile and provides a pathway to the study of strain-induced effects at the nanoscale. Our results provide fundamental insight in the coupling between strain and magnetization in nanostructures at the picosecond timescale, having implications in the design of strain-controlled magnetostrictive nano-devices., 16pages and 3 fig (plus 4 pages and 2 figs in supplemeantray). 3 videos