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Ultrashort and intense extreme ultraviolet (XUV) and X-ray pulses readily available at free-electron lasers (FELs) enable studying non-linear light−matter interactions on femtosecond timescales. Here, we report on the non-linear fluence dependence of magnetic scattering of Co/Pt multilayers, using FERMI FEL’s 70-fs-long single and double XUV pulses, the latter with a temporal separation of 200 fs, with a photon energy slightly detuned to the Co M2,3 absorption edge. We observe a quenching in magnetic scattering that sets-in already in the non-destructive fluence regime of a few mJ/cm² typically used for FEL-probe experiments on magnetic materials. Calculations of the transient electronic structure in tandem with a phenomenological modeling of the experimental data by means of ultrafast demagnetization unambiguously show that XUV-radiation-induced demagnetization is the dominant mechanism for the quenching in the investigated fluence regime of

The generation of non-equilibrium electron spin polarization, spin transport, and spin detection are fundamental in many quantum devices. We demonstrate that a lattice of magnetic nanodots enhances the electron spin polarization in monolayer graphene via carrier exchange. We probed the spin polarization through a resistively-detected variant of electron spin resonance (ESR) and observed resonance amplification mediated by the presence of the nanodots. Each nanodot locally injects a surplus of spin-polarized carriers into the graphene, and the ensemble of all "spin hot spots" generates a non-equilibrium electron spin polarization in the graphene layer at macroscopic lengths. This occurs whenever the interdot distance is comparable or smaller than the spin diffusion length., Title of original submission "A nanomagnetic polarization amplifier for graphene" was changed

We present a systematic 2D spatial-coherence analysis of the soft-X-ray beamline P04 at PETRA III for various beamline configurations. The influence of two different beam-defining apertures on the spatial coherence properties of the beam is discussed and optimal conditions for coherence-based experiments are found. A significant degradation of the spatial coherence in the vertical direction has been measured and sources of this degradation are identified and discussed. The Fourier-analysis method, which gives fast and simple access to the 2D spatial coherence function of the X-ray beam, is used for the experiment. Here, we exploit the charge scattering of a disordered nanodot sample allowing the use of arbitrary X-ray photon energies with this method.

The in-plane orientation of the magnetization in the center of domain walls is measured in Co/Ir(111) as a function of Co thickness via scanning electron microscopy with polarization analysis. Uncapped, thermally evaporated cobalt on an Ir(111) single-crystal surface is imaged in situ in ultrahigh vacuum. The initial pseudomorphic growth with an atomically flat interface of cobalt on iridium ensures comparability to theoretical calculations and provides a study of an interface that is as ideal as possible. Below a cobalt thickness of 8.8 monolayers, the magnetic domain walls are purely N\'eel oriented and show a clockwise sense of rotation. For larger thicknesses the plane of rotation changes and the domain walls show a significant Bloch-like contribution, allowing one to calculate the strength of the Dzyaloshinskii-Moriya interaction (DMI) from energy minimization. From the angle between the plane of rotation and the domain-wall normal an interfacial DMI parameter ${D}_{\mathrm{s}}=\ensuremath{-}(1.07\ifmmode\pm\else\textpm\fi{}0.05)\phantom{\rule{4pt}{0ex}}\mathrm{pJ}/\mathrm{m}$ is determined, which corresponds to a DMI energy per bond between two Co atoms at the interface of ${d}_{\mathrm{tot}}=\ensuremath{-}(1.04\ifmmode\pm\else\textpm\fi{}0.05)\phantom{\rule{4pt}{0ex}}\mathrm{meV}$.

Electron beam lithography is a powerful maskless tool to fabricate structures on the nanometer scale. Here, we show that low-keV-electron beams enable a direct patterning of tetrahedral amorphous carbon (ta-C) thin films by inducing a local graphitization without the need for any resist or development process step. Irradiation with 4 keV electrons leads to a local decrease of the ta-C film's electrical resistance and an increase of both the sp2/sp3-ratio and the material's work function. We investigate the impact of electron exposure on ta-C by a variety of microscopy as well as spectroscopy methods including scanning tunneling microscope-based current-distance spectroscopy, conductive atomic force microscopy, spatially resolved ultraviolet and x-ray photo emission spectroscopy, and m-Raman spectroscopy. The electron exposure has been performed under ultrahigh vacuum conditions to prevent from electron-induced deposition of contaminants which may obstruct the application of surface-sensitive analysis techniques to the modified ta-C films.

