Diluted magnetic semiconductor with Cr-doped CdS nano-structure and preparation method of diluted magnetic semiconductor

Abstract

The invention discloses a diluted magnetic semiconductor with a Cr-doped CdS nanostructure and a preparation method of the diluted magnetic semiconductor. The diluted magnetic semiconductor is composed of three elements of Cr, Cd and S, and the chemical general formula of the diluted magnetic semiconductor is Cd1-xCrxS. According to the diluted magnetic semiconductor, cadmium oxide, powdered sulfur and chromium chloride hexahydrate are used as raw materials, ethanolamine and ethylenediamine are used as organic solvents, and the diluted magnetic semiconductor with the Cr-doped CdS nano structure is synthesized through a solvothermal method. The nanoparticles are small in particle size, can generate strong ferromagnetic properties, are excellent in saturation magnetization, and can be widely applied to electronic components, semiconductor chips and integrated circuits.

Description

Technical Field

[0001] The present invention relates to the technical field of diluted magnetic semiconductors, and particularly to a diluted magnetic semiconductor of Cr-doped CdS nanostructure and a preparation method thereof. Background Art

[0002] As an emerging functional material, diluted magnetic semiconductors (DMSs) can combine the electron charge degree of freedom and the spin degree of freedom, and have excellent magnetic, electrical, and magnetoelectric properties, showing very broad application prospects in the fields of spintronics and optoelectronics. Diluted magnetic semiconductor nanomaterials are considered to be the core key materials for spin-related semiconductor electronics or spintronics. In nanomaterials doped with room-temperature ferromagnetic properties, the doping elements are mainly magnetic elements, such as Fe, Co, and Ni. The incorporation of these magnetic elements generally produces relatively weak ferromagnetism, the doping process is complex, and the preparation cost is high. Madhu et al. prepared CdS nanoparticles by the sol-gel method, and these CdS nanoparticles exhibit diamagnetism or relatively weak ferromagnetism.

[0003] The solvothermal method is generally regarded as an effective method for preparing high-purity crystal structures. Its basic method is to increase the pressure and temperature of the solvent so that the dopant can pass through the grain interface and promote the effective growth of the crystal to directly synthesize nanomaterials. This method has simple process, convenient operation, high yield, and good crystallization. However, there are very few reports on the preparation of room-temperature ferromagnetic Cr-doped CdS by a simple solvothermal method, and there has been little systematic and detailed research.

[0004] The present invention uses ethylenediamine and ethanolamine as a mixed solution, and synthesizes Cr-doped CdS of Cr-doped CdS nanostructure by the solvothermal method. The nanoparticles have small particle size, can produce strong ferromagnetic properties, and have excellent saturation magnetization intensity, and can be widely used in electronic components, semiconductor chips, and integrated circuits. Summary of the Invention

[0005] The purpose of the present invention is to provide a diluted magnetic semiconductor of Cr-doped CdS nanostructure and a preparation method thereof. The Cr-doped CdS nanoparticles of the diluted magnetic semiconductor have regular morphology, small particle size, can produce strong ferromagnetic properties, and have excellent saturation magnetization intensity.

[0006] The technical solution of the present invention: A diluted magnetic semiconductor of Cr-doped CdS nanostructure, the diluted magnetic semiconductor is composed of three elements of Cr, Cd, and S, and the chemical general formula is Cd 1-x Cr x S, where x = 1.15 - 7.16%.

[0007] The aforesaid x = 3.94%.

[0008] The aforesaid dilute magnetic semiconductor has a wurtzite structure.

[0009] The particle diameter of the aforesaid dilute magnetic semiconductor is 30 - 40 nm.

[0010] The preparation method of the aforesaid dilute magnetic semiconductor of Cr-doped CdS nanostructure, wherein the dilute magnetic semiconductor uses cadmium oxide, sulfur powder and chromium chloride hexahydrate as raw materials, ethanolamine and ethylenediamine as organic solvents, and synthesizes the dilute magnetic semiconductor of Cr-doped CdS nanostructure by a solvothermal method.

