  We theoretically analyze surface magnetoplasmon modes in a compact circular
cavity made of magneto-optical material under a static magnetic field. Such a
cavity provides two different physical mechanisms for the surface wave to
circulate in a unidirectional manner around the cavity, which offers more
freedom to realize one-way surface wave. We also show the interaction between
this one-way cavity and waveguides, through an example of a circulator, which
lays the fundamental groundwork for potential nonreciprocal devices.
