The resonance decay function method in the determination of the pre-factor of the neel relaxation time of single-domain nanoparticles

Abstract

In its simple form, the relaxation time of the Neel relaxation process of the magnetic moment of single-domain particles is given by ?N=?0Nexp(?), ? being the ratio of the anisotropy energy to thermal energy. The pre-factor, ?0N , is normally given a value of 10?9 s, but values ranging from 10?8 to 10?12 s have been reported in literature. Here, by means of the field and frequency dependence of the complex magnetic susceptibility, ?(?,H)=??(?,H)-i ??(?,H), of a magnetic fluid sample, in the MHz ? GHz range, in conjunction with the determination of the sample decay function, b(t), the pre-factor ?0N is determined. b(t) is readily obtained through the inverse Fourier transformation relationship which exists between b(t) and ?? (?).