G. Schmahl

Imaging of magnetic domains by transmission x-ray microscopy

The combination of the high-resolution transmission x-ray microscope (TXM) based on the zone plate technique with the x-ray magnetic circular dichroism (X-MCD) providing a huge magnetic contrast is a new technique to image magnetic domain structures. It is inherently element specific and contains information on the local spin and orbital moments of the absorbing species that can be obtained by applying magneto-optical sum rules. A lateral spatial resolution depending on the quality of the zone plates down to 30 nm can be achieved. We report on first results at the Fe edges of Fe both in amorphous and in multilayered Gd-Fe systems. With a TXM set-up at BESSY I adapted to record magnetic images in varying magnetic fields the evolution of magnetic domains within a complete hysteresis loop and magnetic aftereffects have been studied.

Magnetic domain imaging with a transmission X-ray microscope

Abstract The combination of X-ray magnetic circular dichroism being an element-specific local probe for the magnetic microstructure and the transmission X-ray microscope providing a spatial resolution of about 30 nm allows to image magnetic domains with a huge contrast. Special virtues of this technique are the applicability of varying magnetic fields thus allowing technologically relevant studies of the evolution and the switching behaviour of domain structures. Quantitative information on the local magnetization and in particular a separation of spin and orbital moments is possible. Results obtained at the Fe and Co L3 edges in GdFe and PtCo multilayered systems demonstrate the potential of this new technique.

Magnetization reversal of a multilayered FeGd dot array imaged by transmission X-ray microscopy

The magnetization reversal of an array of 1 μm squared FeGd dots has been studied by magnetic transmission x-ray microscopy (MTXM). A (4u200aAu200aFe/4Au200aGd)×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 ...

Magnetic transmission X-ray microscopy: imaging magnetic domains via the X-ray magnetic circular dichroism

X-ray magnetic circular dichroism (X-MCD), i.e. the dependence of the absorption of circularly polarized X-rays on the magnetization of a ferromagnetic sample used as a contrast mechanism in combination with a high resolution transmission X-ray microscope (TXM) enables a quantitative and element-specific imaging of magnetic structures with a lateral resolution down to about 30 nm. Quantitative information on the local magnetization can be obtained, in particular a separation between spin and orbital moments is possible by applying magneto-optical sum-rules. Images in varying external magnetic fields can be recorded and allow to study magnetization reversal processes within a complete magnetization cycle. Multilayered systems of FeGd and PtCo have been studied. Results on the mechanism of pinning of domain walls as, e.g. the density of pinning centers are presented.

Imaging of sub-100-nm magnetic domains in atomically stacked Fe(001)/Au(001) multilayers

In order to study sub-100-nm domains in magnetic multilayers a combination of three high-resolution imaging techniques has been applied to the same samples for the first time: magnetic force microscopy (MFM), Lorentz microscopy with a transmission electron microscope, and magnetic transmission x-ray microscopy (MTXM). The samples—atomically stacked [Fe(001)/Au(001)]n multilayers with an approximate L10-lattice—were prepared by molecular beam epitaxy (MBE) on a GaAs(001) substrate which was then locally removed by laser-induced wet etching to create a window that is transparent for 200 keV electrons and soft x-rays. Magnetization curves with perpendicular and in-plane applied field indicate a spontaneous perpendicular magnetization with an equilibrium domain pattern in small fields and reversible wall motion. About 60 nm wide domains could be observed with MFM and MTXM, respectively. Lorentz images did not show any in-plane magnetic contrast, but the domain pattern appeared when the sample was tilted. This...

Undulation instabilities in laterally structured magnetic multilayers

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.

X-ray magnetic circular dichroism used to image magnetic domains

zation onto the photon propagation direction in ferromagnetic samples. At L-edges in 3d transition metals relative changes in the absorption cross section up to 50% occur, so that X-MCD can serve as a huge magnetic contrast in imaging techniques which are based on photon absorption. The first attempt using X-MCD in magnetic microscopy involved a photoemission microscope (PEEM) (Stoehr et al., 1993) where a spatial resolution of a few/zm could be obtained. This experiment, however, is restricted to studies in zero magnetic field. Several attempts are currently on the way to use XMCD for the imaging of magnetic domains, see e.g. Warwick et al., 1998. A new concept to image magnetic domains even on the nm scale is the combination of a high resolution transmission X-ray microscope (TXM) with X-MCD in the complementary transmission mode (Magnetic TXM = M-TXM) (Fischer et al., 1996).