  We design and explore PT-symmetric behavior of a hybrid non-Hermitian cavity
magnomechanics consisting of a ferromagnetic YIG sphere driven by external
magnetic field. Non-Hermicity is engineered by using a traveling field directly
interacting with YIG. The external magnetic field excites collective mechanical
modes of magnons, which later excites cavity mode leading to a coupling between
cavity magnons and photons. The magnomechanical interaction of the system also
excites phonon and couple them to the system. By computing eigenvalue spectrum,
we demonstrate the occurrence of three-order exceptional point emerge with the
increase of magnon-photon coupling at a specific incidence angle of traveling
field. We illustrate the unique bi-broken and uni-protected PT-symmetry regions
in eigenvalue spectrum unlike previously investigated non-Hermitian system,
which can be tuned with gain and loss configuration by manipulating ratio
between traveling field strength and magnon-photon coupling. Interestingly,
protected PT-symmetry only exists on the axis of exceptional point. We further
show that the PT-symmetry can only be govern at two angle of incident of
traveling field. However, later, by performing stability analysis, we
illustrate that the system is only stable at $\pi/2$ and, on all other angles,
either the system is non-PT-symmetric or it is unstable. Furthermore, we govern
the parametric stability conditions for the system and, by defining stablity
parameter, illustrate the stable and unstable parametric regimes. Our finding
not only discusses a new type of PT-symmetric system, but also could act as
foundation to bring cavity magnomechanics to the subject of quantum information
and process.
