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

本研究的目的是研究纳米或铁磁薄膜与超导薄膜接触的超导基质中分散的磁性粒子对超导电性的影响，即研究超导电性与铁磁性之间的关系。为此，我们增加了对溅射沉积的三个系统的考虑：(1)超导/铁磁多层膜，(2)铁磁粒子分散在其中的超导薄膜，(3)超导/非磁性材料(包括另一类超导体)多层膜。主要结果如下：(1)我们发现了Nb/Co和V/Co多层膜的两步振荡现象。这种现象可以用所谓的π位相理论来解释。(2)分散体系(以Nb为基质，Fe颗粒分散在基质中)表现出随Fe颗粒增多而增加的T_c降解，符合Abrikosov-Gorkov理论。(3)在超导体/超导体多层膜中观察到的上临界场和转变温度的行为服从邻近效应理论。

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.