Pinning potential in highly performant CaKFe4As4 superconductor from DC magnetic relaxation and AC multi-frequency susceptibility studies.

We have investigated the pinning potential of high-quality single crystals of superconducting material CaKFe4As4 having high critical current density and very high upper critical field using both magnetization relaxation measurements and frequency-dependent AC susceptibility. Preliminary studies of the superconducting transition and of the isothermal magnetization loops confirmed the high quality of the samples, while temperature dependence of the AC susceptibility in high magnetic fields show absolutely no dependence on the cooling conditions, hence, no magnetic history. From magnetization relaxation measurements were extracted the values of the normalized pinning potential U*, which reveals a clear crossover between elastic creep and plastic creep. The extremely high values of U*, up to 1200 K around the temperature of 20 K lead to a nearly zero value of the probability of thermally-activated flux jumps at temperatures of interest for high-field applications. The values of the creep exponents in the two creep regimes resulted from the analysis of the magnetization relaxation data are in complete agreement with theoretical models. Pinning potentials were also estimated, near the critical temperature, from AC susceptibility measurements, their values being close to those resulted (at the same temperature and DC field) from the magnetization relaxation data.

A precursor mechanism triggering the second magnetization peak phenomenon in superconducting materials.

The correlation in type-II superconductors between the creep rate S and the Second Magnetization Peak (SMP) phenomenon which produces an increase in Jc, as a function of the field (H), has been investigated at different temperatures by starting from the minimum in S(H) and the onset of the SMP phenomenon detected on a FeSe0.5Te0.5 sample. Then the analysis has been extended by considering the entire S(H) curves and comparing our results with those of many other superconducting materials reported in literature. In this way, we find evidence that the flux dynamic mechanisms behind the appearance of the SMP phenomenon in Jc(H) are activated at fields well below those where the critical current starts effectively to increase. Moreover, the found universal relation between the minimum in the S(H) and the SMP phenomenon in Jc(H) shows that both can be attributed to a sequential crossover between a less effective pinning (losing its effectiveness at low fields) to a more effective pinning (still acting at high fields), regardless of the type-II superconductor taken into consideration.

Pinning energy and anisotropy properties of a Fe(Se, Te) iron based superconductor.

The measurements of DC magnetization M as a function of magnetic field (H) and time (t) have been performed in order to study the superconducting and pinning properties of a Fe(Se, Te) iron based superconductor fabricated by means of the Bridgman technique. By performing the superconducting hysteresis loops M(H) at different temperatures in the case of perpendicular and parallel field, the critical current density Jc (H) has been extracted in the framework of the Bean critical state model for both configurations. The Jc (H) curves have shown the presence of the second magnetization peak effect that causes an anomalous increase in the field dependence of the critical current density. In order to obtain the Jc anisotropy of the sample, we have performed the ratio between perpendicular and parallel critical current density values [Formula: see text] and compared its values with the literature ones. The information regarding the pinning energy U have been extracted by means of the relaxation of the irreversible magnetization M(t) in the case H∣∣c. In particular, performing relaxation measurements at different temperatures and magnetic fields, the temperature dependence of the pinning energy U(T) at different magnetic fields has been obtained showing an anomalous temperature scaling of the curves. The presence of a maximum in the U(T) curves suggests a pinning crossover at a given field and temperature H cr(T). The H cr(T) values have been fitted with the equation H cr(T) = H cr(0) (1 - T/T*) n whose results confirm the correlation between the elastic/plastic crossover and the end of the peak effect phenomenon.

Demagnetization harmonic effects on the magnetization of granular systems on a macroscopic scale: the superconducting case.

A model has been developed to determine the effective ac magnetic response of magnetic systems, taking into account the demagnetization effects arising from the sample geometry which determine the out-of-phase components of the applied fundamental frequency and higher harmonic components. Indeed, demagnetization fields and their intermodulation can significantly affect the ac magnetic response. This approach provides a system of self-consistent linear equations relating the magnetic response to the external magnetic field by means of nonlinear magnetic susceptibility. The model is extended to the magnetic response of granular systems in terms of the contributions of the individual grains and of the whole sample in the presence of demagnetization effects of the whole sample and of the grains on a macroscopic scale. In particular, our model is applied to a granular superconducting system. The comparison between the performed numerical simulations and the experimental data shows that the demagnetization fields of the single grains and of the whole sample, and their intermodulation, are relevant if magnetic measurements are used to extract detailed information about the analyzed material.

Routine use of external cephalic version in three hospitals.

BACKGROUND: External cephalic version has been advocated as a safe alternative to vaginal breech delivery or cesarean birth. The purpose of this study was to determine the efficacy of routine use of external cephalic version at 36 weeks or more of gestation in three different levels of hospitals. METHODS: External cephalic version was performed on 923 women with a single breech fetus at three hospitals in Italy. The procedure was attempted with a tocolytic agent for uterine relaxation and with no maternal analgesia. The version technique adopted was the "forward roll." RESULTS: Version was successfully performed on 579 fetuses (62.7%); each hospital had a similar success rate, and 56.9 percent of the women delivered vaginally. The procedure was more successful in multiparas and in women with an incomplete type of breech, polyhydramnios, and posterior localization of the placenta. Vaginal bleeding was experienced by 14 women; eight cesarean sections were performed for suspected abruptio placentae, confirmed in four cases. Two cephalic-turned fetuses experienced an episode of persistent bradycardia and were turned again to breech; in five cases a nonstress test recorded after the version showed repeated variable decelerations and in one case a cesarean section was performed. Neonatal outcomes were good in 922 infants. A fracture of the femur attributable to the version was observed in one newborn. CONCLUSIONS: External cephalic version is effective in reducing the number of cesarean deliveries in term breech infants in different obstetric settings, with no major neonatal adverse outcomes.

[Communication between neonatologists and obstetricians]. / La comunicazione fra neonatologi ed ostetrici.

A close communication between obstetricians and neonatologists represents a basic tool for the improvement of newborn care. We shall illustrate what obstetric/neonatological communication tools are applied in our hospital. We believe the cooperation between obstetricians and pediatricians/neonatologists is of great importance for the health of both mother and newborn, thus it should become common practice even in those hospitals where neonatological intensive therapy units do not exist.