Evaporation of sessile droplets is a way to organize suspended particles and create surface coating. Many studies have demonstrated that suspensions with various composition can give rise to qualitatively different dried patterns, often by focusing on the radial density profile of deposited particles. We demonstrate that a single suspension of superparamagnetic colloids can give rise to several dried patterns thanks to an external magnetic field applied during the evaporation process. We show the various patterns obtained with zero, constant, rotating and oscillating magnetic fields, and evidence the continuous control given by the intensity of a constant magnetic field. We also show this magnetic control has a substantial effect on the morphological details of the deposits.FIG. 1. Four deposits (four corners of the drop) obtained with different magnetic fields (null, homogeneous, rotating and oscillating fields, amplitude of non-zero magnetic fields are 22.5 G). Each picture has been numerically colorized, cropped as corner and positioned according to the corresponding field condition. The bottom picture is a zoom on the squared area. The global surface density of particles does not change very much. However, the morphological details of the deposit are radically different from one field to the other.

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