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

Complex AC Magnetic Susceptibility as a Tool for Exploring Nonlinear Magnetic Phenomena and Pinning Properties in Superconductors

The versatile AC magnetic susceptibility technique offers a detailed insight into the complex electrodynamic phenomena in superconductors. In the present study, we outline the key effects related to the temperature, AC field amplitude and frequency variations of the fundamental and harmonic components for an investigation of the vortex dynamics in a flux-grown FeSe crystal. By means of higher harmonic (nonlinear) analysis, we have explored certain atypical, asymmetric features in the AC magnetic response. These effects were identified through the detection of an even (second) harmonic and an unusual temperature shift in the odd (third) harmonic, possibly due to the complex interactions related to the composite superconducting/magnetic morphology of the crystal. Using the high-frequency sensitivity of the third harmonic, the basic functional dependencies of the pinning activation energy, as the main mixed state parameter, were determined with the implementation of the Kim–Anderson Arrhenius relation in the framework of the collective creep theory

Fundamental and 3-rd harmonic АС magnetic susceptibility of over-doped polycrystalline Y1-xCaxBa2Cu3O7-δ (x=0.025 and x=0.20) samples

The inter-granular vortex dynamics of two polycrystalline samples Y1−xCaxBa2Cu3O7− (x =0.025 and 0.20) with different levels of over-doping is investigated by AC magnetic susceptibility measurements. The temperature dependence of the fundamental and 3-rd harmonic components of AC magnetic susceptibility shows that the sample with higher Ca content and level of over-doping is less influenced by the change of the AC magnetic field amplitude and frequency. The better inter-granular transport properties for sample Y0.80Ca0.20Ba2Cu3O7− are related to the S-N-S type of the inter-granular links. The observed samples’ behavior is compared to the theoretical models of the AC magnetic response of a superconductor. The dynamical processes show a strong effect upon the inter-granular transition for both samples. Finally, a significant temperature misalignment between the imaginary components of the fundamental and 3-rd harmonic AC magnetic susceptibility is observed

Multiferroic single crystals with layered structure in Pb-Mn-Ni-Ti-O system – growth and investigation of their properties

Single crystals in the prospective multiferroic mixed valence ((Mn3+/Mn4+) novel system Pb-Mn-Ni-Ti-O have been grown from high temperature solution. The new material is having a pronounced layered structure, which gives rise to strong anisotropy on its properties. The temperature and frequency dependences of dielectric properties have been investigated. The loss tangent’ abnormal behavior between 180 and 220K along with the measured complex impedance indicate relaxation process, attributed to small polaron hopping. Temperature dependent transport measurements have been performed and the thermal activation energy has been estimated. The multiferroic system Pb3(Mn7-x-yNix,Tiy)O15 have a sophisticated magnetic nature, which has been investigated by means of DC magnetization and linear and non-linear (harmonic) AC magnetic susceptibility. There is a strong anisotropy effect on the magnetic properties and complex evolution from paramagnetic, short-range antiferromagnetic state, followed by global AF ordering at 48K and some indications for spin canted effects and spin reorientation transitions at lower temperatures. The high magnetic field experiments reveal a metamagnetic behavior