SEMINÁRIO DO GRUPO DE FÍSICA ESTATÍSTICA: “Magnetic and Structural Study of Electric Double Layered Ferrofluid with MnFe2O4@ - Fe2O3 Nanoparticles of Different Mean Diameters: Determination of the Magnetic Correlation Distance”
Magnetic fluids based on manganese ferrite nanoparticles were studied from the structural point
of view through small angle x-rays scattering (SAXS) and from the magnetic point of view through zero-field
cooling and field cooling (ZFC-FC) and ac susceptibility measurements (MS). Three different colloids with
particles mean diameters of 2.78, 3.42, and 6.15 nm were investigated. The size distribution obtained from
SAXS measurements follows a log-normal behavior. The ZFC-FC and MS results revealed the presence of
an important magnetic interaction between the nanoparticles, characterized by a magnetic correlation
distance .The colloidal medium can be pictures as composed by magnetic cluster constituted by N
interacting particles. These magnetic clusters are not characterized by a physical aggregation of particles.
The energy barrier energy obtained is consistent with the existence of this magnetic clusters. Besides the
magnetic interaction between particles, confinement effects must be included to account for the
experimental values of the magnetic energy barrier encountered.