Active magneto-plasmonics in hybrid metal-ferromagnet structures

Surface-plasmon-mediated confinement of optical fields holds great promise for on-chip miniaturization of all-optical circuits. Following successful demonstrations of passive nanoplasmonic devices, active plasmonic systems have been designed to control plasmon propagation. This goal has been achieved either by coupling plasmons to optically active materials or by making use of transient optical nonlinearities in metals via strong excitation with ultrashort laser pulses. Here, we present a new concept in which the active optical component is a metal-ferromagnet-metal structure. It is based on active magneto-plasmonic microinterferometry, where the surface plasmon wave vector in a gold-ferromagnet-gold trilayer system is controlled using a weak external magnetic field. Application of this new technique allows measurement of the electromagnetic field distribution inside a metal at optical frequencies and with nanometre depth resolution. Significant modulation depth combined with possible all-optical magnetization reversal induced by femtosecond light pulses opens a route to ultrafast magneto-plasmonic switching.