354 research outputs found
Rare earth magnetism and ferroelectricity in RMnO3
Magnetic rare earths R have been proven to have a significant effect on the
multiferroic properties of the orthorhombic manganites RMnO3. A re-examination
of previous results from synchrotron based x-ray scattering experiments
suggests that symmetric exchange striction between neighboring R and Mn ions
may account for the enhancement of the ferroelectric polarization in DyMnO3 as
well as the magnetic-field induced ferroelectricity in GdMnO3. In general,
adding a second magnetic species to a multiferroic material may be a route to
enhance its ferroelectric properties.Comment: Contribution to ICM 2009; accepted for publication in Journal of
Physics: Conference Serie
Emergent charge ordering in near half doped NaCoO
We have utilized neutron powder diffraction to probe the crystal structure of
layered NaCoO near the half doping composition of 0.46 over the
temperature range of 2 to 600K. Our measurements show evidence of a dynamic
transition in the motion of Na-ions at 300K which coincides with the onset of a
near zero thermal expansion in the in-plane lattice constants. The effect of
the Na-ordering on the CoO layer is reflected in the octahedral
distortion of the two crystallographically inequivalent Co-sites and is evident
even at high temperatures. We find evidence of a weak charge separation into
stripes of Co and Co,
below \Tco=150K. We argue that changes in the Na(1)-O bond lengths observed at
the magnetic transition at \tm=88K reflect changes in the electronic state of
the CoO layerComment: 7 pages, 6 figures, in press Phys. Rev.
Commensurate Dy magnetic ordering associated with incommensurate lattice distortion in orthorhombic DyMnO3
Synchrotron x-ray diffraction and resonant magnetic scattering experiments on
single crystal DyMnO3 have been carried out between 4 and 40 K. Below TN(Dy) =
5K, the Dy magnetic moments order in a commensurate structure with propagation
vector 0.5 b*. Simultaneous with the Dy magnetic ordering, an incommensurate
lattice modulation with propagation vector 0.905 b* evolves while the original
Mn induced modulation is suppressed and shifts from 0.78 b* to 0.81 b*. This
points to a strong interference of Mn and Dy induced structural distortions in
DyMnO3 besides a magnetic coupling between the Mn and Dy magnetic moments.Comment: submitted to Phys. Rev. B Rapid Communication
Enhanced ferroelectric polarization by induced Dy spin-order in multiferroic DyMnO3
Neutron powder diffraction and single crystal x-ray resonant magnetic
scattering measurements suggest that Dy plays an active role in enhancing the
ferroelectric polarization in multiferroic DyMnO3 above TNDy = 6.5 K. We
observe the evolution of an incommensurate ordering of Dy moments with the same
periodicity as the Mn spiral ordering. It closely tracks the evolution of the
ferroelectric polarization which reaches a maximum value of 0.2 muC/m^2. Below
TNDy, where Dy spins order commensurately, the polarization decreases to values
similar for those of TbMnO3
Incompatible Magnetic Order in Multiferroic Hexagonal DyMnO3
Magnetic order of the manganese and rare-earth lattices according to
different symmetry representations is observed in multiferroic hexagonal (h-)
DyMnO by optical second harmonic generation and neutron diffraction. The
incompatibility reveals that the 3d-4f coupling in the h-MnO system (
= Sc, Y, In, Dy - Lu) is substantially less developed than commonly expected.
As a consequence, magnetoelectric coupling effects in this type of split-order
parameter multiferroic that were previously assigned to a pronounced 3d-4f
coupling have now to be scrutinized with respect to their origin
139La NMR evidence for phase solitons in the ground state of overdoped manganites
Hole doped transition metal oxides are famous due to their extraordinary
charge transport properties, such as high temperature superconductivity
(cuprates) and colossal magnetoresistance (manganites). Astonishing, the mother
system of these compounds is a Mott insulator, whereas important role in the
establishment of the metallic or superconducting state is played by the way
that holes are self-organized with doping. Experiments have shown that by
adding holes the insulating phase breaks into antiferromagnetic (AFM) regions,
which are separated by hole rich clumps (stripes) with a rapid change of the
phase of the background spins and orbitals. However, recent experiments in
overdoped manganites of the La(1-x)Ca(x)MnO(3) (LCMO) family have shown that
instead of charge stripes, charge in these systems is organized in a uniform
charge density wave (CDW). Besides, recent theoretical works predicted that the
ground state is inhomogeneously modulated by orbital and charge solitons, i.e.
narrow regions carrying charge (+/-)e/2, where the orbital arrangement varies
very rapidly. So far, this has been only a theoretical prediction. Here, by
using 139La Nuclear Magnetic Resonance (NMR) we provide direct evidence that
the ground state of overdoped LCMO is indeed solitonic. By lowering temperature
the narrow NMR spectra observed in the AFM phase are shown to wipe out, while
for T<30K a very broad spectrum reappears, characteristic of an incommensurate
(IC) charge and spin modulation. Remarkably, by further decreasing temperature,
a relatively narrow feature emerges from the broad IC NMR signal, manifesting
the formation of a solitonic modulation as T->0.Comment: 5 pages, 4 figure
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