Coupling of magnetization dynamics and superconducting state in artificial superconductor/ferromagnet hybrid structures

ended

The proposal addresses a problem that has received very little experimental attention despite its fundamental and technological interest: the coupling between superconducting state and magnetization dynamics in artificial superconductor (S) / ferromagnet (F) hybrid structures. Most of the studies consider that the superconductor is very strongly affected by the interaction with a ferromagnet which, on the contrary, is in a static, equilibrium state and whose order parameter (the magnetization) remains unaffected. However, theoretical studies and a few recent experiments have shown that superconductivity can strongly affect ferromagnetism in various ways. This is the case for instance if one considers low-energy excitations of the magnetization (e.g. magnons), or if one looks at the relaxation from dynamic non-equilibrium states, e.g. the decay of the precession of the macroscopic magnetic moment. In this regard, the proposal has two central objectives, which correspond to two mechanisms of coupling between superconductivity and magnetization dynamics, respectively of electromagnetic and electronic nature. The former objective is concerned with the experimental demonstration of electrical magnon excitation and detection in superconductor/ferromagnet hybrids, that will be applied to the design of dynamic magnonic crystals. Superconductors with different penetrations lengths and intrinsic flux pinning as well as various ferromagnets will be combined. The latter objective involves the understanding of spin pumping and spin diffusion effects in superconductors through ferromagnetic resonance and electrical detection. Special attention will be paid to the used of Yttrium Iron Garnet in insulating ferromagnet/superconductor interfaces, as it presents low intrinsic damping even in thin films. Further combinations with s-wave and d-wave superconductors as well as half-metal ferromagnets will also be explored in this context.