[0011] The aforesaid preparation method is carried out according to the following steps:

[0012] (1) Dissolve 4 - 6 mmol of cadmium oxide and 4 - 6 mmol of sulfur powder in a mixed solution of 15 - 25 mL of ethanolamine and 8 - 12 mL of ethylenediamine, and add 0.25 - 1.00 mmol of chromium chloride hexahydrate to the mixed solution to obtain mixture A;

[0013] (2) At room temperature, magnetically stir mixture A for 15 - 25 min, then transfer it to a stainless steel reaction kettle lined with polytetrafluoroethylene, continue to stir for 15 - 25 min and then seal it. After sealing, heat the reaction kettle from room temperature to 170 - 190 °C within 35 - 50 min, keep it at 170 - 190 °C for 22 - 26 h, take out the reaction kettle and let it cool naturally to room temperature, and collect the yellow precipitate obtained from the reaction;

[0014] (3) Take the yellow precipitate and wash it repeatedly with deionized water and absolute ethanol for 3 - 6 times. Place the washed precipitate in a vacuum oven at 55 - 65 °C for 5 - 7 h to obtain the dilute magnetic semiconductor of Cr-doped CdS nanostructure.

[0015] In the aforesaid step (1), dissolve 5 mmol of cadmium oxide and 5 mmol of sulfur powder in a mixed solution of 20 mL of ethanolamine and 10 mL of ethylenediamine, and add 0.75 mmol of chromium chloride hexahydrate to the mixed solution to obtain mixture A.

[0016] In the aforesaid step (2), at room temperature, magnetically stir mixture A for 20 min, then transfer it to a stainless steel reaction kettle with a capacity of 40 mL lined with polytetrafluoroethylene, continue to stir for 20 min and then seal it. After sealing, heat the reaction kettle from room temperature to 180 °C within 40 min, keep it at 180 °C for 24 h, take out the reaction kettle and let it cool naturally to room temperature, and collect the yellow precipitate obtained from the reaction;

[0017] In the aforementioned step (3), the yellow precipitate was taken and washed repeatedly with deionized water and absolute ethanol for 4 - 5 times. The precipitate obtained after washing was placed in a vacuum oven at 60 °C for 6 h to obtain the dilute magnetic semiconductor of Cr-doped CdS nanostructure.

[0018] Specifically, in the aforementioned step (3), the purity of the absolute ethanol was 99.9%.

[0019] Advantages of the present invention:

[0020] The present invention uses CdO, sulfur powder, and chromium(III) chloride hexahydrate (CrCl3·6H2O) as raw materials, and synthesizes Cr-doped CdS wurtzite nanostructures by a mixed solvent thermal method. Cr-doped CdS has ferromagnetism. The saturation magnetization M of Cr-doped CdS (Cr = 3.94%) s is 9.258×10-6 A·m2 / g, and the c coercivity is Description of the drawings

[0021] Figure 1 : XRD patterns of CdS samples with different chromium doping amounts ((a): XRD pattern of Cr-doped CdS sample; (b): partially enlarged XRD pattern of Cr-doped CdS sample);

[0022] Figure 2 : Graph of CdS lattice constant ac versus Cr concentration ((a): Graph of -CdS lattice constant a versus Cr concentration; (b): CdS lattice constant c versus Cr concentration);

[0023] Figure 3 : TEM images of CdS with different chromium doping amounts;

[0024] Figure 4 : EDS spectra of CdS with different chromium doping amounts;

[0025] Figure 5 : UV-visible absorption spectrum of Cr-doped CdS nanostructure;

[0026] Figure 6 : Magnetization intensity versus magnetic field intensity (M-H) curve of Cr-doped CdS nanostructure at room temperature ((a): M-H curve; (b) partially enlarged view);

[0027] Figure 7 : Saturation magnetization M of Cr-doped CdS s versus a and c lattice constant graph. Specific embodiments

[0028] The present invention will be further described below in conjunction with embodiments, but it shall not be used as a basis for limiting the present invention. The reagents, materials, etc. used in the following embodiments can be obtained from commercial channels without special instructions; the test methods used are conventional methods without special instructions.

