The Fourth Ferroic Order: Hunting Ferrotoroidicity in Energy Materials

November 22, 2022
(left) Illustrations of the possible four ferroic ordered states. Ferrotoroidic order is associated with unique rings of spins. (right) a-b plane of the magnetic structure of lithiated (LiFe0.2Mn0.8PO4) and de-litheated (Li0.8Fe0.2Mn0.8PO4) samples, purple/orange sphere represent the Mn and Fe atoms and the arrows show the magnetic moment along the b axis.

Scientific Achievement

It is demonstrated that removing lithium from the olivine materials Li1-yFexMn1-xPO4 changes the magnetic structure and ordering temperature, and that the highest ordering temperature compatible with ferrotoroidicity is achieved for x=y=0.3.

Significance and Impact

This work shows a possible avenue of achieving ferrotoroidic order, the long-sought ‘fourth’ ferroic order that is expected to result in useful magnetoelectric properties applicable to new technologies.

Research Details

  • Samples were characterized by X-ray diffraction and bulk magnetic measurements: the ordering temperature TN was seen to be systematically higher for samples that were delithiated via selective chemistry.
  • Neutron diffraction yielded the magnetic point group symmetries of different compositions allowing for the optimal de-lithiation and TN enhancement that still supported ferrotoroidal order to be determined.

“Tuning Magnetic Symmetry and Properties in the Olivine Series Li1–xFexMn1–xPO4 through Selective Delithiation” 
Timothy J. Diethrich, Stephanie Gnewuch, Kaitlyn G. Dold, Keith M. Taddei, and Efrain E. Rodriguez
Chemistry of Materials 34, 5039-5053 (2022). DOI: 10.1021/acs.chemmater.2c00372