ИСТИНА

Coexistence of superconductivity (S) and ferromagnetism (F) leads to superconducting wavefunction oscillating and to the shift of current-phase characteristic on π. π-state is usually investigated on multilayer SFS Josephson junctions, which are called “π-junctions” [1]. Up to the present time the scale of such structures is about hundreds square microns. However, practical utility is consisted in submicron junctions. In connection with it the structural and transport properties of SF-heterostructures should be investigated. We report the observation of a nonmonotonic behavior of resistance in a superconductor/ferromagnetic layered system below superconducting critical temperature. The results were obtained using a superconductor/ferromagnetic-alloy bilayer of Nb/CuNi, where Cu1-xNix, x = 0,51. Sample was structured as two perpendicular thin-film “wedges”. S-layer thickness was 5.5 – 11.0 nm, F-layer: 5.6 – 11.3 nm. Measurements were carried out in the He-3 cryostat. We determine nonmonotonic dependence of superconducting critical temperature and resistance at 0.3 K versus ferromagnetic layer thickness Tc(dF), R0.3(dF). Also steplike current voltage characteristics (phase-slip centers) was observed. We explain the minimum on Tc(dF)-dependence as 0-π transition at 7 nm. Difference in phase appears between superconducting areas which separated by induced ferromagnetic areas. Authors acknowledge the Russian Foundation for Basic Research (RFBR) (research projects No. 16-02-00727, 16-32-60133, 16-32-00309 and No. 16-02-00815) [1] V. A. Oboznov, V. V. Bol’ginov, A. K. Feofanov, V. V. Ryazanov, and A. I. Buzdin, PRL, 96, 197003 (2006).