Low-field anomaly of vortex dynamics in iron-pnictide superconductors

106

109

Various kinds of energetic particles are irradiated into iron-based superconductors, and their effects on the critical current density (J c ) and vortex dynamics have been systematically studied. It is found that J c is enhanced and vortex dynamics is strongly suppressed by energetic particles having a sufficient energy deposition rate, similar to the case of high temperature cuprate superconductors. The enhancement of J c , in general, persists up to much higher irradiation doses than in cuprates. However, details of the effect of irradiation depend on the kind of ion species and their energies. Even with the same ions and energies, the effect is not universal for different kinds of iron-based superconductors. The correlated nature of defects created by heavy-ion irradiation is confirmed by the angular dependence of irreversible magnetization.

Section: Discussionsupporting

confidence: 80%

Effects of particle irradiations on vortex states in iron-based superconductors

Tamegai¹,

Taen²,

Yagyuda³

et al. 2012

106

109

“…The low-field drop can be observed below H J t * ∼ × , and the minimum of S locates at H = 0 for T = 15 K and 25 K, which is very similar to the low-T behavior in the H + -irradiated Ba(Fe 0.93 Co 0.07 ) 2 As 2 [19,39,49]. At T = 5 K, on the other hand, the behavior is different from that at higher T, and similar to 200-MeV Au-irradiated Ba(Fe 0.93 Co 0.07 ) 2 As 2 at T = 5 K [19,37].…”

supporting

confidence: 68%

“…On the other hand, our creep study in a wide range of H up to 50 kOe clearly shows that the low-H behavior is not typical, as can be seen in figure 3. The anomaly at low H is attributable to the self-field effect; namely, the strong curvature of vortices near the sample edge strongly affects the vortex dynamics such as the suppression of S [10,39,42]. As pointed out in [28], we also notice that the conventional method (interpolation formula and Maley's technique) is not adequate for determining the vortex creep mechanism at the self-field-dominant region.…”

Section: Resultsmentioning

confidence: 81%

See 1 more Smart Citation

Critical current density and vortex dynamics in pristine and proton-irradiated Ba_0.6K_0.4Fe₂As₂

Taen

Ohtake

Pyon

et al. 2015

The screening current density (J) and vortex pinning properties for are studied in optimally hole-doped Ba0.6K0.4Fe2As2 single crystals with a superconducting transition of Tc = 38.6 K. We utilize the irreversible magnetization and its relaxation to evaluate the screening current density and vortex dynamics before and after the introduction of point defects created by 3-MeV proton (H+) irradiation with a dose of /cm2. In the as-grown crystal, both J and vortex dynamics are strongly influenced by temperature and magnetic field, indicating that the predominant pinning is not the weak-collective pinning but the strong pinning. With an introduction of point defects, J in the -irradiated crystal at 2 K reaches A cm−2, which is one of the largest values in iron-based superconductors. In contrast to the as-grown sample, the sensitivity to the temperature and magnetic field becomes quite mild, and the vortex system is described by a simple weak-collective pinning scenario.

“…There are two further remarkable features: (1) J c monotonically decreases in the as-grown sample with increasing magnetic field density; (2) after irradiation, the low field behavior of J c changes and a 'dip' shows up. The magnetic field dependence of J c in the as-grown sample is also accompanied by a puzzling behavior found in relaxation measurements [24,25]. We attribute these phenomena to the anisotropic pinning by as-grown planar defects, relating to the former behavior, and to the presence of defects correlated along the c-axis for the 'dip' feature, as also seen in magnetization experiments with high fluence HEHI irradiation [26].…”

Section: Local Critical Currents Of Irradiated and As-grown Ba(fe Co)...supporting

confidence: 58%

Evidence of anisotropic vortex pinning by intrinsic and irradiation-induced defects in Ba(Fe,Co)₂As₂studied by quantitative magneto-optical imaging

Laviano

Gerbaldo

Ghigo

et al. 2014

Here we present a study of the pinning properties of high-quality single crystals of Ba(Fe 1−x Co x ) 2 As 2 (x = 0.07) by means of the quantitative magneto-optical imaging (MOI). This technique allows us to measure the magnetic field and supercurrent distribution as a function of the applied magnetic field and temperature, thus extracting the local parameters such as the critical current density, without any model assumption. Since values of the local supercurrent are obtained on the micron scale, we are able to observe evidence of anisotropic pinning both of intrinsic defects and extrinsic defects induced by high-energy heavy-ion irradiation. In fact, we find that these crystals naturally show anisotropic pinning due to intrinsic planar defects (whose presence is confirmed by the structural measurements through electron microscopy), and with quantitative MOI analysis we are able to analyze the effects of anisotropy coming from irradiation-induced defects. We quantitatively evaluated the dependence of the critical current density on the magnetic field direction with respect to the lattice principal axes.