Two Mechanisms and a Scaling Relation for Dynamics in Ferrofluids

Abstract

Two relaxation peaks were found in the complex susceptibility of ferrofluids. Both can be described by the Vogel-Fulcher law t t 0 f͑T͒ exp͓E͞k͑T 2 T 0 ͔͒. Nevertheless, the physical origins for these two relaxations are quite different. We found that Néel relaxation strongly depends on the dipoledipole interaction. The dramatic dependence can be described by a surprisingly simple scaling relation: t t 0 exp͓E͞k͑T 2 af 0.8 ͔͒, where f is the volume fraction of the dipoles. In contrast, Brownian relaxation is much less sensitive to the concentration of magnetic moments because the interparticle force is mainly hydrodynamic in nature. [S0031-9007(96)00634-5] PACS numbers: 75.50. Mm, 61.20.Lc, 75.40.Gb, 82.70.Dd 0031-9007͞96͞77(2)͞390(4)$10.00

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

“…and the ratio of the anisotropy energy to the thermal energy, σ, the pre-factor, τ 0N =2.06⋅10 -10 s is determined. This value of τ 0N determined here for a magnetic fluid with magnetic particles, is in agreement with the value of τ 0N reported by other researchers using a different method [8,14], however this proposed method has the advantage of being performed at room temperature. • The precessional decay time of the Landau-Lifshitz equations is evaluated.…”

“…L. Dormann and co-workers [8][9][10][11][12], as well as other researchers [13][14][15] have experimentally determined the pre-factor, τ 0N of Eq. (7), for different single-domain …”

Oriented attachment and exchange coupling ofα−Fe2O3nanoparticles

“…For ferro-and ferrimagnetic nanoparticles, strong dipole interactions may result in a divergence of the superparamagnetic relaxation time at a finite temperature, which depends on the strength of the interactions. 1,2 Below this critical temperature, such samples may have many similarities to spin glasses. [2][3][4][5][6] The superparamagnetic relaxation of antiferromagnetic nanoparticles can also be significantly suppressed by interparticle interactions.…”

The Effect of Gelation on the Apparent Magnetism of ZnFe2O4 Sol-Gel Systems

“…For magnetic colloids, under influence of a magnetic field, the increase of orientation of the magnetic moment of the particles leads to an increase of the effective attraction between colloidal particles, so that the randomly distributed nanoparticles in sols can tend to aggregate into chain-like structure by translational motion (Wang, Li, & Gao, 2009). Thus, in the magnetization process, a hydrodynamic interaction among the colloidal particles in a sol (Zhang et al, 1996;Bossis et al, 2002;Liu et al, 1995) could be induced through this translational degree of freedom. Experimental evidence has shown that the hydrodynamic interaction may enhance the self-diffusion of colloidal particles (Zahn et al, 1997).…”

“…In many investigations, the apparent magnetism of magnetic sols has generally been regarded as depending on the magnetic interaction between like particles as dipoles. However, Zhang and co-workers noted an effect of hydrodynamic interaction on alternating current susceptibility (Zhang, Boyd, & Luo, 1996). Gels sensitive to electric or magnetic fields are of interest as "smart" materials with unique potential applications (Tanaka et al, 1982;Qsada et al, 1992;Barsi et al, 1996;Suto et al, 2009;Leveis et al, 2010).…”