  Exchange coupling in an interfacial context is crucial for spin-torque nano
oscillator (STNO) that consists of a non-magnetic spacer which is alloyed with
a ferromagnetic material. Currently, investigations on the dynamics of the free
layer magnetization and frequency enhancement in the STNO with bilinear
coupling are still being actively pursued. In the present work, we investigate
the dynamics of the STNO in the presence of bilinear coupling but in the
absence of an external magnetic field by analyzing the associated
Landau-Lifshitz-Gilbert-Sloncewski(LLGS) equation, and consequently the impact
of the bilinear coupling on the dynamics of the magnetization of the free layer
is studied. It is observed that the frequency of the oscillations in the
magnetization component along the direction of the pinned layer polarization
can be enhanced above 300 GHz by positive bilinear coupling and up to around 30
GHz by negative bilinear coupling. We further reveal a transition from in-plane
to out-of-plane precession both for positive and negative bi-linear couplings.
We also analyze the switching of the magnetization for different values of
current and bilinear coupling. Our detailed investigations of STNO with
bilinear coupling aim at the possibilities of high-frequency devices by
considering the applied current and bilinear coupling in the absence of a
magnetic field.
