Variable temperature electron paramagnetic resonance investigations of an ionic ferrofluid

Abstract

An aqueous based ionic ferrofluid has been studied by EPR spectroscopy technique from room temperature to liquid nitrogen temperature to detect the magnetic phase transitions and their variation at low temperatures. The line-width of EPR signal has been found to increase with decreasing temperature and this has been assigned to magnetic phase transition from ferromagnetic to a spin glass or cluster glass state mainly due to freezing of the carrier fluid. Line-width variation with temperature also suggests that bulk rotation mechanism is the dominant mode of relaxation. Any evidence of the presence of super-paramagnetism has not been observed.