Affiliations: Istituto Nazionale di Ricerca Metrologica, Torino, Italy
Abstract: We present and discuss methods, setups, and results concerning the
characterization of Mn-Zn and Ni-Zn ferrites in the frequency range DC -1
GHz, by which we bring to light the physical mechanisms responsible for the
observed frequency behavior of magnetic losses W and permeability μ and
provide thorough assessment of the broadband response of the material. A
comprehensive array of polarization Jp and frequency f values is
investigated. A fluxmetric approach is applied up to a few MHz, which is
substituted by a transmission line method at higher frequencies, up to 1
GHz. The fluxmetric measurements are made at defined Jp value, typically
from a few mT to some hundred mT. The waveguide characterization, centered
on the use of a network analyzer, is instead made under defined exciting
power. But a full experimental W(Jp, f) matrix up to 1 GHz and Jp
values typically belonging to the Rayleigh region is in any case retrieved,
thanks to the linear response of the material at high-frequencies.
Disaccommodation measurements are the route followed in these experiments to
separate the rotations from the domain wall process at all frequencies.
Whatever the magnetization mode, the role of eddy currents in Mn-Zn ferrite
losses is put in evidence by means of resistivity measurements and ensuing
multiscale numerical modeling, the loss experiments being made on
progressively thinned ring samples. It is concluded that an eddy current
free W(Jp, f$) behavior can always be obtained, which can be decomposed
into domain wall and rotation related contributions. The latter can be
calculated assuming a suitable distribution of the effective internal
anisotropy fields and its introduction in the Landau-Lifshitz-Gilbert
derivation of the rotational susceptibility.
Keywords: Soft ferrites, magnetic losses, spin damping, eddy currents, magnetic disaccommodation