Review of scientific instruments 89(3), 036103 - (2018). doi:10.1063/1.5018396, A transmission polarizer for producing elliptically polarized soft X-ray radiation from linearly polarized light is presented. The setup is intended for use at synchrotron and free-electron laser beamlines that do not directly offer circularly polarized light for, e.g., X-ray magnetic circular dichroism (XMCD) measurements or holographic imaging. Here, we investigate the degree of ellipticity upon transmission of linearly polarized radiation through a cobalt thin film. The experiment was performed at a photon energy resonant to the Co L3-edge, i.e., 778 eV, and the polarization of the transmitted radiation was determined using a polarization analyzer that measures the directional dependence of photo electrons emitted from a gas target. Elliptically polarized radiation can be created at any absorption edge showing the XMCD effect by using the respective magnetic element., Published by American Institute of Physics, [S.l.]

Using time-resolved scanning electron microscopy with polarization analysis (TR-SEMPA) the dynamics of magnetic vortices and antivortices in a cross-tie wall is investigated. Under quasistatic external field drive both quasiparticles oscillate at opposite phase to each other (in analogy to an optical mode). An additional common motion, which stems from the finite boundary conditions in a patterned FeCoSiB rectangle, is observed (in analogy to an acoustic mode), leading in total to a stronger field-dependent displacement for the vortices compared to the antivortices. Both types of magnetic solitons are mutually coupled via the minimization of the total magnetic energy of the structure. It is shown that the TR-SEMPA results can be explained via coupling in the framework of micromagnetic simulations and that the coupling constants can be extracted. The motion is composed from the contributions of the two terminating vortices and a mutual vortex-antivortex coupling along the chain.

About a decade ago, the understanding of the interaction mechanisms between electrical currents and magnetic objects like domain walls or vortices was still in its infancy. Both, theory and experiments were moving on uncharted grounds, with new and many times contradicting results being published from different groups at increasing pace. Previously, only the Oersted field from a current was available to manipulate the magnetic state of a system. The latter was extensively used in magnetic storage devices, starting from the early core memory up to the write heads of the latest hard drive technologies based on perpendicular recording and tunnel-magnetoresistive (TMR) readout sensors, to alter the state of the magnetic bits. Even early prototypes of magnetic random-access memory (MRAM) used the Oersted field for writing.

Physical review applied 8(2), 024008(2017). doi:10.1103/PhysRevApplied.8.024008, The influence of geometric parameters on the magnetic fine structure of domain walls in bent nanowires is investigated. The domain pattern in the soft-magnetic Co$_{39}$Fe$_{54}$Si$_7$ alloy is studied via scanning electron microscopy with polarization analysis and modeled via micromagnetic simulations. It is demonstrated that the bending angle affects details of the microstructure as well as the preponderant domain-wall type. A phenomenological model is developed that provides the global energy minimum of individual types of domain walls as a function of the geometric parameters of the wire. The results can be directly transferred to permalloy wires, as permalloy and Co$_{39}$Fe$_{54}$Si$_7$ alloy have a comparable magnetostatic exchange length., Published by American Physical Society, College Park, Md. [u.a.]

We present a method to determine the two-dimensional spatial coherence of synchrotron radiation in the soft X-ray regime by analyzing the Fourier transform of the magnetic speckle pattern from a ferromagnetic film in a multidomain state. To corroborate the results, a Young's double-pinhole experiment has been performed. The transverse coherence lengths in vertical and horizontal direction of both approaches are in a good agreement. The method presented here is simple and gives a direct access to the coherence properties of synchrotron radiation without nanostructured test objects.

