Texture-induced magnetic interactions in ferrofluids.

We report a method for reversibly controlling the strength of dipole-dipole interactions in maghemite ferrofluids. In order to induce some magnetic texture, the ferrofluid is exposed to a strong magnetic field while it is cooled from room temperature to below its freezing temperature. The experimental data show that the average strength of dipolar interactions increases with increasing texture and that the magnetic relaxation becomes slower. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4709725]