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Synthesis and Characterization of Zirconium Nitride, Magnetic Property of FexMg1-xO

Author: SunYan
Tutor: YaoBin
School: Jilin University
Course: Condensed Matter Physics
Keywords: Ball milling Zirconium nitride Fe-FexMg1-xO composite material Magnetsemiconductor
CLC: TB383.1
Type: Master's thesis
Year: 2009
Downloads: 66
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Abstract


Zirconium nitride has been paid lots of attention in the field of materials for the abroad application of films. ZrN is a technologically important material because of its high hardness, high melting point, good electrical conductivity , excellent thermal properties,and good chemical stability. It has been widely used as wear resistant coating on technical and ornamental applications.The technology of synthesis ZrN films has becoming coming mature, such as reactive magnetron sputtering, PVD and CVD techniques. The purity, size distribution of ZrN powders and sinter condition play important role in the properties of ZrN Ceramic. So it is very interesting to synthesize ZrN powders with small size and high purity. The main method to prepare ZrN in industry is heating up Zr and ZrCl4 in nitrogen and ammonia atmosphere. However this method for synthesize of c-ZrN powders need very long time and temperature, waist raw material and the impurity of Zr cannot be separated.In this experiment, the compounds of LiCl and ZrN was obtained by ball milling of Li3N and ZrCl4 under Ar ambient. After separation of LiCl from the compounds by chemical method pure c-ZrN powders were obtained. Based on thermodynamic and kinetic analysis we find that the reaction was a ball milling induced self-propagating reaction. Formation of the c-ZrN nanopowders is suggested undergoing following processes: Li3N and ZrCl4 powders are co-milled firstly at a given energy and frequency of shocks in milling time between 0 and 7min, leading to refinement of grain size and good surface contact of the Li3N and ZrCl4. The decrease in grain size and good surface contact of Li3N and ZrCl4 increase their reaction activation and createmore chemically active sites, resulting in decrease of the ignition temperature with increasing milling time. When the ignition temperature is below the local temperature generated by collision of steel balls, a self-propagating reaction between Li3N and ZrCl4 occurred and produced LiCl and c-ZrN, accompanied by release of a great deal of heat. Because the time of reaction was very short, the two kinds of products are not dissolve with each other, and the melting point of ZrN was very high, the size of ZrN was in nano scale when the reaction was finished.Magnetic nano-composites have been widely studied because it is not only important in the basic study of physics but also its abroad application foreground. Single domain magnetic particles embedded in an insulating matrix have can induce many interesting physical property. This kind of work manly concentrates on two aspects: one is embedded magnetic particle into semiconductor such as GaAs, ZnO and Si et al, the other is embedded magnetic particle into insulator such as Al2O3, ZrO2 and Ge et al.The saturation magnetization of metal Fe is higher than any other magnetic materials, so Fe particles embedded in nonmagnetic insulating matrix will obtain high saturation magnetization and coercivity. In this experiment we have fabricated magnetic nano-composites Fe-FexMg1-xO by ball milling of Mg and Fe2O3 under Ar atmosphere, and the relation between of structure and magnetic property has been studied in detail.In the experiment we found that the reaction between Mg and Fe2O3 are based on the following equation: Fe 2 O3+ 3（1?x ）Mg→3Fex Mg1? xO+（2?3x）FeThe reason why the products of reaction are not content pure MgO may be due to that, when the self-propagating reaction started the products are c-MgO, c-FeO and Fe accompanied by release of a great deal of heat, and because c-MgO and c-FeO have the same structure（c-NaCl structure）, the two kinds of products are fabricate to c-FexMg1-xO at the condition of reacting heat. Expending milling time we find a little c-FeMg2O4 was fabricated and disappeared in the following milling time. This phenomenon illustrated that c-FeMg2O4 is a metastable phase in milling process. Because of the unbalance effect of ball milling a portion of c-FexMg1-xO was transformed to c-FeMg2O4 in the milling process along with the reducing of proportion of Fe in c-FexMg1-xO. After that c-FeMg2O4 was decomposed into c-FexMg1-xO and Fe again, and the proportion of Fe in c-FexMg1-xO tends to a limit number.When the self-propagating reaction finished the coercivity of the product was about 40Oe which equals to bulk , so the product of Fe powder in large size scale which due to the reason that the temperature of reaction was too high for melting point of Fe and made Fe powder grow bigger. After 1h of milling the coercivity was increased to 110Oe, and the calculated particle size was about 34nm, so the