Thermally activated relaxation time of a single domain ferromagnetic particle subjected to a uniform field at an oblique angle to the easy axis: Comparison with experimental observations

Abstract

New asymptotes of the relaxation time of the magnetic moment of a single domain particle with a uniform magnetic field applied at an oblique angle to the easy axis (in excellent agreement with exact numerical results from the Fokker-Planck equation for the Neel-Brown model) are used to model the experimental angular variation of the switching field for individual Co and BaFeCoTiO particles. Good agreement is obtained, justifying the Neel-Brown (in effect, the Kramers) conception of the superparamagnetic relaxation process and allowing one to deduce the value of the damping constant (hitherto almost unknown).