First-order Raman spectra of hydrogenated nanocrystalline silicon (nc:Si:H) films show unexpected features in their optical vibrational modes for crystallites with sizes ranging from 2 to 6 nm. Two size-dependent spectral regions, one with the stronger intensity peaking at 505–509 cm−1 and another a shoulder-like band between 512 and 517 cm−1, are clearly identified using a detailed line-shape analysis and the strong phonon confinement model. The strong size dependence of the relative integrated intensities of the two bands suggests that the modification of the vibrational spectra can be attributed to an effect induced by the atomic vibrations from the near-surface region of the nanocrystals.
We report on the experimental and theoretical studies of cooling field (HFC) and temperature (T) dependent exchange bias (EB) in FexAu1 − x/Fe19Ni81 spin glass (SG)/ferromagnet (FM) bilayers. When x varies from 8% to 14% in the FexAu1 − x SG alloys, with increasing T, a sign-changeable exchange bias field (HE) together with a unimodal distribution of coercivity (HC) are observed. Significantly, increasing in the magnitude of HFC reduces (increases) the value of HE in the negative (positive) region, resulting in the entire HE ∼ T curve to move leftwards and upwards. In the meanwhile, HFC variation has weak effects on HC. By Monte Carlo simulation using a SG/FM vector model, we are able to reproduce such HE dependences on T and HFC for the SG/FM system. Thus this work reveals that the SG/FM bilayer system containing intimately coupled interface, instead of a single SG layer, is responsible for the novel EB properties.
Giant magnetoresistance (GMR) and tunnel magnetoresistance (TMR) were studied in spin valves of FeCo∕Cu∕(FeCo)1−xGdx and magnetic tunnel junctions of FeCo∕AlO∕(FeCo)1−xGdx, respectively. When the FeCoGd layer is thick enough, both GMR and TMR ratios change their signs from positive to negative at the compensation composition with 0.293⩽x0⩽0.337 as the Gd content is increased. This scenario is originated from a competition of rare-earth and transition-metal spins in FeCoGd layers with antiferromagnetic coupling. Accordingly, it is deduced that in the FeCoGd layer the spin polarizations PN of electrons at the Fermi level and tunneling spin polarization PTSP are negative and positive for x<x0, respectively, and vice versa for x>x0.
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