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Thursday, October 11
Neutron Scattering as a Probe of Magnetic-Ferroelectric
Owen P. Vajk, The University of Missouri, Columbia
Interactions in Hexagonal RMnO3
Spallation Neutron Source Seminar
2:00 PM — 3:00 PM, SNS Central Laboratory and Office Building (8600),
Contact: Steve Nagler (firstname.lastname@example.org), 865.574.5240
AbstractMaterials with both ferroelectric and magnetic order are known as multiferroics, and they have attracted considerable attention recently because coupling between the magnetic and ferroelectric order within these materials may lead to large magnetoelectric effects. The hexagonal rare-earth manganites form a family of multiferroic compounds that share a common layered structure. These materials have high ferroelectric ordering temperatures (~900K) but much lower antiferromagnetic ordering temperatures (~70K), although the exact magnetic structure depends on both the rare earth ion and in some cases the temperature. Strong coupling between the ferroelectricity and magnetism has been observed at a spin reorientation transition in HoMnO3 between a P6'3c'm phase and a P6'3cm' phase, where a change in the Mn3+ spin structure coincides with a change in the ferroelectric polarization magnitude. Most members of the RMnO3 family do not have any spin reorientation transition, and so signs of magnetic-ferroelectric interaction in other RMnO3 compounds are much less pronounced. In order to better understand the strong magnetic-ferroelectric coupling observed in HoMnO3, we have performed systematic doping dependence studies of RMnO3 compounds with mixed rare-earth occupancy. Neutron scattering measurements reveal a complex multi-dimensional phase space where the P6'3c'm to P6'3cm' phase boundary reveals unexpected doping dependency. Inelastic measurements in Y-rich compounds reveal quasielastic scattering corresponding to the "wrong" magnetic phase for those compounds, indicating strong competition between competing magnetic phases. Further measurements are still needed to fully explore the rich physics behind the magnetic-ferroelectric coupling in this rich family of multiferroic compounds.