Synchrotron radiation news 26(6), 27 - 32 (2013). doi:10.1080/08940886.2013.850384, The free-electron laser (FEL) sources FLASH in Hamburg, LCLS at Stanford, and FERMI in Trieste provide XUV to soft X-ray radiation (FLASH and FERMI) or soft to hard X-ray radiation (LCLS) with unprecedented parameters in terms of ultrashort pulse length, high photon flux, and coherence. These properties make FELs ideal tools for studying ultrafast dynamics in matter on a previously unaccessible level. This paper first reviews results obtained at FEL sources during the last few years in the field of magnetism research. We start with pioneering experiments at FLASH demonstrating the feasibility of magnetic scattering at FELs [1, 2], then present pump–probe scattering experiments [3, 4] as well as the first FEL magnetic imaging experiments [5], and finally discuss a limitation of the scattering methods due to a quenching of the magnetic scattering signal by high-fluence FEL pulses [6]. All of the presented experiments exploit the X-ray magnetic circular dichroism effect [7, 8] to obtain element-specific magnetic scattering contrast, as known from synchrotron experiments [9–12]., Published by Taylor & Francis, Philadelphia, Pa.

The coupling of rectangular magnetic 2000×1000×20 nm3 structures with flux-closure domain configurations is studied using micromagnetic simulations with periodic boundary conditions. In order to understand the origin of the interaction, the magnetic structure of a single element is analyzed in detail to calculate its magnetostatic fringe field. Both, our simulations as well as earlier experimental data reveal an interesting phenomenon: instead of four domains forming the well-known Landau state there are six domains. A consistent magnitude of the effect can be obtained, when the highly susceptible paramagnetic “coating layer” used in the experiment is included in the simulation. The coupling behavior of both, horizontally and vertically aligned arrays of rectangles is explained by the magnetostatic field of the single element. We show that for arrays of elements that have a coating layer inter-element coupling depends strongly on properties of this coating layer.

It is demonstrated that the magnetic diffraction pattern of the isotropic disordered maze pattern is well described utilizing a gamma distribution of domain sizes in a one-dimensional model. From the analysis, the mean domain size and the shape parameter of the distribution are obtained. The model reveals an average domain size that is significantly different from the value that is determined from the peak position of the structure factor in reciprocal space. As a proof of principle, a wedge-shaped (Co$_{tÅ}$/Pd$_{10Å}$)8 multilayer film, that covers the thickness range of the spin-reorientation transition, has been used. By means of soft x-ray resonant magnetic scattering (XRMS) and imaging techniques the thickness-driven evolution of the magnetic properties of the cobalt layers is explored. It is shown that minute changes of the domain pattern concerning domain size and geometry can be investigated and analyzed due to the high sensitivity and lateral resolution of the XRMS technique. The latter allows for the determination of the magnetic anisotropies of the cobalt layers within a thickness range of a few angstroms.

This paper presents studies of the size effect on magnetic switching and interlayer magnetostatic coupling in synthetic antiferromagnet (SAF)-pinned spin-valve nanorings connected to nano stripes with a nanoconstriction. Micromagnetic simulation has been successfully used to reveal the detailed magnetization reversal process of these nanorings. It was observed that SAF-pinned spin-valve nanorings exhibit a double (onion-vortex-reverse onion) or single (onion-reverse onion) magnetization switching process depending on the ring diameter, which is contrary to narrow single-layer NiFe rings that show a double switching process only. Micromagnetic simulations of the SAF-pinned spin valve nanorings suggest that the magnetostatic coupling between the pinned layers of the SAF and the free layer is dependent on the ring size: it plays a very important role in the magnetization switching of small nanorings (600 nm outer diameter), but only a minor role in the switching of big nanorings (1600 nm outer diameter). An efficient reduction of the magnetostatic interaction results in a small shift of the minor magnetoresistance curve, which is beneficial to the magnetic memory applications.

The magnetic properties of Co/Pt multilayers grown by ion beam and DC magnetron sputtering techniques are compared. For Pt/Co/Pt films the spin reorientation as a function of Co thickness is investigated in second-order uniaxial anisotropy approximation. The influence of the growth technique on the interface and volume contribution to the first-order anisotropy is investigated. The correlations between structure and magnetic properties are discussed.

