Preparation And Magnetism Of The Frustration Magnet CoCr₂O₄Nanocrystallites

The spinel AB2O4because of its unique structural features has many excellentprospect in physical and chemical properties. With the advancement of nanotechnology,thespinel ferrites has been widely used in various fields of social production and life. Wehave made partial results in the synthesis of nanoscale spinel ferrite by hydrothermalmethod.But its application prospects have not yet achieved a breakthrough. The mainreason is that there are some gaps between the nanocrystals synthesized by hydrothermalmethod in particle size and morphology of the regulation and t he actualrequirements.Therefore,the depth study have been made in process parameters of thehydrothermal synthesis of ferrite.And it caused widespread concern of many researchersto prepare ferrite nanocrystals with a series of different particle size,morphology andcomposition.The research of article contents of magnetic frustration CoCr₂O₄nanocrystallitespreparation,microstructure analysis,UV-visible spectroscopy analysis and magneticanalysis,and three main points including:1.An brief introduction about the crystal structure of the spinel CoCr₂O₄。Then morefocuses has been paid to the concept and the basic theory and research developments ofmagnetic geometrical frustration and the size effect as well as the intrinsic magnetic andresearch progress of CoCr₂O₄bulk. Subsequently,the basis of the subject background andsignificance of the article is put forward.2.CoCr₂O₄nanocrystallites of different particle size were successfully prepared byhydrothermal method.crystal phase and structure and particle size of the CoCr₂O₄crystallites were analyzed by XRD.The morphology of the CoCr₂O₄crystallite wasobserved by TEM. The visible light absorption of the CoCr₂O₄crystallite was observed byUV-visible spectrometer.Magnetism and ac susceptibility of the crystallites was measured by PPMS. The XRD patterns of the samples show that CoCr₂O₄nanocrystallites preparedby hydrothermal method are indeed pure phase and cubic spinel structure.The initialdesign of the experimental requirements of different particle size were reached.It seemsfrom the UV-visible absorption spectrum.The overlap of Absorption bands in the visiblelight range made CoCr₂O₄nanocrystallites ultimately showing a blue-green.TheseAbsorption peeks sttributed to the spin allowed transportation of Co²⁺in tetrahedron andCr³⁺in octahedron.3. The magnetism of CoCr₂O₄nanocrystallites in different particle size have beenobserved and compered.All CoCr₂O₄nanocrystallites from ferromagnetic tosuper-paramagnetic transition were occurd with decreasing particle size.As the particlesize increases,the ferromagnetism have been increased and the antiferromagnetic havebeen enhancement.But the magnetic anisotropy,the saturation magnetization and thecoercive force have been increased.The measurements of the ac susceptibility of CoCr₂O₄nanocrystallite at5nm between5and40K in10Oe field shows that nanocrystallite exhibitmagnetic frustration behavior.