Study On Magnetic Properties And Exchange Bias Effect Of Perovskite-Like Nanoparticles

With the continuous development of the information age,the demand for information storage is further increased.Therefore,we need to further miniaturize the storage devices and further improve the storage density.However,as the device is further miniaturized,the size of the magnetic nanoparticles will be further reduced.When the size of nanoparticles is lower than the critical size,the magnetic nanoparticles will show superparamagnetism and lose the storage function.In 2003,Shumryev reported in Nature that in the composite particles of Co and CoO,the ferromagnetic/antiferromagnetic exchange bias effect can improve the temperature stability of magnetic nanoparticles and increase the coercivity of ferromagnetic materials.This achievement provides a solution for breaking the super-smooth effect of magnetic nanoparticles,which has aroused extensive interest in the research of ferromagnetic/anti-ferromagnetic nanocomposites.This paper focuses on the magnetic properties and magnetic bias effect of metal oxide nanoparticles.The specific research results are as follows:?1?Different concentrations of BaFe_12-xCu_xO₁₉9 nanoparticles were synthesized by hydrothermal method.The morphology of the sample was characterized by scanning electron microscope.It was found that with the increase of Cu²⁺concentration,the grain size of the sample BaFe_12-xCu_xO₁₉9 also increased,and the grains were gradually dispersed from each other.When the incorporation amount reached x=0.8,the grains basically dispersed from each other and presented regular hexagonal structure.The results of magnetic measurement show that proper incorporation of Cu²⁺can reduce the coercivity and saturation magnetization of BaFe₁₂O₁₉,so that BaFe₁₂O₁₉9 nanoparticles begin to change from hard magnetic properties to soft magnetic properties.Finally,the ion occupancy inside the crystal can be clearly obtained by analyzing the data of the M?ssbauer spectrum.?2?The rare earth ferrite LaFeO₃ nanoparticles were synthesized by hydrothermal method,and the morphology of the samples was qualitatively modified by adjusting the concentration of KOH and urea.The morphology of the samples was characterized by field emission scanning electron microscopy?SEM?and the magnetic properties were measured by Physical Property Measurement System?PPMS?.The results show that as the KOH concentration increases,the morphology of the sample gradually changes from cube to polygonal prism.The increase in urea causes the sample to stretch laterally,changing from a cubic structure to a cuboid structure.In terms of magnetic properties,the increase of either KOH or urea will increase the coercivity of the sample.?3?La₂CoMnO₆ nanoparticles with different Ni doping concentrations were synthesized by molten salt method.The test results show that the incorporation of Ni element causes the particles of La₂CoMnO₆ to gradually disperse and the size begins to decrease.In terms of magnetic properties,the incorporation of Ni significantly increases the Curie temperature of the La₂CoMnO₆ sample.The data shows that the Curie temperature of the pure La₂CoMnO₆sample is about 213K,and when the concentration of Ni reaches 60%,the Curie temperature has been increase to 241K.At the same time,as the concentration of Ni increases,the coercive force also decreases.