The Study Of Physical Properties Of Mn Doped Sr₂FeMoO₆

The studies of transition-metal oxides with perovskite structure started in 1950's. In the recent ten years, double perovskite Sr₂FeMoO₆(SFMO)has draw much attentions, because of its considerable tunneling magnetoresistance effect. The ground state SFMO is half metal, which give rise to 100% spin-polarized charge carriers. Besides,the Curie temperature of SFMO is more than 410K, which shows promise for the development of ordered perovskite magnetoresistance devices that are operable at room temperature.In this dissertation, we devoted efforts to the study SFMO by doping ions at B-site. We mainly discuss many physical properties such as the magnetism and magnetoresistance in doped compound.In the first chapter, we give a summarization on different magnetoresistance effects and related physical properties, and specially introduce the tunnel magnetoresistance effect. According to this chapter, we will introduce more physical conception such as half metal, superexchange, double perovskite and so on. From those instructions, we can make good preparation for the following study in that system.In the second chapter, we study the physical properties of Sr₂Fe_1-xMn_xMoO₆. We discover some interesting phenomena:with the doping Mn ions, the order of sample raises gradually. In this system, the valence of Mn is mainly 3+ rather than 2+, which is only assumption in relevant previous papers. Doping Mn can increase the resistivity, while decrease the magnetoresistance. Besides, with the dope of Mn ions, the ferromagnetic-paramagnetic transition temperature decreases. In the low temperature region, the magnetization of the high doped compound drops greatly with the decrease of temperature. According to the measurement of relevant hysteresis loops, we propose the reasonable explanation: the doping Mn ions increase the magnetic anisotropy and domain wall pinning, resulting in the decrease of magnetization. Considering the anti-site defect, we calculate the saturation magnetic moment and find the magnetic moment of Mn ions is antiparallel to the magnetic moment of nearest Mo ions in this system.