An experimental study of the dynamic properties of nanoparticle colloids with identical magnetization but different particle size

摘要

Measurements of the frequency dependent complex magnetic susceptibility, χ(ω)=χ'(ω)-iχ"(ω).have been used to determine the dynamic properties of three specially prepared 400 G (0.04 T) magnetic fluids. The samples, denoted by sample 1, sample 2 and sample 3, consisted of magnetite particles of mean diameter 6.4 nm, 7.5 nm and 9 nm respectively and were identical in terms of carrier liquid, surfactant and particle material. From polarized ferromagnetic measurements, the anisotropy field, H_A, the Landau-Lifshitz damping parameter, α, and the precessional decay time, τ_0 of the particles were determined. The results show that the H_A value for sample 3 was almost twice that of sample 1 and 2, thus confirming that the smaller the particle size, the lower the value of H_A. The damping parameter, a, was found to be 0.174 (for sample 1), 0.18 (for sample 2) and 0.16 (for sample 3). The values determined for the precessional decay time, τ_0 were 1.197 × 10~(-9) s, 1.157 × 10~(-9) s and 0.789 × 10~(-9) s, for samples 1, 2 and 3 respectively.