A Study Of Fabrication, Structure And Magnetic Properties For Magnetic Semiconductors Of (In_1-xFe_x)₂O₃ And XFeTiO₃-(1-x)Fe₂O₃

Magnetic semiconductor is considered as one of the candidate materials.for creating the next generation of spintronics devices. One method to obtain magnetic semiconductor is to dope magnetic element into semiconductor host, and induce magnetic exchange interaction between elements, and thus form a ferromagnetic diluted magnetic semiconductor (Diluted Magnetic Semiconductor-DMS). In the past, the Curie temperature of DMS (Tc) is generally lower (<110K), which is not adapt to practical application. In 2000. using the Zener model and mean-field theoretical method Dietl predicted the Cutie temperature to be higher than the room temperature in the P-type wide band semiconductor ZnO doped about 5% of the Mn magnetic ions. Then, in 2001. Y. Matsumoto reported that doping a small amount of Co into wide bandgap semiconductor TiO2 formed a diluted magnetic semiconductor with Cuie temperature of ferromagnetism above 400K. Since then, the oxided diluted magnetic semiconductors have been extensively studied. But the origin of ferromagnetism in the oxided diluted magnetic semiconductors is still unclear:Some people think that ferromagnetism obtained in samples is intrinsic properties, and its formation mechanism mainly invovle three parts:the first is carrier-induced ferromagnetic exchange coupling, such as the RKKY exchange interaction. The second is related to defects in sample, a representative is bound magnetic polaron (BMP) model, the third is the traditional exchange model, such as double exchange interaction. In addition, some people believe that ferromagnetism comes from the ferromagnetic cluster or the conamination. but this is not the intrinsic properties of the samples.Therefore, it is essential to deep study the origin of ferromagnetism in oxided diluted magnetic semiconductors. For another magnetic semiconductor FeTiO3-Fe2O3 solid solution, it has an intrinsic magnetic property and a good semiconductor property. However, the study of the magnetic semiconductor FeTiO3-Fe2O3 solid solution now only remain on the bulk and thin-film samples which were prepared by solid-state reaction and vacuum sputtering. The study on the preparation of magnetic semiconductor FeTiO3 solid solution powders by chemical method will contribute to future applications and enlarge the area of study of properties. This paper is the study of diluted magnetic semiconductor Fe-doped InO3 magnetic and their origin and magnetic semiconductor FeTiO3-Fe2O3 solid solution prepared by chemical methods. We used s sol-gel method to prepare Fe-doped In2O3 powder samples and a chemical co-deposition method to prepare FeTiO3-Fe2O3 solid solution. Using Mossbauer spectrum, X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and other methods to systematically study the Fe-doped In2O3 and FeTiO3-Fe2O3 solid solution powder samples for their micro-structure and magnetic properties. The main results obtained are as follows:1. (Inl-xFex)2O3 samplesFor the (Inl-xFex)2O3powder samples prepared by sol-gel methods, our main work was to systematic study the conditions for obtainting ferromagnetism and the origin of ferromagnetism1.1 Through the sol-gel method., the Fe ion solubility in (Inl-xFex)2O3 powder samples can be up to 50%. this value is the highest of all reported in the literature. Using the XRD rietvled refinements and Mossbauer spectra study, we first time studied the occupation of Fe ions in the In12O3 lattice. Our research showed that when the Fe content was low the Fe ions would be preferred to occupy the 24d sites in In2O3 crystal lattice, while with increasing Fe content the Fe ions tended to occcpy randomly. This result would provide useful information for future further investigation about the magnetic and other properties in Fe doped In2O31.2 In order to obtain ferromagnetism in (Inl-xFex)2O3 samples, we used vacuum annealing and Sn co-doped two methods to treat our samples, and found that vacuum annealing could induce ferromagnetism. while the Sn co-doping did not induce ferromagnetism. This result indicates that ferromagnetism in (Inl-xFex)2O3 can be induced through the introduction of oxygen vacancies rather than the carriers.1.3 We first time used the annealing approach of carbon-thermal reduction to treat the (Inl-xFex)2O3 samples and obtained ferromagnetism with magnetic moment up to 1.4μB/Fe Through XPS analysis we concluded that ferromagnetism in (Inl-xFex)2O3 samples come from the Fe2+ ions which were produced by oxygen vacancies and had a double exchange interaction with Fe3+ ions.1.4 For the first time, we used a simple method of decomposition of PTFE to achieve F doping in (Inl-xFex)2O3 samples, and thus obtained ferromagnetism which is also very stable even under the high temperature in air. Through XPS and other experiments we confirmed that ferromagnetic directly originated from double exchange interaction bewteen Fe3+ ions and Fe2+ ions, while the F-doping and oxygen vacancies just induced the Fe+ ions, and was not the directly origin of ferromagnetism.2. FeTiO3-Fe2O3 solid solution samplesFor the first time, we made use of the chemical co-deposition method to prepare ferrimagnetic semiconductors FeTiO3-Fe2O3 solid solution powder samples.2.1 We found that it was hard to prepare pure phase FeTiO3-Fe2O3 solid solution unless we used the mixed valence of Fe2+ and Fe3+ salt as raw materials, and to ensure as far as possible Fe2+ in the whole preparation process can not be oxidized to Fe3+. During the process of preparation we used hot water to avoid oxygen dissolved in water, and used Ar gas as a protective gas for the process of co-deposition and heat treatment, and thus successfully prepared pure phase FeTiO3-Fe2O3 solid solution powder samples.2.2 For the xFeTiO3-(l-x) Fe2O3 samples, when x<0.5. it is antiferromagnetic due to the disorder for the distribution of Ti ions. We used magnetic field annealing to treat the xFeTiO3-(1-x) Fe2O3 samples (x= 0.2. x= 0.15) and found that ferromagnetism was enhanced for the samples after treatment. We analyzed and considered that this was due to the influence of magnetic field on the the distribution of Ti ion in the Fe2O3 host.