J. Barthel

Hexagonally ordered 100 nm period nickel nanowire arrays

The magnetic behavior of 100 nm period arrays of Ni nanowires embedded in a highly ordered alumina pore matrix were characterized by magnetometry and magnetic force microscopy. Reducing the diameter of the nanowires from 55 to 30 nm while keeping the interwire distance constant leads to increasing coercive fields from 600 to 1200 Oe and to increasing remanence from 30% to 100%. The domain structure of the arrays exhibits in the demagnetized state a labyrith-like pattern. These results show that stray field interactions of single domain nanowires are entirely dependent on the nanowire diameter.

High density hexagonal nickel nanowire array

Nickel nanowires were grown in highly ordered pore channels of an alumina membrane using pulsed electrodeposition. A complete metal filling of the hexagonal arranged pores with a pitch of 100 nm and a monodisperse pore diameter of iO30 nm was obtained. The bulk-magnetic behavior of the ferromagnetic nanowire arrays was characterized by SQUID-magnetometer measurements. Magnetic-force-microscopy investigation measurements with a variable external magnetic field were applied on magnetized and demagnetized samples. In addition, magnetic wires have been locally switched by a strong MFM tip and an external magnetic field. The MFM results show a good agreement with the bulk magnetic hysteresis loop.

Switching behaviour of single nanowires inside dense nickel nanowire arrays

Summary form only given. The suitability of nickel nanowire arrays for perpendicular magnetic storage media with areal densities beyond the superparamagnetic limit (>70 Gbit/in/sup 2/) is analyzed in this paper. Highly ordered alumina pore channel arrays are used as templates for the fabrication of magnetic nanowire arrays with a periodicity of 65 (180 Gbit/in/sup 2/) and 100 nm (75 Gbit/in/sup 2/) and pore diameters between 30 and 55 nm. A nearly perfect hexagonal arrangement for the magnetic columns occurs only inside very narrow process windows for periodic distances of 65, 100 and 500 nm, and - in contrast to most publications in this field - a degree of pore filling of almost 100% was achieved. Here, we will focus on nickel as a filling material due to its negligible magneto-crystalline anisotropy, so that the interactions between the anisotropy resulting from the nanowire shape and the stray field inside the magnetic arrays can be studied in detail. The small magnetic moment and the large exchange lengths (/spl lambda//sub ex/= (A/2K/sub 1/)/sup 05/ /spl ap/ 20 nm) of nickel leads to low dipole interactions between nanowires and a huge anisotropy along the column axis which enables nickel as a suitable material for pattern perpendicular magnetic media.

Growth, structure and magnetic properties of Co ultrathin films on Cu(111) by pulsed laser deposition

Deposition of Co on Cu(111) substrate by laser ablation changes the morphology, structure and magnetic properties of Co ultrathin films. The pulsed laser deposition method induces a good layer-by-layer growth of Co films and delays the face centred cubic to hexagonal close packed structural phase transition in the films. As a result, the pulsed laser deposited films retain an in-plane easy axis of magnetization at all thicknesses investigated (0-15 monolayers Co) while the thermally deposited films also exhibit a hysteresis loop in the perpendicular direction as soon as the hexagonal close packed structure is dominant in the film. In addition, the suppression of hexagonal close packed stacking in the pulsed laser deposited films leads to a complete antiferromagnetic coupling in Co/Cu/Co/Cu(111) trilayers for both in-plane and out-of-plane magnetization directions.

Self-assembled magnetic nanostripes by organic patterning

Selective adsorption of Fe deposited on the organic molecule 3,4,9,10-perylene-tetracarboxylic-3, 4,9,10-dianhydride (PTCDA) is used to prepare a self assembled magnetic nanostripe structure on a vicinal Ag surface. Scanning tunneling microscopy reveals that after PTCDA deposition on the Ag(10 8 7) surface a grating-like domain pattern is formed. It consists of alternating stripes of molecule-covered facets and uncovered (111) terraces. Fe adsorption takes place selectively on the molecule-covered stripes forming disk-shaped super-paramagnetic islands with a polar easy magnetization axis.

Influence of growth temperature on the spin reorientation of Ni/Cu(100) ultrathin films

Ni/Cu(100) films were prepared by thermal deposition at room temperature (RT) and 170 K low temperature (LT) separately to study the influence of substrate temperature on the spin reorientation. The critical thickness of the LT grown films is observed to be about 1 ML smaller than that of the RT films. Though both types of films show similar tetragonal distortion and chemical composition, their morphology differs dramatically: the island density of the LT films is significantly higher than that of the RT films. We use this to interpret the different magnetic behavior between the RT and LT films.

Fabrication and uniaxial magnetic anisotropy of Co nanowires on a Pd(110) surface

We have fabricated Co atomic chains and nanowires on a Pd(110) surface oriented along the [1-10] direction. This is possible due to high diffusion anisotropy of the Co adatom on the Pd(110) surface. The Co nanowires on Pd(110) exhibit a strong uniaxial in-plane magnetic anisotropy, in which the easy axis is along [1-10], i.e., nanowire direction.

Suppression of the face-centered-cubic-hexagonal-close-packed stacking fault in Co/Cu(111) ultrathin films by pulsed laser deposition

The thermal deposition of Co onto Cu(111) results in three-dimensional island growth and a face-centered-cubic-hexagonal-close-packed stacking fault, which hinders a complete antiferromagnetic coupling in Co/Cu(111) superlattices. We report that Co/Cu(111) films can be grown with good layer-by-layer morphology and significantly less stacking faults by pulsed laser deposition. We show that a complete antiferromagnetic coupling can be achieved in the pulsed laser deposited Co/Cu trilayer.

Nucleic Acid Organizations Visualized by Scanning Force Microscopy

Both DNA and RNA domains and microdomainsEto a certain degree comparable to self-organizational mesophase areasEhave been visualized as graphite surface adlayers by scanning force microscopy in contact force mode. More polar substrate surfaces, sharper tip geometries and tapping mode procedures proved less favourable, due to sample distortions and prevention of organization within the adlayer by dominant adhesive forces in the interface. 1997 by John Wiley & Sons, Ltd.

Selforganization of Nucleic Acids Visualized by Scanning Force Microscopy

Abstract SFM-investigations visualize domains and microdomains of selforganizational DNA- and RNA-adlayer patterns on graphite substrates and contribute by this to general approaches of elucidating biomesogen pre-life states complexity.