Fyzikální ústav Akademie věd ČR

Selected results of department 11

Graphene-based nanostructures

Electronic structure of graphene is closely related to the mechanical deformation and interactions with surroundings (i.e. with the supporting substrate). From a general point of view, it is driven by the intrinsic topography of the layer itself. We proposed a unique approach for custom modification of the graphene topography based on shaping of the single-layer graphene using monodisperse magnetic nanoparticles [1, 2].  The full text >>

Temperature dependent Raman spectro-microscopy of graphene

When heating or cooling a crystal, the lattice parameters expand or contract depending on its thermal expansion coefficient (TEC). Also the graphene has a non-negligible TEC and when it is placed on a substrate, the lattice parameters of both the graphene and the substrate change when the sample is heated or cooled. The different TECs of graphene and the substrate results in topographic changes associated with induction or release of the strain.  The full text >>

Intrinsic structure of magnetic nanoparticles and related phenomena

Nanoparticles (NPs) are very often viewed as the bulk-like material and their internal alignment is neglected. The main conjunction of the ideal NP with the corresponding bulk substance is that both are homogeneous within their whole volume, which means that any material parameter is constant within all unit cells of both the bulk and NP.

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Detection of Small Amounts of Residual Metal Catalyst in Carbon Nanotubes (CNTs)

Existence of magnetic alignment in Carbon nanotubes (CNTs) has been theoretically predicted [1, 2], but the existence of localized magnetic moment on carbon atoms has not been experimentally observed yet. The main complication is the presence of residual metal catalyst, which is used in the preparation of CNTs, thus the removal of catalyst and subsequent approval of CNT purity is essential [3].

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Highly anisotropic f-electron magnets

The rare earth (4f) intermetallic compounds with Fe or Co are famous as extremely powerful permanent magnets with exceptionally high uniaxial magneto-crystalline anisotropy. In R2Co17 compounds (R is a rare-earth metal), the strongest interaction is the Co-Co exchange interaction which primarily determines their Curie temperature, TC.  The full text >>

Exchange bias in UO2/Fe3O4 thin films

The exchange interaction through interface of dissimilarly ordered magnetic materials (e.g. an antiferromagnet (AF) in contact with a ferro- or ferrimagnet (F)) gives rise to a characteristic exchange bias (EB) effect [1] (i.e. shifted magnetic hysteresis loop with an enhanced coercivity), which is of fundamental importance for novel hard magnets, recording media, spin valve and tunneling devices.  The full text >>

Fundamental properties of superfluidity: electrical activity of He II studied with second-sound

The electrical activity of superfluid 4He induced by the relative motion of normal and superfluid components has been recently observed. It was induced in two different types of experiments. In a first experiment the electric potential oscillations were generated by a wave of second-sound, the out-of-phase oscillation of the normal and superfluid components. In a second experiment liquid helium was involved in motion by a torsional oscillator whose walls affected the normal component only.  The full text >>

Quantum turbulence: pure superflow through channels

We are studying experimentally the turbulent state of bellows-driven 4He superfluid flows in channels. Turbulence in a superfluid takes the form of a tangle of atomically-thin vortex lines with quantized velocity circulation, which arise as a consequence of the Bose-Einstein condensation of the superfluid [1]. In one project [2-4] we have studied the dependence of the total length of vortex lines, L, with mean flow velocity, v, in conditions of steady-state turbulence.  The full text >>

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