Microscopic Research of Spin, Charge and Orbital Ordering in A-Site Ordered Manganites

点击翻译按钮获取中文摘要

In these years various kind of and a lot of researches have been made concerning the well-known CMR manganites. Recently A-site ordered manganese oxides have been synthesized. We have been investigating the A-site ordered LaBaMn_2O_6 and YBaMn_2O_6 by measuring ^<139>La and ^<55>Mn NMR. We could observe the ^<55>Mn NMR signals from Mn nuclei both in ferromagnetic and antiferromagnetic regions as well as ^<139>La NMR signals from La nuclei both in ferromagnetic and antiferromagnetic regions at the ground state of LaBaMn_2O_6. Therefore it is evidenced that the ferromagnetic and antiferromagnetic regions are coexisting in LaBaMn_2O_6 from a microscopic point of view although LaO,BaO and MnO_2 layers are ordering crystallographically. The fact that the antiferromagnetic region appears and grows in the ferromagnetic region below 200 K and that it occupies about 50 % at the ground state has been shown by comparing the temperature dependence of Mn internal field with that of the neutron scattering intensity by the ferromagnetic region. It has been also evidenced that the ferromagnetic region is not nano-scale but mezzo-scale because ^<55>Mn NMR signals show a very big enhancement due to the domain walls. The ferromagnetic state coexistent with antiferromagnetic region in LaBaMn_2O_6 is proved to be the same as that in disordered La_<0.5>Ba_<0.5>MnO_3. from the same temperature dependence of spin-spin relaxation rate. We have been also measuring μSR at TRIUMF and KEK.