SrZrO3 (SZO) is a material that has lately received much attention due to properties such as high dielectric constant and switching between resistance states. Our interest was the possible use of SZO as a buffer layer on various substrates for the epitaxial growth of ferroelectric thin films. SZO was laser deposited onto SrTiO3 and Si substrates under various deposition conditions. SZO deposited on SrTiO3 substrates presented highly oriented c-axis epitaxial growth, as evidenced by X-ray diffraction data. A dependence of the crystalline properties of the deposited films on the deposition temperature was observed.In depositing SZO directly onto Si substrates, a thin layer of silicon dioxide is formed on the Si, and an amorphous SZO film results.When SZO was deposited on top of YSZ/Si, the silicon dioxide is completely removed from the surface of the silicon substrate, and a-axis growth of good quality SZO films is possible. This result is very important for the subsequent growth of ferroelectric thin films such as SrBi2Ta2O9, which present a large anisotropy in ferroelectric properties, with much better results for a-axis orientation.

Bi2Sr2Ca2Cu3O10+δ HTSC epitaxial thin films with thickness in the order of 6.0 nm were prepared onto (100) aligned SrTiO3 single-crystal substrates by DC sputtering from stoichiometric targets. As-grown samples were characterized by X-ray diffraction, AC-susceptibility and scanning electron microscopy. X-ray diffraction patterns show that all obtained superconducting thin films were c-axis oriented with a Bi-2223 phase. All reflections (except the substrate ones) can be assigned to the (00l) reflections of the film material (h=k=0, l≠0), indicating that the films were grown preferentially with the c-axis normal to the film plane. In order to investigate the crystal quality of these Bi-2223 films, the rocking curves of the (0012) peaks were explored by ω-scans. The rocking curve of the (0012) reflection had a full width at half maximum (FWHM) of 0.30°. This demonstrates that our prepared Bi-2223 thin films have good crystalline quality and high degree of c-axis orientation. The grain size has well known important effects in the magnetic, optical, and electrical properties of metals and alloys. High temperature superconducting thin films, obtained in this work, have nanometer grain size. The mean size of the grains of the samples were determined by X-ray diffraction (XRD) and found to be in the order of 34.8 nm. The superconducting transitions temperature of several Bi-2223 samples is about 103 K. Surface morphology of the films and chemical composition were studied using scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDX).

On the quest for the intrinsic origin of ferromagnetism (FM) in ZnO doped with a few percent transition metal, we show detailed X-ray resonant magnetic reflectivity (XRMR) measurements, performed at the Co L2,3 and the O K edges of pulsed laser deposition (PLD) prepared samples. These samples show ferromagnetism at room temperature (RT) (QUID: about 2μB /Co). But in contrast to the QUID measurements, element specific reflection measurements as a function of angle (θ-2θ scans) and energy (const. qz) do not show any sign of ferromagnetism. Therefore, we can exclude without doubt Co as a possible origin for FM in this system. Our results are in perfect agreement with earlier published XMCD data and strongly support the new proposed grain boundary based model for oxygen vacancies related RT-FM.

YBa2Cu3O7/PrBa2Cu3O7 (YBCO/PBCO) superlattices with a different ratio of the superconducting and insulating layer thicknesses were prepared by high pressure dc sputtering. The vortex-creep activation energy U0 was determined by analyzing the in-plane resistive transition of 200μm wide bridges with the external magnetic field B oriented along the c axis. It was found that U0 is proportional to the thickness of the YBCO layers, and does only weakly depend on the PBCO layer thickness, when the latter exceeds two unit cells. We observed a change in the variation of U0 with the current I in the specimen: U0 exhibits a plateau in the low-I region, then decreases significantly with increasing I. This behaviour is explained in terms of a crossover plastic vortex creep – elastic (collective) creep induced by the transport current.

