摘要
研究多晶Nd1-xCax-δBaaMnO3(x=0．5,0．45)中,大尺寸Ba2+对Ca2+的替代可在样品中导致铁磁基态以及低温下阶梯状的磁化强度跳变．结果表明,因Ba2+的“反畸变效应”,样品中的铁磁百分比随Ba替代量的增加迅速增大,当δ为0．03-0．04时达到一极大值,然后随Ba替代量的增加而减小,这是由于此时对铁磁不利的A位阳离子间的尺寸失配占了优势．对相同的Ba替代量,高Nd(x=0．45)体系中的铁磁含量总是比低Nd(x=0．5)体系中的大很多．当增加磁场时,前一体系磁化强度的增加比后一体系迅速得多,在5．5 T磁场下其磁化强度极大值要显著大于后一体系的相应值,前一体系出现阶梯状跳变的临界磁场要小于后一体系．指出上述结果是由于Nd0.55Ca0.45MnO3中的电荷轨道序比Nd0.5Ca0.5MnO3较弱造成的．奇异的磁化强度跳变用建立在相分离基础上的类马氏体相变模型得到了较合理解释．
The substitution of Ba for Ca in polycrystalline Nd1-xCax-δBaδMnO3 （x =0. 5, 0. 45） can induce a ferromagnetic （FM） ground state and magnetization steps at low temperature. The FM fraction first quickly increases with δ due to the local ＂counter-distortion＂ effect, reaching a maximum value for δ = 0. 03 -0. 04, then decreases as excess Ba is introduced because the A-site size mismatch has increased dramatically. The FM fraction for the x = 0. 45 system is much higher than that of the x = 0. 5 system for the same barium content. When the magnetic field is increased, the former series show higher magnetization and lower critical fields where the steps appear. These results are due to the weak orbital and charge ordering of Nd0.55Ca0.45MnO3 compared to that of Nd0.5Ca0.5MnO3. The magnetization steps can be explained by a martensitic-like mechanism on the basis of phase separation.
出处
《深圳大学学报（理工版）》
EI
CAS
北大核心
2007年第1期18-23,共6页
Journal of Shenzhen University(Science and Engineering)
基金
深圳市科技计划资助项目(200503
200501)
关键词
多晶Nd1-xCax-δBaδMnO3
电荷轨道有序
类马氏体相变
相分离
铁磁态
反铁磁态
A位
尺寸失配
反畸变效应
polycrystalline Nd1-xCax-δBδMnO3
orbital and charge ordering
martensitic-like mechanism
phase seperation
ferromagnetic state
antiferromagnetic state
A-site size mismatch
the ＂counter-distortion＂ effect