[0029] Example 1:

[0030] (1) Dissolve 5 mmol of cadmium oxide and 5 mmol of sulfur powder in a mixed solution of 20 mL of ethanolamine and 10 mL of ethylenediamine, and add 0.75 mmol of chromium(III) chloride hexahydrate to the mixed solution to obtain mixture A;

[0031] (2) At room temperature, stir mixture A magnetically for 20 min, then transfer it to a 40 mL stainless steel autoclave with a polytetrafluoroethylene liner, continue stirring for 20 min and then seal it. Heat the autoclave from room temperature to 180 °C within 40 min, keep it at 180 °C for 24 h, take out the autoclave and let it cool naturally to room temperature, and collect the yellow precipitate obtained from the reaction;

[0032] (3) Take the yellow precipitate and wash it repeatedly with deionized water and absolute ethanol for 5 times. Place the washed precipitate in a vacuum oven at 60 °C for 6 h to obtain a dilute magnetic semiconductor of Cr-doped CdS nanostructure.

[0033] Example 2:

[0034] (1) Dissolve 5 mmol of cadmium oxide and 5 mmol of sulfur powder in a mixed solution of 20 mL of ethanolamine and 10 mL of ethylenediamine, and add 1.0 mmol of chromium(III) chloride hexahydrate to the mixed solution to obtain mixture A;

[0035] (2) At room temperature, stir mixture A magnetically for 20 min, then transfer it to a 40 mL stainless steel autoclave with a polytetrafluoroethylene liner, continue stirring for 20 min and then seal it. Heat the autoclave from room temperature to 180 °C within 40 min, keep it at 180 °C for 24 h, take out the autoclave and let it cool naturally to room temperature, and collect the yellow precipitate obtained from the reaction;

[0036] (3) Take the yellow precipitate and wash it repeatedly with deionized water and absolute ethanol for 6 times. Place the washed precipitate in a vacuum oven at 60 °C for 6 h to obtain a dilute magnetic semiconductor of Cr-doped CdS nanostructure.

[0037] Example 3:

[0038] (1) Dissolve 5 mmol of cadmium oxide and 5 mmol of sulfur powder in a mixed solution of 20 mL of ethanolamine and 10 mL of ethylenediamine, and add 0.50 mmol of chromium(III) chloride hexahydrate to the mixed solution to obtain mixture A;

[0039] (2) At room temperature, the mixture A was magnetically stirred for 18 min, then transferred to a 40 mL stainless steel autoclave with a PTFE liner, and continuously stirred for 25 min before sealing. After sealing, the autoclave was heated from room temperature to 180 °C within 38 min, maintained at 180 °C for 25 h, taken out and naturally cooled to room temperature, and the yellow precipitate obtained from the reaction was collected.

[0040] (3) The yellow precipitate was repeatedly washed alternately with deionized water and absolute ethanol three times, and the obtained precipitate after washing was placed in a vacuum oven at 55 °C for 7 h to obtain the dilute magnetic semiconductor of Cr-doped CdS nanostructure.

[0041] Example 4:

[0042] (1) 5 mmol of cadmium oxide and 5 mmol of sulfur powder were dissolved in a mixed solution of 20 mL of ethanolamine and 10 mL of ethylenediamine, and 0.25 mmol of chromium(III) chloride hexahydrate was added to the mixed solution to obtain mixture A.

[0043] (2) At room temperature, the mixture A was magnetically stirred for 25 min, then transferred to a 40 mL stainless steel autoclave with a PTFE liner, and continuously stirred for 18 min before sealing. After sealing, the autoclave was heated from room temperature to 180 °C within 42 min, maintained at 180 °C for 23 h, taken out and naturally cooled to room temperature, and the yellow precipitate obtained from the reaction was collected.

