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−xMn_xFe₂O₄ (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 (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 Mn²⁺ 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.