Effect of Surfactant and Solvent on Spin−Lattice Relaxation Dynamics of Magnetic Nanocrystals

The effect of varying the surfactant and solvent medium on the dynamics of spin−lattice relaxation in photo- excited Fe3O4 nanocrystals has been investigated by measuring the time-dependent magnetization employing pump−probe transient Faraday rotation technique. The variation of the surfactants having surface-binding functional groups modified not only the static magnetization but also the dynamics of the recovery of the magnetization occurring via spin−lattice relaxation in the photoexcited Fe3O4 nanocrystals. The variation of the polarity and size of the solvent molecules can also influence the spin−lattice relaxation dynamics. However, the effect is limited to the nanocrystals having sufficiently permeable surfactant layer, where the small solvent molecules (e.g., water) can access the surface and dynamically modify the ligand field on the surface.