The exact magnetization pattern of magnetic films close to a spin-reorientation transition is difficult to analyze due to the intrinsically three-dimensional (3d) variation of the orientation of the local magnetization. We present a technique how this can be performed, based on the analysis of high quality 2d polarization maps from a single scanning electron microscope with polarization analysis (SEMPA) measurement with tilted sample. The key tool is the statistical distribution of all occurring polarization doublets, visualized in a 2d histogram plot. From the shape of the distribution the type of transition—canted-phase, or coexisting phases—can be inferred. For the canted-phase state, the canting angle can be accurately determined from geometrical considerations. With help of the histogram the image data can be analyzed and the three components of the magnetization can be calculated for most points of the image. For a Co/Pt multilayer film we found a cone state. The magnetization forms a complex pattern consisting of out-of-plane domains while the in-plane magnetization shows a maze pattern.

We present a simple method for the production of magnetic antidot arrays utilizing polystyrene-poly-2-vinylpyridine micelles filled with amorphous SiO 2 . By dip coating, a micellar monolayer is deposited onto Co/Pt multilayers. A hexagonal pattern with periodicity of 80 nm is obtained. By Ar + ion etching the micelle layer is transformed into an antidot array due to preferred sputtering of the SiO 2 core. Further ion bombardment transfers the pattern into the magnetic film and leads to a reorientation of the perpendicular to in-plane easy axis which is attributed to intermixing of the Co/Pt multilayers.

In elastically coupled multiferroic heterostructures that exhibit full domain correlations between ferroelectric and ferromagnetic subsystems, magnetic domain walls are firmly pinned on top of ferroelectric domain boundaries. In this work, we investigate the influence of pinned magnetic domain walls on the magnetization reversal process in a ${\mathrm{Co}}_{40}{\mathrm{Fe}}_{40}{\mathrm{B}}_{20}$ wedge film that is coupled to a ferroelectric ${\mathrm{BaTiO}}_{3}$ substrate via interface strain transfer. We show that the magnetic field direction can be used to select between two distinct magnetization reversal mechanisms, namely, (1) double switching events involving alternate stripe domains at a time or (2) synchronized switching of all domains. Furthermore, scaling of the switching fields with domain width and film thickness is also found to depend on the field orientation. These results are explained by considering the dissimilar energies of the two types of pinned magnetic domain walls that are formed in the system.

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY)., The in-plane orientation of the magnetization vector M in bcc-like Fe(110) films grown on Cu(001) is determined by means of scanning electron microscopy with polarization analysis. For thicknesses of 2 nm, slightly above the fcc/bcc phase transition, it is found that M is oriented along the directions of the Cu(001) substrate. Following the Pitsch orientational relationship these correspond to magnetically hard and axes of bulk iron. This finding is in strong contrast to the behavior reported for thicker films (above 3 nm) of bcc Fe/Cu(001), where the directions of the substrate are preferred. The role of strain in the iron film is discussed, inferring that the presence of a shear strain is mandatory to explain the spin reorientation via the magnetoelastic contribution to the magnetic anisotropy energy., This work has been supported by Spanish MICINN (Grants No. MAT2009-10040 and No. MAT2012-31309) and Gobierno de Aragón (Grants No. E81) and Fondo Social Europeo, as well as by the Deutsche Forschungsgemeinschaft within SFB 668. E.C.C. acknowledges the financial support from Ministerio de Educación, through program Campus de Excelencia Internacional Iberus.

The domain pattern and the domain wall microstructure throughout the spin-reorientation transition of an epitaxial NdCo5 thin film are investigated by micromagnetic simulations. The temperature-dependent anisotropy constants K 1 and K 2, which define the anisotropy energy term in the model, are chosen to reflect the easy axis—easy cone—easy plane spin-reorientation transition observed in epitaxial NdCo5 thin films. Starting at the high-temperature easy c-axis regime, the anisotropy constants are changed systematically corresponding to a lowering of the temperature of the system. The character of the domain walls and their profiles are analysed. The calculated domain configurations are compared to the experimentally observed temperature-dependent domain structure of an in-plane textured NdCo5 thin film.

