Anharmonic Magnon Excitations in Noncollinear and Charge-Ordered ${\mathrm{RbFe}}^{2+}{\mathrm{Fe}}^{3+}{\mathrm{F}}_{6}$

Anharmonic Magnon Excitations in Noncollinear and Charge-Ordered ${RbFe}^{2 +} {Fe}^{3 +} F_{6}$

M. Songvilay, E. E. Rodriguez, R. Lindsay, M. A. Green, H. C. Walker, J. A. Rodriguez-Rivera, and C. Stock

Phys. Rev. Lett. 121, 087201 – Published 21 August 2018

Abstract

${RbFe}^{2 +} {Fe}^{3 +} F_{6}$ is an example of a charge ordered antiferromagnet where iron sites, with differing valences, are structurally separated into two interpenetrating sublattices. The low temperature magnetically ordered ${Fe}^{2 +}$ ( $S = 2$ ) and ${Fe}^{3 +}$ ( $S = 5 / 2$ ) moments form a noncollinear orthogonal structure with the ${Fe}^{3 +}$ site displaying a reduced static ordered moment. Neutron spectroscopy on single crystals finds two distinct spin wave branches with a dominant coupling along the ${Fe}^{3 +}$ chain axis ( $b$ axis). High resolution spectroscopic measurements find an intense energy and momentum broadened magnetic band of scattering bracketing a momentum-energy region where two magnon processes are kinematically allowed. These anharmonic excitations are enhanced in this noncollinear magnet owing to the orthogonal spin arrangement.

Received 17 January 2018
Revised 10 May 2018

DOI:https://doi.org/10.1103/PhysRevLett.121.087201

Physics Subject Headings (PhySH)

Antiferromagnetism Exchange interaction Jahn-Teller effect Magnons Spin waves

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

M. Songvilay^1,*, E. E. Rodriguez², R. Lindsay³, M. A. Green³, H. C. Walker⁴, J. A. Rodriguez-Rivera^5,6, and C. Stock¹

¹School of Physics and Astronomy and Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
²Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA
³School of Physical Sciences, University of Kent, Canterbury CT2 7NH, United Kingdom
⁴ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom
⁵NIST Center for Neutron Research, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, USA
⁶Department of Materials Science, University of Maryland, College Park, Maryland 20742, USA