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We study the melting behavior of a finite number (N45) of paramagnetic colloidal spheres in a two-dimensional circular hard wall cavity. The interaction strength between the particles is varied by applying a magnetic field B. At high B, i. e. , strong interaction, the particles are arranged in a highly ordered shell-like structure. With decreasing B we observe first a loss of angular order between adjacent shells. Upon further reduction of the external B field, however, angular order is restored again before the system melts completely. We propose a simple mechanism to account for this reentrance phenomenon.
Bubeck et al. (Mon,) studied this question.