We study the magnetostatic interaction of submicron $\mathrm{Ni}{}_{81}$$\mathrm{Fe}{}_{19}$ rectangles arranged in a linear chain by measuring the anisotropic magnetoresistance (AMR) of a single rectangle. The rectangles have a lateral aspect ratio of 2 : 1 and are lined up with the long axis oriented side by side varying the interelement distance down to $60\phantom{\rule{0.3em}{0ex}}\mathrm{n}\mathrm{m}$. The energy density of the Landau state is determined from the hard-axis magnetization reversal for a field applied along the chain direction. As a second approach identical energy densities are deduced from the switching field (Landau to quasisingle domain state) like in the case of a Stoner-Wohlfarth particle. The results show that the impact of the magnetostatic interaction on the energy density of the Landau state in remanence is negligibly small $(l1\phantom{\rule{0.3em}{0ex}}\mathrm{k}$$\mathrm{J}$$/$$\mathrm{m}$${}^{3}$$)$. The magnetostatic interaction between field-distorted Landau states, however, is the same as for rectangles in a single domain state and is therefore governed by the compensation of surface charges at the rim. By studying rectangles with only one neighbor, the important role of symmetry on the magnetostatic interaction is shown.

We present a method to characterize the spatial coherence of soft X-ray radiation from a single diffraction pattern. The technique is based on scattering from non-redundant arrays (NRA) of slits and records the degree of spatial coherence at several relative separations from one to 15 microns, simultaneously. Using NRAs we measured the transverse coherence of the X-ray beam at the XUV X-ray beamline P04 of the PETRA III synchrotron storage ring as a function of different beam parameters. To verify the results obtained with the NRAs additional Young's double pinhole experiments were conducted and show good agreement., Comment: 15 pages, 6 figures, 2 tables, 42 references

FERMI@Elettra, the first vacuum ultraviolet and soft X-ray free-electron laser (FEL) using by default a "seeded" scheme, became operational in 2011 and has been opened to users since December 2012. The parameters of the seeded FERMI FEL pulses and, in particular, the superior control of emitted radiation in terms of spectral purity and stability meet the stringent requirements for single-shot and resonant coherent diffraction imaging (CDI) experiments. The advantages of the intense seeded FERMI pulses with variable polarization have been demonstrated with the first experiments performed using the multipurpose experimental station operated at the diffraction and projection imaging (DiProI) beamline. The results reported here were obtained with fixed non-periodic targets during the commissioning period in 2012 using 20-32 nm wavelength range. They demonstrate that the performance of the FERMI FEL source and the experimental station meets the requirements of CDI, holography, and resonant magnetic scattering in both multi- and single-shot modes. Moreover, we present the first magnetic scattering experiments employing the fully circularly polarized FERMI pulses. The ongoing developments aim at pushing the lateral resolution by using shorter wavelengths provided by double-stage cascaded FERMI FEL-2 and probing ultrafast dynamic processes using different pump-probe schemes, including jitter-free seed laser pump or FEL-pump/FEL-probe with two color FEL pulses generated by the same electron bunch. © 2013 AIP Publishing LLC.

We present results of single-shot resonant magnetic scattering experiments of $\mathrm{Co}/\mathrm{Pt}$ multilayer systems using 100 fs long ultraintense pulses from an extreme ultraviolet (XUV) free-electron laser. An x-ray-induced breakdown of the resonant magnetic scattering channel during the pulse duration is observed at fluences of $5\text{ }\text{ }\mathrm{J}/{\mathrm{cm}}^{2}$. Simultaneously, the speckle contrast of the high-fluence scattering pattern is significantly reduced. We performed simulations of the nonequilibrium evolution of the $\mathrm{Co}/\mathrm{Pt}$ multilayer system during the XUV pulse duration. We find that the electronic state of the sample is strongly perturbed during the first few femtoseconds of exposure leading to an ultrafast quenching of the resonant magnetic scattering mechanism.

