Preparation of Transparent Oxides With Ferromagnetic and Ferroelectric Properties at room temperature by Doping Mn and La

本论文研究了La-Mn掺杂的钙钛矿型介电氧化物ABO_3（A=Sr，Ba，Ca，Pb，B=Ti，Zr）的铁磁行为及其高居里温度的机理。此外，通过对铁磁和介电性质之间关系的研究，探讨了电场控制磁性的可能性。主要研究结果如下：1. La-Mn掺杂的ATiO_3（A=Sr，Ba，Ca）陶瓷在室温下具有铁磁性，磁化强度与Mn的含量成正比。观察到的磁化强度的大小取决于最终的烧结温度，在1200℃以上迅速降低，此时烧结密度变高.高分辨TEM观察和EDX成分分析表明，某些La-Mn：BaTiO_3陶瓷在晶界附近存在富Mn晶区。此外，随着La和Mn掺杂量的增加，这些陶瓷中出现了指示铁磁相（La，Ba）MnO_3的小峰，这些结果表明室温下观察到的铁磁性可能归因于少量铁磁锰氧化物沉淀到介电基质中。3. 1 mol.首次成功地制备了室温下同时具有大磁化强度和铁电性的La-Mn掺杂BaTiO_3陶瓷。在1.3KV/mm的外加电场下，La-Mn掺杂BaTiO_3陶瓷的磁化强度降低了45%，这是首次实现的，为利用电场控制磁矩打开了大门。

In this research, we have investigated the mechanism of ferromagnetic behavior exhibiting high Curie temperatures observed for perovskite-type dielectric oxides ABO_3(A=Sr, Ba, Ca, Pb, B=Ti, Zr) doped with La-Mn. In addition, we discussed the possibility of electric field-controlled magnetism through the investigation of relationship between the ferromagnetic and dielectric properties. The obtained results are as follows;1. La-Mn doped ATiO_3 (A=Sr, Ba, Ca) ceramics are ferromagnetic at room temperature, exhibiting magnetizations proportional to the Mn amount. The magnitude of observed magnetization depends on the final sintering temperature, reduced rapidly above 1200℃ at which the sintering density becomes higher.2. The high-resolution TEM observation and EDX composition analysis showed that there is a Mn-rich crystalline region around the grain boundaries for some La-Mn : BaTiO_3 ceramics. In addition, small peaks indicative of the ferromagnetic phase (La, Ba) MnO_3 were detected for these ceramics with the doped amount of La and Mn increasing.These result indicated that the ferromagnetism observed at room temperature is possibly ascribed to precipitation of a small amount of ferromagnetic manganite into the dielectric matrix.3. The 1 mol. % La-Mn doped BaTio_3 ceramics exhibiting simultaneously large magnetization and ferroelectricity at room temperature have been successfully prepared for the first time.It was found that the spontaneous magnetization of 1 mol. % La-Mn doped BaTio_3 ceramics exhibits the reduction as large as 45% for the applied electric field of 1.3 KV/mm. This reduction of magnetization by the electric field is of achieved for the first time and open the door to the control of magnetic moment using electric field.