二元掺杂镧锰氧化物La-Ca-Ba-Mn-O的庞磁电阻特性

COLOSSAL MAGNETORESISTANCE IN TWO ELEMENT DOPED La Ca Ba Mn O

用固相反应法制备了二元掺杂的镧锰氧化物Ｌａ０－６７（Ｃａ０－６Ｂａ０－４）０－３３ ＭｎＯｚ（ＬＣＢＭＯ） 立方多晶体材料，研究了其磁特性和庞磁电阻特性， 并与用类似方法制备的一元掺杂的Ｌａ０－６７Ｃａ０－３３ ＭｎＯｚ（ＬＣＭＯ） 及Ｌａ０－６７Ｂａ０－３３ ＭｎＯｚ（ＬＢＭＯ） 的庞磁电阻特性进行了比较．研究表明，ＬＣＢＭＯ 的居里温度ＴＣ 为３１２ Ｋ，介于ＬＣＭＯ 和ＬＢＭＯ 的ＴＣ（ 分别为２８０ ，３６２ Ｋ） 之间，其金属半导体转变温度Ｔｐ 和μ０ Ｈ＝ ０－６ Ｔ 下的磁电阻（ ＭＲ） 峰值温度Ｔｍ 分别为３０６ ，２９８Ｋ，接近于其ＴＣ，也介于ＬＣＭＯ 和ＬＢＭＯ 的Ｔｐ 和Ｔｍ 之间．μ０ Ｈ＝ ０－６ Ｔ 下，在各自的Ｔｍ处，ＬＣＭＯ，ＬＣＢＭＯ 和ＬＢＭＯ 的庞磁电阻值分别达到４１ ％ ，２４－７ ％ 和８ ％ ，但在室温（３００ Ｋ）处，ＬＣＢＭＯ 的ＭＲ 值仍达到２０ ％ ，远大于ＬＣＭＯ 和ＬＢＭＯ 的值（ 分别为２－０ ％ 和２－４ ％ ） ．研究还发现，在温度远低于Ｔｍ 时，ＬＣＭＯ 仍保持一定的磁电阻效应，而ＬＣＢＭＯ 和ＬＢＭＯ 的磁电阻随温度降低而增加，这些低温磁电阻特性与材料的结构特征（ 如晶界和致密度） 有关．

Bulk materials of two\|element\|doped manganite La\-\{0\^67\}(Ca\-\{0\^6\}Ba\-\{0\^4\})\-\{0\^33\}MnO\- z (LCBMO) which were prepared by solid state reaction method,where shown to have cubic polycrystalline structure.The magnetic and colossal magnetoresistive properties of LCBMO were investigated and were compared with those of one\|element\|doped La\-\{0\^67\}Ca\-\{0\^33\}MnO\- z (LCMO) and La\-\{0\^67\}Ba\-\{0\^33\}MnO\- z (LBMO) prepared by the similar technique.The results showed that the Curie temperature( T \-C)of LCBMO was 312?K,which was between those of LCMO and LBMO,and that the metal\|semiconductor transition temperature( T \-p) and magnetoresistance (MR) peak temperature( T \-m) of LCBMO under μ 0H= 0\^6?T field were 306 and 298?K respectively,both of which were close to its T \-C and were also between the T \-p and T \-m of LCMO and LBMO.Under μ 0H= 0\^6?T applied field,the colossal magnetoresistance value at corresponding T \-m was 41% for LCMO,24\^7% for LCBMO,8% for LBMO,but at room temperature (300?K) the MR value of LCBMO still reached 20%,which was greatly larger than those of LCMO and LBMO,i.e.2\^0% and 2\^4%,respectively.It was observed that at low temperatures far below T \-m there still existed magnetoresistance effect in LCMO,and the MR value of LCBMO and LBMO increased with decreasing temperature.These magnetoresistance properties at low temperatures could be ascribed to the intrinsic structural characteristics such as grain boundaries and density.