S/F/S Josephson junctions with single-domain ferromagnets for memory applications

Josephson junctions containing ferromagnetic materials are being considered for applications in cryogenic random access memory. The road to such applications requires thorough characterization of junction properties, including critical current and ground-state phase shift, as a function of the thickness of a single ferromagnetic layer. We carried out such a study for elliptically-shaped submicron Josephson junctions containing a Ni 0.73 Fe 0.21 Mo 0.06 alloy similar to commercial Supermalloy. From the field dependence of the critical current, we conclude that the ferromagnets in our junctions are primarily single-domain. These measurements also produce pertinent information about the switching properties of the nanomagnet. We observe a 0– π transition occurring at a NiFeMo thickness of 2.25 ± 0.10 nm, while the critical current decays exponentially with a characteristic length scale of 0.48 ± 0.04 nm.