Doped Manganese Oxides La <sub> 0.75-z </ Sub> (sra) <sub> 0.25-y + Z </ Sub> The ¡õ <sub> Y </ Sub> Of Mno <sub> 3 </ Sub> (a = Of Ag And Na; "= Vacancy), The Magnetoresistance Effect

Since the early 1990s , the colossal magnetoresistance (CMR) behaviors in perovsikite-manganese oxides have attracted great attention due to both the effect of the strong correlation concerning metal-insulator transition and potential application of CMR material in magnetic recording as well as maganetic field sensor. At present, many researches have been concentrated on making new material system that can provide low field magnetoresistance (LFMR) around room temperature and improving temperature stability of magentoresistance at room temperature range by means of substituting Sr by other element. In this paper, La0.75-zSr0.25-x-y+zNax□yMnO3 and Agδ-La0.75Sr0.25-x-yAgx-δ□y+δMnO3 (sign "□ "represents vacancies) samples were prepared by sol-gel method.Their structure, electrical and magnetic propertie as well as colossal magnetoresistance were researched in detail. There are several interesting results we have got:1.The phase identification of samples has been carried out by the X-ray diffraction (XRD) with a Rigaku Dmax-RB diffractometer with Cu Kα radiation. The results indicate that the matrix compound La0.75Sr0.25MnO3 is rhombohedral structure; the samples substituting a few of Sr2+ ions by Na+ ions, Sr2+ vacancies and changing the ratio of Sr2+ to La3+ are still a single phase with rhombohedral structure. If Ag was doped in the matrix compound La0.75Sr0.25MnO3, it is found that there are two phases in samples with cubic structure Ag phase and rhombohedral structure perovskite phase for x>0.04. Therefore samples were composite material Agδ-La0.75Sr0.25-x-yAgx-δ□y+δMnO3, here 8 is the mol content of Agphase.2. For La0.75Sr0.15Na0.10MnO3 bulk samples, under an applied filed of 5T, the room temperature magnetoresistance reaches 32.7% , which enhances 3.7% than one of bulk sample La0.7Sr0.1Na0.2MnO3 in N.Abdelmoula report . Under an applied filed of 1.8T, we obtained that the maximum MR is 27.5% at 312K and 23% at 300K for3. For bulk sample La0.75Sr0.19Na0.04□0.02MnO3, under an applied filed of 1.8T, there are a stable MR (9.90±0.08)% in temperature range between 284K and 309K. Therefore temperature stability of magentoresistance at room temperature range was enhanced. It is important for the potential application of this magnetoresistance material.4.We obtained that field susceptivity is about 26.6%/T for sample N0.A7 in 0-0.7T field range, thereby field susceptivity is highly improved.