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Local Spin-coupled Distortions in Multiferroic Hexagonal HoMnO3

Journal Article · · Physical Review B: Condensed Matter and Materials Physics
Local structural measurements have been performed on hexagonal HoMnO{sub 3} in order to ascertain the specific changes in bond distances, which accompany magnetic ordering transitions. The transition from the paramagnetic to the antiferromagnetic (noncollinear) phase near -70 K is dominated by changes in the a-b plane Mn-Mn bond distances. The spin rotation transition near -40 K involves both Mn-Mn and nearest-neighbor Ho-Mn interactions while the low-temperature transition below 10 K involves all interactions, Mn-Mn, Ho-Mn (nearest and next nearest), and Ho-Ho correlations. These changes in bond distances reveal strong spin-lattice coupling. The similarity in magnitude of the change in J(Mn-Mn) and J(Ho-Mn) enhances the system frustration. The structural changes are interpreted in terms of a model of competing spin order and local structural distortions. Density-functional calculations are used to estimate the energies associated with ionic displacements. The calculations also reveal asymmetric polarization of the charge density of Ho, O3, and O4 sites along the c axis in the ferroelectric phase. This polarization facilitates coupling between Ho atoms on neighboring planes normal to the c axis.
Research Organization:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Organization:
DOE - OFFICE OF SCIENCE
DOE Contract Number:
AC02-98CH10886
OSTI ID:
1020025
Report Number(s):
BNL--95871-2011-JA
Journal Information:
Physical Review B: Condensed Matter and Materials Physics, Journal Name: Physical Review B: Condensed Matter and Materials Physics Journal Issue: 5 Vol. 81; ISSN 1098-0121
Country of Publication:
United States
Language:
English

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