Magnetically induced femtoscale strain modulations in HoMn 2 O 5

X-ray scattering was used to investigate the magnetically induced ionic displacements in the low-temperature commensurate ferroelectric/ antiferromagnetic phase of the multiferroic HoMn2O5. The structural modulation signal appearing at twice the magnetic wave vector km=(12014) has been used, combined with symmetry analysis, to determine a model for the ionic displacements up to a precision of 10-3Å. The symmetry-breaking operations that are associated to the active irreducible representation have been experimentally determined from the analysis of the modulation modes. They reveal a lowering of symmetry to the polar point group m2m. Calculations based on the determined model show that the magnetic structure along the c direction is stabilized via nearest-neighbor and next-nearest-neighbor interactions through the rare-earth layer. We also show that by knowing both the magnetic and the magnetically induced strain waves patterns, it is possible to remove any phase ambiguity between the crystal and magnetic structures.