The Synthesis And Magnetic Properties Of Transiton Metals Alloy/spinel Ferrite Composites

In the paper, the preparation conditions, their structure and magnetic behaviors were studied. Now many methods are used to synthesize the composites, but in this paper, we attempted two methods, the Fe²⁺ disproportion under argon pretection and the Fe²⁺ disproportion under hydrothermal condition.First, the method of Fe²⁺ disproportion under argon pretection were used to synthesize Fe/Fe3O4 and FexCo1-x/FeyCo1-yFe2O4 composites. The aging time of the Fe/Fe3O4 synthesis needs between 2.5 hours and 3.5 hours. The KOH concentration is heigher than 14 mol/L. The sizes of Fe/Fe3O4 composites are 130 nm(α--Fe)and 500 nm(Fe3O4). The combination of metal and ferrite produces more excellent magnetic properties. Fe/Fe3O4 has high saturation magnetization and low coercivity, which make it have more extensive application. The maximum saturation magnetization of sample is 108.4emu/g, and coercivity is 61.2Oe. When the Co²⁺ cation was involved into the reaction, it accelerated the disproportion reaction and decreased the KOH concentration and aging time. FexCo1-x/FeyCo1-yFe2O4 has moderate saturation and high coercivity. The maximum coercivity of sample reaches 2925.44 Oe, and saturation magnetization is 73.0emu/g. Such excellent performance can satisfy the need of permanent information storage. Second, we synthesized FexCo1-x/FeyCo1-yFe2O4, FexCo1-x/FeyMnzCo1-y-zFe2O4, and FexCo1-x/FeyNizCo1-y-zFe2O4 composites by the method of the Fe²⁺ disproportion under hydrothermal condition. Then the above composites were reduced by H2, we got the Co-Fe,Fe0.82Co0.08Mn0.10 and Fe0.769Co0.077Ni0.154 alloys. The synthesises of these composites needed a less basic medium than first method, but in this method the Co²⁺ cation must be involved into the reaction. This is important to note at this point that similar composites produced in hydrothermal condition have much smaller grains(20±7 nm forα--Fe and 170±50 nm for Fe3O4 ). When the Ni²⁺, Mn²⁺ cations were involved into the composites, the FexCo1-x/FeyMnzCo1-y-zFe2O4, and FexCo1-x/FeyNizCo1-y-zFe2O4 composites were synthesized. Because the cations occupied A and B sites, so the cations largely influenced the magnetic properties of the composites. Co-Fe,Fe0.82Co0.08Mn0.10 and Fe0.769Co0.077Ni0.154 alloys had different structures. There was only BCC structure in Co-Fe alloy, but the others had both BCC andα-Mn structures.Finally, we compared two methods above. As the KOH concentrations were same, both the saturation magnetization and coercivity which composites were synthesized by the method of the Fe²⁺ disproportion under hydrothermal condition are higher than that composites synthesized by the method of Fe²⁺ disproportion under argon pretection.