Structure And Magnetic Properties Of Diluted Magnetic Semiconductor Oxides Study

Diluted magnetic semiconducting oxides (DMS-O) have attracted considerableattention in recent years due to the possibility of inducing room temperatureferromagnetism and the potential technological applications in spin-dependentmicroelectronic devices. Although the origin and the nature of the ferromagnetism haveremained confused and controversial, it has been shown that the distribution and thelocal environment of the dopant has a significant effect on the magnetic structure.Therefore, it is important to study the local environment of the dopant in order to clarifythe mechanism of magnetism. At present, most of research on DMS has focused on thinfilms, but there is not much work on bulk DMS prepared by mechanical alloying. In thispaper, we investigated the microstructure and the magnetic properties of the Fe-dopedTiO₂ and the Fe-doped ZnO powders, which were respectively prepared by mechanicalalloying using Degussa P-25 TiO₂, ZnO andα-Fe as the starting powders, employingX-ray diffraction, M(o|¨)ssbauer spectroscopy and a vibrating sample magnetometer.It has been shown that the milled Ti_0.9Fe_0.1O₂ powder is the mixture of anatase, rutileandα-Fe. During high energy ball milling, some anatase in the starting Ti_0.9Fe_0.1O₂powder transforms to srilankite and futile at room temperature and ambient pressure andsomeα-Fe substitutionally dissolves into the TiO₂ lattice in Fe²⁺ and Fe³⁺ state. Theresidualα-Fe leads to the ferromagnetism in the milled Ti_0.9Fe_0.1O₂ powder. As millingtime increases, the amount ofα-Fe gradually decreases and the saturation magnetizationof the milled Ti_0.9Fe_0.1O₂ powder reduce as a result of the incorporation of Fe into thelattice of TiO₂. However, the coercivity and the ratio of the remanent magnetizationdrastically enlarge at the early stage of milling. The coercivity amounts to the maximumat 10 hours of milling and then reduces with continued milling, and the ratio of theremanent magnetization approaches to saturation on further processing. The residualα-Fe ununiformally distributes in the milled Ti_0.9Fe_0.1O₂ powder and some of theresidualα-Fe exists in the form of the fine cluster with a disorder or amorphous structure, which riches on the interface or surface of TiO₂ crystalline.The results show that in the Ti_0.96Fe_0.04O₂ powder prepared by mechanical alloying,allα-Fe substitutionally dissolves into the TiO₂ lattice in Fe²⁺ and Fe³⁺ state during ballmilling. The solid solution of Fe results in the increase in the oxygen vacancies in theTiO₂ lattice, which accelerates the milling-induce transformation from anatase to rutile.And consequently the milled Ti_0.96Fe_0.04O₂ powder is pure rutile. Magnetizationmeasurement indicates that the milled Ti_0.96Fe_0.04O₂ powder is ferromagnetic showing aCurie temperature (T_C) close to 650K, and the saturation magnetization and thecoercivity of the ferromagnetic phase are about 0.15μ_B/Fe and 150Oe at roomtemperature, respectively. No sextet in the M(?)ssbauer spectrum can be explained byparamagnetic spin-lattice relaxation. Based on the saturation magnetization, thecoercivity Curie temperature and M(?)ssbauer spectrum, it can be concluded thatIt has been shown that below x=0.0708, the milled Zn_1-xFe_xO powder contains onlywurzite and allα-Fe substitutionally dissolves into the ZnO lattice in Fe²⁺ and Fe³⁺ stateduring ball milling, which leads to the lattice expansion of wurzite. The lattice constants,a and c, and cell volume increase with the growth of the Fe content. The saturationmagnetization of the milled Zn_1-xFe_xO powder, showing a Curie temperature close to650K, reduces with the increase in the Fe content, which suggests that theferromagnetism in our milled Zn_1-xFe_xO powder seemingly does not come from Fe andiron oxides particles/clusters but from the powder matrices. However, the milledZn_1-xFe_xO powder with the Fe content of 0.0898 is the mixture of wurzite andα-Fe. Theresidualα-Fe leads to the ferromagnetism in the milled Zn_1-xFe_xO(x=0.0898) powderand enlarge the saturation magnetization.