Fyzikální ústav Akademie věd ČR

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Selected results of department 11

The extensive study of the magnetic systems appropriate for use in medicine, in particular for the magnetic hyperthermia, has been devoted especially to nanoparticles of CoFe2O4. Annealing of the nanoparticle powder at temperatures of 400-800 °C resulted in the average particle size of 18 to 40 nm. By Mössbauer spectroscopy of the 57Fe isotope enabled to determine the distribution of Fe ions between tetrahedral and octahedral positions. Based on these data the inversion degree of the spinel lattice was determined.  The full text >>

The thermally activated quantum turbulence in He II has been studied, in a canal with superfluid holes not allowing the normal component of a finite viscosity to flow through. Thus, the turbulence in the canal was generated by a longitudinal flow of the pure superfluid component. Besides the already in literature described stationary state of the flow, we discovered a new turbulent state in which the density of quantum vortices is proportional to the transport superfluid velocity, with a parabolic velocity profile like in a classical viscous liquid flow.  The full text >>

The ferromagnetic layout in solid solutions of Lu2Fe17-xSix in homogeneity range (x ≤ 3.4) is accompanied by a giant volume magnetostriction, anisotropic with respect to principal axes of the hexagonal crystallographic structure. The volume effect in the ground state of Lu2Fe17 reaches 1.5% and decays monotonously to 0.9% for x = 3.4, together with the magnetic moment decrease with increasing x. The compounds with x < 2 exhibit invar behavior in a broad temperature range, including room temperature.  The full text >>

We have participated in study of electromagnetic properties of topic bulk high-Tc superconductors of the (Nd,Eu,Gd)BaCuO composition in which a tiny doping by Nb, Mo or Ti oxides leads to a substantial critical current density enhancement. In the composite doped by Nb2O5 the critical current density, Jc, reached the record values of 925 kA/cm2 (65 K), both in the remnant state and at 4.5 T, and 100 kA/cm2 at the self-field at 90 K [1].  The full text >>

We discovered that in thin amorphous tapes with an extremely low magnetostriction, annealed under mechanical pension, it is possible to reach enormously high level of non-diagonal magnetoimpedance with nearly linear dependence on the applied magnetic field [L. Kraus: J. Magn. Magn. Mater. 320 (2008) e746, doi:10.1016/j.jmmm.2008.04.043]. This phenomenon was successfully utilized for design of a simple, extremely sensitive, and cheap magnetic field sensor [M. Malátek, L.  The full text >>

The developed technique is based on the idea of optimization of earlier known magnetic hysteresis methods. Instead of collecting the usable information from measurement of the classical major hysteresis loop and keeping under surveillance dependence of its traditional parameters (coercive force, remanence, and saturation magnetization) on structural variations, MAT gets its test parameters from the complex set of minor hysteresis loops.  The full text >>

The spin and orbital magnetic moment and g-factor of FeSi Heusler alloys were determined experimentally by ferromagnetic resonance (FMR) and SQUID magnetometry and compared with calculations performed by fully relativistic density functional theory. The experimental data are in a good agreement with the theoretical ones. Further on, using FMR, very low intrinsic relaxation constant G data were obtained, of the order of 10 Mrad/s.  The full text >>

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