23 research outputs found
The nature of Ho magnetism in multiferroic HoMnO3
Using x-ray resonant magnetic scattering and x-ray magnetic circular
dichroism, techniques that are element specific, we have elucidated the role of
Ho3+ in multiferroic HoMnO3. In zero field, Ho3+ orders antiferromagnetically
with moments aligned along the hexagonal c direction below 40 K, and undergoes
a transition to another magnetic structure below 4.5 K. In applied electric
fields of up to 1x10^7 V/m, the magnetic structure of Ho3+ remains unchanged.Comment: 4 pages, 3 figures Manuscript accepted for publication in Phys. Rev.
Lett. 200
High-temperature phase transitions of hexagonal YMnO3
We report a detailed high-resolution powder neutron diffraction investigation
of the structural behaviour of the multiferroic hexagonal polymorph of YMnO3
between room temperature and 1403 K. The study was aimed at resolving previous
uncertainties regarding the nature of the paraelectric- ferroelectric
transition and the possibilities of any secondary structural transitions. We
observe a clear transition at 1258 +/- 14 K corresponding to a unit cell
tripling and a change in space group from centrosymmetric P6_3/mmc to polar
P6_3cm. Despite the fact that this symmetry permits ferroelectricity, our
experimental data for this transition analysed in terms of symmetry-adapted
displacement modes clearly supports previous theoretical analysis that the
transition is driven primarily by the antiferrodistortive K3 mode. We therefore
verify previous suggestions that YMnO3 is an improper ferrielectric.
Furthermore, our data confirm that the previously suggested intermediate phase
with space group P6_3/mcm does not occur. However, we do find evidence for an
isosymmetric phase transition (i.e. P6_3cm to P6_3cm) at ~920 K which involves
a sharp decrease in polarization. This secondary transition correlates well
with several previous reports of anomalies in physical properties in this
temperature region and may be related to Y-O hybridization.Comment: Submitted to PR
Local magnetism and magnetoelectric effect in HoMnO3 studied with muon-spin relaxation
We present the results of muon-spin relaxation (μ+ SR) measurements on the hexagonal manganite HoMnO3. Features in the temperature-dependent relaxation rate λ correlate with the magnetic transitions at 76, 38, and 34 K. The highest temperature transition, associated with the ordering of Mn3+ moments has the largest effect on λ. The application of a static electric field of E=5× 106 Vm-1 below T=50K causes a small reduction in λ which is suggestive of coupling between ferroelectric and magnetic domain walls in the ordered state of the material. © 2010 The American Physical Society