[0044] (3) The yellow precipitate was repeatedly washed alternately with deionized water and absolute ethanol four times, and the obtained precipitate after washing was placed in a vacuum oven at 65 °C for 5 h to obtain the dilute magnetic semiconductor of Cr-doped CdS nanostructure.

[0045] Example 5:

[0046] (1) 4 mmol of cadmium oxide and 6 mmol of sulfur powder were dissolved in a mixed solution of 15 mL of ethanolamine and 12 mL of ethylenediamine, and 0.45 mmol of chromium(III) chloride hexahydrate was added to the mixed solution to obtain mixture A.

[0047] (2) At room temperature, the mixture A was magnetically stirred for 15 min, then transferred to a stainless steel autoclave with a PTFE liner, and continuously stirred for 25 min before sealing. After sealing, the autoclave was heated from room temperature to 190 °C within 50 min, maintained at 190 °C for 26 h, taken out and naturally cooled to room temperature, and the yellow precipitate obtained from the reaction was collected.

[0048] (3) The yellow precipitate was repeatedly washed alternately with deionized water and absolute ethanol three times, and the obtained precipitate after washing was placed in a vacuum oven at 55 °C for 7 h, thus obtaining the dilute magnetic semiconductor of Cr-doped CdS nanostructure.

[0049] Example 6:

[0050] (1) 6 mmol of cadmium oxide and 4 mmol of sulfur powder were dissolved in a mixed solution of 25 mL of ethanolamine and 8 mL of ethylenediamine. 0.75 mmol of chromium(III) chloride hexahydrate was added to the mixed solution to obtain mixture A;

[0051] (2) At room temperature, mixture A was magnetically stirred for 25 min, then transferred to a stainless-steel reaction kettle lined with polytetrafluoroethylene, and continuously stirred for 15 min before sealing. After sealing, the reaction kettle was heated from room temperature to 170 °C within 35 min, maintained at 170 °C for 22 h, taken out and naturally cooled to room temperature, and the obtained yellow precipitate was collected;

[0052] (3) The yellow precipitate was repeatedly washed alternately with deionized water and absolute ethanol six times, and the obtained precipitate after washing was placed in a vacuum oven at 65 °C for 5 h, thus obtaining the dilute magnetic semiconductor of Cr-doped CdS nanostructure.

[0053] To verify the beneficial effects of the present invention, the inventors conducted a large number of experimental studies, and the experimental processes and results are as follows:

[0054] 1 Experimental section

[0055] 1.1 Reagents and instruments

[0056] 1.1.1 Main reagents: Ethanolamine (EA), ethylenediamine (EN), cadmium oxide (CdO), sulfur (S) powder, and chromium(III) chloride hexahydrate (CrCl3·6H2O). All the reagents used were of analytical grade.

[0057] 1.1.2 Main instrument equipment: Stainless-steel reaction kettle lined with polytetrafluoroethylene (model KH-40ML), high and low temperature alternating test chamber (model: GDSZ-50L), vertical vacuum drying oven (model JC-6050SA).

[0058] 1.2 Preparation method

[0059] (1) 5 mmol of cadmium oxide (CdO) and 5 mmol of sulfur (S) powder were dissolved in a mixed solvent of 20 mL of ethanolamine (EA) and 10 mL of ethylenediamine (EN). 0, 0.25, 0.50, 0.75, and 1.00 mmol of chromium(III) chloride hexahydrate (CrCl3·6H2O) were respectively added to the mixed solution.

[0060] (2) At room temperature, the mixture was magnetically stirred for 20 min and then transferred to a 40 mL stainless-steel autoclave with a polytetrafluoroethylene liner, and stirring was continued for 20 min. After sealing, the autoclave was heated from room temperature to 180 °C within 40 min and maintained at 180 °C for 24 h. After 24 h, the autoclave was taken out and naturally cooled to room temperature.

