Low-temperature charge and magnetic order of Bi0.5Sr0.5MnO3 -: art. no. 054401

Low-temperature structural and magnetic properties of Bi0.5Sr0.5MnO3 investigated by neutron and synchrotron x-ray diffraction are reported. High-resolution powder diffraction data evidenced two-phase coexistence. One of the phases presents charge-exchange (CE) -type magnetic ordering and q= 1/2b* structural modulation indicating orbital and charge ordering. The other phase adopts the A-type magnetic structure and orbital ordering with q = 0. The charge order of the CE phase and the orbital order of the A phase are unusually stable when heating the sample (T-OO= 525 K). A mechanism, based on the 6s(2) lone pair of Bi3+ ions, is proposed to strongly decrease the mobility of e(g) electrons in both phases. This fact, as well as some structural and magnetotransport results, indicates that the A-phase is quite different from previous A phases found in manganites and it cannot be described as a "metallic antiferromagnet." A possible ordered arrangement of the Mn3+/Mn4+ ions in this phase is examined.