title: Seeded growth of ferrite nanoparticles from Mn oxides: observation of anomalies in magnetic transitions.
abstract: A series of magnetically active ferrite nanoparticles (NPs) are prepared by using Mn oxide NPs as seeds. A Verwey transition is identified in Fe3O4 NPs with an average diameter of 14.5 nm at 96 K, where a sharp drop of magnetic susceptibility occurs. In MnFe2O4 NPs, a spin glass-like state is observed with the decrease in magnetization below the blocking temperature due to the disordered spins during the freezing process. From these MnFe2O4 NPs, MnFe2O4@Mn(x)Fe(1-x)O core-shell NPs are prepared by seeded growth. The structure of the core is cubic spinel (Fd3¯m), and the shell is composed of iron-manganese oxide (Mn(x)Fe(1-x)O) with a rock salt structure (Fm3¯m). Moiré fringes appear perpendicular to the 〈110〉 directions on the cubic shape NPs through the plane-matched epitaxial growth. These fringes are due to the difference in the lattice spacings between MnFe2O4 and Mn(x)Fe(1-x)O. Exchange bias is observed in these MnFe2O4@Mn(x)Fe(1-x)O core-shell NPs with an enhanced coercivity, as well as the shift of hysteresis along the field direction.
authors.affiliation: Department of Chemistry, Dong-A University, Busan 604-714, South Korea. hyonmin1@dau.ac.kr.
authors.forename: Hyon-Min
authors.initials: HM
authors.lastname: Song
authors.forename: Jeffrey I
authors.initials: JI
authors.lastname: Zink
authors.forename: Niveen M
authors.initials: NM
authors.lastname: Khashab