Magnetic properties of low Mn-doped NiCuZn nanocrystalline ferrites

Low Mn-doped NiCuZn ferrites with compositions of (Ni0.6Zn0.3Cu0.1)1−xMnxFe2O4 (where x = 0, 0.01, 0.02 and 0.03) were synthesized directly with sol–gel method. The influence of the Mn2+ content (parameter x) and the sintered temperature on the microstructure and the magnetic properties of these ferrites were mainly discussed. With the increasing Mn2+ content, saturation magnetization (Ms) of the powder samples decreased. Saturation magnetic flux density (Bs) and remnant magnetic flux density (Br) of the toroidal specimens decreased with the Mn2+ content up to x = 0.02, followed by increasing. Br and Bs both increased with the increasing sintered temperature, while coercivity (Hc) decreased. The real part of permeability (μ′) of the toroidal specimens increased up to x = 0.01, followed by decreasing. The sintered temperature also affected the resonance frequency and the useable frequency (from which the value of tan δ increased more) obviously. Furthermore, the low-frequency permeability and the secondary maximum (the maximum of the permeability appearing the secondary time) both increased with the sintered temperature from 70 to 120 and 150 to about 600.