Effective Magnetic Field Dependence of the Flux Pinning Energy in FeSe0.5Te0.5 Superconductor

The role of a layered structure in superconducting pinning properties is still at a debate. The effects of the vortex shape, which can assume for example a staircase form, could influence the interplay with extrinsic pinning coming from the specific defects of the material, thus inducing an effective magnetic field dependence. To enlighten this role, we analysed the angular dependence of flux pinning energy U(H,θ) as a function of magnetic field in FeSe0.5Te0.5 thin film by considering the field components along the ab-plane of the crystal structure and the c-axis direction. U(H,θ) has been evaluated from magneto-resistivity measurements acquired at different orientations between the applied field up to 16 T and FeSe0.5Te0.5 thin films grown on a CaF2 substrate. We observed that the U(H,θ) shows an anisotropic trend as a function of both the intensity and the direction of the applied field. Such a behaviour can be correlated to the presence of extended defects elongated in the ab-planes, thus mimicking a layered superconductor, as we observed in the microstructure of the compound. The comparison of FeSe0.5Te0.5 with other superconducting materials provides a more general understanding on the flux pinning energy in layered superconductors.

A microscopic study of spin-polarized neutron matter

In this work, the static fluctuation approximation (SFA) is used to investigate the thermodynamic properties of spin-polarized neutron matter. The energy per particle, pressure, entropy per particle, specific heat capacity, and effective magnetic field are studied as functions of density, temperature, and polarization fraction. The Argonne v18 nucleon–nucleon potential is used here. It is found that the energy per particle, pressure, entropy per particle, and effective magnetic field increase as the density or temperature increases. Also, the energy per particle and pressure are linearly dependent on the quadratic spin polarization δ2. The system becomes more ordered as δ increases. Our calculations are found to be in good agreement with previously published results obtained with different many-body techniques, such as the lowest order constrained variational (LOCV) method, the Brueckner–Hartree–Fock (BHF) approach, and the Dirac–Brueckner–Hartree–Fock (DBHF) technique.

Size effects in ultrafine iron. New structures: 2D - 3D

This article is devoted to the analysis of the size of iron nanoparticles impact on the structure, to comparison of the results obtained for the nanopowders in the various authors’ researches. The article considers factors that may impact on the form and parameters of the Mössbauer spectra of iron nanopowders obtained by the inert gas condensation technique (Gen-Miller’s method). Possible causes of the new state of the iron are proved with the effective magnetic field at the 57 Fe nucleus (H=365 kOe). But the results related to size effects differ from the researches of other authors. It was revealed that nanoparticles with a mean (X-ray data) particle size of 50 nm have also Angstrem patterns, which can meet the new structure. Presence of small amounts of superparamagnetic oxide could be a catalyst, impetus for the formation of the new structure, and also, at the exchange interactions, could modify the charge of the electron density at the Fe nuclei. Reviewed and other factors can result in appearing of such a high value of the effective magnetic field at the iron nuclei.