Development of novel exchange spring magnet by employing nanocomposites of CoFe₂O₄ and CoFe₂

CoFe₂O₄-CoFe2 hard-soft nanocomposites were prepared via reduction of the cobalt ferrite CoFe₂O₄ in hydrogen atmosphere at different temperature. The structure and the room temperature magnetization of the samples were characterized by X-ray diffraction, field emission scanning electron microscope (FESEM) and vibrating sample magnetometer (VSM). It was found that the saturation magnetization of the nanocomposite powders increases by reduction temperature while their coercivity decreases. The highest M_r/M_s ratio of 0.52 was obtained for sample reduced at 550 °C. Single smooth hysteresis loops of nanocomposites show that these nanocomposites behave as the single-phase materials. This result indicates the presence of exchange coupling between two different hard and soft phases.