Magnetic Loss Decomposition in Co-Doped Mn-Zn Ferrites

The magnetic properties of sintered Mn-Zn ferrites, Co
²⁺
enriched by addition of CoO up to 6000 ppm, were measured in ring samples for a broad range of peak polarization values (2-200 mT) and frequencies (dc - 1 GHz). The results were analyzed by separating the contributions to the magnetization process of domain wall motion and magnetization rotation, and applying the concept of loss decomposition. By determining the value and behavior of the rotational permeability μ
_rot
as a function of the CoO content, we obtain the average effective magnetic anisotropy <;K> and its effect on the loss. We thus identify the hysteresis (quasi-static) Wh, rotational Wrot, and excess W
_exc
loss components and their dependence on CoO. The quasi-static loss W
_h
, the domain wall permeability μ
_dw
, and <;K> have minima, and μ
_rot
has a maximum, for CoO in the range 3000-4000 ppm. The rotational loss by spin damping Wrot,sd is calculated by use of the Landau-Lifshitz equation by assuming distributed anisotropy field amplitudes. Wrot,sd covers the experimental loss behavior beyond about 1 MHz. Wexc and Wh, both directly generated by the moving domain walls, share the dissipative response of the material at lower frequencies and show similar trends versus CoO content. It is concluded that the modulation of the magnetic anisotropy of Mn-Zn ferrites through Co
²⁺
enrichment, leading to maximum magnetic softening for CoO in the range 3000-4000 ppm, can be assessed in terms of separate effects of domain wall motion and moment rotations and their related dissipative properties.