Studies on the magnetism of cobalt ferrite nanocrystals synthesized by hydrothermal method

Fe–Co/CoFe2O4 nanocomposite and CoFe2O4 nanopowders were prepared by the hydrothermal method. The structure of magnetic powders were characterized by X-ray diffraction diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermal gravity analysis (TGA) and differential thermal analysis (DTA) analysis, X-ray photoelectron spectrometry (XPS), and Fourier transform infrared spectra (FTIR) techniques, while magnetic properties were determined by using a vibrating sample magnetometer (VSM) at room temperature. The effects of hydrothermal reaction conditions on magnetic properties were also discussed in details. The values of saturation magnetization (Ms) and coercive fore (Hc) for Fe–Co/CoFe2O4 nanocomposite are 113 emu/g and 1.4 kOe, respectively. Furthermore, CoFe2O4 ferrite with a single-domain critical size of 70 nm was fabricated by controlling the hydrothermal reaction conditions carefully, which presents high coercive force (ca. 4.6 kOe) and high squareness ratio (ca. 0.65). One interesting thing is Ms value of CoFe2O4 ferrite with a diameter of 40 nm is 86 emu/g which is comparable to that of the bulk counterpart.