Marek Kuzminski

Magnetite nanoparticles with a cobalt ferrite shell provide the opportunity to obtain a tunneling magnetoresistance structure and offer an additional degree of freedom in shaping the magnetoresistive characteristics. In order to investigate the effect of the relative fractions of the shell on magnetic and magnetoresistive properties, we have prepared (by chemical co-precipitation) a bi-magnetic (soft/hard) core–shell Fe3O4/CoFe2O4 nanoparticle system (with diameters of a few nm). The structural, magnetic, and electric transport properties of the as-prepared core precursor, core–shell nanoparticles, and sintered powder were determined. It was found that the obtained particles, which are few nanometers in size, have the desired single-crystalline spinel structure with a core–shell architecture and the expected magnetic properties associated with core–shell interactions. Sintering leads to more complex magnetic behavior and tunneling conductance.

The method of planar flow casting has been used for preparation of single-, bi- and tri-layered ribbons of the two different or the same composition to attain multi-layered ribbons suitable for an application. Prepared bilayer was composed of positively and negatively magnetostrictive layers Fe_77.5Si_7.5B₁₅/Co_72.5Si_12.5B_15. Other aim was to suppress potentially undesired surface effects of differences between ribbon surfaces and volume. We prepared the ribbons with composition Co₄₇Fe₂₁Mo_6.5B₂₁Si_4.5 as single layer and trilayer with the thickness ratio more than 3:1. Structural, chemical and magnetic properties in amorphous (as-cast) and crystalline state were investigated. The composition was chosen to obtain low saturation magnetostriction. Nanocrystallization improved soft magnetic properties namely for trilayer. Work proved that reduction of large surface/volume ratio enables to reduce undesired effects of shrinking surfaces that squeeze the small volume of a single ribbon more efficiently.