This content may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This material originally appeared in Review of Scientific Instruments 84, 013906 (2013) and may be found at https://doi.org/10.1063/1.4773543. An endstation for pump–probe small-angle X-ray scattering (SAXS) experiments at the free-electron laser in Hamburg (FLASH) is presented. The endstation houses a solid-state absorber, optical incoupling for pump–probe experiments, time zero measurement, sample chamber, and detection unit. It can be used at all FLASH beamlines in the whole photon energy range offered by FLASH. The capabilities of the setup are demonstrated by showing the results of resonant magnetic SAXS measurements on cobalt-platinum multilayer samples grown on freestanding Si3N4 membranes and pump-laser-induced grid structures in multilayer samples.

We have investigated the magnetization reversal in V-shaped permalloy (Py) nanowires under high dc currents via anisotropic magnetoresistance (AMR) measurements. Utilizing a diamond substrate as heat sink, current densities up to $2\ifmmode\times\else\texttimes\fi{}{10}^{12}\phantom{\rule{0.16em}{0ex}}{\text{A}/\text{m}}^{2}$ can be applied. These high current densities enabled us to observe spin-torque assisted switching in thermal equilibrium, without the influence of transient effects. At high currents, the field driven magnetization reversal process is influenced by Joule heating, Oersted fields, and spin-torque effects. These contributions can be identified in our experiment due to their different symmetry properties under magnetization and current reversal. We obtain two important results when evaluating the spin-torque efficiency $\ensuremath{\epsilon}$, which is proportional to the nonadiabaticity parameter $\ensuremath{\beta}$. First, we find different values for $\ensuremath{\epsilon}$ within the same sample, obtained with just a slight variation of the experimental parameters. Second, within the temperature range of 77 to 327 K, $\ensuremath{\epsilon}$ is found to be constant.

A magnetic domain texture has been deterministically engineered in a topographically flat exchange-biased (EB) thin film system. The texture consists of long-range periodically arranged unit cells of four individual domains, characterized by individual anisotropies, individual geometry, and with non-collinear remanent magnetizations. The texture has been engineered by a sequence of light-ion bombardment induced magnetic patterning of the EB layer system. The magnetic texture's in-plane spatial magnetization distribution and the corresponding domain walls have been characterized by scanning electron microscopy with polarization analysis (SEMPA). The influence of magnetic stray fields emerging from neighboring domain walls and the influence of the different anisotropies of the adjacent domains on the Neel type domain wall core's magnetization rotation sense and widths were investigated. It is shown that the usual energy degeneracy of clockwise and counterclockwise rotating magnetization through the walls is revoked, suppressing Bloch lines along the domain wall. Estimates of the domain wall widths for different domain configurations based on material parameters determined by vibrating sample magnetometry were quantitatively compared to the SEMPA data.

We demonstrate the feasibility of investigating periodically driven magnetization dynamics in a scanning electron microscope with polarization analysis based on spin-polarized low-energy electron diffraction. With the present setup, analyzing the time structure of the scattering events, we obtain a temporal resolution of 700 ps, which is demonstrated by means of imaging the field-driven 100 MHz gyration of the vortex in a soft-magnetic FeCoSiB square. Owing to the efficient intrinsic timing scheme, high-quality movies, giving two components of the magnetization simultaneously, can be recorded on the time scale of hours.

The basics of the scanning electron microscope with polarization analysis are briefly reviewed, emphasizing the achievable magnetic resolution and image contrast. The design of an optimized spin-polarization detector based on the well-established LEED scattering principle is presented. Results of first tests are reported.

