Critical Current Decay in Josephson Junctions Containing Antiferromagnetic Ni₄₁Mn₅₉

We report on the fabrication and measurement of antiferromagnetic (AF) S/N/AF/N/S Josephson junctions where Ni₄₁Mn₅₉ is used as the AF layer, Nb as the S layer, and Cu as the N layer. From measurement of critical current in samples with NiMn thicknesses in the range from 1.2 nm to 6.0 nm, we measure the characteristic decay length within NiMn to be 2.1 nm. One potential application of AF layers inside Josephson junctions is to pin the magnetization of an adjacent ferromagnetic (F) layer by exchange bias. We have characterized NiMn/NiFe and NiMn/Ni bilayer sheet films magnetically to confirm the pinning behavior of NiMn. Such a bilayer AF/F system could potentially be used as a pinned hard layer in a proposed cryogenic memory cell whose design takes the form of an S/F/F’/S spin valve where the two ferromagnetic layers [F, F’] have different switching fields [1]. This design requires a robust magnetization of the hard layer which would be strengthened by the exchange bias effect.

[1] Dayton I.M., et. al., IEEE Magnetics Letters, 9, 3301905 (2018)