Controllable Synthesis And Saturatation Magnetism Of Low-dimensional Fe-based Nanomaterials

In recent years,low-dimensional magnetic materials with shape and size controllable are one of the hotspots in physics research of materials science and condensed matter physics,which based on not only the important basic research but also further miniaturization of the spin electronics,track memory,and further improvement of the magnetic recording density.At present in the hysteresis motor or magnetic storage and other magnetic properties（energy density）requirements of relatively high equipment,the most widely used material is NdFeB permanent magnet.NdFeB rare earth permanent magnet as the third generation of permanent magnet material is due to the very high coercivity in the other permanent magnet material in front of an unparalleled advantage.However,in the microstructure analysis of NdFe B permanent magnets,it is found that NdFeB magnets contain a large amount of non-magnetic phase,which is the main reason for the low saturation magnetization.And it can’t be a good method to increase the magnetic properties which though doping the iron/cobalt/nickel magnet materials with high saturation magnetization,thus it can reduce the coercivity of the whole part.In the construction of nanostructured magnetic materials,it is found that the hard magnetic/soft magnetic interface will increase the remanence of the soft magnetic material under the influence of the magnetic coupling between the magnetic moments,which provides the new research direction of high density storage material.The newly founding of nanocomposite Nd-Fe-B permanent magnet material is a new type of permanent magnetic material,which is composed of high saturation magnetization soft magnetic phase and high anisotropy field of hard magnetic phase in the nano-scale compound.The magnetic properties can be obtained by the exchange coupling interaction between the soft and hard magnetic phases at the nanometer scale,and the saturation magnetization can be effectively promoted while maintaining the high coercivity.In this case,the low-dimensional magnetic nanomaterials with different morphologies were prepared by solvothermal method and sol-gel method respectively.The microstructure and magnetic properties of the materials were studied through the hard magnetic/soft magnetic interface.The main research results of this dissertation are summarized as follows:（1）In this dissertation,Fe₃O₄ hollow microspheres with uniform structure and uniformity were prepared by one-step hydrothermal method.In the experiment through with X ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X ray photoelectron spectroscopy（XPS）,superconducting quantum interference device（SQUID）test,the morphology and structure of magnetic materials have been tested.The formation mechanism of Fe₃O₄ hollow microspheres was analyzed,and the abnormality of nanometer hollow spheres on the saturation magnetization was deduced reasonably.（2）Single crystal iron nanoparticles with uniform size and good structure were prepared by solvothermal method,in which the single nanoparticles were stacked on the axis of the iron nanoparticles.Through the regulation of induced magnetic and experimental equipment in the reaction parameters adjustment,the formation of products is coated with PVP（polyvinylpyrrolidone）and（100）along with the single-crystal iron nanochains.And the reason for the magnetic change of PVP coated iron nanochains is studied in detail.（3）Nanocrystalline NdFeB oxide particles were prepared by sol-gel method,then Nd₂Fe₁₄B alloy was obtained by reduction of oxide with CaC₂,and Nd₂Fe₁₄B/Fe nanocomposites were formed by further annealing with iron nanochains which produced in the previous experiments.Based on the interface coupling principle of hard magnetic and soft magnetic,the magnetic energy product of Nd₂Fe₁₄B/Fe interface is increased by preparing nanocomposites.The results show that the iron nanochains can be combined with NdFeB nanoparticles to form a flaky structure by the annealing process,and the effect has obvious remanence enhancement.