Interpolation formula between very low and intermediate-to-high damping Kramers escape rates for single-domain ferromagnetic particles - art. no. 021102

It is shown that the Mel'nikov-Meshkov formalism for bridging the very low damping (VLD) and intermediate-to-high damping (IHD) Kramers escape rates a s a function of the dissipation parameter for mechanical particles may be e xtended to the rotational Brownian motion of magnetic dipole moments of sin gle-domain ferromagnetic particles in nonaxially symmetric potentials of th e magnetocrystalline anisotropy so that both regimes of damping, occur. The procedure is illustrated by considering the particular nonaxially symmetri c problem of superparamagnetic particles possessing uniaxial anisotropy sub ject to an external uniform field applied at an angle to the easy axis of m agnetization. Here the Mel'nikov-Meshkov treatment is found to be in good a greement with an exact calculation of the smallest eigenvalue of Brown's Fo kker-Planck equation, provided the external field is large enough to ensure significant departure from axial symmetry, so that the VLD and IHD formula s for escape rates of magnetic dipoles for nonaxially symmetric potentials are valid.