Josephson tunnel junctions with ferromagnetic Fe_0.75Co_0.25barriers

Abstract

Josephson tunnel junctions with the strong ferromagnetic alloy Fe0.75Co0.25 as the barrier material were studied. The junctions were prepared with high quality down to a thickness range of a few monolayers of Fe-Co. An oscillation length of ξF 2 ≈ 0.79 nm between 0 and π-Josephson phase coupling and a very short decay length ξF 1 ≈ 0.22 nm for the amplitude of the superconducting pair wave function in the Fe-Co layer were determined. The rapid damping of the pair wave function inside the Fe-Co layer is caused by the strong ferromagnetic exchange field and additional magnetic pair breaking scattering. Josephson junctions with Fe-Co barriers show a significantly increased tendency towards magnetic remanence and flux trapping for larger thicknesses dF .

Observation of Josephson coupling through an interlayer of antiferromagnetically ordered chromium

“…Similar SI-F-S-type JJs showed a uniform increase in the average interlayer thickness and low-interface interdiffusion despite the polycrystalline growth. 6,15,17,18 The lithographically patterned JJs had areas of 10ϫ 5 and 50ϫ 10 m 2 , and an effective length ranging from the intermediate to the short JJ limit, i.e., L / J = ͓4...0.1͔ with the Josephson penetration length J ϳ 1 / ͱ j c . Inserting a tunnel barrier in the S-AF-S stack increases the normal-state and subgap resistances.…”

“…The strong spreads in j c require an interlayer-thickness variation in roughly half the coherence length AF , i.e., ϳ1 nm, and have not been observed in previous experiments with otherwise similar SI-F-S JJs ͑F=3d magnets͒ with a considerably shorter F . 6,17,18 The steeper slope of j c ͑d AF ͒ for thicker Cr layers makes j c even more prone to variations in d AF but such large variations in j c were not seen for d AF Ͼ 6 nm. Furthermore, the magnetic diffraction pattern indicates uniform flux penetration in the barrier for all AF thicknesses, see Fig.…”

Magnetic interference patterns in0−πsuperconductor/insulator/ferromagnet/superconductor Josephson junctions: Effects of asymmetry between 0 andπregions

“…To overcome this problem, an additional insulating ͑I͒ layer can be used to increase R, although at the expense of a highly reduced critical current density j c . [7][8][9][10] In a SFS or SIFS junction, the proximity effect in the ferromagnetic layer leads to a damped oscillation of the superconducting order parameter in the F-layer. Thus, depending on the thickness d F of the F-layer, the sign of the order parameters in the superconducting electrodes may be the same or not.…”

Giant thermoelectric effects in a proximity-coupled superconductor–ferromagnet device

“…Later this effect was considered further in mesoscopic Andreev interferometers [20][21][22][23][24] and used to explain partially the experimental findings [9].During the last decade superconductor-ferromagnet heterostructures have attracted a considerable interest. Driven by the prospect to create, among other perspectives, unconventional triplet pairing [25][26][27][28][29][30], superconducting spin-valves [31,32] or to study spin-polarized Andreev reflection [33][34][35][36][37], many aspects of superconductor-ferromagnet heterostructures have been investigated theoretically [38][39][40][41][42][43][44] and experimentally [45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61]. However, the field of thermoelectricity has remained largely unexplored.Recently, we have pointed out the possibility to generate large local and non-local thermoelectric effects [62] in heterostructures of ferromagnets and superconductors by the combined effect of induced spin splitting and spin-polarized tra...…”