[0061] (3) The yellow precipitate obtained from the reaction was collected, and finally washed several times alternately with deionized water and absolute ethanol (purity 99.9%). The washed precipitate was placed in a vacuum oven at 60 °C for 6 h. Several groups of samples were synthesized using the same method, corresponding to samples a - e.

[0062] 1.3 Testing and Characterization

[0063] The crystal structure and chemical composition of the product were analyzed using an X-ray diffractometer (Cu Ka target, λ = 0.154 nm) from Mac-Science Co., Ltd., Japan. The scanning rate was 2° / min, and the measurement range was 10° - 90°.

[0064] The microscopic morphology and structure of the nanomaterials were observed using a Hitachi-8100 transmission electron microscope (TEM).

[0065] The chemical composition of the samples was characterized by energy-dispersive spectroscopy (EDS). The optical properties of the samples were tested using a discrete double-source PerkinElmer Lambda-20 spectrometer-type ultraviolet-visible reflection spectrum (UV-Vis). For the tungsten lamp, the wavelength range was 350 - 800 nm, and for the deuterium lamp, the wavelength was 185 - 395 nm. When measuring, the distance between the ultraviolet lamp and the sample was 2 cm, and the ultraviolet light intensity at this position was 20 mW / cm 2 ; The magnetic properties of the product were measured using a superconducting magnet vibrating sample magnetometer (VSM, Lake 7400). The characterization conditions of the superconducting magnet vibrating sample magnetometer were carried out at room temperature, with an external magnetic field of -11000 Oe - 11000 Oe, and each 500 Oe was a test point.

[0066] 2 Results and Discussion

[0067] 1.1 XRD Characterization

[0068] Figure 1 is the XRD pattern of the obtained product CdS, Figure 2 is the enlarged XRD pattern of the obtained product CdS at the local (100), (002), and (101) peaks.

[0069] By comparing with the standard card of hexagonal wurtzite structure CdS in the JCPDS card (the lattice constants are a = 0.415 nm and c = 0.675 nm for card No. 41-1049), it can be seen that the obtained product is hexagonal wurtzite structure CdS. The 8 diffraction peaks correspond to the crystal planes of (100), (002), (101), (102), (110), (103), (112) and (201) respectively, and no Cr2S3 or other second phases are observed.

[0070] Curve Figure 1 When the percentage content of Cr atoms in the curve is 0.00%, (100) is the strongest peak. When the percentage content of Cr atoms in the curve Figure 1 is 1.15%, (002) is the strongest peak. When the percentage content of Cr atoms in the curve Figure 1 is 1.72%, Figure 1 when the percentage content of Cr atoms in the curve is 3.94%, and Figure 1 when the percentage content of Cr atoms in the curve is 7.16%, (101) is the strongest peak. The main reason may be preferred orientation. After doping with an appropriate amount of Cr, the growth rate of grains, the change of grain size, the change of grains with different orientations, and the change of grain boundaries are also accompanied. From Figure 1 (b), it can be seen that the peak position of (100) in Cr-doped CdS is slightly shifted to a higher angle by 0.4° compared with that in undoped CdS (100), which further indicates that Cr is doped into the CdS lattice.

[0071] Figure 2 (a) is the graph of the lattice constant a of Cr-doped CdS versus the Cr concentration (Cr: 0% - 7.16%), Figure 2 (b) is the graph of the lattice constant c of Cr-doped CdS versus the Cr concentration (Cr: 0% - 7.16%). The doping concentrations of 4 doped samples are calculated by stoichiometry. From Figure 2 it can be seen that in the range of 0% - 7.16%, as the Cr doping concentration increases, the lattice constant of CdS becomes smaller, which is the result of the substitution effect caused by smaller ions replacing larger ions.

