Structure, Microstructure and Magnetic Properties of CoxNi100-x Powders Synthesized by Hydrothermal Method

Abstract

Pure NiCo nanoparticles with different compositions were synthesized by hydrothermal route at 100 degrees C during 2 h. From x-ray diffraction analysis, we have shown that the structure varies from face-centered cubic (FCC) phase to a mixture of FCC and hexagonal closepacked (HCP) phases depending on the composition. For all CoxNi(100-x) powders, the microstructural analysis reveals an anisotropic crystallite size with a nanometric scale. The powder morphology looks like agglomerates of CoNi that drastically change their shape depending on the Co concentration, from an agglomeration of quasi spherical nanoparticles (Co20Ni80 and Co30Ni70) to submicrospheres self-assembled by nanoplatelets (Co50Ni50) and finally, to a dendritic morphology (Co80Ni20). Magnetic measurements show that CoxNi(100-x) exhibit a soft ferromagnetic with a saturation magnetization, which increases with increasing Co concentration. The coercive field, Hc, decreases firstly from 199 Oe (Co20Ni80) to a minimum value of 175 Oe (Co30Ni70) then it increases to reach a maximum of 280 Oe (Co80Ni20). The high values of Hc can be attributed to the magneto-crystalline anisotropy due to presence of HCP phase and to the shape anisotropy induced by the changes in the form of nanoparticles.