Magnetic Field Controlled Composite Paramagnetic–Diamagnetic Colloidal Phases

We report on differently ordered colloidal phases of a mixture of paramagnetic and diamagnetic colloids subject to a quickly varying time dependent magnetic field. Effectively paramagnetic and effectively diamagnetic colloids are created from paramagnetic and nonmagnetic colloids immersed into a thin film of aqueous ferrofluid. The time-averaged dipole interaction between induced dipoles can be characterized by a uniaxial external precession angle and a biaxial eccentricity characterizing the anisotropy of the external field modulation. The variation of both control parameters causes a sequence of transitions between differently correlated orientation order between the paramagnetic and diamagnetic colloids. We observe the formation of bonds between paramagnets and diamagnets along one or two directions with a staggered order of the magnetic moments. Bonds between similar particles with uniform order of the magnetic moments form along directions orthogonal to bonds between different particles along the sta...