  This paper describes a robust, modular, and physics- based circuit framework
to model conventional and emerging Magnetic Tunnel Junction (MTJ) devices.
Magnetization dynamics are described by the stochastic Landau-Lifshitz-Gilbert
(sLLG) equation whose results are rigorously benchmarked with a Fokker-Planck
Equation (FPE) description of magnet dynamics. We then show how sLLG is coupled
to transport equations of MTJ-based devices in a unified circuit platform. Step
by step, we illustrate how the physics-based MTJ model can be extended to
include different spintronics phenomena, including spin-transfer-torque (STT),
voltage-control of magnetic anisotropy (VCMA) and spin-orbit torque (SOT)
phenomena by experimentally benchmarked examples. To demonstrate how our
approach can be used in the exploration of novel MTJ-based devices, we also
present a recently proposed MEMS resonator- driven spin-torque nano oscillator
(STNO) that can reduce the phase noise of STNOs. We briefly elaborate on the
use of our framework beyond conventional devices.
