H.-M. Song, J.I. Zink, N.M. Khashab
Chem. Phys., 17, 18825-18833, (2015)
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@MnxFe1−xO core–shell NPs are prepared by seeded growth. The structure of the core is cubic spinel (Fdm), and the shell is composed of iron–manganese oxide (MnxFe1−xO) with a rock salt structure (Fmm).
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 MnxFe1−xO. Exchange bias is observed in these MnFe2O4@MnxFe1−xO core–shell NPs with an enhanced coercivity, as well as the shift of hysteresis along the field direction.