Cedeño Mattei, Yarilyn

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    Composition-structure and size/shape-controlled synthesis and characterization of high coercivity ferrite nanocrystals
    (2010) Cedeño Mattei, Yarilyn; Perales Pérez, Oscar J.; College of Arts and Sciences - Sciences; Román, Felix; Meléndez, Enrique; Rinaldi, Carlos; Department of Chemistry; Quintero, Pedro
    Cobalt ferrite (CoFe2O4) possesses excellent chemical stability, good mechanical hardness and a large positive first order magnetocrystalline anisotropy constant, making it a promising candidate for magneto-optical recording media. In addition to precise control of the composition and structure of CoFe2O4, its practical application will require the capability to control particle size at the nanoscale. It has been well-established that a fine tuning in cobalt ferrite nanocrystals size within the magnetic single domain region would lead to the achievement of extremely high coercivity values at room-temperature. The development of a size-sensitive phase separation method for cobalt ferrite nanocrystals that is based on selective dissolution of the superparamagnetic fraction and subsequent size-sensitive magnetic separation of single-domain nanoparticles is presented. The attained colossal room temperature coercivity value of 11.9 kOe was mainly attributed to the enlargement of the average crystal size within the single domain region coupled with the removal of the superparamagnetic fraction in the ferrite powders. The strong influence of crystal size, ferrite composition, cations distribution in the ferrite lattice and lattice distortion on the corresponding magnetic properties at the nanoscale, was also confirmed. The superparamagnetic and magnetic single domain limits were experimentally determined by synthesizing extremely small (4 nm) and large (over 100 nm) single crystals of cobalt ferrite. The first ones were produced using sodium oleate in-synthesis whereas the large crystals were produced by thermal treatment of starting 16 nm cobalt ferrite nanocrystals.