Magnetic properties of low Mn-doped NiCuZn nanocrystalline ferrites

Low Mn-doped NiCuZn ferrites with compositions of (Ni 0.6Zn 0.3Cu 0.1) 1− x Mn x Fe 2O 4 (where x = 0, 0.01, 0.02 and 0.03) were synthesized directly with sol–gel method. The influence of the Mn 2+ content (parameter x) and the sintered temperature on the microstructure and the magnetic properties of these ferrites were mainly discussed. With the increasing Mn 2+ content, saturation magnetization ( M s) of the powder samples decreased. Saturation magnetic flux density ( B s) and remnant magnetic flux density ( B r) of the toroidal specimens decreased with the Mn 2+ content up to x = 0.02, followed by increasing. B r and B s both increased with the increasing sintered temperature, while coercivity ( H c) 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.