掺杂和复合钙钛矿锰氧化物的室温磁电阻增强

【作者】 原晓波；

【导师】 刘宜华；

【作者基本信息】 山东大学 ， 凝聚态物理， 2006， 博士

【摘要】 庞磁电阻（简称CMR）效应的发现使得具有钙钛矿结构的稀土锰氧化物体系受到了人们的广泛关注。一方面因为CMR效应在磁存储器、磁传感器件中具有潜在的巨大的应用潜力，另一方面这类CMR材料是电子强关联体系，还包含着非常丰富的物理内涵。近年来，钙钛矿锰氧化物中CMR效应的研究是国际上的热点课题之一，不同科研组分别从实验和理论方面进行了大量的研究。但是至今为止，由于CMR效应的应用磁场较高，使用温度较低使得CMR效应的应用前景暂不明朗。因此，从应用方面考虑，提高CMR效应的磁场灵敏度和使用温度成为当前实验方面的研究焦点。 本论文主要选择居里温度（T_C）高于室温的La_0.67Ba_0.33MnO₃（简称LBMO）作为母体材料，采用溶胶-凝胶法制备，一方面利用掺杂来调节T_C到室温，另一方面利用多晶体系的界、表面特性来改善低场磁电阻。首先研究了微量元素替代A、B位对LBMO的结构、磁、电特性以及室温和低场磁电阻的影响，寻找具有室温T_C的CMR锰氧化物材料。然后，选择适当的良导体金属与具有室温T_C的锰氧化物进行复合，成功地将金属的良导电特性甚至磁特性应用到复合体系中，显著地提高了体系的室温磁电阻效应，甚至获得了到目前为止在CMR材料中发现的最大的室温磁电阻。 本论文的主要工作和结果 1、La_0.67Ba_0.33MnO₃中A位掺杂效应 本论文将少量的Bi₂O₃掺入到溶胶-凝胶法制备的La_0.67Ba_0.33MnO₃母体材料中。研究了微量Bi掺杂对母体材料各性能的影响。Bi掺杂可以明显改变材料的电特性和磁电阻（MR）特性，但对材料的磁化强度和T_C影响不大，后者与La³⁺和Bi³⁺的离子半径相近有关。Bi掺杂对低场磁电阻的影响明显，低温77K，0.1T磁场，10％mole比的Bi掺杂使低场磁电阻增加近一倍，达到33％。但Bi掺杂对低温下的高场磁电阻几乎没有影响，说明掺Bi不会明显影响双交换作用。掺Bi使室温下的磁电阻得到增强，掺入1％mol比的Bi使室温磁电阻增加了50％。更多还原

【Abstract】 Perovskite manganites have been gaining much attention since the discovery of the colossal magnetoresistance （CMR） in these materials. Recently, the investigation of CMR in Perovskite manganites is one of the important subjects. Considerable works have been done on the experimental and theoretical studies for two reasons. On the one hand, CMR effect possesses giant application potential in the magnetic memories and sensors. On the other hand, there are many rich physical contents in these perovskite manganites. However, a large magnetoresistance （MR） value is often obtained in a very large magnetic field （up to several tesla） and at low temperature, these conditions severely limit its application. From the viewpoint of the practical applications, a large MR obtained at low field and room temperature is desirable. So how to increase the field sensitivity and working temperature has become one of the important investigation subjects.Polycrystalline La_0.67Ba_0.33MnO₃ （abbreviated to LBMO） synthesized by the sol-gel technique is selected as the parent material. On the one hand, its Curie temperature （T_C） can be adjusted by ion substituting to room temperature, since its T_C is higher than room temperature. On the other hand, the boundary effect of polycrystalline can be used to improve the low-field MR. At first, the substituting effects of A or B sites on the magnetism, electrical property, room-temperature and low-field MR are investigated, in which, the substituting amount is small, limited in 10% mole ratio, in order to adjust T_C to room temperature. And then, some good conductive metals are composed with the perovskite manganites, in which T_C are near room temperature. The good conductivity, even magnetism of the metal is applied into the composites. As a result, the room-temperature MR can be enhanced obviously. In fact, an extra-large room-temperature MR is obtained, which is the largest MR obtained at room temperature in all CMR materials so far.更多还原