The temperature T dependence of the normalized magnetization relaxation rate S in optimally doped YBa(2)Cu(3)O(7-delta) films with the external dc magnetic field H oriented along the c axis exhibits the well-known plateau in the intermediate T range, associated with the presence of elastic (collective) vortex creep. The disappearance of the S(T) plateau in the high-H domain (H >= 20 kOe) is not completely understood. We show that in the case of high-temperature superconductors with significant quenched disorder the S(T) plateau is directly related to a crossover in the vortex-creep process generated by the macroscopic currents induced in the sample. In dc magnetization measurements the creep-crossover temperature decreases rapidly with increasing H, reaching the low-T region where the magnetization decay is dominated by micro flux jumps. Consequently, at high H no well-defined elastic-creep domain is present and the S(T) plateau disappears.

The relaxation of the irreversible magnetization of MgB2 bulk samples obtained by electric-field assisted sintering was investigated using the SQUID magnetometry for a magnetic field H up to 50 kOe applied in zero-field-cooling conditions. We observed a crossover plastic creep at high temperatures T-elastic creep at low T, described by H ∝ T−2 in the low T range, which appears to be caused by the macroscopic currents induced in the sample during magnetization measurements. By decreasing T below this line the determined creep exponent rapidly overcomes the widely accepted theoretical values for elastic (collective) pinning. This behaviour can easily be explained through the occurrence of micro flux jumps, leading to a finite magnetization relaxation rate in the low-T limit.

Well-compacted MgB2 specimens with the density higher than 90 % of the theoretical value were obtained by electric-field assisted sintering. This method assures a good grain connectivity, which leads to the appearance of efficient pinning centres at the grain boundaries. We measured the DC magnetization curves and the relaxation of the irreversible magnetization using the SQUID magnetometry for a magnetic field H up to 50 kOe applied in zero-field-cooling conditions. The critical current density is of the order of 1010 A/m(2) at H = 20 kOe and T = 10 K. A crossover plastic creep at high temperatures T - elastic creep at low T described by H proportional to T-2 in the low T - high H domain was observed. This is caused by the macroscopic currents induced in the sample during magnetization measurements. By decreasing T below this line the determined creep exponent rapidly overcomes the widely accepted theoretical values for elastic (collective) pinning. This behaviour can be explained through the occurrence of micro flux jumps, which seem to be responsible for the finite magnetization relaxation rate in the low-T limit. The relaxation of the irreversible magnetization allowed us the precise determination of the characteristic pinning energy barrier.

Zn 0.95 Co 0.05 O thin films have been prepared by pulsed laser deposition at different preparation conditions. By optimizing the deposition parameters we were able to increase the reproducibility of our ferromagnetic films up to 50% as well as the magnetization to 2.3μB∕Co. The ferromagnetic properties could be improved by a special multilayered deposition technique. Investigations of the magnetic and magnetotransport properties showed a clear correlation between the magnetic properties and the deposition conditions as well as a clear dependence between the transport and the magnetic properties. This hints to an intrinsic origin of the ferromagnetism.

The complex AC conductivity of YBaZ(Cu, -,Zn,),O, thin films has been investigated in the frequency range 10 Hz< U < 109 Hz and for temperatures 10 K g T g 300 K . The influence of the substrate material on the complex conductivity is studied in detail. In the normal conducting state no intrinsic frequency dependence of the real part of the conductivity a' could be detected, a finding which excludes a doping-induced localization of the charge carriers in this System. Below T„ a ' (T) reveals a coherencelike peak which has been predicted in the framework of the BCS theory. However, we propose that, in the doped superconductors, it is due to a distribution of T, values. Finally, from the temperature dependence of the imaginary part of the conductivity we deterrnine the T-dependence of the gap.

The bias voltage and magnetization direction dependent differential conductivity dI∕dV(Vbias) of tunneling junctions with the Heusler compound Co2Cr0.6Fe0.4Al (CCFA) was investigated. The junctions contain AlOx tunneling barriers and Co counter electrodes. A pronounced shoulder in the differential conductivity with parallel electrode magnetization and a sign change of the tunneling magnetoresistance at a bias voltage of ≃±500 mV were the most prominent features observed. The measurements are discussed in the framework of band structure related effects and inelastic excitations. X-ray absorption spectroscopy (XAS-TEY) investigations show that the CCFA/Al interface has an increased Fe content compared to the sputter target composition, presumably due to Fe buffer layer interdiffusion.

