Large arrays of ordered magnetic nanostructures have been fabricated by sputter depositing Fe/Gd multilayers on an array of self-assembled nanospheres. On a planar substrate the system shows an in-plane magnetization whereas a spin reorientation transition (SRT) to out-of-plane orientation occurs on the spherules. This SRT cannot only be explained by the reduction in the shape anisotropy due to patterning of the extended film into nanometer sized islands. In fact, more important is the curved surface of the film on the nanocaps. Micromagnetic simulations of various geometries reveal that the crescent shape of the magnetic film on the spheres is ideal to get small values of the shape anisotropy for all diameters of the spheres, ranging from 1 mu m down to 20 nm. The observed SRT enables a simple and cost effective bottom-up approach to produce patterned perpendicular magnetic nanostructures, having a high potential for magnetic data storage and spintronic applications. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3327797]

Owing to its magnetoelectric properties the antiferromagnetic ( AF) domain structure of Cr2O3 can be controlled when cooling through the Neel- point in simultaneously applied magnetic and electric fields. Recently we achieved complete switching of the perpendicular exchange bias field from positive to negative values and vice versa by variation of the applied electric freezing field at constant external magnetic field in the system Cr2O3/[Co/Pt](n) [ P. Borisov, et al., Phys. Rev. Lett. 94 ( 2005) 117203]. In order to image uncompensated spins at the ferromagnetic - AF interface, X- ray photoemission electron microscopy ( X- PEEM) was performed on Cr2O3 ( 1 1 1)/ Pt/ Co/ Pt heterolayers after cooling in magnetic and electric freezing fields. The orientation of the uncompensated spins and the magnetic structure at the interface measured at the Cr and the Co L-3,L-2 absorption edges are discussed. (c) 2006 Elsevier B. V. All rights reserved.

A new method is proposed for the imaging of the flux-line lattice of a type-II superconductor by soft X-ray absorption microscopy. It is shown that the method is very demanding but probably realisable in the foreseeable future. The new method has the potential to image in real space static and dynamical properties of the flux-line lattice at arbitrary external fields and with single-flux-line resolution.

Domain imaging techniques are used to analyze the micromagnetic behavior of microelements applied in spin-transport devices. Micromagnetic simulations enable direct comparison of the experimental results and give additional information which is not directly accessible experimentally. As a case study we investigate the stray-field interaction of microelements prepared on thin Si 3 N 4 membranes with magnetic-transmission X-ray microscopy and magnetic-force microscopy. Micromagnetic simulations yield internal parameters such as local stray fields and total magnetic energy. Values for the strength of the stray-field interaction between two microelements of several milli Tesla are deduced. Results also show that pinned magnetizations can explain the magnetization patterns observed in the experiments.

Ferromagnetic microcontacts are key components for future spintronic devices in full metal as well as in hybrid ferromagnet/semiconductor systems. Control of the micromagnetic behavior and especially the reversal process is crucial for the functionality of such devices. We have prepared isolated and strayfield coupled micron sized rectangular Ni∕Fe double layer contacts on silicon nitride membranes. High-resolution magnetic microscopy studies in external fields are performed on identical samples comparing full field magnetic transmission x-ray microscopy and magnetic-force microscopy. The results of both techniques are in good agreement. We find evidence for a strayfield-induced coupling of the domain structure in adjacent contacts in accordance with micromagnetic simulations.

The element specific domain configuration of a microstructured Co86Fe10B4∕Mn77Ir23∕Ni80Fe20∕Si3N4 exchange bias film was studied by photoemission electron microscopy using x-ray magnetic circular dichroism. In the dots the magnetization shows less preferred orientation along the exchange bias direction than in unstructured areas. Uncompensated Mn spins at the CoFeB/MnIr interface with an antiferromagnetic coupling between the Mn and the Co magnetic moments could be studied by imaging and spectromicroscopy.

Magnetic transmission soft X-ray microscopy has been used to study element—specifically the magnetization reversal behavior of (Co84Cr16)87Pt13 alloy thin films with a lateral resolution of 35nm. Our results indicate that the magnetization switching is carried out by a random nucleation process that can be attributed to the reversal of individual grains. We found evidence of a large distribution of the switching fields at the nanogranular length scale, which has to be considered seriously for applications of CoCrPt systems as magnetic high-density storage materials.