[0072] Cd 2+ has a radius of 0.0970 nm, and Cr 3+ has a radius of 0.0890 nm. After Cr 3+ replaces Cd 2+ , the unit cell volume will decrease and the lattice will become smaller. According to Bragg's formula 2dsinθ = kλ (d is the interplanar spacing, k is the diffraction order, λ is the incident wave wavelength, and θ is the diffraction angle), the diffraction peak shifts to a higher angle after doping. And the full width at half maximum of the X-ray diffraction peak (δ observed ) is the sum of the full width at half maximum of the sample (δ L ) and the instrumental magnification full width at half maximum (δ instrumentalThe function of (). To determine the magnification of the instrument, standard materials (strain-free materials) such as silicon are used in the XRD pattern to analyze these two effects. Their relationship is as follows,

[0073] δ L = [(δ observed ) 2 -(δ instrumental ) 2 12 (1)

[0074] In addition, the grain size of CdS nanoparticles can be calculated by the Scherrer formula

[0075] L hkl = pλ / (δ L cosθ) (2)

[0076] In formula (2): δ L is the full width at half maximum of the diffraction peak (rad); P is the Scherrer constant (usually taken as 0.94); θ is the Bragg diffraction angle (°); λ is the wavelength of the incident X-ray (the CuKa wavelength is 0.15406 nm); L hkl is the grain diameter perpendicular to the crystal plane (hkl) direction. Taking the logarithm of equation (2) gives

[0077]

[0078] The grain sizes corresponding to the peaks (a = 0%, b = 1.15%, c = 1.72%, d = 3.94%, e = 7.16%) are 25, 41, 38, 35, and 33 nm respectively.

[0079] 1.2 TEM analysis

[0080] Figure 3 are the TEM images of Cr-doped CdS products with different doping concentrations.

[0081] From Figure 3 (a)-3(b), it can be seen that the morphologies of undoped and low-Cr-doped CdS are short nanorods. With the increase of the Cr doping amount, the morphology of CdS changes greatly, gradually changing from short nanorods to nanoparticles. From Figure 3 (c)- Figure 3 (e), it can be seen that the morphology of high-Cr-doped CdS with higher doping concentration is mainly smaller nanoparticles, and the nanoparticle yield is higher. By comparing the TEM images of Cr-doped CdS with different doping concentrations, it can be known that the morphology of the nanostructure has a great relationship with the Cr doping amount. With the increase of the Cr doping amount, the CdS nanoparticles tend to become finer. Figure 3 ​(d) shows Cr-doped CdS (Cr = 3.94%) nanoparticles with uniform particle size, regular morphology, and particle diameter of 30 - 40 nm.

[0082] 2.3 EDS Analysis

[0083] The EDS spectrum of the Cr-doped CdS nanostructure is as Figure 4 shown. Figure 4 It can be seen that the prepared sample is composed of three elements: Cd, S, and Cr, and no other impurities are found.

[0084] In the EDS system, the spectrum collected is point analysis. The detection of the presence of Cr proves that Cr 3+ ions are incorporated into the CdS lattice. Based on the EDS measurement and stoichiometry calculation, the percentage contents of Cr atoms in CdS are 1.15%, 1.72%, 3.94%, and 7.16% respectively.

[0085] 2.4 UV-Vis Analysis

[0086] The absorption and emission optical properties of nanostructures are size-dependent. As Figure 5 can be seen, the approximate absorption band edge of CdS nanorods appears at 553 nm, while the approximate absorption band edges of Cr-doped CdS nanoparticles with different doping concentrations appear at 550 nm, 547 nm, 545 nm, and 540 nm respectively. Elavarthi et al. studied that the band gaps of undoped and Cr (3% and 5%) CdS nanoparticles are 2.99 eV, 2.93 eV, and 2.82 eV respectively. Compared with the CdS standard gap (2.53 eV), the blue shift amplitudes are 0.46 eV, 0.40 eV, and 0.29 eV respectively. This blue shift to higher energy is a direct result of the quantum confinement effect related to small particle size. The absorption spectrum of doped CdS nanoparticles shows a slight blue shift at 537 nm compared with undoped CdS, which indicates that the CdS absorption spectrum is related to the characteristics of the quantum confinement effect. The quantum size effect of the nanostructure is directly reflected in the blue shift of the absorption peak, about 2 nm after doping. The change in the band gap of different Cr-doped CdS samples is caused by the change in the size of CdS.

