Nanoscale physics

Magneto-optical visualization of the mechano-thermal effect on the pinning structure in the NbTi

V. F. Rusakov1, V. Chabanenko2, O. I. Kuchuk2, O. M. Chumak3,   I. Abaloszewa3, O. Abaloszew3, A. Nabiałek3, and R. Puźniak3

1 National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic    Institute”, Kyiv 03056 Ukraine
 E-mail: vladimir.rusakov26@gmail.com   
2 O. Galkin Donetsk Institute for Physics and Engineering, NAS of Ukraine, Kyiv 03028 Ukraine
3 Institute of Physics, Polish Academy of Sciences, Warsaw 02-668, Poland

The paper considers the effect of magnetic flux pinning centers that arise in the Nb50%Ti superconducting alloy obtained as a result of thermo-mechanical cycling, consisting of a series of material drawing and heat treatment on the front of the magnetic flux penetrating the superconductor in an external magnetic field. A magneto-optical technique was used to determine the structure of the flux front of both the hydroextruded sample, which is determined by the pinning centers that appear during the flow of the material under the action of external pressure during extrusion, and the heat-treated sample. As a result, successive positions of the flux fronts in the samples obtained with different processing methods and different temperatures were plotted. The scaling analysis of the flux profile behind the front using fast Fourier transform method was carried out of the roughness exponent [1] of both the methods of processing the sample and the temperature was studied. It is shown that the depth of flux penetration into the sample after annealing decreased significantly, which indicates an increase in the critical current density, which in turn indicates a change in the pinning structure. The dependence of the roughness exponent on the external field is nonmonotonic. Other features of magnetic field penetration into SC are discussed. 

[1] Michel Geahel, Isabelle Jouanny et.al. Edge Contamination, Bulk Disorder, Flux Front Roughening, and Multiscaling in Type II Superconducting Thin Films // Condens. Matter. – 2017. – 2. – 27.