The current achievements in magnetic transmission soft X-ray microscopy will be reviewed. The magnetic contrast is given by X-ray magnetic circular dichroism (X-MCD), i.e., the dependence of the absorption coefficient of circularly polarized X rays on the projection of the magnetization in a ferromagnetic system onto the photon propagation direction. X-MCD contrast can reach, e.g., at L2,3 edges in transition metals, large values up to 50%. Combined with a soft X-ray microscope where Fresnel zone plates acting as optical elements provide a lateral resolution down at 25 nm, it allows for imaging magnetic microstructures. Specific features of this photon-based technique are the recording of images in varying external magnetic fields, an inherent chemical specificity, a high sensitivity to thin magnetic layers, due to the large contrast, and the possibility to distinguish between in-plane and out-of plane contributions. In this report, recent results obtained with the XM-1 microscope at the ALS (Berkeley/CA) demonstrate the broad applicability of this novel experimental technique to both fundamental and technological relevant issues in nanomagnetism. The future potential will be briefly outlined.

Accurately determining the resolution of x-ray microscopes has been a challenge because good test patterns for x-ray microscopy have been hard to make. We report on a sputter-deposited multilayer imaged in cross section as a test pattern with small features and high aspect ratios. One application of high-resolution imaging is magnetic materials. Off-axis bend magnet radiation is known to have a component of circular polarization which can he used for x-ray magnetic circular dichroism. We calculate the integrated circular polarization collected by the illumination optics in the XM - full-field x-ray microscope.

Recent achievements in magnetic transmission soft X-ray microscopy are reviewed. The magnetic contrast is given by X-ray magnetic circular dichroism, i.e., the dependence of the absorption coefficient of circularly polarized X-rays on the projection of the magnetization in a ferromagnetic system onto the photon propagation direction. A lateral resolution down at 25 nm is provided by Fresnel zone plates used as optical elements. Recording the images in varying external magnetic fields, inherent chemical specificity, a high sensitivity to thin magnetic layers due to the large contrast, and the possibility to distinguish between in-plane and out-of plane contributions allows detailed studies of magnetization reversal processes in magnetic patterned elements and thin films. Micromagnetic simulations support the experimental findings. The potential to study spin dynamics will be briefly outlined.

Transmission x-ray microscopy with the x-ray magnetic circular dichroism as a contrast mechanism was used to image the field dependent evolution of magnetic domains in artificially nanostructured strips of a multilayered Fe/Gd system. A diversity of domain configurations have been imaged for different strengths of the applied magnetic field and different widths of the strips, varying between 100 nm and 1 μm. Undulating domain patterns, analogous to those observed in other condensed matter systems could be found.

We have investigated element-specific magnetization reversal behavior of (Co83Cr17)87Pt13 alloy thin films with a lateral resolution of 35-nm using magnetic transmission soft x-ray microscopy. We report that the magnetization switching is carried out by a random nucleation process that can be attributed to individual grains. We found evidence of a large distribution of the switching fields at the nanogranular-length scale, which has to be considered seriously for applications of CoCrPt systems as high-density magnetic storage materials.

The first transmission x-ray microscope, dedicated for magnetic imaging is currently being built at the beamline ID-10 at BESSY II in Berlin using a helical undulator which provides photons with circular-, horizontal-, vertical. and linear polarization under various angles in the energy range between 0.2 and 2 keV. The microscope will use the x-ray circular and the x-ray linear magnetic dichroism as a magnetic contrast to study ferromagnetic and antiferromagnetic domains. A condenser with dynamical aperture synthesis will produce a reduced, spatially fixed, incoherent, and vertically dispersed image of the source, which will be matched to the aperture of the micro zone plate (MZP). In an object field of 15 mum by 15 mum a monochromaticity of E/DeltaE = 1700 will be obtained, which is sufficient for magnetic spectromicroscopy, enabling us to investigate lateral distributions of magnetic moments separated by different elements, chemical shifts and even by spin and orbital contributions. A solenoid and/or lithographically patterned microcoils will allow studying magnetization reversal processes on different time scales, down to a sub-nanoseconds level where precessional switching and damping mechanisms occur.

The current achievements in magnetic transmission soft X-ray microscopy are reviewed. The magnetic contrast is given by X-ray magnetic circular dichroism (X-MCD), i.e., the dependence of the absorption coefficient of circularly polarized X-rays on the projection of the magnetization in a ferromagnetic system onto the photon propagation direction. X-MCD contrast can reach, e. g., at L-2,L-3 edges in transition metals large values up to 50%. Combined with a soft X-ray microscope where Fresnel zone plates as optical elements provide a lateral resolution down to 25 nm, it allows for imaging magnetic microstructures. Recording the images in varying external magnetic fields, inherent chemical specificity, a high sensitivity to thin magnetic layers due to the large contrast, and the possibility to distinguish between in-plane and out-of plane contributions allow detailed studies of static magnetization reversal processes in magnetic patterned elements and thin films. Micromagnetic simulations support the experimental findings. The broad applicability of this novel experimental technique to both fundamental and technologically relevant issues in nanomagnetism is demonstrated by selected examples. Future directions towards imaging spin dynamics on a psec time scale are briefly outlined.

