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Multi-segment cores have been developed by cutting standard MnZn ferrite cores into thin segments and then re-assembling the segments together. All the segments were separated by a thin film of air or insulation materials of microscopic dimensions. The core loss properties of these experimental samples have been investigated between the frequencies of 200 kHz to 2 MHz. The real and imaginary parts of the effective permeability have been determined from these measurements. Experiment results show that the multi-segment ferrite cores are effective in reducing the core loss by possible mechanisms of reduction in the internal electromagnetic field strength and of reduction in the influence of the magnetic skin effect. Index Terms--Core loss, dielectric loss, ferrites, skin effect.

Polycrystalline hexagonal ferrites (Y, Z and W-phases) were prepared by the usual ceramic sintering. Their complex permeability spectra were natural resonance type, and numerically separated into spin rotational and domain wall motion components. For the spin rotational component, it was found that the Snoek's product values of them were far beyond the product values of spinel ferrite. It enabled us to design the thin electromagnetic wave absorbers in the quasimicrowave region. Index Terms--Electromagnetic wave absorber, hexagonal ferrite, permeability, Snoek's product.

Grain growth behavior in correlation with magnetic loss has been investigated in Mn-Zn ferrites with the variation of additive content and particle size of the system. The powders of [([Mn.sub.0.76][Zn.sub.0.24]O).sub.0.94] [([Fe.sub.2][O.sub.3]).sub.1.06] composition and the average particle size of 0.94 [micro]m and 1.93 [micro]m are prepared by milling the calcined powder in an attritor. CaO and Si[O.sub.2] are chosen as the additives and their content is varied from 0-5 wt%, respectively. It has been found that the grain morphology and the magnetic loss are greatly dependent upon the amount of additives and the particle size of the system. There is an optimum content of the additives to produce normal grain structure and low magnetic loss. Under a sufficient driving force of the system (approximately, submicron-sized powders), the abnormal (duplex) grain structure is developed in the specimens with the additives in excess of the optimum value. The possible mechanism of such impurity-induced abnormal grain growth is explained from the observed faceted ferrite grains which has been known to have singular surface structure and their growth kinetics controlled by two-dimensional nucleation. It is suggested that the additives content along with particle size control is one of the important processing variables to obtain the low-loss Mn-Zn ferrites with fine and uniform grain structure. Index Terms--Abnormal grain, additives, magnetic loss, Mn-Zn ferrites.

We report variations in the coercivity of Co[Fe.sub.2][O.sub.4] nanoparticles as a function of particle size, temperature and light intensity. For 30 nm particles, this change in was 2300 Oe at 10K, 120 Oe at 170K, for a light intensity of under 2 milliwatts. The remanent magnetization was nearly unchanged by illumination. A simple model of optical absorption followed by electron transfer between [Co.sup.2+] and [Fe.sup.3+] ions is proposed. Index Terms--Cobalt ferrite, coercivity, photomagnetic effect, remanent magnetization.