Oriented CoFe2O4/CoO Nanocomposite Films from Layered Double Hydroxide Precursor Films by Calcination: Ferromagnetic Nanoparticles Embedded in an Antiferromagnetic Matrix for Beating the Superparamagnetic Limit

摘要

A cobalt-iron layered double-hydroxide (CoFe-LDH) film with c-axis orientation has been fabricated through a solvent evaporation method and an oriented CoFe2O4/CoO nanocomposite film formed in a subsequent thermal treatment process. The resulting product is composed of nanosized ferromagnetic (FM) CoFe2O4 particles embedded in antiferromagnetic (AFM) CoO matrix with (111)-orientation. A topotactic transformation from the LDHs precursor film to the CoFe2O4/CoO nanocomposite film was proposed to cause an exchange coupling between the FM CoFe2O4 and AFM CoO phases in the nanocomposite, leading to an enhanced magnetic stability of the CoFe2O4, as shown by the higher value of the blocking temperature (T_B, >400 K) compared with the values reported in previous studies for pure CoFe2O4 nanoparticles with similar size. Furthermore, the orientation of the CoFe2O4/CoO nanocomposite film is found to be attributed to the magnetic anisotropy when the magnetic field was applied on different directions. Such an improvement in magnetic stability has the potential to facilitate practical applications of FM spinel ferrite/AFM oxide nanocomposite films at room temperature.