Inter-granular effects at high magnetic fields of cuprate and iron chalcogenide superconducting materials

The weak links effects are one of the main challenges for effective power applications of high temperature superconducting materials. Studies of these effects help for their better understanding and subsequent improvement. An overview analysis of the intergranular properties of cuprate (Y0.8Ca0.2Ba2Cu3O7-δ) and iron-based chalcogenide (FeSe0.5Te0.5) polycrystalline samples was carried out, by means of series of electro-transport experiments at different magnetic fields. The temperature evolution of the Josephson coupling and intrinsic superconductivity effects for the both systems was constructed. The FeSe0.5Te0.5 compound shows very stable and superior behavior compared to Y0.8Ca0.2BCO up to the highest magnetic fields (14T) used. We have explored FeSe0.5Te0.5 Josephson weak links influence (as a non-linear process) over the resistive transition using different AC current amplitudes and applying the sensitive AC transport third harmonics technique

Magneto-Optical and Multiferroic Properties of Transition-Metal (Fe, Co, or Ni)-Doped ZnO Layers Deposited by ALD

ZnO doped with transition metals (Co, Fe, or Ni) that have non-compensated electron spins attracts particular interest as it can induce various magnetic phenomena and behaviors. The advanced atomic layer deposition (ALD) technique makes it possible to obtain very thin layers of doped ZnO with controllable thicknesses and compositions that are compatible with the main microelectronic technologies, which further boosts the interest. The present study provides an extended analysis of the magneto optical MO Kerr effect and the dielectric properties of (Co, Fe, or Ni)-doped ZnO films prepared by ALD. The structural, magneto optical, and dielectric properties were considered in relation to the technological details of the ALD process and the corresponding dopant effects. All doped samples show a strong MO Kerr behavior with a substantial magnetization response and very high values of the Kerr polarization angle, especially in the case of ZnO/Fe. In addition, the results give evidence that Fe-doped ZnO also demonstrates a ferroelectric behavior. In this context, the observed rich and versatile physical nature and functionality open up new prospects for the application of these nanostructured materials in advanced electronic, spintronic, and optical devices

Harmonic AC magnetic susceptibility analysis of FeSe crystals with composite morphology

The AC magnetic response of multi-domain FeSe crystals has been explored by means of fundamental and third harmonic AC magnetic susceptibility (ACMS) analysis. Our previous studies have revealed a complex morphology which especially modifies the mixed state properties. The effects were expressed by an additional ‘pseudo’ peak feature of the magnetic hysteresis and in the present study we analyze its vortex dynamics nature and irreversibility behavior in the context of ACMS.We find that the effect is detectable mainly with the sensitive third harmonic component and especially at high AC field frequencies. From the analysis, the temperature dependence of the ‘pseudo’ peak effect at different DC fields ranges was determined, confirming the previously established superconductor–normal metal–superconductor type links between the domains in the crystal. The irreversibility line, the most important parameter for high power applications, shows a typical glass/liquid transition in the vortex matter. In addition we have observed surface barrier effects and vortex avalanche activity, the behavior of which appears to be influenced by the superconducting and magnetic nature coexistence and morphology. The presented results show the effective application of the harmonic AC magnetic susceptibility technique for a versatile analysis of complex nonlinear phenomena in materials with a sophisticated AC magnetic response

Mixed state properties of iron based Fe(Se,Te) superconductor fabricated by Bridgman and by self-flux methods

The superconducting and transport properties of iron based Fe(Se,Te) superconductors fabricated by means of Bridgman (B) and Self-flux (S) methods have been compared using dc Magnetization (M) measurements as a function of temperature (T) and magnetic field (H). The M(T) measurements performed in Zero Field Cooling-Field Cooling conditions show higher critical temperature Tcand a lower spurious magnetic background signal for the sample (B) rather than the (S) one. By considering the superconducting M(H) hysteresis loops, the sample (B) shows a stronger superconducting signal together with the presence of a peak effect. The field and temperature dependence of the critical current densities Jcare extracted from the superconducting hysteresis loops M(H) within the Bean critical state model, and the high ratio between the J c B and the J c S, relative to the two typologies of samples, together with the comparison between their upper critical field Hc2, points out that the Bridgman method is most attractive for exploiting superconducting and transport properties in view of applications