X-ray magnetic circular dichroism serves as a strong element-specific magnetic contrast mechanism in full-field transmission soft x-ray microscopy to image micromagnetic domain structures. A lateral resolution down to 25 nm is provided by Fresnel zone plates used as optical elements. Recording the images in varying external magnetic fields and the sensitivity to the direction of the magnetization allows for detailed studies of static magnetization reversal processes in magnetic thin films and nanopatterned elements. Results on highly magnetostrictive Terfenol-D layers are reported. The experimental findings of the switching processes in soft magnetic permalloy rectangular structures are consistent with micromagnetic simulations. The pulsed time structure of polarized synchrotron radiation allows for a stroboscopic imaging of spin dynamics on a sub-nanosecond timescale.

Undulation instabilities of magnetic domains have been observed in nanostructured strips of a ferromagnetic Fe/Gd multilayer. The novel technique of magnetic transmission x-ray microscopy, which is based on the x-ray magnetic circular dichroism, was used for imaging. Below a critical magnetic field, sinus-like modulations of the magnetic domains could be observed. At a higher rate of field induced strain rectangular patterns occur. They seem to be characteristic for the reduced lateral width of the magnetic system and are in contrast to chevron patterns observed in extended systems. The domain morphologies found in different magnetic fields H, and in nanowires of various widths Lz, have been summarized in a H–Lz “phase” diagram. An analogy with theoretical predictions for extended systems could be found.

Magnetic transmission x-ray microscopy is a novel technique to image element specifically magnetic domain structures. A lateral resolution down to 25 nm is provided by the Fresnel zone plates used as optical elements in soft x-ray microscopy. The magnetic contrast is given by x-ray magnetic circular dichroism, i.e., large magnetic contributions up to 25% to the absorption cross section of circularly polarized x rays that occur in the vicinity of, e.g., the Fe L3,2 edges~706 and 719 eV! and depend on the relative orientation of the projection of the magnetization of the sample onto the photon propagation direction. Thus, both in-plane and out-of-plane contributions to the magnetization are accessible. Here we present images of the magnetic domain structure of a ~3 nm Cr/50 nm Fe/6 nm Cr ! thin film system with a preferentially in-plane magnetization recorded at the FeL edges. The samples have been prepared by thermal evaporation onto a 100 nm thin Si 3N4 membrane and were mounted under a tilt of 30° with respect to the transmission direction of the photons in the full-field microscope. Corresponding images taken under a tilt of 0° ruled out out-of-plane contributions. Images recorded in applied varying external magnetic fields allowed to study the switching behavior. These trial results have a large impact on further investigations of nanostructured magnetic systems, e.g., spintronic devices and magnetic sensors with magnetic soft x-ray microscopy. ©2001 American Institute of Physics. @DOI: 10.1063/1.1355333 #

X-ray magnetic circular dichroism (X-MCD) was used as a large, element-specific and quantitative magnetic contrast mechanism in the soft X-ray microscopes at BESSY I (Berlin) and the ALS (Berkeley). The present state and potential of magnetic transmission X-ray microscopy (MTXM) is outlined. The possibility to record images in varying magnetic fields and the high spatial resolution down to 25 nm were used to image out-of-plane magnetized (4 ÅFe / 4 ÅGd)×75 systems. Magnetic domains could be studied in arrays of circular and square dots with lateral dimensions down to 180 nm. Hysteresis loops of individual dots were deduced using the direct proportionality of the X-MCD contrast to the sample magnetization. Images of a 3 nmCr / 50 nmFe / 6 nmCr film demonstrate for the first time that MTXM is also able to observe in-plane magnetized domains. In the future the possible applications of MTXM will be extended with regard to the strength of the external field, the available energy range and the sample conditions by building a dedicated transmission X-ray microscope for magnetic imaging at BESSY II.

The magnetization reversal of an array of 1 μm squared FeGd dots has been studied by magnetic transmission x-ray microscopy (MTXM). A (4 Å Fe/4Å Gd)×75 multilayered FeGd system has been prepared on a 30 nm thin Si3N4 membrane by sputtering and structured by optical lithography and ion beam etching techniques. Both the domain structure within each single dot and the collective switching behavior could be observed with MTXM. A large variation in the nucleation field of the dots was found and can be attributed to the shape of the dots. A correlation between the nucleation field and the perimeter of each dot could be deduced. Hysteresis loops of individual dots are derived, taking into account the proportionality of the dichroic contrast to the magnetization of the sample. The stepped profile of the magnetization loop of a single dot is found to be clearly distinct from a continuous film. The high lateral resolution and the possibility to record the images in varying external magnetic fields proves that MTXM is a highly adapted tool to investigate nanostructured magnetic systems.