Superspin relaxation in Fe3O4/hexane magnetic fluids: A dynamic susceptibility study

► Néel and Brown magnetic relaxation are investigated in Fe3O4-based magnetic fluids. ► Brown mechanism yields the major contribution to the overall superspin dynamics. ► Brown relaxation time exhibits a100-fold decrease upon heating from 237 to 270 K. ► Observed behavior is driven by the reduction of the magnetic fluid's viscosity.