V. Kataev

Flux dynamics and avalanches in the 122 pnictide superconductor Ba0.65Na0.35Fe2As2.

In this work we present the results of the bulk magnetization measurements in a superconducting state of single crystals of Ba0.65Na0.35Fe2As2. The isothermal magnetic field (Hxa0∥xa0c axis) dependent magnetization (M) loops exhibit a second peak (SP) or fishtail effect, as well as remarkable flux jumps at low temperatures. The critical current density Jc obtained from the M(H) loops is rather high, of the order of 10(6)xa0Axa0cm(-2). The analysis of the temperature-xa0and field-dependent Jc implies that high Jc is mainly due to collective (weak) pinning of vortices by dense microscopic point defects with some contribution from a strong pinning mechanism. Pronounced magnetic instabilities in terms of flux jumps depend strongly on temperature as well as on the field sweep rate. The field for the first flux jump as calculated from an adiabatic model, however, is much lower than the experimentally observed values, and this enhanced stability is attributed to a flux creep phenomenon. The analysis of field-dependent magnetic relaxation data additionally supports a collective pinning model. The data further suggest that SP in M(H) is likely related to the crossover in creep dynamics from an elastic to a plastic mechanism. We have constructed the vortex phase diagram on the field-temperature plane.In this work we present the results of the bulk magnetization measurements in a superconducting state of single crystals of Ba0.65Na0.35Fe2As2. The isothermal magnetic field (H ||c axis) dependent magnetization (M) loops exhibit a second peak (SP) or ‘fishtail effect’, as well as remarkable flux jumps at low temperatures. The critical current density Jc obtained from the M(H) loops is rather high, of the order of 10 A/cm. The analysis of the temperature and field dependent Jc implies that high Jc is mainly due to collective (weak) pinning of vortices by dense microscopic point defects with some contribution from a strong pinning mechanism. Pronounced magnetic instabilities in terms of flux jumps depend strongly on temperature as well on the field sweep rate. The field for first flux jump as calculated from an adiabatic model, however, is much lower than the experimentally observed values, and this enhanced stability is attributed to a flux creep phenomenon. The analysis of field dependent magnetic relaxation data additionally supports a collective pinning model. The data further suggests that SP in M(H) is likely related to crossover in creep dynamics from elastic to plastic mechanism. We have constructed the vortex phase diagram on field-temperature plane.

Multigap superconductivity in single crystals of Ba0.65Na0.35Fe2As2: A calorimetric investigation

We investigate the electronic properties and the superconducting gap characteristics of a single crystal of hole-doped 122 Fe-pnictide Ba

Quantum electric dipole glass and frustrated magnetism near a critical point in Li2ZrCuO4

_{0.65}

Dzyaloshinsky-Moriya spin canting in the low-temperature tetragonal phase of La2-x-yEuySrxCuO4

Na

Realization of the Nersesyan-Tsvelik model in (NO)[Cu(NO3)3]

_{0.35}

Orthogonal spin arrangement as possible ground state of three dimensional Shastry – Sutherland network in Ba3Cu3In4O12

Fe

Electron spin dynamics of the superconductor CaC 6 probed by ESR

_2

Microwave absorption study of polycrystalline SmO1-xFxFeAs

As

Strong enhancement of spin fluctuations in the low-temperature tetragonal phase of antiferromagnetically ordered La2-x-yEuySrxCuO4

_2

Frustrated magnet Li2ZrCuO4 – paramagnetism meets paraelectricity

by means of specific heat measurements. The specific heat exhibits a pronounced anomaly around the superconducting transition temperature