  In this paper we numerically conduct micromagnetic modelling to optimize
computational boundaries of magnetic thin-film elements applicable to single
and double point contact spin torque nano-oscillators. Different boundary
conditions have been introduced to compensate spin waves reflections at
boundaries that are based on extended layers, absorbing boundaries, and focal
point methods and are compared with a technique based on scattering theory. A
surface roughness boundary model is presented which is modelled according to
the Rayleigh criterion to minimize specular reflections at computational
boundaries. It is shown that the surface roughness model disperses the
reflected spin waves and improves the signal to background noise ratio. The
model is tested in comparison to conventional approaches such as extended layer
systems, variable damping constant and focal point methods for double point
contacts. The surface roughness model gives solutions that are stable in time,
in qualitative agreement with experiments and capable to reproduce phenomena
such as phase locking in double point contacts.
