Exchange-Biased NiFe2O4/NiO Nanocomposites Derived from NiFe-Layered Double Hydroxides as a Single Precursor

NiFe2O4 nanoparticles (<10 nm) embedded in a NiO matrix have been fabricated by calcining the corresponding (NiFeIII)-Fe-II-layered double hydroxide (LDH) precursors at high temperature (500 degrees C). Compared with the NiFe2O4/NiO nanocomposite obtained by calcination of a precursor prepared by a traditional chemical coprecipitation method, those derived from NiFe-LDH precursors show much higher blocking temperatures (T-B) (similar to 380 K). The enhanced magnetic stability can be ascribed to the much stronger interfacial interaction between NiFe2O4 and NiO phases due to the topotactic nature of the transformation of the LDH precursor to the NiFe2O4/NiO composite material. Through tuning the Ni-II/Fe-III molar ratio of the NiFe-LDH precursor, the NiFe2O4 concentration can be precisely controlled, and the T-B value as well as the magnetic properties of the final material can also be regulated. This work represents a successful example of the fabrication of ferro(ferri)magnetic (FM)/antiferrimagnetic (AFM) systems with high magnetic stability from LDH precursors. This method is general and may be readily extended to other FM/AFM systems due to the wide range of available LDH precursors.