  Here we propose and study a novel type of plasmonic resonators based on a
metal-insulator-metal waveguide and a side-coupled magneto-optical disk
controlled by an external magnetic field. The wavenumber change and the
transmission of surface-plasmon-polaritons (SPPs) can be tuned by altering the
magnetic field and reversible on/off switching of the running SPP modes by a
reversal of the direction of the external magnetic field is demonstrated.
Resonant enhancement of the magneto-plasmonic modulation by more than 200 times
leads to a modulation contrast ratio more than tenfold ratio (90-\%-modulation)
keeping a moderate insertion loss within an optical bandwidth of hundreds of
GHz. Numerical simulations confirm the predictions by the derived analytical
formulas of a high-contrast magneto-plasmonic modulation by the submicron
ultra-small disk resonator.
