  We demonstrate an enhanced, bidirectional, in-plane magnetic field tuning of
the gyrotropic resonance frequency of a magnetic vortex within a disk by
introducing a flat edge. When the core is in its vicinity, the flat edge
locally reduces the core's directional dynamic stiffness for movement parallel
to the edge. This strongly reduces the net dynamic core stiffness, leading to
the gyrotropic frequency being significantly less than when the core is
centered (or located near the round edge). This leads to the measurable range
of gyrotropic frequencies being more than doubled and also results in a clear
chirality-mediated bistability of the gyrotropic resonance frequency due to
what is effectively a chirality-dependence of the core's confining potential.
