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

Abstract

In its simple form, the relaxation time of the Néel relaxation process of the magnetic moment of single-domain particles is given by τN=τ0Nexp(σ), σ being the ratio of the anisotropy energy to thermal energy. The pre-factor, τ0N , 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, χ(ω,H)=χ′(ω,H)-i χ″(ω,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 τ0N is determined. b(t) is readily obtained through the inverse Fourier transformation relationship which exists between b(t) and χ″ (ω).