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Re-entrance superconductivity in nanostructures based on Nb and Cu-Ni – alloy layers


Author: Morari Roman
Degree:doctor of physics and mathematics
Speciality: 01.04.07 - Condensed matter physics
Year:2012
Scientific adviser: Anatolie Sidorenko
doctor habilitat, professor, Institute of the Electronic Engineering and Nanotechnologies
Institution: Institute of the Electronic Engineering and Nanotechnologies
Scientific council: DH 24-01.04.07-27.03.08
Institute of the Electronic Engineering and Nanotechnologies

Status

The thesis was presented on the 6 February, 2012
Approved by NCAA on the 5 April, 2012

Abstract

Adobe PDF document – 0.88 Mb / in romanian
Adobe PDF document – 0.76 Mb / in russian

Keywords

superconductor, thin films, the critical temperature, oscillations, LOFF-like state, spintronics

Summary

Dissertation contents:introduction, four chapters, general conclusions and recommendations, bibliography – 116 references. The work contains 129 pages of the main part, 4 tables and 58 figures.

Number of publications:the obtained results are presented in 43 scientific papers and one patent

Field of research: superconductivity in hybrid structures, spintronics.

The aim of the work: Establishment of conditions for reproducible manifestation of oscillations of the critical temperature and the re-entrance effect of superconductivity in layered structures superconductor-ferromagnet as a function of the thickness of the ferromagnetic layer; examination of the superconducting properties of single films of Niobium, and bi-layer structures of Niobium/Copper-Nickel; elaboration of practical recommendations for application of the obtained results for the development of superconducting spintronic devices.

The scientific originality of the research consists in: An original vacuum technology is developed for preparation of high quality nanostructures “superconductor/ferromagnet”, which allows to produce a series of superconducting structures with variable thickness of the films and strictly identical and controllable parameters in a single cycle of deposition; a double re-entrance of the superconductivity was primary observed on the bi-layered structures with constant thickness of superconducting Niobium layer and variable thickness of Copper-Nickel ferromagnetic alloy layer.

In frame of this work the main scientific and technical problem was resolved: for the first time a multiperiod reentrance superconducting behavior of multi structures based on Niobium and Cupper-Nickel alloy was observed and studied. The structures was produced using a special developed vacuum technology of magnetron sputtering, which can be exploited for reproducing of the necessary structures.

The practical importance of the research consists in: An original vacuum technology is developed for preparation of high quality nanostructures “superconductor/ferromagnet”, which can be used for producing of superconducting devices; passivation technological process is elaborated for a long-term stability of parameters of the fabricated nano-elements for superconducting spintronics.