Effects of crystal size and sphere diameter on static magnetic and electromagnetic properties of monodisperse Fe3O4 microspheres.

We demonstrate an easy solvothermal method for the synthesis of monodisperse polycrystalline Fe 3 O 4 microspheres ranging in size from 82 nm to 1116 nm. Results show that controlling H 2 O volume fraction ( γ ) modulates the crystal size ( D ) and sphere diameter ( d ) of Fe 3 O 4 microspheres and also changes their surface state. D and d values of Fe 3 O 4 microspheres change with γ in a Gauss model and a Boltzmann mode, respectively. Adding nonreductive H 2 O favors the increased O content. In these cases, the saturation magnetization ( M s ) and coercivity ( H c ) values follow various Gauss models of variation with γ because of the weakened interaction with decreased d , the enhanced surface spin disorder with D , the increased O content, and the critical size for multidomain–monodomain behavior. The cooperation of size ( D and d ) with surface state induces ε ″ and tanδ E to gradually decrease with γ , and μ ″ and tan δ M are significantly enhanced at γ = 9.2% ( d = 728 nm). This work clearly shows the potential to tune magnetic and microwave properties of polycrystalline magnetic nanomaterials by controlling crystal/particle size and surface state. [ABSTRACT FROM AUTHOR]