[0087] According to the effective mass theory of the continuous medium spherical model, the band gap is approximately calculated. Under quantum confinement, the band gap of the nanostructure undergoes a blue shift, which is calculated using quantization theory.

[0088]

[0089] In Equation (4): R is the particle radius; M is the molar mass; is the reduced Planck constant; and are the band gaps of the nanomaterial and the bulk material respectively; ΔEg is the band gap difference between the nanomaterial and the bulk material. The band gap of bulk CdS is 2.53 eV. It is calculated by Equation (4) that the band gap of CdS nanoparticles has a blue shift of 3.2 nm, which is basically consistent with the experimental results in this paper.

[0090] 2.5 VSM analysis

[0091] Figure 6 is the magnetization intensity and magnetic field strength (M-H) curve of Cr-doped CdS nanostructures at room temperature.

[0092] It can be seen from Figure 6 (a) that the Cr-doped CdS nanostructures obviously have a hysteresis loop. At room temperature, the ferromagnetism of Cr-doped CdS is significantly stronger than that of undoped CdS. It can be seen from Figure 6 (b) that the saturation magnetization intensities of Cr-doped CdS nanoparticles are M s respectively 1.029×10 -6 , 2.143×10 -6 , 3.792×10 -6 , 9.258×10 -6 and 5.376×10 -6 A·m 2 / g, and the coercive forces H c are 84.83, 116.27, 130.19, 73.25 and

[0093]

[0094] It can be seen from the local enlarged view of the magnetization intensity and magnetic field strength of Cr-doped CdS nanoparticles with different doping concentrations that the coercive forces of CdS nanostructures with different doping amounts are significantly different. When the Cr doping amount is in the range of 0% - 3.94%, the saturation magnetization intensity of Cr-doped CdS nanostructures increases with the increase of Cr concentration. Although the observed saturation magnetic moment in CdS is very small, it is comparable to that of non-magnetic oxides. The origin of the ferromagnetism of CdS can be discussed from the perspective of surface defects of CdS nanoparticles. Aggregated large particle CdS shows extremely weak ferromagnetism, while the saturation magnetization intensity of Cr-doped CdS nanoparticles can reach up to 9.258×10 -6 A·m 2 / g, and the maximum coercive force can reach This result provides a strong guarantee for the production and application of dilute magnetic semiconductor Cr-doped CdS nanoparticles. The relationship between the saturation magnetization intensity M s of Cr-doped CdS and the lattice constant is as Figure 7 shown.

[0095] Cd 1-x Cr xMagnetization M of S nanoparticles s Within a certain range of Cr doping, Cd 1-x Cr x The lattice constant of the S nanoparticles is slightly smaller than that of the undoped CdS nanorods. In the range of x = 0 - 3.94%, the lattice constant and saturation magnetization of the nanoparticles increase linearly with the increase of Cr concentration. When x > 3.94%, the saturation magnetization shows a downward trend, and the change of the lattice constant affects the change of the saturation magnetization. The proportional relationship between the lattice constant and the Cr concentration in the CdS nanosheets indicates that the saturation magnetization is proportional to the Cr concentration.

[0096] 3 Conclusions

[0097] Using CdO, sulfur powder, and chromium(III) chloride hexahydrate (CrCl3·6H2O) as raw materials, different Cr-doped CdS nanostructures were synthesized by the mixed solvent thermal method. Through a series of characterizations, the following conclusions can be drawn:

[0098] 1) Cr-doped CdS is a hexagonal wurtzite nanostructure, and the diameter of the nanoparticles is about 30 - 40 nm. EDS tests show that a small amount of Cr is incorporated into the CdS lattice.

[0099] 2) Undoped CdS has weak ferromagnetism, while Cr-doped CdS has strong ferromagnetism. The saturation magnetization M of CdS with a Cr doping amount of Cr = 3.94% s is 9.258×10-6 A·m2 / g, and the coercivity H c is

Claims

1. A Cr-doped CdS nanostructured diluted magnetic semiconductor, characterized in that: Diluted magnetic semiconductors are composed of three elements: Cr, Cd and S. The general chemical formula is Cd 1-x Cr x S,x = 1.15-7.16%.

