Investigation of Dynamic Magnetic Properties of Surfactant Coated Monodispersed Fe₃O₄ Nanomagnetic Particles

Dynamic magnetic properties of oleic acid/oleyamine coated monodispersed magnetite particles have been investigated. The narrow distribution in particle size is found through TEM with mean diameter of 4.9 nm. The static magnetic properties shows flatness in FC curve at temperature below blocking temperature. At higher fields the onset temperature of irreversibility merges with peak temperature suggesting that these particles may exhibit a super-spin-glass (SSG) like behaviour. The ac magnetic susceptibility was measured as a function of temperature for frequencies ranging from 67 to 1800 Hz. The temperature at which the maximum in the ac-susceptibility curve observed is well accounted by the Vogel-Fulcher law for both χ′ and χ′′. The peak is also observed in a plot of χ′′/χ′ versus temperature, which may mean the existence of magnetic aftereffect.