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Notes: We have investigated the propagation of surface and backward volume spin waves (BVSW) with the in-plane wavevector k(parallel)=10–900 cm−1 excited by microwaves in YIG and Lu2.04Bi0.96Fe5O12 (LBIG) films with the film thicknesses 5 and 1.5 μm, respectively. In all cases the magnetization and k(parallel) were in the film plane. The frequencies of the spin wave excitations as well as the spatial distribution of their intensities in the linear and in the nonlinear excitation regime were measured by means of a fully automated, high-stabilization, small-angle Brillouin light scattering (BLS) setup with a spatial resolution of 30 μm. It is well known1 that in the case of BVSW modes, the Lighthill criterion2 for modulational instability is fulfilled for both the longitudinal and the transverse perturbations of the initially constant-amplitude wave beam. Therefore, this mode is very much suitable for the investigation of the evolution of a plane-front, constant-amplitude initial beam, and for a direct experimental study of two-dimensional nonlinear diffraction effects of the beam leading to self-focusing. The garnet films with in-plane dimensions of 2×10 mm2 were grown by liquid phase epitaxy onto a single crystalline (111)-oriented gallium gadolinium garnet substrate. Two strip antennas, 35 μm wide and situated at the ends of the films, were used for the excitation of the spin waves and for monitoring. The working frequency was 8.10 GHz. Special efforts were taken to minimize the beam divergence due to the finite length of the input antenna. For all nonlinear studies the initial angular beam divergence was not larger than aitch-thetamax=0.05 rad. In the linear regime the attenuation factor was measured, and the reflection of the spin waves from the sample boundaries was studied. We also observed the interference between the two lowest order lateral modes having different initial spatial distributions of the magnetization. The BLS technique was shown to provide a signal to noise ratio exceeding 60 dB. In the nonlinear regime the propagation of the BVSW mode was thoroughly investigated. We have found clear evidence for the self-focusing effect, which exists in a narrow interval of input powers. In these studies overheating of the sample by the microwave power was carefully avoided by using an intermittent source of maximum average power of 100 mW working at a frequency of 4 kHz. That allowed us to claim that the observed focusing of the spin waves was not an artifact caused by sample heating. The distance between the focusing maximum and the antenna was 1.5 mm for LBIG sample and 6 mm for YIG sample. These values are in a good agreement with our theoretical calculations, if one takes into account the thicknesses of the films. For a comparison of the observed values of the width and the length of the focusing spot and their dependence on the microwave power with the theory, more numerical calculations are needed. Our results demonstrate the wide applicability of an advanced combined microwave-BLS technique for a two-dimensional mapping of the spin wave amplitudes in the media. © 1997 American Institute of Physics.

Notes: All contributing magnetic anisotropies in (110)-oriented exchange biased Ni80Fe20/Fe50Mn50 double layers prepared by molecular beam epitaxy on Cu(110) single crystals have been determined by means of Brillouin light scattering. Upon covering the Ni80Fe20 films by Fe50Mn50, a unidirectional anisotropy contribution appears, which is consistent with the measured exchange bias field. The uniaxial and fourfold in-plane anisotropy contributions are largely modified by an amount, which scales with the Ni80Fe20 thickness, indicating an interface effect. The strong uniaxial anisotropy contribution shows an in-plane switching of the easy axis from [11¯0] to [001] with increasing Ni80Fe20-layer thickness. The large mode width of the spin wave excitations, which exceeds the linewidth of uncovered Ni80Fe20 films by a factor of more than six, indicates large spatial variations of the exchange coupling constant. © 1998 American Institute of Physics.

Notes: Short magnetic-field pulses may be used in the near future to change the magnetization state in magnetic storage devices. In order to minimize the time required for this process, and thus to maximize the switching speed of such devices, the magnetization precession after the termination of the magnetic-field pulse needs to be suppressed to a maximum degree. It is demonstrated experimentally that the appropriate adjustment of the field pulse parameters may lead to a full suppression of the magnetization precession immediately upon termination of the field pulse. © 2000 American Institute of Physics.

