Proximity effect in a superconductor/exchange-spring-magnet hybrid system

We investigate the proximity effect in a superconductor/ferromagnet (S/F) hybrid system with a noncollinear magnetic configuration. A new structure of an S/exchange-spring (ES) magnet is fabricated, where an ES magnet is employed as an F layer since the magnetization configuration is varied from a collinear state to a noncollinear state by a rotating external magnetic field in a well controllable way. We found that the resistance decreases and the superconducting transition temperature increases, as noncollinearity is introduced starting from a collinear state. We interpret that our experimental observation is due to the contribution of the odd-triplet superconducting condensate that survived in a noncollinear magnetization configuration in the ES magnet.