Ground-state Phase Oscillations in Josephson Junctions Containing Iron*

Ferromagnetic Josephson junctions with a controllable ground-state phase difference are now well-established as a potential system for cryogenic memory applications. Many recent demonstrations of this phase control have used nickel as a fixed layer, with the phase controlled by the relative orientation of a magnetically soft layer. While nickel is a hard ferromagnet that allows high transmission of supercurrent, its multidomain structure and stray field have been obstacles to implementation in devices. Iron is another hard ferromagnet that has been investigated in S/F/S Josephson junctions and shown to undergo 0 – π phase oscillations with thickness [1]. We present a further investigation of iron Josephson junctions and their potential for use as memory devices. SQUID magnetometer measurements show that iron grown on a copper buffer layer gives a narrower magnetic transition and thinner magnetic dead layer than if grown directly on niobium. We also present junction transport measurements showing the critical current and 0 – π phase oscillations for a range of iron thickness grown on a 2nm copper buffer.


[1] S. Piano, et al., Eur. Phys. J. B 58, 123 (2007)