  We show that the axial component of the magnetic permeability tensor is
resonant for a wire medium consisting of high-index epsilon-positive nanowires,
and its real part changes the sign at a certain frequency. At this frequency
the medium experiences the topological transition from the hyperbolic to the
elliptic type of dispersion. We show that the transition regime is
characterized by extremely strong dependence of the permeability on the wave
vector. This implies very high density of electromagnetic states that results
in the filamentary pattern and noticeable Purcell factor for a transversely
oriented magnetic dipole.
