Using the POLREF neutron reflectometer, researchers have found that the order in which superconducting and ferromagnetic layers are assembled influences the interfacial magnetic interactions between them, leading to consequences for device applications.
Conventional theory about superconductors requires pairs of electrons, called Cooper pairs, to have their spins pointing in opposite directions to propagate a superconducting current. Whereas, for ferromagnetism, the spins in the material are all parallel to one another. When a superconducting material is layered next to a ferromagnetic one, these conflicting behaviours can lead to interesting emergent properties.
In particular, the superconducting Cooper pairs can penetrate into the ferromagnetic layer and the ferromagnetism into the superconductor, causing complex behaviours that may be exploited for potential superconducting spintronic devices (systems that exploit the spin property of electrons as well as the more familiar charge of the electron). This 'magnetic proximity effect' (MPE) is only observed close to the interface between the materials, making polarised neutron reflectometry an ideal tool for investigations.
In this study, published in ACS Applied Materials & Interfaces, a group of researchers funded by the Department of Science and Technology, India, in collaboration with ISIS, used the POLREF instrument to investigate layered superconducting/ferromagnetic systems both with and without an insulating layer in between them. They established that the MPE is an intrinsic phenomenon, which arises due to tunnelling of Cooper pairs in these superconducting/insulator/ferromagnetic systems.
They found that the order in which the layers were assembled influenced the magnetic and superconducting properties of the materials, and therefore the strength of MPE. This showed that the MPE is therefore not solely due to the properties of the superconducting layer but depends on the competing interactions between it and the ferromagnetic layer.
Being able to understand the influence of these behaviours on the MPE is another step towards designing these systems in a way that makes it possible to tune the magnetic behaviour in future devices, as well as furthering the knowledge of the interactions of the complex phenomena.
The full paper can be found online at DOI: 10.1021/acsami.1c22676