RELAXATION-TIME OF FINE MAGNETIC PARTICLES IN UNIAXIAL SYMMETRY

Models for fine magnetic particles are shortly reviewed. A method for the solution of the partial differential equation occurring in Brown's model is presented, which in the uniaxial case permits us to calculate numerical solutions for a large range of alpha values. An approximate formula for the relaxation time is given. The expression obtained is valid for 0 less-than-or-equal-to alpha less-than-or-equal-to 60, which corresponds to all the physical cases (including geological scale). This formula is used to fit experimental results and good agreement is obtained. In addition, the question of the validity of Brown's treatment when the magnetization is not uniform, the meaning of the dissipation constant, and quantum effects are discussed.