MIPT Conference 2016 Superconducting Hybrid Nanostructures: Physics and Application

MIPT Conference 2016 “ Superconducting hybrid nanostructures: physics and application”

Controllable tuning of spin-singlet and spin-triplet currents in a Josephson spin-valve

V. M. Krasnov, A. Iovan, and T. Golod

Department of Physics, Stockholm University, AlbaNova University Center, SE-10691 Stockholm, Sweden

Josephson spin valve is a device in which a spin valve structure is implemented as a barrier in a Josephson junction. It has been predicted theoretically that the proximity effect in a superconducting spin-valve should strongly depend on a relative orientation of magnetization in ferromagnetic layers of the spin valve [1,2]. An odd-spin-triplet component of the superconducting order parameter can be generated in the non-collinear state of the spin-valve. Several experimental reports were confirming such a behavior [3-5]. However, unambiguous interpretation of the data requires accurate control of the spin-valve state. This also presumes a mono-domain state of the spin-valve. In this talk we present our recent results on experimental analysis of nano-scale Josephson spin-valves with sizes down to 150 nm made by 3D nano-sculpturing [6]. Small dimensions were necessary both for mono-domain switching of spin valves and for enhancement of junction resistances to comfortably measurable values. Ferromagnetic layers in the spin-valve are made dissimilar using a combination of diluted (CuNi) ferromagnets with different Ni concentration of with combination of different strong (Ni, Co, Py) ferromagnets. Our Josephson spin- valves exhibit clear Fraunhofer-type modulation of the Josephson critical current Ic(H) and a regular spin-valve magnetoresistance with minima/maxima at parallel/ anti-parallel orientations of the spin valve [7]. We put special efforts to development of accurate ways for in-situ analysis of the spin-valve state. We demonstrate how two-dimensional angular orientation of magnetic moments of ferromagnetic layers in the spin-valve can be accurately measured in-situ. This allows us to make an unambiguous connection between the relative orientation of magnetizations and the amplitude of the Josephson current, which indicate that both the spin-singlet and the spin-triplet components of the supercurrent are tuned with changing the orientation of the spin-valve. Finally, we discuss possible application of Josephson spin-valves as memory cells [8].

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