Magnetic properties for the single-domain CoFe₂O₄ nanoparticles synthesized by the hydrothermal method

The aim of this work was to investigate the size-related magnetism for the single-domain CoFe₂O₄ nano-particles synthesized using the hydrothermal method. The effects of the reaction temperature and the reaction time on the lattice constants, particle morphologies, and the room-temperature magnetic properties were studied from the X-ray diffraction, the transmission electron microscope, and the vibrating-sample magnetometer. The experimental results show that the samples are composed of CoFe₂O₄ nano-particles with an average crystallite size (D) smaller than 40 nm, and the magnetic properties of the samples can be manipulated in a wide range: the M_S values vary from smaller than 50 emu/g to close to 80 emu/g, and the H_C values are between about 200 Oe and 2000 Oe. Additionally, the relationship between H_C and 1/D^3/2 satisfies linearship, showing the characteristic of single-domain structure. These results indicate that the single-domain CoFe₂O₄ nano-particles with size controlled between the superparamagnetic critical size and single-domain critical size can be easily prepared using this hydrothermal method. © 2015, Wuhan University of Technology and Springer-Verlag Berlin Heidelberg.