The chain length of anisotropic paramagnetic particles in a rotating field

Abstract

In this article the maximal length of a chain of paramagnetic particles with magnetic anisotropy in a rotating magnetic field is studied. The theory of paramagnetic particle chains usually assumes that the particles are magnetically isotropic and do not rotate in a rotating field. In experiments it is seen that spherical paramagnetic particles rotate, which can be explained by small magnetic anisotropy. In this article, the maximal chain length is calculated for paramagnetic particles with magnetic anisotropy in a rotating magnetic field. Results show that the maximal chain length as a function of field frequency has the same trend for isotropic magnetic particles and particles with magnetic anisotropy if the field frequency is much higher or much lower than the critical frequency of an individual particle. Initially randomly distributed particles will form chains that will collide and exchange with particles till they obtain a typical chain length. The typical chain length of a small cluster is shorter than the maximal chain length of an isolated chain for the same field frequency. The distribution of chain lengths in a small cluster of chains is narrower for particles with higher magnetic anisotropy. Due to the narrower distribution of chain lengths, particles with magnetic anisotropy can suit better for mass-production. This article will show how magnetic anisotropy parameters of paramagnetic particles influence chain length of chains which form in a rotating magnetic field.