Notes: We demonstrate that magnetization measurements by Hall probe arrays are well suited for the reel-to-reel determination of critical currents along long lengths of coated conductors. The technique is contact-free, fast, simple, and it has a high spatial resolution. A quantitative measure of the critical current as a function of position was obtained by fitting a simple critical state model to the field distribution. The technique is demonstrated for YBa2Cu3O7 films on single-crystal substrates and then applied to samples of coated conductors. © 2001 American Institute of Physics.

Notes: Static magnetic and spin wave properties of square lattices of permalloy micron dots with thicknesses of 500 and 1000 Å and with varying dot separations have been investigated. A magnetic fourfold anisotropy was found for the lattice with dot diameters of 1 μm and a dot separation of 0.1 μm. The anisotropy is attributed to an anisotropic dipole–dipole interaction between magnetically unsaturated parts of the dots. The anisotropy strength (order of 105 erg/cm3) decreases with increasing in-plane applied magnetic field. © 1997 American Institute of Physics.

Notes: Glial cell line-derived neurotrophic factor (GDNF) protects dopaminergic neurones against toxic and physical damage. In addition, GDNF promotes differentiation and structural integrity of dopaminergic neurones. Here we show that GDNF can support the function of primary dopaminergic neurones by triggering activation of GTP-cyclohydrolase I (GTPCH I), a key enzyme in catecholamine biosynthesis. GDNF stimulation of primary dopaminergic neurones expressing both tyrosine 3-monooxygenase and GTPCH I resulted in a dose-dependent doubling of GTPCH I activity, and a concomitant increase in tetrahydrobiopterin levels whereas tyrosine 3-monooxygenase activity was not altered. Actinomycin D, asan inhibitor of de novo biosynthesis, abolished any GDNF-mediated up-regulation of GTPCH I activity. However, GTPCH I mRNA levels in primary dopaminergic neurones were not altered by GDNF treatment, suggesting that the mode of action for that up-regulation is not directly connected to the regulation of GTPCH I transcription. We conclude that GDNF, in addition to its action in structural differentiation, also promotes differentiation regarding expression and enzymatic activity of a crucial component in the dopaminergic biosynthetic pathway.

Notes: Axon degeneration after disruption of fibre tracts in the mammalian nervous system is accompanied by myelin breakdown which leads to changes in its magnetic resonance properties. In two patients with pure motor strokes due to small ischaemic lesions restricted to the internal capsule, magnetic resonance imaging disclosed a narrow band of pathological signal increase descending band-like into the brain stem and ascending to the precentral gyrus, which corresponded to the well-known path of the pyramidal tract. The findings suggest that in man anterograde and possibly retrograde fibre degeneration can be traced in vivo by conventional magnetic resonance imaging techniques. Critical conditions are the presence of small, strategically located lesions, appropriate choice of imaging plane, and the interval between time of lesion and of imaging. This demonstration may open a new era for functional neuroanatomy of man.

Notes: Although several clinical studies have shown that increased serum concentrations of protein S100B predict ischaemic brain damage after cardiac surgery, S100B may also be released from the heart or other injured tissue. We therefore investigated the correlation between serum S100B levels and those of the specific cardiac marker troponin I in order to assess the cerebral vs. extracerebral origin of S100B. In 64 cardiac surgical patients, serial blood samples were drawn for the measurement of S100B and troponin I before surgery and for seven days after surgery. Neurological function was assessed before with the National Institutes of Health Stroke Scale and the Folstein Mini Mental Test. The data show that a sustained increase in serum S100B levels is associated with neurological dysfunction, as witnessed by a positive correlation between S100B values and the results of the neuropsychological tests. In contrast, the early postoperative increased levels of protein S100B derive from cardiac tissue, as shown by the positive correlation between S100B and cardiac troponin I levels.