Study On The Preparation And Magnetic Properties Of Sm-Co Based Composite Nanoparticles With Core-shell Structure

With the constant development and innovation of permanent magnetic materials,hard/soft exchange-coupled composite magnetic materials have become a hot spot, becausethis kind of materials possesses both high coercivity and saturation magnetization, resultingin a high energy product. In this paper, we have designed a core-shell structure to improvethe exchange coupling effect through increasing the interface surface between hard and softmagnetic phases.Sm-Co/Fe(Co) hard/soft exchange-coupling nanocomposite particles with core-shellstructure were prepared under the following conditions: Sm(Co, Hf)7nanoparticlesobtained by rapid quenching and high energy ball-milling technology were used as the hardmagnetic cores, FeCl2·H2O or CoCl2·H2O were used as the raw materials, hydrazinehydrate (N2H2·H2O) or sodium borohydride (NaBH4) were used as the reducing agents.Fe2+and Co2+were reduced in an inorganic solvent (water) or organic solvent (ethanol,ethylene glycol, polyethylene glycol) system. The XRD, TEM (HRTEM) and VSManalytical methods were used to characterize the microstructure and magnetic properties ofthe materials. The influences various technological parameters on the formation ofcore-shell structure and the hard/soft exchange coupling were studied.The results showed that, Fe2+tends to transform into oxides of iron (Fe3O4or Fe2O3)with lower chemical potential rather than Fe nanoparticles with higher chemical potential.On the other side, fcc and hcp soft magnetic Co shells were obtained successfully on thesurface of Sm(Co, Hf)7cores since Co2+has a higher reduction potential. The soft phaseFe7Co3shell with a higher saturated magnetization were formed when Fe2+and Co2+werereduced simultaneously, because the existence of Co2+can improve effectively, thereduction rate of Fe2+and prevent the re-oxidation of the obtained metals through reduction.In addition, the phase composition, the microstructure and the magnetic properties of thecomposite particles were influenced by various process parameters, including the acidifiedconcentration of solutions acidifying the Sm-Co particles, the concentration of metal ions inthe precursors, the heating time in the water bath and the types of alkali precipitators,solvents or reducing agents.