  Magnetically induced topological transitions of isofrequency surfaces of bulk
waves propagating through an unbounded biaxial gyrotropic medium are studied.
The medium is constructed from a two-component superlattice composed of
magnetized ferrite and semiconductor layers. To derive the constitutive
parameters of the gyrotropic medium, a homogenization procedure from the
effective medium theory is applied. The study is carried out in the frequency
range near the frequency of ferromagnetic resonance, where the magnetic
subsystem possesses the properties of natural hyperbolic dispersion. The
topological transitions from an open type-I hyperboloid to several intricate
hyperbolic-like forms are demonstrated for the extraordinary waves. We reveal
how realistic material losses change the form of isofrequency surface
characterizing hyperbolic dispersion. The obtained results broaden our
knowledge on the possible topologies of isofrequency surfaces that can appear
in gyrotropic media influenced by an external static magnetic field.
