Magneto-orbital ordering in the divalent A-site quadruple perovskite manganites AMn7O12(A=Sr, Cd, and Pb)
Abstract:
Through analysis of variable temperature neutron powder diffraction data, we present solutions for the magnetic structures of SrMn7O12, CdMn7O12, and PbMn7O12 in all long-range ordered phases. The three compounds were found to have magnetic structures analogous to that reported for CaMn7O12. They all feature a higher temperature lock-in phase with commensurate magneto-orbital coupling, and a delocked, multi-k magnetic ground state where incommensurate magneto-orbital coupling gives rise to a constant-moment magnetic helix with modulated spin helicity. CdMn7O12 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 CaMn7O12. Furthermore, we show that the model is universal to the A
Electrical switching of magnetic polarity in a multiferroic BiFeO3 device at room temperature
Abstract:
We have directly imaged reversible electrical switching of the cycloidal rotation direction (magnetic polarity) in a (111)pc-BiFeO3 epitaxial-film device at room temperature by non-resonant x-ray magnetic scattering. Consistent with previous reports, fully relaxed (111)pc-BiFeO3 epitaxial films consisting of a single ferroelectric domain were found to comprise a sub-micron-scale mosaic of magneto-elastic domains, all sharing a common direction of the magnetic polarity, which was found to switch reversibly upon reversal of the ferroelectric polarization without any measurable change of the magneto-elastic domain population. A real-space polarimetry map of our device clearly distinguished between regions of the sample electrically addressed into the two magnetic states with a resolution of a few tens of micron. Contrary to the general belief that the magneto-electric coupling in BiFeO3 is weak, we find that electrical switching has a dramatic effect on the magnetic structure, with the magnetic moments rotating on average by 90 degrees at every cycle.