Magnetic and Impedance Properties of Nanocomposite CoFe 2 O 4 / Co 0.7 Fe 0.3 and Single‐Phase CoFe 2 O 4 Prepared Via a One‐Step Hydrothermal Synthesis

Using a one‐step hydrothermal method and at different stirring speeds ( V s ), we have synthesized different types of CoFe 2 O 4 ‐based magnetic nanocrystalline samples. With increasing V s , the sample changes from a nanocomposite of CoFe 2 O 4 / Co 0.7 Fe 0.3 ( CFO / CF ) to single‐phase CoFe 2 O 4 ( CFO ). The maximum magnetization, 88.9 emu/g, and coercivity, 3010 Oe, were obtained when V s  = 0. As V s increases, the saturation magnetization M s decreases, because the amount of soft magnetic CF phase decreases. A clear enhancement in the remanence, M r , was observed, with the maximum M r / M s  = 0.67; the coercivity H c also exhibits a local maximum for the sample with V s  = 200 r/min. These trends can be explained well by the interplay between dipolar interaction, magnetocrystalline anisotropy, and shape anisotropy. The stirring speed also influences the impedance of the materials; the related mechanism is discussed.