Dispersion medium crystallization effect on the magnetic susceptibility of ferrofluids

Abstract

Ferrofluids (magnetic colloids) with a dispersion medium crystallizing with a decrease in temperature are investigated. Temperature dependences of the dynamic magnetic susceptibility of such ferrofluids were measured. For comparison, similar susceptibility dependences of ferrofluids with a dispersion medium that does not form a crystalline structure when solidified by cooling are also presented. It is demonstrated that crystallization of the dispersion medium leads to an inhomogeneous spatial distribution of dispersed phase particles and the formation of regions of high particle concentration. This does not happen in the case of colloids with a dispersion medium that does not form a crystalline structure. It is concluded that the formation of regions of high concentrations of dispersed phase particles during crystallization is the cause for a jump in colloid magnetic susceptibility. This conclusion refutes the previously existing opinion that the reason for the jump in the susceptibility of a ferrofluid at the temperature of transition to a solid state is the blocking of Brownian degrees of freedom of particles.