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M Bode

Publications and source records attributed to M Bode.

At least 19 recordsLinked to original sources
PubMed2002

Magnetization-direction-dependent local electronic structure probed by scanning tunneling spectroscopy.

Scanning tunneling spectroscopy (STS) of thin Fe films on W(110) shows that the electronic structure of domains and domain walls is different. This experimental result is explained on the basis of first-principles calculations. A detailed analysis reveals that the spin-orbit induced mixing between minority d(xy+xz) and minority d(z(2)) spin states depends on the magnetization direction and changes the local density of states in the vacuum detectable by STS. As a consequence nanometer-scale magnetic structure information is obtained even by using nonmagnetic probe tips.

Journal Article↗
PubMed2002

Direct observation of internal spin structure of magnetic vortex cores.

Thin film nanoscale elements with a curling magnetic structure (vortex) are a promising candidate for future nonvolatile data storage devices. Their properties are strongly influenced by the spin structure in the vortex core. We have used spin-polarized scanning tunneling microscopy on nanoscale iron islands to probe for the first time the internal spin structure of magnetic vortex cores. Using tips coated with a layer of antiferromagnetic chromium, we obtained images of the curling in-plane magnetization around and of the out-of-plane magnetization inside the core region. The experimental data are compared with micromagnetic simulations. The results confirm theoretical predictions that the size and the shape of the vortex core as well as its magnetic field dependence are governed by only two material parameters, the exchange stiffness and the saturation magnetization that determines the stray field energy.

Journal Article↗
PubMed2002

Spin-polarized scanning tunneling microscopy with antiferromagnetic probe tips.

We have performed low temperature spin-polarized scanning tunneling microscopy (SP-STM) of two monolayers Fe on W(110) using tungsten tips coated with different magnetic materials. We observe stripe domains with a magnetic period of 50 +/- 5 nm. Employing Cr as a coating material we recorded SP-STM images with an antiferromagnetic probe tip. The advantage of its vanishing dipole field is most apparent in external magnetic fields. This new approach resolves the problem of the disturbing influence of a ferromagnetic tip in the investigation of soft magnetic materials and superparamagnetic particles.

Journal Article↗
PubMed2001

Atomic-scale magnetic domain walls in quasi-one-dimensional Fe nanostripes.

Fe nanostripes on W(110) are investigated by Kerr magnetometry and spin-polarized scanning tunneling microscopy (SP-STM). An Arrhenius law is observed for the temperature dependent magnetic susceptibility indicating a one-dimensional magnetic behavior. The activation energy for creating antiparallel spin blocks indicates extremely narrow domain walls with a width on a length scale of the lattice constant. This is confirmed by imaging the domain wall by SP-STM. This information allows the quantification of the exchange stiffness and the anisotropy constant.

Journal Article↗
PubMed2001

Observation of magnetic hysteresis at the nanometer scale by spin-polarized scanning tunneling spectroscopy.

Using spin-polarized scanning tunneling microscopy in an external magnetic field, we have observed magnetic hysteresis on a nanometer scale in an ultrathin ferromagnetic film. An array of iron nanowires, being two atomic layers thick, was grown on a stepped tungsten (110) substrate. The microscopic sources of hysteresis in this system-domain wall motion, domain creation, and annihilation-were observed with nanometer spatial resolution. A residual domain 6.5 nanometers by 5 nanometers in size has been found which is inherently stable in saturation fields. Its stability is the consequence of a 360 degrees spin rotation. With magnetic memory bit sizes approaching the superparamagnetic limit with sub-10 nanometer characteristic lengths, the understanding of the basic physical phenomena at this scale is of fundamental importance.

Journal Article↗
PubMed2001

Experimental evidence for intra-atomic noncollinear magnetism at thin film probe tips.

The energy-dependent spin-density orientation (SDO) at the apex of thin magnetic film tips is studied by spin-polarized scanning tunneling spectroscopy (SP-STS) at different bias voltages. At most energies the SDO is collinear with the tip magnetization resulting in a domain or domain-wall contrast in SP-STS images of out-of-plane magnetized samples measured with Gd or Fe coated tips, respectively. For some bias voltages, however, the SDO of the tip is found to be almost perpendicular to its magnetization. This result is explained in terms of intra-atomic noncollinear magnetism.

Journal Article↗
PubMed2000

Topology-induced spin frustrations at the Cr(001) surface studied by spin-polarized scanning tunneling spectroscopy

The magnetic structure of the Cr(001) surface was investigated by spin-polarized scanning tunneling spectroscopy by making use of the spin-polarized surface state located close to the Fermi level. Periodic alternations of the intensity of the surface state peak in local tunneling spectra measured above different ferromagnetic terraces separated by monatomic steps confirm the topological antiferromagnetic order of the Cr(001) surface. Screw dislocations cause topology-induced spin frustration, leading to the formation of domain walls with a width of about 120 nm.

