Magnetoresistance in La1-xAxMnO3-x films Prepared by a Dipping-Pyrolysis Process
[[abstract]]本研究以可溶性之金屬醋酸鹽及硝酸鹽化合物為原料，去離子水及無水酒精互相混合作為溶劑，在常壓下以浸鍍法配合有機金屬熱分解法，經適當熱處理，在矽晶片上沉積鈣鈦礦結構之La1-xAxMnO3-x (A＝Ca、Sr、Ba)氧化物系薄膜。由實驗得知，溶液之溶質總克數2克，浸鍍速度100mm/min所製備出之薄膜表面品質較好。由X-光繞射圖知，薄膜經650℃熱分解後，已有鈣鈦礦結構產生。隨後續緻密化熱處理溫度增高，薄膜顯微組織愈加緻密化。 La-Ca-Mn-O薄膜於室溫下並無鐵磁性，磁阻效應小。其磁阻比值隨溫度下降而增加，於半導體─金屬轉換溫度(70K)附近得到最大磁阻比值-58.8％。添加Ba之La-(Ca, Ba)-Mn-O薄膜之磁化及磁阻行為與La-Ca-Mn-O薄膜相似，其磁阻郊應隨溫度降低而增大，惟於量測溫度範圍內(300K-30K)並無最大值出現。添加Sr之La-(Ca, Sr)-Mn-O薄膜於室溫下已有鐵磁性磁滯現象，Tc溫度應於室溫之上。其磁阻效應卻隨溫度下降而增加，此可能與組織不完整有關。La-Sr-Mn-O薄膜於室溫下也有鐵磁性，其室溫磁阻比值為(-16.2％)，由於Tc溫度高於室溫，故磁阻比值隨溫度降低而減少。
[[abstract]]La1-xAxMnO3-x films (A＝Ca, Sr, Ba) were deposited on Si substrate under atmosphere by a dipping-pyrolysis process. The precursor solution were prepared by disolving nitrate and acetyla-cetonate into the mixture of water and alcohol. Upon annealing at 650℃, the polycrystal perovskite structure of films were obstained. A dense and continuous structure of films is obtained after sintering at 800-900℃. La-Ca-Mn-O films is paramagnetic and only a small MR ratio is obtained at room temperature. The MR ratio increases as temperature decreases, and reaches a maximum of -58.8% at 70K, which is close to the semiconductor-metal transition temperature. The Ba2+ doping of CLMO films do not significantly influence the magnetic and magnetoresistance behavior, except the shift of semiconductor-metal transition temperature to lower temperatures. However, the curie temperature of LCMO films is raised to be above room temperature by a Sr2+ doping. The maximum MR ratio of LCSMO film is not obtained as temperature decreases from room to 30K, which is believe to be a result of the loose microstrocture of films. The LSMO films is also ferromagnetic, and a MR ratio of -16.2% is obtained at room temperature, which also decreases as temperature is lowered.
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