arXiv subjects

A. Morawski

Publications and source records attributed to A. Morawski.

5 recordsLinked to original sources

arXiv2014

The high gas pressure HIP influence on structure and transport properties of $MgB_2$ superconductors of single and multicore composition

Superconducting $MgB_2$ wires in Cu, GlidCop or Monel sheath with Nb or Fe barrier are prepared. Wires vary by sheath material, number of superconducting cores and their chemical composition. Wires are HIP-ed (Hot Isostatic Pressing) at various temperatures ($600-800^oC$) and pressure (up to 1.4 GPa). SEM pictures of cross sections are investigated in order to investigate barrier reactivity and cracking, superconducting material density and grain sizes. Transport measurements are made in magnetic field up to 14 T leading to calculations of critical current density $j_c$ and global pinning force $F_p$. Improvement of transport properties due to higher density of superconducting material is shown.

cond-mat.supr-con↗

arXiv2011

Synthesis, Crystal Growth and Epitaxial Layer Deposition of FeSe0.88 Superconductor and Other Poison Materials by Use of High Gas Pressure Trap System

The FeSe samples in the form of polycrystals, single crystals and thin films have been prepared and characterized. The synthesized material has been hot isostatically pressed under pressure of 0.45 GPa of 5N purity argon with the use of the high gas pressure trap system (HGPTS). Thin films have been fabricated by the mixed procedures with the use of DC sputtering from various types of targets and processed employing the HGPTS. The used HGPTS assures a full separation of the active volume for synthesis or crystal growth of material and the inert gas medium. The obtained FeSe0.88 samples have Tc between 8 and 12 K. The samples have been characterized by SEM, EDX, XRD, magnetic susceptibility and resistivity measurements.

cond-mat.supr-con↗

arXiv2006

Magneto-resistive memory in ferromagnetic (Ga,Mn)As nanostructures

We show a novel magneto-resistive effect that appears in lithographically shaped, three-arm nanostructure, fabricated from ferromagnetic (Ga,Mn)As layers. The effect, related to a rearrangement of magnetic domain walls between different pairs of arms in the structure, reveals as a dependence of zero-field resistance on the direction of previously applied magnetic field. This effect could allow designing devices with unique switching and memory properties.

cond-mat.mtrl-sci↗

arXiv2004

Magnetotransport and Domain Wall in Nanoconstriction of Ferromagnetic Semiconductor (Ga,Mn)As

We studied magnetoresistance (MR) of nanoconstrictions created in (Ga,Mn)As epilayers by O+ ion implantation. Original layers exhibit a negative MR that is plausibly caused by weak localization (WL) effects at the lowest temperatures. In constricted samples, additionally, jumps of an enhanced conductance appear on the background of the negative MR, whose positions reflect the hysteresis of magnetization. We argue that they are manifestation of a suppression of WL due to the nucleation of a domain wall in the constriction

cond-mat.mtrl-sci↗

arXiv1999

Superconducting Gap vs. Wave Vector: Evidence for Hot Regions on the Fermi Surface

We have used angular resolved photoemission to measure the angular dependence of the superconducting gap in highly overdoped Bi2212 (Tc=65K). While the node at 45 degrees is conserved, we find substantial deviation from a first order d-wave dependence away from the node. The pairing susceptibility is peaked at special regions on the Fermi surface. Comparing these results with a detailed mapping of the Fermi surface we performed, we could measure the extension and location of these hot regions. We find the hot regions to be evenly spread about the nominal locations of hot spots. The decrease of the gap amplitude away from these hot regions follows very closely theoretical calculations within the spin fluctuation approach. These results strongly suggest that the pairing susceptibility is peaked at Q=(Pi,Pi).

cond-mat.supr-con↗