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The correlation between the crystal/defect and the magnetic domain structure of nanocrystalline (nc) bulk nickel produced by electrodeposition was investigated. By means of conventional and high resolution transmission electron microscopy, an average grain size of 23 nm was determined; nano-grains surrounded by low angle and high angle boundaries and the presence of nanotwins and stacking faults were observed. The nc nickel exhibited soft magnetic properties. Lorentz TEM (LTEM) in the Fresnel mode revealed magnetic domains of various sizes in the micrometer range extending over many grains, with a few random pinning sites, exhibiting a magnetic ripple structure and vortices. The LTEM was used to investigate the motion of domain walls driven by an external in situ magnetic field and to determine the domain wall width. Domain wall movement was observed at very small magnetic fields along the hysteresis loop. The correlation of the grain size and magnetic properties shows good agreement with the Herzer random anisotropy model for nanocrystalline materials, although the nc nickel studied here has no traces of an amorphous phase. [ABSTRACT FROM AUTHOR]

The micromagnetic structural characteristics of permalloy cross-tie walls were investigated using the modified differential phase contrast mode of Lorentz electron microscopy. The results showed the presence of a large dip in the wall width at the center of the cross-tie wall vortex structure. The wall thickness was determined by fitting the calculated image signal of an analytical function to the wall profile.

The magnetization pattern of ferromagnetic Co was studied.

Epitaxial lateral overgrown (ELOG) gallium nitride (GaN) on SiC is being studied as a possible substrate for blue laser diodes. A defect density below 2.2 × 107 cm-2 in the wings, compared to 2 × 109 cm-2 in the windows, was achieved. Interaction of the overgrown GaN with the SiO2 mask causes a few degree wing tilt and a transition region of high defect density between windows and wings. Diminished PL, strong tensile stress, and a defect correlated line at around 3.4 eV emerge in this up to two-micron-wide transition region. By changing the mask material from SiO2 to SiN we were able to reduce the wing tilt drastically to below 0.7°. This eliminates the defective transition region and extends the low strain and the low defect density area of the ELOG wings. The methods used to study strain, wing tilt, and threading dislocations in the ELOG samples are microphotolmninescence (μPL), transmission electron microscopy, x-ray diffraction, and scanning electron microscope. We also demonstrate the use of the faust momentum of the μPL spectra as an effective means to measure strain distribution. [ABSTRACT FROM AUTHOR]

We have investigated the magnetic properties of flat permalloy cylinders by Lorentz transmission electron microscopy and micromagnetic simulations. The magnetization patterns during in situ magnetizing experiments have been imaged and they revealed that the magnetization reversal of the cylindrically shaped dots investigated is determined by the formation and annihilation of magnetic vortices. Furthermore, the experiments and micromagnetic simulations showed a dependence of the vortex annihilation field not only on the aspect ratio but also on the absolute thickness of the cylinders. The diameter of the cylindrical dots was varied between 150 and 1000 nm, and the thicknesses were 3, 5.5, 8.3, 15, and 20 nm, respectively. The formation of inhomogeneous magnetization patterns prior to vortex evolution was observed and by a comparison of the experimental to simulated Fresnel images these patterns can be identified as S- and C-like states. [ABSTRACT FROM AUTHOR]

Presents a study that discussed the reliability of scanning tunneling microscopy (STM) images of rough surfaces of polycrystalline thin films. Details of the etching procedure; Estimation of the tip shape of the rough surfaces; Comparison of the images from STM and transmission electron microscopy.

Micropatterned Hall-sensors are used to measure the magnetic switching of nanopatterned rhombic Ni-elements at temperatures below 4.2 K. The length of the short axis ('waist') was systematically varied between 700 and 100 nm while the length of 2 [micro]m of the long axis was kept fixed. The thickness of the Ni-rhombs was 70 nm. Whereas the hysteresis loops of the broader rhombs show many small steps, which seem to be connected to domain wall movement and pinning, the narrowest two only reveal one single step during magnetization reversal. The process of magnetization reversal is additionally studied by Lorentz transmission electron microscopy. Placing Hall-sensors on both ends of acicular Ni elements allows one to investigate the switching process on both sides simultaneously. Index Terms--Hall-magnetometry, individual ferromagnetic particles, magnetization reversal, micro-rhombs.

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)][sub n] multilayers with an approximate L1[sub 0]-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 indicates that the magnetization is indeed strictly perpendicular. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]