  We present a new, high-performance coupled electrodynamics-micromagnetics
solver for full physical modeling of signals in microelectronic circuitry. The
overall strategy couples a finite-difference time-domain (FDTD) approach for
Maxwell's equations to a magnetization model described by the
Landau-Lifshitz-Gilbert (LLG) equation. The algorithm is implemented in the
Exascale Computing Project software framework, AMReX, which provides effective
scalability on manycore and GPU-based supercomputing architectures.
Furthermore, the code leverages ongoing developments of the Exascale
Application Code, WarpX, primarily developed for plasma wakefield accelerator
modeling. Our novel temporal coupling scheme provides second-order accuracy in
space and time by combining the integration steps for the magnetic field and
magnetization into an iterative sub-step that includes a trapezoidal
discretization for the magnetization. The performance of the algorithm is
demonstrated by the excellent scaling results on NERSC multicore and GPU
systems, with a significant (59x) speedup on the GPU using a node-by-node
comparison. We demonstrate the utility of our code by performing simulations of
an electromagnetic waveguide and a magnetically tunable filter.

Computational Physics;Mathematical Software;Applied Physics