Journal Article↗
PubMed2000

Real-space imaging of two-dimensional antiferromagnetism on the atomic scale

A two-dimensional antiferromagnetic structure within a pseudomorphic monolayer film of chemically identical manganese atoms on tungsten(110) was observed with atomic resolution by spin-polarized scanning tunneling microscopy at 16 kelvin. A magnetic superstructure changes the translational symmetry of the surface lattice with respect to the chemical unit cell. It is shown, with the aid of first-principles calculations, that as a result of this, spin-polarized tunneling electrons give rise to an image corresponding to the magnetic superstructure and not to the chemical unit cell. These investigations demonstrate a powerful technique for the understanding of complicated magnetic configurations of nanomagnets and thin films engineered from ferromagnetic and antiferromagnetic materials used for magnetoelectronics.

Journal Article↗
PubMed2000

Real-space observation of dipolar antiferromagnetism in magnetic nanowires by spin-polarized scanning tunneling spectroscopy

We have performed spin-polarized scanning tunneling spectroscopy of dipolar antiferromagnetically coupled Fe nanowires with a height of two atomic layers and an average separation of 8 nm grown on stepped W(110). Domain walls within the nanowires exhibit a significantly reduced width when pinned at structural constrictions. The lateral spin reorientation in the direction perpendicular to the wires has been studied with subnanometer spatial resolution. It is found that the spin canting in the Fe nanowires monotonously increases towards the step edges.

Journal Article↗
PubMed2000

Traveling pairs of spots in a periodically driven gas discharge system: collective motion caused by interaction

We report on a new type of interaction between solitary current density spots observed in an ac-driven gas discharge system. These spots behave as independent particles as long as they are far apart from each other. Upon collision, in most cases one of the spots is extinguished. However, we also observe the formation of stable bound pairs of spots that move rather fast. We argue that both the rapid motion and the binding itself are due to a pronounced symmetry breaking with respect to size and breakdown phase of the individual spots. Basic features of pairs of spots traveling due to a true two-spot mechanism are discussed.

Journal Article↗
PubMed2000

Secretion and differential localization of the proteolytic cleavage products Abeta40 and Abeta42 of the Alzheimer amyloid precursor protein in human fetal myogenic cells.

Abeta peptides are major components of the amyloid plaques that characterize Alzheimer's disease. These peptides are proteolytic cleavage products of the amyloid precursor protein (APP) and are generated by beta- and gamma-secretases. Here we show by multiparameter immunofluorescence imaging in muscle cells that localization of the Abeta40 and Abeta42 cleavage products reveals different myocyte types in a three-dimensional culture system. These myocyte types are heterogeneous by selective intracellular concentration of either Abeta40 or Abeta42 in vesicular structures, whilst only the Abeta40 peptide is secreted as indicated by Western blot analysis. This cellular pattern of APP proteolysis and Abeta peptide secretion correlates with lack of L-APP mRNA splice isoforms. Differential secretion and intracellular accumulation of Abeta peptides is characteristic for the early myocyte development and might be related to cell fusion.

Amyloid Precursor Protein Secretases↗
PubMed1998

[Alcoholism in the elderly. A review of diagnosis, therapy and psychological effects].

Alcohol abuse and alcohol dependence are frequent disorders in the elderly. The disorders often develop as a response to burdensome life events which have to be treated specifically. Old alcoholics often respond well to age-specific interventions, if co-existing depressive symptoms are also treated. Because of the non-specific nature of the initial symptoms, the majority of the elderly alcoholics remain unrecognised during the diagnostic process. This review, therefore, gives a synopsis of clinical clues to alcoholism and associated psychic complications in elderly patients. Psychic complications in persistent alcoholism include Wernicke-Korsakow's syndrome, symptom patterns of delusions and hallucinations and specific types of organic brain syndromes.

Aged↗
PubMed1994

Differences in P3 amplitudes between schizophrenics and healthy controls vary between the different events presented in a guessing task.

P3 amplitudes were often found to be reduced in schizophrenics, but in varying degree. We studied in a guessing task whether variations of group differences could even be obtained within the same task, by measuring P3 in the potentials evoked by the three qualitatively different events that occurred in each trial. We hypothesized that such variations were due to variations of subjective task relevance associated with each event. In each trial, a light or a sound was presented. Subjects had to confirm this 'primary event' by a delayed response, and then the current amount of money earned by correct responses was displayed. In the certain condition, the primary event was preceded by the appropriate cue on the screen ('light' or 'sound') whereas in the uncertain condition, the word 'guess' appeared. The task-relevance hypothesis predicted that schizophrenics would have smaller P3s than the control group with the primary event in the uncertain condition, but that the groups would not differ for the P3s evoked by the other events (certain primary event, cue and earnings display in uncertain and certain conditions). Essentially, this predicted pattern of results was obtained, but additional assumptions are needed for the task-relevance hypothesis to account for the precise pattern of results. Analysis of subjects' guessing behavior showed that control subjects' guesses were affected by the outcome of their preceding guesses while schizophrenics' guesses were not. This result provides some additional support for the hypothesis that the guessing task is less relevant to schizophrenics than to control subjects.

Adult↗