Investigation Of Physical Property Of Novel Magnetic Semiconductors: (Sn, Mn)O₂ And (Cu, Mn)O

In spintronics, diluted magnetic semiconductor has attracted considerable interest in recent years. There have been some groups reporting their works about Mn-doped SnO₂ [i.e. (Sn,Mn)O₂] and Mn-doped CuO [i.e. (Cu,Mn)O]. However, many questions are not been resolved, e.g. the valence state and lattice site of Mn in semiconductor matrix, the origin of ferromagnetism, the mechanism of ferromagnetic coupling, and so forth. In order to clarify these questions, we fabricated series (Sn,Mn)O₂ and (Cu,Mn)O bulk samples by solid-state reaction method. Some new results are obtained by systemically investigating their structural, magnetic, and electrical properties.For (Sn,Mn)O₂, all our samples are single-phase structure (rutile) and no sencondary phases is found when Mn doping content is less than 5%. Magnetic data indicate that the Curie temperatures of all the samples are lower than 30 K (no room-temperature ferromagnetism), which is different from the reported result. A fact that manganese in the state of Mn⁴⁺ incorporates into the Sn sublattice of SnO₂ matrix can be indirectly deduced by both the Mn effective magnetic moment and the variation of lattice parameters as increasing Mn content. The saturated moment per Mn decreases with increasing of Mn doping content, which can be explained using F-center model.For (Cu,Mn)O, we find that the solubility limit of Mn in CuO is less than 3%. When Mn doping concentration is bigger than 0.2%, all the (Cu,Mn)O samples show the ferromagnetic behavior. Analyses of the X-ray photoelectron spectroscopy, the unit cell volume, and magnetism indicate that manganese in the form of Mn²⁺ incorporates into CuO when x≤0.0125 in Cu_1-xMn_xO. To investigate the role of electron in ferromagnetism, Al is co-doped into the Cu_0.9925Mn_0.0075O and an improvement of ferromagnetism is observed. In order to clarify the part of hole in ferromagnetism, we also prepare series Li-doped Cu_0.9925Mn_0.0075O samples using the sol-gel method. Hole is successfully introduced into the CuO as a result of Li co-doping. As increasing Li doping concentration, the observed ferromagnetism is weakened and at last disappears. The observed ferromagnetism in (Cu,Mn)O is discussed on the basis of the formation of bound magnetic polaron.In addition, Cr-doped ZnO samples are fabricated by the sol-gel method. X-ray diffraction spectra show that the solubility limit of Cr in ZnO is less than 5%. For the impurity-free samples, only antiferromagnetic behavior is observed and no ferromagnetism appears. With increasing Cr doping concentration, the antiferromagnetic interaction between Cr spins is enhanced.