Micromanipulation of colloidal structures at interfaces using magnetic tweezers

Magnetic tweezers have evolved into an indispensable tool in soft condensed matter and biological physics. They are used to study local forces in biological tissue, to stretch and manipulate DNA, to transport ferrofluids, and to probe protein networks in the cell environment. Magnetic tweezers are stronger and cover a wider range of forces (femto- to nano-Newtons) than optical tweezers (pico-Newtons). However, optical tweezers have proven more versatile than conventional magnetic-tweezers in performing complex local manipulations on the micron scale. Here we use nanomagnets formed by movable domain walls in magnetic films to combine the advantages of conventional, magnetic and optical tweezers. Recently nanomagnetic elements were proposed for micro-manipulation of vortices in superconductors. It was shown that a movable magnetic domain wall can be used to generate, trap, and move vortices due to the wall’s highly inhomogeneous magnetic stray field. Our research builds on recent accomplishments including the application of nanomagnets for the controlled manipulation of paramagnetic colloids, and the measurement of the forces that arrange the colloids in different low-dimensional states of aggregate.