Helical scattering signatures of strain and electronic textures in YbFe 2 O 4 from three-dimensional reciprocal-space imaging
Physical Review B - Condensed Matter and Materials Physics 85:1 (2012)
Abstract:
The insulating ternary oxide YbFe 2O 4 displays an unusual frustration-driven incommensurate charge-ordering (CO) transition, linked to possible ferroelectricity. Based on high-resolution synchrotron data, we report a detailed structural model showing that the CO phase is an incommensurate charge-density wave and cannot be ferroelectric, since the electrical dipole moments are also incommensurately modulated. The change between continuous and "spotty" helices of scattering at the CO transition is attributed to three-dimensional fluctuations of the direction of the ordering wave vector. © 2012 American Physical Society.Electric field control of the magnetic chiralities in ferroaxial multiferroic RbFe(MoO4)2
arXiv [cond-mat.str-el] (2012) 1202.2317
Helical scattering signatures of strain and electronic textures in YbFe2O4 from three-dimensional reciprocal-space imaging
Phys. Rev. B 85 (2012) 014115
Magneto-orbital helices as a route to coupling magnetism and ferroelectricity in multiferroic CaMn₇O₁₂.
Nat Commun 3 (2012) 1277
Abstract:
Orbital physics drives a rich phenomenology in transition-metal oxides, providing the microscopic underpinning for effects such as Colossal Magnetoresistance. In particular, magnetic and lattice degrees of freedom are coupled through orbital ordering, and it has long been hoped that this coupling could be exploited to create high-temperature multiferroics with large values of the electrical polarization. Here we report an unprecedented magneto-orbital texture in multiferroic CaMn(7)O(12), found to give rise to the largest magnetically induced ferroelectric polarization measured to date. X-ray diffraction characterization of the structural modulation in these 'magneto-orbital helices', and analysis of magnetic exchange shows that orbital order is crucial in stabilising a chiral magnetic structure, thus allowing for electric polarization. Additionally, the presence of a global structural rotation enables the coupling between this polarization and magnetic helicity required for multiferroicity. These novel principles open up the possibility of discovering new multiferroics with even larger polarization and higher transition temperatures.Symmetry in Crystallography
Oxford University Press, 2011