Research On Ferromagnetic-antiferromagnetic Core-shell Magnetic Composite Nanoparticles

Research on core-shell composite nanoparticles with ferromagnetic-antiferromagnetic structures has received attention.This article uses two different preparation methods,Mainly studying the Fe₃O₄-Co₃O₄ and Ni-NiO systems of transition metal oxides,adjust the microstructure of the sample by changing the reaction conditions and raw material ratio parameters,The structure、morphology and magnetism of the sample particles were systematically studied by X-ray diffraction（XRD）,scanning electron microscopy（SEM）and vibrating sample magnetometer（VSM）,Finalize the relationship between the microstructure and magnetic properties of the sample.For the Fe₃O₄-Co₃O₄ system,We use solvothermal method,Mainly regulate the final calcination temperature and raw material ratio of the sample,The results showed that with the increase of calcination temperature,the Co₃O₄ shell in the sample increased in thickness due to continuous oxidation,And at the calcination temperature of 400℃,the maximum thickness of the shell occurs,followed by the fragmentation of the nanosheet like shell,At the same time,at the calcination temperature of 350℃,the saturated magnetization and residual magnetization of the sample are the largest,which are 30.85 emu.g^-1 and 12.04 emu.g^-1,respectively.However,the coercive force continues to increase with the calcination temperature and reaches a maximum value of 753Oe at450℃.In addition,after changing the molar ratio of raw material Fe₃O₄ to Co（NO₃）₂·6H₂O to 1:1,Co₃O₄ shell cannot be generated.However,an increase in calcination temperature will cause oxidation of the Fe₃O₄ core structure,which is generally manifested as Fe₃O₄ orientedγ-Fe₂O₃ orientedα-Fe₂O₃.And due to the appearance of the antiferromagnetic phaseα-Fe₂O₃ can also cause abnormal magnetic behavior in the system,At the same time.the residual magnetization and saturated magnetization decreased and the coercivity increased.The comprehensive performance of the magnetic parameters of the sample was the best at the calcination temperature of 800℃,They are coerciveforce H_C=2109Oe,saturation magnetization M_S=47emu.g^-1,residual magnetization Mr=32emu.g^-1.For Ni NiO system,we use the sol gel method.In the sol gel method,the final calcination temperature of the sample was changed and the PH value was adjusted.The results showed that the increase of calcination temperature promoted the reduction of NiO,which was manifested in the increase of Ni phase content,making the saturation magnetization and residual magnetization of the sample show an upward trend.The increase in p H value is accompanied by a non monotonic change in the content of Ni NiO two-phase,but the aggregation of sample particles is not conducive to the study of the magnetic properties of the system.It is summarized that at a calcination temperature of450℃and a p H value of 1,the crystallinity and agglomeration of the sample particles constitute an optimistic microstructure.At this time,the saturation magnetization of the sample Ms=29.56emu.g^-1,the residual magnetization Mr=1.78 emu.g^-1,and the coercivity H_C=23Oe.