An opto-thermal approach for rotating a trapped core-shell magnetic microparticle with patchy shell.

The ability to trap and rotate magnetic particles has important applications in biophysical research and optical micromachines. However, it is difficult to achieve the spin rotation of magnetic particles with optical tweezers due to the limit in transferring spin angular momentum of light. Here, we propose a method to obtain controlled spin rotation of a magnetic microparticle by the phoretic torque, which is originated from inhomogeneous heating of the microparticle's surface. The microparticle is trapped and rotated nearby the laser focus center. The rotation frequency is several Hertz and can be controlled by adjusting the laser power. Our work provides a method to the study of optical rotation of microscopic magnetic particles, which will push toward both translational and rotational manipulation of the microparticles simultaneously in a single optical trap.