CrTe Based Rare-Earth-Free Hard Magnetic Nanostructures Synthesized By High-Temperature Organic-Solution-phase Method

With the rapid development of science and technology,hard magnetic materials?permanent magnet materials?have a wide range of applications.Due to the high magnetic anisotropy?Ku?and high magnetic energy product??BH?max?,the hard magnetic material not only can be used in clean energy vehicles,wind power,energy-saving appliances,industrial motors and other civilian areas,but also can be used as basic materials in aerospaces,weapons and equipments,electronic information and other cutting-edge science and technology.In recent years,due to the excellent magnetic properties,rare earth hard magnetic materials have become a research boom.However,with the implementation of national rare earth resources protection rules,the price of rare earth elements soared,which makes the low-or zero content of rare earth hard magnetic materials have become a new field to explore.In this paper,Cr Te-based rare-earth-free hard magnetic nanostructures were prepared by high-temperature organic-solution-phase method.The influence of doping on the structures and properties were also studied.The main results are as follows:?1?Taking Fe?acac?₃ as Fe source,FeTe₂ spherical magnetic nanoparticles were synthesized by high-temperature organic-solution-phase method.The structures,magnetic properties,compositions and morphology of nanoparticles were mainly studied.Compared with the undoped FeTe₂ nanoparticles,above particles have a narrower particle size distribution.When x = 0.15,it has the excellent magnetic properties and the saturation magnetization of Fe_0.85Cr_0.15Te₂ is 7.34 emu/g at room temperature,which is 20 times higher than that of pure FeTe₂ nanoparticles.This is due to the fact that Fe-Fe interaction is converted from antiferromagnetism to ferromagnetism by lattice distortion and the superexchange coupling among Cr-Te-Cr is also one of the reasons of the enhancement of magnetic properties.?2?Due to the strong ferromagnetic interaction among Cr-Te-Cr,we synthesized the Cr₂Te₃ based soft/hard nanocomposites for the first time,in which Cr₂Te₃ is hexagonal hard magnetic phase and Cr₅Te₈ is monoclinic soft magnetic phase.Through analyzing the phase structures and magnetic properties,the change law of magnetic properties for Cr-Te has been studied.When the ratio of precursors is 1:1.8,Cr₂Te₃ nanorods have the best magnetic properties.And its coercivity is as high as 9.63 k Oe and the saturation magnetization and remanence magnetization are 23.04 emu/g and 9.85 emu/g respectively.The large magnetocrystalline anisotropy constant is derived from the low symmetry and the spin-orbit coupling of the Cr-Te phase,and its strong ferromagnetism is derived from the superexchange coupling of Cr-Te-Cr.The strength of the soft/hard magnetic coupling can be improved by adjusting the initial ratio of Cr: Te precursors.When Cr is excessive,it is favorable for the formation of hard magnetic phase of Cr₂Te₃.On the contrary,it is favorable for the growth of soft magnetic phase of m-Cr₅Te₈ when Te is excessive.?3?On the basis of successful fabrication of Cr₂Te₃ hard magnetic nanomaterials and regulation role of 3d transition metal element doping on the lattice and magnetic properties,Cr_2-xM_xTe₃ hard magnetic nanomaterials with 3d transition metal M?M=Mn,Fe,Co,Ni?elements doping were synthesized.When x=0.2,all the 3d transition metals can enter the Cr₂Te₃ lattice,the peak location and numbers of all the samples are consistent with the hexagonal Cr₂Te₃.Besides,there is no peaks of M,Te,Cr and their oxidation,and Cr_1.8Co_0.2Te₃ hard magnetic material has achieved the best magnetic properties.Moreover,we investigated the effects of Co doping on the structure,morphology and magnetic properties of Cr₂Te₃ systematically.At 0=0.4,Hc reaches a maximum of 14.01 k Oe,which is 1.5 times higher than that of Cr₂Te₃ hard magnetic material.Meanwhile,the main phase of the prepared nanomaterial is Cr₂Te₃ hard magnetic phase.In conclusion,we synthesized Cr₂Te₃ rare-earth-free hard magnetic nanocrystals by high-temperature organic-solution-phase method for the first time.Cr_2-xM_xTe₃ hard magnetic nanomaterials with better magnetic properties were prepared by doping the 3d transition metal,which laid an important foundation for the preparation of Cr-based rareearth-free hard magnetic nanomaterials.