Correlation between superconductivity and ferromagnetism for nano-sized particle-dispersion-controlled thin films

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The purpose of this study is to investigate the influence of magnetic particles dispersed in superconducting matrix with nano-scale or ferromagnetic thin films touched by superconducting thin films to the superconductivity, that is, to investigate the correlation between superconductivity and ferromagnetism. To do so, we have added the consideration for the three systems made by sputter deposition as (1) superconductor/ferromagnet multilayer, (2) superconducting thin film dispersed by ferromagnetic particles in it, and (3) superconductor/non-magnetic material (including another type superconductor) multilayers. The main results are as follows: (i) We have found the 2-step oscillation phenomenon for Nb/Co and V/Co multilayers. This phenomenon is interpreted by the so-called π-phase theory. (ii) The dispersion system (Nb-matrix with Fe particles dispersed in matrix) shows the Tc degradation accompanied by the increase of Fe particle as obeying the law of the Abrikosov-Gorkov theory. (iii) The behavior of upper critical field and transition temperature observed in the superconductor/superconductor multilayers obeys the proximity-effect-theory.