The Synthesis And Various Physical Properties Of Two-dimensional Layered Magnetic Materials (Fe_（1-x）Ni_x)₅GeTe₂

Due to unique layered structure and large specific surface area,as well as the adjustment of the active sites by phase change and doping,etc.,two-dimensional layered magnetic materials are considered as an alternative to noble metal materials for the field of catalysis;Two-dimensional layered magnetic materials are used to the field of microwave absorption because of low density,good toughness,low thickness and ferromagnetic properties;The Curie temperature of two-dimensional layered magnetic materials is lower than room temperature,which hinders the application in the field of spintronics.Therefore,the search for two-dimensional magnetic materials with higher Curie temperature is a major problem to be solved at present.Fe₅GeTe₂ is a two-dimensional van der Waals ferromagnet near room temperature,and how to adjust it to obtain a higher Curie temperature is still in the early stage of experiments.In this paper,the magnetic,catalytic and microwave absorption properties of Fe₅GeTe₂ and Ni-doped Fe₅GeTe₂ are systematically studied.The results are as follows:（1）Single crystal(Fe_（1-x）Ni_x)₅GeTe₂ was successfully synthesized by chemical vapor transport method,and scanning electron microscopy showed that the single crystals were layered structure.The experimental results show that the Curie temperature of Fe₅GeTe₂ is295.07 K,and when the Ni atom doping content is 5%,10%,15%,20%,30%,the corresponding Curie temperatures is 349.38 K,386.23 K,397.72 K,408.41 K,514.54 K,respectively.The Curie temperature of Fe₅GeTe₂ is effectively increased by Ni doping,but the coercivity of all single crystal samples is less than 200 Oe.（2）(Fe_（1-x）Ni_x)₅GeTe₂ thin-layer nanosheets were obtained by liquid phase separation method,and electrocatalytic properties were subsequently studied.When the Ni atom doping amount is 10%,the oxygen evolution test results show that the starting potential of the nanosheet is 1.54 V,theTafel slope is 48 m V/dec,and the electrochemical bilayer capacitance is 0.238 m F/cm²;the hydrogen evolution performance test results show that the overpotential corresponding to the current density of-10 m A/cm² is 257 m V,theTafel slope is 254.8 m V/dec,and the electrochemical bilayer capacitance is 26.55 m F/cm².（3）Fe₅GeTe₂ and polypyrrole composites were prepared by ultrasonic blending method,and microwave absorption performance was subsequently studied.The test results show that when the composite ratio of Fe₅GeTe₂ and polypyrrole is 50%,the composite material has the strongest loss ability in high frequency electromagnetic wave reflection.When the thickness is 1.64 mm and the frequency is 15.15 GHz,the minimum reflection absorption value of the composite material reaches-56.63 d B,and the corresponding effective absorption bandwidth（RL≤-10 d B）is up to 5 GHz.