We determined the Berezinskii-Kosterlitz-Thouless transition temperature T-KT at the superconducting layer level and the mean-field critical temperature T-c0 in oxygen-deficient YBa2Cu3Oy films (y similar to 6.5, 6.55, and 6.65). We used the T dependence of the quasi-two-dimensional I-V exponent for T <= T-KT, and the analysis of the resistive transition in the framework of the Ginzburg-Landau two-dimensional Coulomb gas model for T>T-KT. Both procedures give essentially the same results, with T-c0 remaining in the domain of the electrical resistivity drop.

To perform high precision measurements of the transport anisotropy, epitaxial, a*-oriented thin films of UPd2Al3 have been prepared on LaAlO3 (110) substrates. The critical temperature Tc≈1.75K and the upper critical field Bc2≈3T are comparable to typical bulk values. In contrast to UNi2Al3, we observed only a weak anisotropy in directional resistivity measurements, especially no dependence of the superconducting transition temperature on the direction of the applied current. Hall effect measurements show two characteristic minima at T=16K≈TN and T≈6K, which corresponds to features seen in earlier measurements on c*-oriented films.

Zero-field-cooling dc magnetisation relaxation measurements performed on optimally doped epitaxial YBa2Cu3O7−δ films with the external magnetic field H oriented parallel to the c-axis reveal the ordering of the creeping vortex-system in the low temperature T domain, due to the macroscopic currents induced in the sample. This dynamic ordering manifests itself through the appearance of a maximum in the T variation of the normalised vortex-creep activation energy. The location of this maximum in the H–T plane describes a well-defined current induced order–disorder line. Our results suggest the absence of a static elastic vortex glass in disordered high-temperature superconductors at high H, and the current induced ordering of the vortex-system as a possible origin for the current–voltage characteristic scaling in terms of an elastic vortex glass–vortex liquid transition.

An incorrect version of figure 3 was included in the published article. The detail should be rotated by 45° as in the corrected figure below. This new image also shows more detail than the previously published one, and is in colour in the online edition.

Epitaxial thin films of the highly spin polarized Heusler compound Co2Cr0.6Fe0.4Al are deposited by DC magnetron sputtering. It is shown by XRD and TEM investigations how the use of an Fe buffer layer on MgO(100) substrates supports the growth of highly ordered Co2Cr0.6Fe0.4Al at low deposition temperatures. The as-grown samples show a relatively large ordered magnetic moment of μ≃3.0μB/f.u. providing evidence for a low level of disorder.

We report the deposition of thin Co_2FeSi films by RF magnetron sputtering. Epitaxial (100)-oriented and L2_1 ordered growth is observed for films grown on MgO(100) substrates. (110)-oriented films on Al_2O_3(110) show several epitaxial domains in the film plane. Investigation of the magnetic properties reveals a saturation magnetization of 5.0 mu_B/f.u. at low temperatures. The temperature dependence of the resistivity rho_xx(T) exhibits a crossover from a T^3.5 law at T<50K to a T^1.65 behaviour at elevated temperatures. rho_xx(H) shows a small anisotropic magnetoresistive effect. A weak dependence of the normal Hall effect on the external magnetic field indicates the compensation of electron and hole like contributions at the Fermi surface.

In-plane zero-magnetic-field current–voltage (I–V) characteristics of oxygen-deficient YBa2Cu3O7−δ films (7−δ∼6.5, 6.55, and 6.65) were thoroughly investigated. A good agreement with the quasi two-dimensional (2D) vortex–antivortex unbinding scenario was observed, similar to the behaviour of highly anisotropic Bi2Sr2CaCu2O8+δ films. The temperature variation of the I–V exponent allows the determination of the Berezinskii–Kosterlitz–Thouless transition temperature TKT at the superconducting Cu–O layer level, and the mean-field critical temperature Tc0. We found that both TKT and Tc0 increase with increasing doping, and Tc0 remains in the region of the electrical resistivity drop. These results do not support the vortex fluctuation scenario for the superconducting transition in underdoped cuprates.