On magnetic ordering in colloids of single-domain particles

Abstract

Observed data supporting the possibility of magnetic ordering in magnetic colloids are reported. Conditions under which magnetized structures arise in magnetic colloids, initial samples in which these mag netized structures can be formed, and colloids with a developed system of magnetized aggregates are ana lyzed.

On the temperature dependence of ferrofluid susceptibility

“…In this case, it is possible to form both nanoscale chain aggregates [10,11] and larger ones with non-zero magnetic moments [12][13][14]. The possibility of its formation was previously presented in [1]. We did not observe aggregates in vivo but found it presence qualitatively by means of the laser correlation spectroscopy and the Vogel-Fulcher behavior analysis.…”

“…A magnetic colloid, also known as a ferrofluid (FF), is a colloidal suspension of single-domain magnetic particles, with typical dimensions of about 10 nm, dispersed in a liquid carrier [1][2][3]. The liquid carrier can be polar or nonpolar.…”

On the Nature of the maximum in the temperature dependence of magnetic liquid susceptibility

“…Relaxation τ and measurement τ u times must be close to each other for observation of the transition of the system to the superparamagnetic state [9]. It is known from [10] that the relaxation time of the activa tion reversal of magnetization is given by (1) where τ 0 = 10 -10 -10 -9 s and ΔE is the energy barrier for the rotation of the moment of the particle upon field reversal.…”

“…Note that a problem of magnetic ordering due to the dipole-dipole interac tion [1,2] remains unsolved. A transition of the system to an ordered state must affect the temperature depen dences of the magnetic parameters, in particular, mag netic susceptibility.…”

Nanoparticles concentration influence on magnetic gyrotropy in ferrocolloids

“…Sample 2 was a structurally ordered kerosene-based magnetic fluid, which had a well-developed system of magnetized aggregates (investigated earlier in [4,5]). Such aggregates have anisotropic shape.…”