The electromagnetic response of a superconducting ferromagnets

The electromagnetic response of the superconducting ferromagnets RuSr₂Gd₁.₅Ce₀.₅Cu₂O₁₀ (Ru–1222 Gd) in an ac magnetic field of finite amplitude is investigated. Taking into account weak links between granules and magnetization of the magnetic sublattice, it is shown that the response of a sample in a superconducting state with the fundamental frequency and frequency of the 3rd harmonic can be described by the nonlinear equation for the macroscopic field. Generation of the harmonic at temperatures above superconducting transition corresponds to Rayleigh`s mechanism. Using various regimes of a sample cooling, the internal magnetic field determined by the magnetic sublattice was measured. This is direct evidence of the coexistence of ferromagnetic and superconductive order parameters in high-Tc ruthenocuprates

AC conductivity of a niobium thin film in a swept magnetic field

We report the results of the measurement the ac conductivity of a Nb superconducting thin film in a swept dc magnetic field. In the mixed state the swept dc field creates vortices at the film surface which pass through the film and form the observed ac conductivity. Vortex rate generation does not depend on the value of the dc field and there is a large plateau-like region of dc magnetic fields where the dissipation is approximately constant. A proposed phenomenological model describes quite well the main features of the ac response in these fields including its dependency on the sweep rate, ac amplitude, frequency, and value of the second and third harmonics.Comment: 7 pages and 10 figures; Journal of Physics: Condensed Matter, 201