Head-on domains having saw-tooth wall configurations in Ni/Fe/Co films are discussed in relation to the existing theoretical models. The existence of Ndel tails within such wall structures as previously proposed is supported and discussed with respect to: (a) direct magneto-optic observations and measurements, and (b) a comparison of the predicted saw-tooth amplitude and angles with the observed values.A large number of films were investigated and the wall angles were found to be dependent upon the ratio of the coercivity to anisotropy field, Hc/ffk, as predicted in the Ndel tail model, whilst the saw-tooth amplitude was determined predominantly by the coercivity. Effective wall widths of the order of 100 Km have been observed in 0.14 pm thick 18/17/3 Ni/Fe/Co films.
Thermoreflectance spectra of Pb,_,Ge,Te ( x = 0,0.02,0.03,0.07 and 0.1) have been investigated in the energy range 1.2 to 4.4 eV at temperatures above and below the phase transition temperature. The change of the interband transitions on the G e content x in the cubic phase (300 K) have been obtained. Thermoreflectance spectra in the range of the transition temperature are broad, the structures are not clearly pronounced, which does not give the possibility of following the changes of the band structure in the range of the phase transition. The thermoreflectance spectrum of the rhombohedral Pb, sGeo ,Teat 40 K, well below the transition temperature of the compound, indicates the appearance of three additional structures of M O type. These structures have been attributed to transitions at the critical points along the TW direction of the Brillouin zone.
Gallium arsenide nanowires were synthesized by gallium-assisted molecular beam epitaxy. By varying the growth time, nanowires with diameters ranging from 30 to 160 nm were obtained. Raman spectra of the nanowire ensembles were measured. The small linewidth of the optical phonon modes agree with an excellent crystalline quality. A surface phonon mode was also revealed, as a shoulder at lower frequencies of the longitudinal optical mode. In agreement with the theory, the surface mode shifts to lower wavenumbers when the diameter of the nanowires is decreased or the environment dielectric constant increased.
The room-temperature pressure dependence of the Mossbauer spectra of the iron(ii1) trisdithiocarbamate complexes, Fe[RZdtcIz, where R represents the N,N'-disubstitution with methyl, ethyl. benzyl, n-hexyl and cyclohexyl groups, has been measured between zero and ca. 80 kbar. As expected, the Mossbauer-effect isomer shift decreases slightly with increasing pressure, whereas the quadrupole splitting. the linewidth and the recoil-free fraction increase with increasing pressure. The pressure dependence of the Mossbauer absorption area is modelled by using the Debye theory of lattice vibrations, this analysis being consistent with that of the temperature dependence of the Mossbauer absorption area and also with the mean square displacements of the iron(m) ions, as determined from single-crystal x-ray thermal parameters. The Mossbauer spectra do not show any changes with pressure that can be associated exclusively with changes in the electronic spin state with increasing pressure. We conclude that these compounds are completely low-spin even at small applied pressures of a few kilobars. Experimental techniques required to obtain reproducible Mossbauer spectra at high pressure, through the use of an opposed diamond-anvil cell. are critically evaluated.
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