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Schematic diagram of the TIRM setup. The scattered light of the colloidal particle is focused onto a photomultiplier. A magnet creates a magnetic field with adjustable field gradient at the particle position.
(a) Interaction potential of a superparamagnetic bead and a glass surface, measured at different laser intensities levels of the lower laser tweezers. (b) Resulting light pressure for upper and lower tweezers.
As Fig. 2 but with the magnetic field varied. At a field of 20 mT (●) the potential is folded back (◇) by increasing the power of the upper tweezer.
(a) Magnetisation curve of a superparamagnetic particle. The solid line shows a Langevin fit with parameters: , . (b) Same curve but for a particle. The magnetization and the observed forces are about a factor of 10 smaller.
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