Probing of pair interaction of magnetic microparticles with optical tweezers

Magnetic interaction of paramagnetic Brownian submicron-sized particles is studied by optical tweezers technique. Correlation analysis allows one to extract magnetic interaction of two particles $0.4$ $\mu$m in size, which are optically trapped at the distance of 3 $\mu$m one from each other and placed in a static magnetic field of $30$ Oe, from the background of their Brownian motion. The magnetic interaction force is estimated to be of approximately $100$ fN. Two configurations of the mutual orientation of the magnetic field vector and the line connecting two centers of optical traps are used in the experiment. For field vector orientation parallel/perpendicular to this line, the magnetic interaction is detected by the cross-correlation function increase/decrease in comparison with the absence of magnetic field on the time scales of $1$ ms.