Magnetic-field effects on fractal electrodeposits

A uniform magnetic field unexpectedly alters the form of copper deposits grown in a flat electrochemical cell; the patterns change from radial to unidirectional when the cell is horizontal and vice versa when the cell is vertical. The electrodeposits are characterised by their chirality and fractal dimension. Complex impedance spectra show that the effective diffusion coefficient of the copper ions is doubled in a field of 1 T. The results demonstrate that the field produces a body force comparable to that of gravity. From dimensional analysis, it is inferred that the field modifies convective flow on a scale of a few microns close to the cathode.