Theory of domain-wall superconductivity in superconductor/ferromagnet bilayers

Abstract

We analyze the enhancement of the superconducting critical temperature of superconducting/ferromagnetic bilayers due to the appearance of localized superconducting states in the vicinity of magnetic domain walls in the ferromagnet. We consider the case when the main mechanism of the superconductivity destruction via the proximity effect is the exchange field. We demonstrate that the influence of the domain walls on the superconducting properties of the bilayer may be quite strong if the domain wall thickness is of the order of superconducting coherence length.

Altering the Superconductor Transition Temperature by Domain-Wall Arrangements in Hybrid Ferromagnet-Superconductor Structures

“…It is known [1,2] that the appearance of domain walls can induce superconductivity such as that shown in Fig. 1 with H ?…”

“…A variety of novel phenomena have been reported in F-S hybrids [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17], such as the spin switch effect [3][4][5][6][7][8][9][10] and the domainwall superconductivity [1,2,8,12 -16]. In the latter, in both bilayers and trilayers, the transition temperature T c of the S layer depends on the appearance of domain walls in the F layer during magnetization reversal, an effect attributed to the lowered average exchange field sensed by the Cooper pairs in the domain-wall region.…”

Guiding superconducting vortices with magnetic domain walls

“…1 A special case of the proximity effect should appear in FM/SC bilayers due to the FM domain walls where the reduced effective exchange at the wall could lead to a locally enhanced superconducting transition temperature T c in the SC layer. 10 The long-range effects in FM/SC bilayers are associated with interactions of the FM stray fields with the SC screening currents. Due to such interactions, more robust superconductivity just above the FM domain walls is expected when domains are magnetized perpendicular to the SC/FM interface and the stray fields at the domain wall are at a minimum ͑see Ref.…”

Josephson effect in superconductor/ferromagnet-normal/superconductor structures

“…41,42 The transformation of decay length from F1 to F might also take place in a vicinity of a domain wall even without generation of an odd triplet component. [43][44][45][46][47][48][49][50][51] This enhancement depends on an effective exchange field which is determined by thicknesses and exchange fields of the neighboring domains. If a sharp domain wall is parallel 47,50 or perpendicular to SF interface 51 and the thickness of ferromagnetic layers, d f Շ F1 , then for antiparallel direction of magnetization the exchange field effectively averages out, and the decay length of superconducting correlations becomes close to that of a single nonmagnetic N metal F = ͱ D F / 2T C .…”