Soft magnetic composite of Ni3Fe/ZnFe2O4 type obtained by mechanical alloying/milling and spark plasma sintering

Abstract

Soft magnetic composite powder of Ni3Fe/ZnFe2O4 type has been obtained by mechanical milling of nanocrystalline Permalloy (Ni3Fe) particles with ZnFe2O4 particles. The nanocrystalline Ni3Fe particles were synthesised by mechanical alloying of elemental Ni and Fe powder. During the milling time, some of the ZnFe2O4 particles are embedded on the surface, and others are encapsulated in the volume of the Permalloy particles, creating a „raisin-bread” like structure. Also, at the surface of the Ni3Fe particles, a quasi-continuous layer of zinc ferrite is formed. The as formed composite particles have a structure of pseudo core-shell type, with a “raisin-bread” core. Upon mechanical milling, the phases are preserved according to X-ray diffraction (XRD) investigations, although the system magnetisation presents a slight decrease. The densification of the composite powder has been carried out using spark plasma sintering (SPS) technique at a sintering temperature range of 500–700 °C without holding time. The density and the electrical resistivity of the samples increase upon increasing the sintering temperature. Higher magnetisation is obtained for the sample sintered at 700 °C and accompanied by a lower coercive field. Upon sintering, a reaction at interface, between the Ni-based alloy and zinc ferrite occurs, leading to the formation of a new phase. The testing of the toroidal-shaped magnetic composite in the alternative current regime shows that the best results are obtained on the sample sintered at 700 °C. The losses decomposition was performed and showed that the dynamic losses become predominant after 1 kHz. The samples have been investigated by X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), vibrating sample magnetometer (VSM) for powder samples and by DC and AC magnetic investigation by hysteresisgraph method and electrical resistivity investigations for the sintered compacts.