Charge ordering in half-doped manganites

Abstract

Alternative descriptions for the ground state structure of the half-doped manganite Pr 0.5 Ca 0.5 MnO 3 have been tested against high-resolution 10 K x-ray and neutron powder diffraction data. The best fit is obtained using a P2 1 / m symmetry model, which supports the striped charge and orbital ordering picture. The magnitude of the charge ordering is, however, only 25% of the ideal Mn 3+ /Mn 4+ separation. An alternative Pnm2 1 pseudosymmetry, used to describe Zener polaron ordering in Pr 0.6 Ca 0.4 MnO 3 [Phys. Rev. Lett. 89, 097205 (2002)], gives a different, bistriped, charge and orbitally ordered model that does not fit the data as well.

Lattice-form-dependent orbital shape and charge disproportionation in charge- and orbital-ordered manganites

“…Detailed crystal structural data are listed in APPENDIX, and CIF-files are available at elsewhere 49 . Figure 4 (a) shows a schematic view of the CO-OO state of Pr 0.5 Ca 0.5 MnO 3 , which is based on the crystal structural data by Goff et al 22 , in which the space group …”

“…In the Q 2 -Q 3 plane, the orbital state is thus described as |d θ =cos ( θ 2 )|d 3z 2 −r 2 + sin ( θ 2 )|d x 2 −y 2 . Similar analysis based on the bond valence sum and the Kanamori representation has been applied to manganites in some literatures 22,45,46,47 .…”

“…For the analysis, we used thus determined crystal structure data for Eu 0.5 Ca 1.5 MnO 4 and Pr(Sr 0.1 Ca 0.9 ) 2 Mn 2 O 7 , and the published data for Pr 0.5 Ca 0.5 MnO 3 by Goff et al 22 .…”

“…The crystal structural data reported by Goff et al 22 were used for the analysis of Pr0.5Ca0.5MnO3. generacy with almost isotropic electron density, namely, ρ(r) ∝ λ|Ψ 3z 2 −r 2 | 2 + |Ψ x 2 −y 2 | 2 , with λ slightly smaller than 1.…”

“…Many diffraction and theoretical studies have reported the checkerboard type charge order of Mn 3+ and Mn 4+ ions with charge disproportionation and stripe-type orbital order, explaining a complex antiferromagnetic spin order at low temperatures in half-doped manganites 7,8,9,10,11,12,13,14,15,16 . On the other hand, another model with less distinct charge disproportionation has also been proposed 17,18,19,20,21,22,23,24,25 . For example, taking into account the on-site Coulomb interaction, Brink et al have suggested 17 that maximum value of charge disproportionation is as little as 20%.…”