Magnetic Losses in Soft Ferrites

We review the basic phenomenology of magnetic losses from DC to 1 GHz in commercial and laboratory-prepared soft ferrites considering recent concepts regarding their physical interpretation. This is based, on the one hand, on the identification of the contributions to the magnetization process provided by spin rotations and domain walls and, on the other hand, the concept of loss separation. It additionally contemplates a distinction between the involved microscopic dissipation mechanisms: spin damping and eddy currents. Selected experimental results on the broadband behavior of complex permeability and losses in Mn-Zn ferrites provide significant examples of their dependence on sintering methods, solute elements, and working temperature. We also highlight the peculiar frequency and temperature response of Ni-Zn ferrites, which can be heavily affected by magnetic aftereffects. The physical modeling of the losses brings to light the role of the magnetic anisotropy and the way its magnitude distribution, affected by the internal demagnetizing fields, acts upon the magnetization process and its dependence on temperature and frequency. It is shown that the effective anisotropy governs the interplay of domain wall and rotational processes and their distinctive dissipation mechanisms, whose contributions are recognized in terms of different loss components

Measuring and modeling broadband magnetic losses versus temperature and aging effects in CoO-doped Mn-Zn ferrites

We analyze the physical mechanisms associated with addition of CoO to sintered Mn-Zn ferrites and the ensuing stabilization versus temperature of their magnetic properties. We determine, in particular, the value and behavior of the magnetic anisotropy as a function of doping and temperature and we model in physical terms the evolution of the energy loss in the investigated frequency (DC - 1 GHz) and temperature (20 degrees C - +130 degrees C) ranges. We show that magnetic aging by long exposure of the CoO-doped ferrites at 200 degrees C is minimized by additional TiO2 doping. This is observed to restrain the increase of the extra-anisotropy induced by directional ordering of the Co2+ cations

MnZn-ferrites: Targeted Material Design for New Emerging Application Products

In this article the main characteristics for emerging MnZn-ferrite applications are described on the basis of the new demands they possess on the ferrite material development. A number of recently developed MnZn-ferrite materials is presented together with the main scientific principles lying behind their development. These include: (i) high saturation flux density MnZn-ferrites (i.e. Bsat=550 mT at 10 kHz, 1200 A/m, 100°C), (ii) low power losses MnZn-ferrites (i.e. Pv~210 mW cm-3 at 100 kHz, 200mT, 100°C), (iii) MnZn-ferrites with broad temperature stability (i.e. PV<375 mW cm-3 for 25°C<T<140°C at 100 kHz, 200 mT), and (iv) MnZn-ferrites with high and frequency stable permeability (i.e. μi~12600 at 10 kHz, 0.1 mT, 25°C and tan(δ)/μi=20.5×10-6 at 100 kHz). In a final discussion the importance of defect chemistry for the time stability and stress sensitivity of the magnetic properties is discussed and some important issues are addressed, encountered during the transfer of a laboratory developed material to a large scale industrial production process

MnZn-ferrites: Targeted Material Design for New Emerging Application Products

In this article the main characteristics for emerging MnZn-ferrite applications are described on the basis of the new demands they possess on the ferrite material development. A number of recently developed MnZn-ferrite materials is presented together with the main scientific principles lying behind their development. These include: (i) high saturation flux density MnZn-ferrites (i.e. Bsat=550 mT at 10 kHz, 1200 A/m, 100°C), (ii) low power losses MnZn-ferrites (i.e. Pv~210 mW cm-3 at 100 kHz, 200mT, 100°C), (iii) MnZn-ferrites with broad temperature stability (i.e. PV<375 mW cm-3 for 25°C<T<140°C at 100 kHz, 200 mT), and (iv) MnZn-ferrites with high and frequency stable permeability (i.e. μi~12600 at 10 kHz, 0.1 mT, 25°C and tan(δ)/μi=20.5×10-6 at 100 kHz). In a final discussion the importance of defect chemistry for the time stability and stress sensitivity of the magnetic properties is discussed and some important issues are addressed, encountered during the transfer of a laboratory developed material to a large scale industrial production process