Magnetic particles form chain-like clusters in the magnetic field. This phenomenon is of interest in two separate fields, one is a development system of the laser printer and another is an electromagnetic manipulation of biological cells. Experiments on the chain formation in air and oil have been performed in the ultra high magnetic field created by a superconducting magnet. It has been clarified that the chain length first increased and then decreased in accordance with the increase of the magnetic field. The result has been confirmed by a numerical calculation with the Distinct Element Method that included the mechanical contact force between particles and the magnetic force due to the field created by the coil and adjacent magnetized particles. A periodic boundary condition was employed to perform realistic calculation in a reasonable calculation time. The effect of the density and the diameter of particles was investigated experimentally. The effect of the dry friction between particles was also examined by comparing experimental results performed in air and oil. Lastly, it has been discussed that the static stability of the chain was determined by a minimization principle of the potential energy that consists of the gravitational and magnetic potential energy.

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