Domain-wall enhancement of superconductivity in superconductor/ferromagnet hybrids: Case of weak ferromagnets

Abstract

We use magnetotransport measurements to study the influence of the domain structure on the superconducting transition temperature T c in ferromagnetic ͑F͒/superconducting ͑S͒ bilayers and F / S / F trilayers based on Nb and the weak ferromagnet Cu 43 Ni 57 . By comparing the anisotropic magnetoresistance above T c with the resistance behavior in the transition and with critical current measurements below T c , we show that in bilayers enhanced superconductivity is found when the F layer is in a domain state. We also find that, below T c , the magnetic fields where domains occur are significantly higher than above or around T c , suggesting that the magnetization rotation in the F layers is influenced by the adjacent superconductor. In trilayers the effects are similar. A domain-state dominated mechanism even for reported spin-valve effects therefore cannot be ruled out.

Magnetic coupling in superconducting spin valves with strong ferromagnets

“…A special remark concerns the point that no traces are found of an enhancement of the superconductivity by domain averaging from Cooper pairs, as found before both in CuNi-and Py-based devices, 6,7 and also more recently in a different set of Py-based devices. 20 In particular, for the large-area bilayer sample BL20, enhanced superconductivity in the domain state might have been expected.…”

“…This we ͑consis-tently͒ found before on S films and S/F bilayers. 6,16,17 The measurement is thus directly sensitive to the amplitude of the superconducting gap, which limits the critical current. Additionally, the value of I c is well defined due to the sharp transition.…”

“…Recent measurements on S/F bilayers made of Nb/ CuNi showed that a T c lowering of a few millikelvin is also found when the ferromagnet is in a domain state. 6 This is basically due to the fact that Cooper pairs break less easily when they sample an inhomogeneous exchange field, which can be considered a lateral variant of the spin-valve effect. 7 For spin-valve systems with strong ferromagnets, the situation is more complicated.…”

Ubiquitous long-range antiferromagnetic coupling across the interface between superconducting and ferromagnetic oxides

“…While the understanding of S/F heterostructures based on classical low-T c metals has been progressing considerably [4][5][6] , a proper description of S/F oxide type interfaces is still lacking, although several intriguing interfacial phenomena have been reported [7][8][9][10] . To date, most work in this field has been focusing on the coupling of YBa 2 Cu 3 O 7-d (YBCO) and half-metallic manganites, like La 0.66 Ca 0.33 MnO 3 (LCMO) or La 0.66 Sr 0.33 MnO 3 (LSMO), being the superconducting and ferromagnetic layer, respectively.…”

Suppression of superconductivity in Nb by IrMn in IrMn/Nb bilayers

“…Antiferromagnet/ferromagnet (AFM/FM) 1,2 and ferromagnet/superconductor (FM/S) [3][4][5][6][7] heterointerfaces have been investigated intensively in the last few decades due to their importance in both fundamental physics studies and device applications. Compared to the AFM/FM and FM/S interfaces, however, the amount of work on antiferromagnet/superconductor (AFM/S) heterointerfaces is quite limited.…”