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.

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.

The combination of magnetic circular dichroism as a magnetic contrast mechanism and a transmission x-ray microscope allows imaging of magnetic structures with lateral resolutions down to 25 nm. Results on magneto-optical Tb25(Fe75Co25)75 layers system with thermomagnetically written bits of various sizes were obtained at the x-ray microscope XM-1 at the Advanced Light Source in Berkeley, CA. The results prove the thermal stability of the bits in the recording process. Furthermore the capability of soft x-ray microscopy with respect to the achievable lateral resolution, element specificity and sensitivity to thin magnetic layers is demonstrated. The potential of imaging in applied magnetic fields for both out-of-plane and in-plane magnetized thin magnetic films is outlined.

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 L-3,L-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 Fe L edges. The samples have been prepared by thermal evaporation onto a 100 nm thin Si3N4 membrane and were mounted under a tilt of 30 degrees with respect to the transmission direction of the photons in the full-field microscope. Corresponding images taken under a tilt of 0 degrees 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. (C) 2001 American Institute of Physics.

We report both technical advances in soft X-ray microscopy (XRM) and applications furthered by these advances. With new zone plate lenses we record test pattern features with good modulation to 25nm and smaller. In combination with fast cryofixation, sub-cellular images show very fine detail previously seen only in electron microscopy, but seen here in thick, hydrated, and unstained samples. The magnetic domain structure is studied at high spatial resolution with X-ray magnetic circular dichroism (X-MCD) as a huge element-specific magnetic contrast mechanism, occurring e.g. at the L2,3 edges of transition metals. It can be used to distinguish between in-plane and out-of-plane contributions by tilting the sample. As XRM is a photon based technique, the magnetic images can be obtained in unlimited varying external magnetic fields. The images discussed have been obtained at the XM-1 soft X-ray microscope on beamline 6.1 at the Advanced Light Source in Berkeley.

Continuous films and nanostructures of atomically stacked epitaxial Fe(001)/Au(001) multilayers have been studied by soft X-ray and Lorentz microscopy as well as micromagnetic simulations. Domain imaging shows about 65nm wide magnetic stripe domains, in which the magnetization is oriented perpendicular to the film plane. These results are confirmed by micromagnetic simulations, which also yield additional information about the internal structure of domains and walls.

A multilayered FeGd system sputtered on a Si3N4-membrane was used to demonstrate that magnetic transmission x-ray microscopy enables the imaging of the domain structure with high resolution in a quantitative way and in varying external magnetic fields. The field-dependent evolution of sub-100 nm out-of-plane magnetized domains, i.e., the transition from stripe into bubble domains, could be observed in detail. It has been shown that critical fields like the bubble collapse field can be described by a wall energy model. Contrary to the assumption of the theory, the magnetization does not remain perpendicular to the film plane in all cases. This is only true inside the bubbles. In the stripe domains the magnetic moments rotate. Their angle could be measured as a function of the external applied field. Internal stray fields can cause a rotation of moments leading to a contrast at the edges of stripe domains. The results indicate that the magnetization reversal in 3d/4f multilayers is not only determined by wall motions and is therefore more complex than previously assumed.

We studied the growth and magnetic properties of ultrathin Fe(001) films on Au(001) buffer layers grown by molecular-beam epitaxy on MgO(001) single crystals. Epitaxial growth could be achieved by use of a Cr seed layer. Epitaxial quality and surface structure were verified in situ by low-energy and reflection high-energy electron diffraction and scanning tunneling microscopy (STM). Magnetic anisotropy of Fe films in the range of 3–155 monolayers (ML) was determined by alternating gradient magnetometry, superconducting quantum interference device, and magneto-optic Kerr effect. The spontaneous magnetization was always in the film plane. Below a critical thickness of 7.3±0.7 ML we observe a rotation of the cubic easy axes by 45° from the 〈100〉 to the 〈110〉 directions within the film plane. This spin reorientation transition is equivalent to a sign reversal of an effective fourth order anisotropy constant K1eff. In addition, a uniaxial in-plane anisotropy is observed, which may be attributed to the step structure of the samples obtained from STM images.