Using Lorentz transmission electron microscopy we investigate the behavior of domain walls pinned at non-topographic defects in Cr(3 nm)/Permalloy(10 nm)/Cr(5 nm) nanowires of width 500 nm. The pinning sites consist of linear defects where magnetic p
roperties are modified by a Ga ion probe with diameter ~ 10 nm using a focused ion beam microscope. We study the detailed change of the modified region (which is on the scale of the focused ion spot) using electron energy loss spectroscopy and differential phase contrast imaging on an aberration (Cs) corrected scanning transmission electron microscope. The signal variation observed indicates that the region modified by the irradiation corresponds to ~ 40-50 nm despite the ion probe size of only 10 nm. Employing the Fresnel mode of Lorentz transmission electron microscopy, we show that it is possible to control the domain wall structure and its depinning strength not only via the irradiation dose but also the line orientation.
We report on self-assembled iron oxide nanoparticle films on silicon substrates. In addition to homogeneously assembled layers, we fabricated patterned trenches of 40-1000 nm width using electron beam lithography for the investigation of assisted sel
f-assembly. The nanoparticles with a diameter of 20 nm +/- 7% were synthesized by thermal decomposition of iron oleate complexes in trioctylamine in presence of oleic acid. Samples with different track widths and nanoparticle concentration were characterized by scanning electron microscopy and by superconducting quantum interference device magnetometry.
We report about a combined structural and magnetometric characterization of self-assembled magnetic nanoparticle arrays. Monodisperse iron oxide nanoparticles with a diameter of 20 nm were synthesized by thermal decomposition. The nanoparticle suspen
sion was spin-coated on Si substrates to achieve self-organized arrays of particles and subsequently annealed at various conditions. The samples were characterized by x-ray diffraction, bright and dark field high resolution transmission electron microscopy (HRTEM). The structural analysis is compared to the magnetic behavior investigated by superconducting interference device (SQUID) magnetometry. We can identify either multi-phase FeO/g-Fe2O3 or multi-phase FeO/Fe3O4 nanoparticles. The FeO/g-Fe2O3 system shows a pronounced exchange bias effect which explains the peculiar magnetization data obtained for this system.