We have investigated the magnetism of the bare and graphene-covered (111) surface of a Ni single crystal employing three different magnetic imaging techniques and ab initio calculations, covering length scales from the nanometer regime up to several millimeters. With low-temperature spin-polarized scanning tunneling microscopy we find domain walls with widths of 60--90 nm, which can be moved by small perpendicular magnetic fields. Spin contrast is also achieved on the graphene-covered surface, which means that the electron density in the vacuum above graphene is substantially spin polarized. In accordance with our ab initio calculations we find an enhanced atomic corrugation with respect to the bare surface, due to the presence of the carbon ${p}_{z}$ orbitals and as a result of the quenching of Ni surface states. The latter also leads to an inversion of spin polarization with respect to the pristine surface. Room temperature Kerr microscopy shows a stripelike domain pattern with stripe widths of 3--6 $\ensuremath{\mu}$m. Applying in-plane-fields, domain walls start to move at about 13 mT and a single domain state is achieved at 140 mT. Via scanning electron microscopy with polarization analysis a second type of modulation within the stripes is found and identified as 330 nm wide V lines. Qualitatively, the observed surface domain pattern originates from bulk domains and their quasidomain branching is driven by stray field reduction.

Physical review / B 84, 104412 (2011). doi:10.1103/PhysRevB.84.104412, Published by APS, College Park, Md.

The seeding of vortex domain walls in soft magnetic V-shaped nanowires by magnetic fields has been investigated via scanning electron microscopy with polarization analysis and micromagnetic simulations. It is found that the orientation of the magnetic seeding field determines the sense of rotation and the position of single vortex domain walls in the state of remanence. The topology of the magnetic microstructure in combination with symmetry considerations gives the key for the explanation of this behavior.

A spin-polarized current traversing a ferromagnet with continuously varying magnetization exerts a torque on the magnetization. The nonadiabatic contribution to this spin-transfer torque is currently under strong debate, as its value differs by orders of magnitude in theoretical predictions and in measurements. Here, a measurement scheme is presented that allows us to determine the strength of the nonadiabatic spin torque accurately and directly. Analytical and numerical calculations show that the scheme is robust against the uncertainties of the exact current direction and Oersted fields.

Physical review / B 81, 100401(R) (2010). doi:10.1103/PhysRevB.81.100401, Published by APS, College Park, Md.

We have investigated the magnetic properties of single submicron permalloy rectangles with a thickness of 20 nm and an aspect ratio of 2:1 via anisotropic magnetoresistance AMR . Preparation and investigation via magnetotransport are performed in situ in ultrahigh vacuum. The field-dependent magnetization behavior of the two generic cases with the magnetic field applied perpendicular and parallel to the long axis of the rectangles is studied. Due to the high sensitivity of our setup, single field sweeps are sufficient to obtain magnetoresistance curves of structures with dimensions as small as 600 300 nm2. To link features of the AMR to changes in the micromagnetic states, the remanent state has been investigated via scanning electron microscopy with polarization analysis. Our main result is that the energy density of micromagnetic states can be obtained from the hard-axis magnetization behavior. It is demonstrated that a C/S state can be distinguished from a Landau state and the energy difference between both states is determined.

We have studied the magnetic domain structure in Permalloy rectangles that reveal flux-closure domain configurations. Arrays with varying spacing between the rectangles are investigated by scanning electron microscopy with polarization analysis as well as by micromagnetic simulation. In contrast to general expectation, rectangles in the flux-closure Landau state show significant coupling and form a magnetic pattern of common chirality. The coupling is due to the stray field that originates from small changes of the magnetization alignment, which is sensitive to the exact shape and the separation of the rectangles.

We report on a resonant magnetic scattering experiment using soft x-ray pulses generated from a free-electron laser (FEL). The free-electron laser was operated at a fundamental wavelength of 7.97 nm and radiation at the fifth harmonic originating from self-amplified stimulated emission at 1.59 nm with an average energy of 4 nJ per pulse was detected. We demonstrate the feasibility of resonant magnetic scattering at FEL sources by using a Co/Pd multilayer as prototype sample that was illuminated with 20-fs-long soft x-ray pulses tuned to the Co L{sub 3} absorption edge at 778.1 eV (1.59 nm)

A UHV instrument is presented for in situ fabrication of nanostructures and in situ investigation of their magnetoresistance. Nanostructures of diverse shape and size are created from thin films utilizing a focused ion beam. The magnetic nanostructures are contacted via a micromanipulator, which makes it possible to address the individual structures. The system is additionally equipped with a scanning electron microscope column, which is used for damage-free navigation and control of the structuring and contacting. First magnetoresistance measurements of structures carved into a Permalloy film demonstrate the high sensitivity and the flexibility of the new setup.

