Long range triplet Josephson effect through a ferromagnetic trilayer

Abstract

We study the Josephson current through a ferromagnetic trilayer, both in the diffusive and clean limits. For colinear (parallel or antiparallel) magnetizations in the layers, the Josephson current is small due to short range proximity effect in superconductor/ferromagnet structures. For non colinear magnetizations, we determine the conditions for the Josephson current to be dominated by another contribution originating from long range triplet proximity effect.Comment: 4 pages, 2 figure

Area-dependence of spin-triplet supercurrent in ferromagnetic Josephson junctions

“…24 In the future, it would be interesting to measure the current-phase relation of our junctions, both in the virgin and magnetized states. According to the ZS theory, 24 the virgin state junctions should be in a π/2 state, while according to spin-triplet junction theory, [20][21][22] the magnetized junctions should be in the π state. Current-phase measurements are technically more challenging than the critical current measurements reported here, but they might provide more direct evidence of the underlying physics than do the area-dependent measurements reported area.…”

“…16 The explanation is that the F' and F" layers are magnetized parallel to the field, while the SAF undergoes a "spinflop" transition whereby the two Co layers end up with their magnetization perpendicular to the direction of the applied field. 17,18 According to theory, [19][20][21][22] this configuration with perpendicular magnetizations maximizes the magnitude of the spin-triplet supercurrent. If angles θ1 and θ2 have the same sign (where we constrain |θ1|, |θ2| < π), the junction will have π coupling; if they have opposite signs, the junction will have 0 coupling.…”

“…16,23 The question that motivated this paper arises from the theoretical prediction that Josephson junctions of the form S/F'/F/F"/S, carrying spin-triplet supercurrent, can be either in the 0-state or the π-state depending on the relative orientations of the three ferromagnetic layers. 19,20 (It does not matter whether the central F layer is a single ferromagnetic layer or an SAF. 21,22 ) The situation is illustrated in Figure 1, which shows the relative orientations of the magnetizations of all four ferromagnetic layers in our junctions.…”

“…According to theory, if the two angles θ 1 and θ 2 have the same sign, then the junction will have π coupling; if they have opposite signs, the junction will have 0 coupling. [20][21][22] (We define the angles by the constraint |θ 1 |, |θ 2 | < π.) Since the magnetic layers in our samples consist of many domains when the samples are first grown, we would expect the Josephson coupling in our junctions to exhibit a random spatially-varying pattern of 0-coupling and π-coupling across the junction area.…”

Experimental observation of the triplet spin-valve effect in a superconductor-ferromagnet heterostructure

“…At least two ferromagnetic layers (F 1 ,F 2 ) with a non-collinear alignment of their magnetizations, are required to couple the conventional opposite-spin singlet s-wave pairing channel with the unconventional, odd-triplet s-wave pairing channel. The latter one is of extraordinary long range in F layers [1,2,4], because the magnetized conduction band of a ferromagnetic metal serves as an eigenmedia supporting the equal-spin pairing.Intense activities followed to formulate optimal conditions and realize experimental schemes for the generation and detection of this odd-triplet pairing utilizing the Josephson effect [5][6][7][8][9][10][11][12][13][14]. …”