Electrochemical Growth of Iron Arborescences under In-Plane Magnetic Field: Morphology Symmetry Breaking

Pattern formation in the electrochemical deposition of iron from a thin layer of $\mathrm{Fe}\left({\mathrm{SO}}_4\right)$ aqueous solution was investigated in a circular geometry under a magnetic field applied in the plane of growth. Arborescent aggregates were obtained whose macroscopic morphology changes from circular in zero field to rectangular in finite field, one edge of the rectangle being parallel to the field. This field-induced symmetry breaking is explained as resulting from a selection at the microscopic scale of the orientation of the branches with respect to the field, associated with a minimization of the magnetic dipolar energy of the growing branches.