Coherent diffractive imaging for the reconstruction of a two-dimensional (2D) finite crystal structure with a single pulse train of free-electron laser radiation at 7.97 nm wavelength is demonstrated. This measurement shows an advance on traditional coherent imaging techniques by applying it to a periodic structure. It is also significant that this approach paves the way for the imaging of the class of specimens which readily form 2D, but not three-dimensional crystals. We show that the structure is reconstructed to the detected resolution, given an adequate signal-to-noise ratio.

The scanning electron microscope with polarization analysis (SEMPA or spin-SEM) is a powerful tool to investigate the magnetic structure of ferromagnetic surfaces with high spatial resolution. In the article the spin polarized secondary electron emission is described and discussed as the contrast generating process that is utilized in SEMPA. Taking the secondary electron emission from itinerant ferromagnets as starting point, the properties and best case performance of spin-SEM are derived. The consequences of these properties for the realization of such a microscope and the polarization analyzer, as well as the resulting strengths and weaknesses of the technique are discussed. The best case performance is compared to the actual performance of a newly designed microscope. Several examples for the application of spin-SEM are presented; e.g. the study of the spin-reorientation transition in ultrathin films and interlayer exchange coupling. It is shown how a decoration technique can be used to analyze ferromagnets where the surface is non-magnetic due to contamination or capping by a protective layer. Finally, the influence of sample morphology on the polarization detection and details of the analysis of the vectorial polarization measurement are comprehensively discussed. Keywords: SEMPA; spin-SEM; magnetic imaging; surface magnetism; thin-film magnetism; magnetic nanostructures; spin-polarization

The magnetization behavior and the domain pattern in remanence are studied in Co/Pt multilayers. The reorientation of magnetization from perpendicular to in plane is found to happen via the state of canted magnetization. In the transition from an easy axis to an easy plane a stable domain pattern in the in-plane magnetization components is found for Co/Pt multilayers. The analysis of the domain pattern reveals that the magnetization canting is such that all in-plane orientations of magnetization are equally occupied. The found structure is appointed to the cone state.

We characterize the magnetic domain structure of Co/Pt multilayer films on length scales below one hundred nanometers using resonant magnetic scattering and magnetic force microscopy. The extreme ultraviolet light for the scattering experiment is created by a laser-based high-order harmonic generation source. After illumination with intense ultrashort infrared laser pulses, we observe pronounced changes in the magnetic structure and morphology. This study points out the importance of a detailed analysis of the different laser-induced modifications of a magnetic thin film that influence the scattering patterns.

Generation of circularly polarized light in the extreme ultraviolet (EUV) spectral region (about 25 eV-250 eV) is highly desirable for applications in spectroscopy and microscopy but very challenging to achieve in a small-scale laboratory. We present a compact apparatus for generation of linearly and circularly polarized EUV radiation from a gas-discharge plasma light source between 50 eV and 70 eV photon energy. In this spectral range, the 3p absorption edges of Fe (54 eV), Co (60 eV), and Ni (67 eV) offer a high magnetic contrast often employed for magneto-optical and electron spectroscopy as well as for magnetic imaging. We simulated and designed an instrument for generation of linearly and circularly polarized EUV radiation and performed polarimetric measurements of the degree of linear and circular polarization. Furthermore, we demonstrate first measurements of the X-ray magnetic circular dichroism at the Co 3p absorption edge with a plasma-based EUV light source. Our approach opens the door for laboratory-based, element-selective spectroscopy of magnetic materials and spectro-microscopy of ferromagnetic domains.

The dynamics of magnetic vortices in microsquares with local modifications of magnetic parameters and thickness are investigated. By implanting gallium ions with focussed ion beam into permalloy thin-film elements, we have locally tailored their magnetic properties and the layer thickness. The vortex of the Landau domain pattern of a square is resonantly excited to a gyrotropic motion and crosses regions with and without implantation. With time-resolved scanning transmission x-ray microscopy, we observe an abrupt change in the vortex velocity close to the borders between the two regions.