Preparation And Properties Of Heusler Alloy X₂YZ?X,Y=Fe,Co;Z=Al,Ga?by Electrospinning Method

The X₂YZ?X and Y are transition metals and Z is a main group element?Heusler compounds are of paramount importance for basic scientific interests and potential applications due to their excellent magnetic and electrical properties.So far,researchers have prepared the Heusler compound including bulk and nanoparticles by vacuum arc melting,high energy ball milling,molecular beam epitaxy,template growth method,electrochemical deposition,polyol reduction and so on.In this work,Fe₂CoAl and Co₂FeGa nanofibers are prepared by an electrospinning method which has the advantages of simple equipment,easy operation,high productivity and low cost.We have studied the effects of the experimental conditions on the samples' structure,morphology and chemical composition,and the samples of magnetic properties are characterized.This paper is of great importance to the preparation and application of one-dimensional Heusler alloy.Firstly,in this thesis,a series of Fe₂CoAl samples were prepared by electrospinning.The effects of PVP concentration,metal salt ion concentration and annealing method on the structure and morphology of the product were studied.The results show that the diameter of Fe₂CoAl nanofibers is the smallest when PVP concentration is 6wt%.It was found that the crystal structure,fiber diameter and magnetic properties of the samples varied with the metal salt ion concentration in the precursor solution.The Fe₂CoAl nanofibers prepared at 1.5³.5 mol/L metal salt ion concentration show typical ferromagnetic behavior.These samples' coercivity?HC?is 603⁷20 Oe and the Curie temperature might be greater than 600?.The low temperature magnetic measurements show that the saturation magnetic moment of Fe₂CoAl nanofibers at 5K is estimated to be 4.5-5.1?B.The high Curie temperature and large magnetic moments of Fe₂CoAl nanofibers prepared by electrospinning have potential applications in high-density information storage and nanoscale magnetic devices.Secondly,we also prepared a series of Co₂FeGa nanofibers by electrospinning.The effects of different experimental conditions: PVP concentration,annealing temperature,metal salt ion concentration,heat treatment and power source on structure and morphology of the sample were studied.A series of experiments shows that the prepared samples have A2-type structure with fibrous shape,long length and no fracture,with the diameter of 301nm,when the PVP concentration is 6wt%,the electrospinning voltage is +29kV and the annealing temperature is 750?.With the change of the metal salt ion concentration in the precursor solution,the crystal structure of the sample is unchanged.However,the diameter of the fiber increased from 270nm to 1160nm.The different heat treatment cause the change of the diameter and morphology of the sample.The Co₂FeGa nanofibers prepared by direct hydrogen annealing have smaller diameter,smoother surface,longer fiber and no fracture comparing with the sample firstly annealed in air and then annealed in hydrogen.Magnetic measurement reveals that the obtained Co₂FeGa nanofibers exhibit typical ferromagnetic behavior at room temperature.The saturation magnetization of the sample is from 120 to 158emu/g.The coercivity is smaller at low voltage and with air annealing,however,the coercivity of the samples annealed at high voltage and direct hydrogen annealing is greater than the coercivity of the sample at low voltage and with air annealing.When the sample is in the form of nanofibers,the magnetic moment is 5.2-6.9?B,which is significantly larger than the magnetic moment of Co₂FeGa bulk and nanoparticles reported in the literature.