我們以(La0.85Zr0.15)MnO3系統為母體，使用沒有磁性的Ga取代Mn，研究龐磁阻性質的現象。在本文中，我們使用標準的固態反應法來製作實驗樣品，研究發現樣品燒結的最佳條件只有存在很窄的溫度範圍內，並且當燒結持續時間超過12小時，並不能改善樣品的品質。
由X-Ray分析可以得知，所有的樣品均可以合成單相結構。由Rietveld精算法得知，其為( )斜方晶系。，樣品都屬於相同的( )相稱群。
磁阻測量結果知道，隨著外加磁場增加而電阻值越小，而且隨著外加磁場變大磁阻比也跟著變大，磁阻比在220K~250K附近有峰值出現，並與磁性相變範圍一致，並且隨著摻雜量增加而磁阻比值增加，磁轉變溫度降低，在低場下，磁阻比在低於150K時，會隨著溫度降低而升高，在高場下，使磁阻比值呈現飽和，而且在掺雜的樣品，在低溫下磁阻比會隨溫度下降而下降。
由磁化率測量結果可以得知，樣品的居禮溫度會隨著摻雜Ga的成分而降低，沒有摻雜Ga的居禮溫度為223K~226K之間發生，摻雜3%Ga的居禮溫度在215K~220K之間發生，摻雜7%Ga的居禮溫度則在200K~210K，而轉變溫度隨著外加磁場增加而降低，轉變溫區也隨著外加磁場增加而越寬。在相同磁場下，所添加的Ga越多也會造成轉變溫度下降，轉變溫區變寬。由此可以發現，樣品由順磁性轉變為鐵磁性的變化會因為摻雜Ga的成分越多而變弱，主要是Ga降低了Mn-O-Mn之間的磁作用力所致。
We study the colossal magnetoresistance property of (La0.85Zr0.15)MnO3 system by using no-magnetic moment Ga3+ ions substitution for Mn ions. In this thesis, all the electron-doped manganites samples are prepared by the solid-state reaction method. Those compounds only can be synthesized in very narrow sintering temperature range and can’t be improved by extended the sintering time over 12hours.
All samples are proven by powder X-ray diffraction, which are single-phase. Based on the “Rietveld profile-fitting method”, the all compounds are the same symmetric space group ( ).
The magnetoresistance (MR) are decreasing with the external field increasing. The temperature of the peak value of MR is rising with the external field increasing. The modulus of MR ratio is increasing with the external field increasing and those maximum values are between 220K and 250K that are same with the magnetic phase transition regions. In the low field, the modulus of MR ratios of the undoping and doping samples are increasing with temperature decreasing below 150K. In the high field, the modulus of MR ratios of the 3%Ga and 7%Ga doping samples are decreasing with temperature decreasing below 150K and 100K, respectively.
The Curie temperature of the La0.85Zr0.15MnO3, La0.85Zr0.15(Mn0.97Ga0.03)O3 and La0.85Zr0.15(Mn0.97Ga0.07)O3 samples are 237K, 225K and 221K, respectively. The magnetic moment of the sample with Ga doping is saturated at lower temperature than the un-doping sample, which is due to the Ga ions’ diluted effect. The magnetic transition temperature regions of samples are increasing with Ga doping level increasing and magnetic field increasing. This is provided for the evidence that the Ga ions reduced magnetic interaction between the Mn ions.
