Evolution of the fishtail-effect in pure and Ag-doped MG-YBCO

We report on magnetic measurements carried out in a textured YBa$_2$Cu$_3$O$_{7-\delta}$ and YBa$_2$(Cu$_{1-x}$Ag$_x$)$_3$O$_{7-\delta}$ (at $x \approx$ 0.02) crystals. The so-called fishtail-effect (FE) or second magnetization peak has been observed in a wide temperature range 0.4~$<T/T_c<$~0.8 for $\textbf{H}\parallel c$. The origin of the FE arises for the competition between surface barrier and bulk pinning. This is confirmed in a non-monotonically behavior of the relaxation rate $R$. The value $H_{max}$ for Ag-doped crystals is larger than for the pure one due to the presence of additional pinning centers, above all on silver atoms.Comment: 6 pages, 6 figure

Glancing angle deposition of sculptured thin metal films at room temperature

Metallic thin films consisting of separated nanostructures are fabricated by evaporative glancing angle deposition at room temperature. The columnar microstructure of the Ti and Cr columns is investigated by high resolution transmission electron microscopy and selective area electron diffraction. The morphology of the sculptured metallic films is studied by scanning electron microscopy. It is found that tilted Ti and Cr columns grow with a single crystalline morphology, while upright Cr columns are polycrystalline. Further, the influence of continuous substrate rotation on the shaping of Al, Ti, Cr and Mo nanostructures is studied with view to surface diffusion and the shadowing effect. It is observed that sculptured metallic thin films deposited without substrate rotation grow faster compared to those grown with continuous substrate rotation. A theoretical model is provided to describe this effec

Glancing angle deposition of sculptured thin metal films at room temperature

Metallic thin films consisting of separated nanostructures are fabricated by evaporative glancing angle deposition at room temperature. The columnar microstructure of the Ti and Cr columns is investigated by high resolution transmission electron microscopy and selective area electron diffraction. The morphology of the sculptured metallic films is studied by scanning electron microscopy. It is found that tilted Ti and Cr columns grow with a single crystalline morphology, while upright Cr columns are polycrystalline. Further, the influence of continuous substrate rotation on the shaping of Al, Ti, Cr and Mo nanostructures is studied with view to surface diffusion and the shadowing effect. It is observed that sculptured metallic thin films deposited without substrate rotation grow faster compared to those grown with continuous substrate rotation. A theoretical model is provided to describe this effect

Effect of Long Aging on the Resistivity Properties of Aluminum Doped YBa2Cu3−y Al y O7−δ Single Crystals with a Given Twin Boundary Topology

We investigate the conducting properties in the basal ab-plane before and after a long time exposure in air atmosphere of aluminum doped YBa2Cu3−y Al y O7−δ single crystals. Prolonged exposure leads to an increase of the effective scattering centers of the normal carriers. The excess conductivity in a wide temperature range has exponential temperature dependence and near the critical temperature (T c ) can be adequately described within the Aslamazov-Larkin theoretical model. Nevertheless, the description of the excess conductivity through the relation Δσ∼(1−T/T∗)exp(Δ∗ab/T), can be interpreted in terms of the mean-field theory, where T ∗ is the mean field temperature of the superconducting transition and the temperature dependence of the pseudo-gap is satisfactorily described by the BEC-BCS crossover theory. It is determined that the prolonged exposure increases significantly the temperature range of the implementation of the pseudogap state, thus narrowing the linear section of the resistivity dependence ρ ab (T)

Ion-irradiation-assisted tuning of phase transformations and physical properties in single crystalline Fe₇Pd₃ ferromagnetic shape memory alloy thin films

Control of multi-martensite phase transformations and physical properties constitute greatly unresolved challenges in Fe7Pd3-based ferromagnetic shape memory alloys. Single crystalline Fe7Pd3 thin films reveal an austenite to martensite phase transformation, continuously ranging from the facecentered cubic (fcc) to the face-centered tetragonal (fct) and body-centered cubic (bcc) phases upon irradiation with 1.8 MeV Kr+ ions. Within the present contribution, we explore this scenario within a comprehensive experimental study: employing atomic force microscopy (AFM) and high resolution transmission electron microscopy (HR-TEM), we first clarify the crystallography of the ionirradiation-induced austenite⇒martensite and inter-martensite transitions, explore the multivariant martensite structures with c-a twinning and unravel a very gradual transition between variants at twin boundaries. Accompanying magnetic properties, addressed locally and globally, are characterized by an increasing saturation magnetization from fcc to bcc, while coercivity and remanence are demonstrated to be governed by magnetocrystalline anisotropy and ion-irradiationinduced defect density, respectively. Based on reversibility of ion-irradiation-induced materials changes due to annealing treatment and a conversion electron Mößbauer spectroscopy (CEMS) study to address changes in order, a quantitative defect-based physical picture of ion-irradiation-induced austenite⇔martensite transformation in Fe7Pd3 is developed. The presented concepts thus pave the way for ion-irradiation-assisted optimization strategies for tailored functional alloys

Modification by high pressure of fluctuation paraconductivity of underdoped HoBa2Cu3O7-δ single crystals

In this work, we investigate the effect of high pressure on the conductivity in the basal plane of the high temperature super conducting (HTSC) single crystals HoBa2Cu3O7-δ. It is determined that the excess conductivity Δσ(T) of the HoBa2Cu3O7- δ single crystals in the temperature interval near the critical temperature (Tc) is described within the framework of the Aslamazov-Larkin theoretical model. It is shown that the evolution of the transverse coherence length ξc(0) in the case of application/removal of high pressure is largely determined by the “relaxation” pressure effect during prolonged exposure of the sample under load at room temperature.The final publication is available at Springer via 10.1007/s10854-016-4797-6Copyright © and Moral Rights are retained by the author(s) and/ or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This item cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder(s). The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders<br/

Ion-irradiation-assisted tuning of phase transformations and physical properties in single crystalline Fe7Pd3ferromagnetic shape memory alloy thin films

Control of multi-martensite phase transformations and physical properties constitute greatly unresolved challenges in Fe7Pd3-based ferromagnetic shape memory alloys. Single crystalline Fe7Pd3 thin films reveal an austenite to martensite phase transformation, continuously ranging from the face-centered cubic (fcc) to the face-centered tetragonal (fct) and body-centered cubic (bcc) phases upon irradiation with 1.8 MeV Kr+ ions. Within the present contribution, we explore this scenario within a comprehensive experimental study: employing atomic force microscopy (AFM) and high resolution transmission electron microscopy (HR-TEM), we first clarify the crystallography of the ion-irradiation-induced austenite $\Rightarrow$ martensite and inter-martensite transitions, explore the multi-variant martensite structures with c-a twinning and unravel a very gradual transition between variants at twin boundaries. Accompanying magnetic properties, addressed locally and globally, are characterized by an increasing saturation magnetization from fcc to bcc, while coercivity and remanence are demonstrated to be governed by magnetocrystalline anisotropy and ion-irradiation-induced defect density, respectively. Based on reversibility of ion-irradiation-induced materials changes due to annealing treatment and a conversion electron Mößbauer spectroscopy (CEMS) study to address changes in order, a quantitative defect-based physical picture of ion-irradiation-induced austenite ⇔ martensite transformation in Fe7Pd3 is developed. The presented concepts thus pave the way for ion-irradiation-assisted optimization strategies for tailored functional alloys