Publications by Roger Johnson

Magneto-orbital ordering in the divalent A-site quadruple perovskite manganites AMn7O12(A=Sr, Cd, and Pb)

Physical Review B American Physical Society 96 (2017) 054448-

R Johnson, DD Khalyavin, P Manuel, PG Radaelli, IS Glazkova, N Terada, AA Belik

<p>Through analysis of variable temperature neutron powder diffraction data, we present solutions for the magnetic structures of SrMn<sub>7</sub>O<sub>12</sub>, CdMn<sub>7</sub>O<sub>12</sub>, and PbMn<sub>7</sub>O<sub>12</sub> in all long-range ordered phases. The three compounds were found to have magnetic structures analogous to that reported for CaMn<sub>7</sub>O<sub>12</sub>. They all feature a higher temperature lock-in phase with <i>commensurate</i> magneto-orbital coupling, and a delocked, multi-<b>k</b> magnetic ground state where <i>incommensurate</i> magneto-orbital coupling gives rise to a constant-moment magnetic helix with modulated spin helicity. CdMn<sub>7</sub>O<sub>12</sub> represents a special case in which the orbital modulation is commensurate with the crystal lattice and involves stacking of fully and partially polarized orbital states. Our results provide a robust confirmation of the phenomenological model for magneto-orbital coupling previously presented for CaMn<sub>7</sub>O<sub>12</sub>. Furthermore, we show that the model is universal to the <i>A</i><sup<2+< sup=""> quadruple perovskite manganites synthesised to date, and that it is tunable by selection of the <i>A</i>-site ionic radius.</sup<2+<></p>

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