Anti-Lenz supercurrents in superconducting spin valves

Abstract

Here, we present a study on Si(111)/Ta(150 Å)/IrMn(150 Å)/NiFe(50 Å)/Nb(x)/NiFe(50 Å)/-Ta(50 Å) and Si(111)/Ta(150 Å)/NiFe(50 Å)/Nb(x)/NiFe(50 Å)/IrMn(150 Å)/Ta(50 Å) spin-valves with x = 100 to 500 Å. For both sample families, above a specific critical thickness of the Nblayer and below Tc, the superconducting Nb-layer contributes strongly to the magnetization. These systems show an anomalous hysteresis loop in the magnetization of the superconducting layer; the hysteresis loop is similar to what is generally expected from hard superconductors and many superconductor/ferromagnet hybrid systems, but the direction of the hysteresis loop is inverted when compared to what is generally observed (paramagnetic for up sweeping fields and diamagnetic for down sweeping fields). This means that the respective samples exhibit a magnetization, which is contrary to what should be expected from the Lenz' rule.

Absence of magnetic interactions in Ni–Nb ferromagnet–superconductor bilayers

“…Additionally, there are several experimental observations of magnetic interactions in F-S systems where the underlying mechanism either falls outside of the categories outlined previously or remains unexplained [45][46][47][48][49][50]. For example, a previous report of Flokstra observed a measurable inverse proximity effect in a trilayer sample of Py-Nb-Py by the muon technique, but with a decay length from the F-S interface much shorter than either ξ or λ L [45].…”

Superconducting spin valve under magnonic control

“…Nevertheless, the improvement and optimization of SSVs still remains both a theoretical and experimental challenge [32][33][34][35][36][37][38]. The possible ways to improve the SSV properties call for the optimization of the structures, via their technology of preparation, quality of interfaces, and choice of materials, including strong, half-metallic, and insulating ferromagnets.…”

Sudden magnetization drops in superconductor/ferromagnet bilayered structures

“…Most of the previous works dealt with transport measurements of S/F structures and only a few [2,24,26,27] investigated magnetic properties of the superconductor under the influence of the ferromagnet. Indeed, as recent experiments suggest the magnetic properties of F/S/F spin valve structures may strongly be affected by proximity effect leading to strong variations of the superconductor's magnetization [24].…”