2. The Cr-doped CdS nanostructured diluted magnetic semiconductor according to claim 1, characterized in that: Said x=3.94%.

3. The Cr-doped CdS nanostructured diluted magnetic semiconductor according to claim 1, characterized in that: The diluted magnetic semiconductor has a wurtzite structure.

4. The Cr-doped CdS nanostructured diluted magnetic semiconductor according to claim 1, characterized in that: The particle diameter of the diluted magnetic semiconductor is 30-40nm.

5. The method for preparing a Cr-doped CdS nanostructured diluted magnetic semiconductor according to any one of claims 1 to 4, characterized in that: The dilute magnetic semiconductor is prepared by using cadmium oxide, sulfur powder and chromium chloride hexahydrate as raw materials, ethanolamine and ethylenediamine as organic solvents, and using a solvent thermal method to synthesize a Cr-doped CdS nanostructured dilute magnetic semiconductor.

6. The method for preparing the Cr-doped CdS nanostructured diluted magnetic semiconductor according to claim 5, characterized in that: The preparation method is carried out according to the following steps: (1) dissolving 4-6 mmol of cadmium oxide and 4-6 mmol of sulfur powder in a mixed solution of 15-25 mL of ethanolamine and 8-12 mL of ethylenediamine, and adding 0.25-1.00 mmol of chromium chloride hexahydrate to the mixed solution to obtain a mixture A; (2) At room temperature, the mixture A is stirred magnetically for 15-25 minutes, and then transferred to a stainless steel reactor lined with polytetrafluoroethylene, and stirred for 15-25 minutes before sealing. After sealing, the reactor is heated from room temperature to 170-190° C. within 35-50 minutes, and maintained at 170-190° C. for 22-26 hours, and then the reactor is taken out and naturally cooled to room temperature, and the yellow precipitate obtained by the reaction is collected; (3) The yellow precipitate is washed alternately with deionized water and anhydrous ethanol for 3-6 times, and the precipitate obtained after washing is placed in a vacuum box at 55-65° C. for 5-7 hours to obtain a Cr-doped CdS nanostructured diluted magnetic semiconductor.

7. The method for preparing the Cr-doped CdS nanostructured diluted magnetic semiconductor according to claim 6, characterized in that: In the step (1), 5 mmol of cadmium oxide and 5 mmol of sulfur powder are dissolved in a mixed solution of 20 mL of ethanolamine and 10 mL of ethylenediamine, and 0.75 mmol of chromium chloride hexahydrate is added to the mixed solution to obtain a mixture A.

8. The method for preparing the Cr-doped CdS nanostructured diluted magnetic semiconductor according to claim 6, characterized in that: In the step (2), the mixture A is stirred magnetically for 20 minutes at room temperature, and then transferred to a stainless steel reactor with a capacity of 40 mL and lined with polytetrafluoroethylene, and the mixture is sealed after continued stirring for 20 minutes. After sealing, the reactor is heated from room temperature to 180° C. within 40 minutes, and after being kept at 180° C. for 24 hours, the reactor is taken out and naturally cooled to room temperature, and the yellow precipitate obtained by the reaction is collected.

9. The method for preparing the Cr-doped CdS nanostructured diluted magnetic semiconductor according to claim 6, characterized in that: In the step (3), the yellow precipitate is washed alternately with deionized water and anhydrous ethanol for 4-5 times, and the precipitate obtained after washing is placed in a vacuum box at 60° C. for 6 hours to obtain a Cr-doped CdS nanostructured dilute magnetic semiconductor.

10. The method for preparing the Cr-doped CdS nanostructured diluted magnetic semiconductor according to claim 6 or 9, characterized in that: In the step (3), the purity of anhydrous ethanol is 99.9%.

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