increase of coercivity was induced by the decrease of particle size. After that the coercivity was continually increase, and at the milling time of 10h the coercivity reached the maximum 350Oe, corresponding particle size was about 20 nm. Then coercivity was decreasing with expending milling time, when the milling time increased to 50h the coercivity stopped changing in the following milling process, and the calculated calculated particle size was about 11nm. Maximum coercivity of Fe particles occurs at about 15 nm, when the particles size bigger than 15nm walls of magnetic domain is fabricated, and when the particle size smaller than 15 nm the heat vibration plays an important role in the move of particle. So the coercivity of Fe powders increases along with the decrease of particle size when particle is bigger than 15nm, and decreases along with the decrease of particle size when particle is smaller than 15nm.α?FeDiluted magnetic semiconductor （DMS） has been paid lots of attention due to its widely application foreground. Most of the works are concentrated on doping magnetic atom, such as Fe, Co, Ni, Cu, into semiconductor materials such as ZnO, GaN and Si et al. However, most DMS have a low Curie temperature, which limits their use in practical applications, and the source of Ferromagnetism is not clear.During the work of preparing magnetic composite Fe-FexMg1-xO it has found that the solid solution of c-FexMg1-xO is very easy to be fabricated. The energy band gap of MgO is 7.5eV which belongs to insulate. We hope that the energy band gap can be changed by Fe doping, and because of the existence of Fe the c-FexMg1-xO may have ferromagnetism. So c-FexMg1-xO may be an magnetic semiconductor in certain condition.In our experiment we have synthesized pure c-FexMg1-xO by ball milling of Fe and MgO, and the magnetic and electrical properties was studied basically. It was found that the c-FexMg1-xO exhibits weak ferromagnetic property at room temperature, the coercivity was about 150Oe and increased a little along with the increase of Fe content. The Fe ions in solid solution are +2 and +3 change state, the proportion of Fe3+ about 90%, Fe2+ about 10%. So we draw the conclusion that the souse of ferromagnetic property was the coupling of Fe2+ and Fe3+. When the contend of Fe was increased both Fe3+ and Fe2+ increase at the same time, and remnant magnetic moment of the coupling effect so the saturation magnetization of c-FexMg1-xO was increased along with the content of Fe. From the Sherrer Formula the calculated particle size was 22 nm which can synthesize single domain magnetic particles, so the sample has big coercivity. The radius of Fe2+ ions is bigger than Mg2+ ions, when Fe2+ substitutes Mg2+ in c-FexMg1-xO the stress increases and the coercivity increases along with the increase of Fe content.After annealing 2h at the temperature of 500 under vacuum, a little amount of c-MgFe2O4 was appeared, the coercivity and saturation magnetization decreased. In the annealing the stress was decreased, p article size increased which induced the decrease of coercivity. The decrease of saturation magnetization due to the formation of c-MgFe2O4. The formation of c-MgFe2O4 would consume some Fe in c-FexMg1-xO, the content of Fe in c-FexMg1-xO would decrease, and the magnetism of c-FexMg1-xO very weak, so the saturation magnetization would decreased after annealing.When the atom ratio between Fe and Mg increased to 17.74: 82.26, after 2h-annealed at 450 under vacuum the resistivity decreased distinctly, from 2×107Ω*cm to 6×105Ω*cm, exhibiting semiconductor’s electrical property. From the Photoluminescence （PL） at room temperature it was found that the electrical property comes from the impurity energy band due the doped Fe ions which is about 3.2704eV higher than valence band edge. As milled and as-annealed samples at 450 o C was consisted of pure solid solution c-FexMg1-xO, and the as-annealed samples at 500 o C and 800 o C were consisted of c-FexMg1-xO and c-MgFe2O4. The quantity of c-MgFe2O4 increased with the increase of annealing temperature. The change of electrical resistivity may due to the density of c-FexMg1-xO and c-MgFe2O4. When the annealing temperature was low the density of was low, particle size was too small, too many interstices exist. So the electrical resistivity of samples annealed at low temperature was high. Increase annealing temperature, the density was increased, particles grow bigger, the quality of crystal becomes better, and the electrical resistivity was decreased. But the generation of c-MgFe2O4 made the resistivity increase, the more of c-MgFe2O4 the higher of resistivity, so the resistivity of sample annealed at 800 was higher than that annealed at 500 . Because the main state of Fe ions was Fe CoC3+, the carriers should be electron, and the conclusion was consisted with the Hall-effect measurement of 800 -annealed sample. In conclusion, a magnetic semiconductor material c- FeoCxMg1-xO has been fabricated.

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