APPROACH TO SATURATION AND MAGNETIC-PROPERTIES OF MELT-SPUN FE-CU GRANULAR SYSTEMS

The aim of the work is to analyze the correlation between structure, s hape and volume distribution of magnetic aggregates and magnetic prope rties in FexCu100-x(x = 30, 50, 70) melt-spun ribbons. The structural analysis, performed by X-ray diffraction and scanning electron microsc opy, shows that the sample is mainly composed of a mixture of Cu rich, non-magnetic, and BCC-Fe ferromagnetic aggregates widely distributed in size. Evidence of a partial mutual solubility between both immiscib le elements is found in the as-cast state, so the main effect of the t hermal treatment is to produce an almost complete segregation of both purl BCC-Fe and FCC-Cu immiscible phases, and thus, an increase in the corresponding mean grain sizes. The magnetization process of the samp les reflects the complex magnetic behavior associated with a wide dist ribution in size of magnetic aggregates. The law of approach to satura tion has been found to be an excellent complementary technique to corr elate nanostructure and magnetic properties. The observed magnetic beh avior can be interpreted as the contribution of superparamagnetic part icles, single domain and multidomain aggregates, the multidomain being the first-order contribution. The results show that the shape of the magnetic aggregates governs through the internal demagnetizing field t he macroscopic magnetization curve. This shape can be controlled throu gh the Fe content, since as the Fe content increases the ferromagnetic aggregates evolve from spherical to ribbon-shaped.