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

Area of Science:

• Condensed Matter Physics
• Magnetism and Magnetic Materials
• Solid State Chemistry

Background:

• RbFe2Fe3F6 is a charge-ordered antiferromagnet with distinct iron valences (Fe2+ and Fe3+).
• These iron sites form two interpenetrating sublattices, leading to a noncollinear magnetic structure at low temperatures.
• The Fe3+ sites exhibit a reduced static ordered moment.

Purpose of the Study:

• To investigate the magnetic excitations in RbFe2Fe3F6 single crystals.
• To understand the spin wave dynamics and the nature of magnetic ordering in this noncollinear system.
• To explore the role of anharmonic excitations in the magnetic properties.

Main Methods:

• Single-crystal neutron spectroscopy.
• High-resolution spectroscopic measurements.
• Analysis of spin wave branches and magnetic scattering.

Main Results:

• Two distinct spin wave branches were identified, with dominant coupling along the Fe3+ chain axis (b axis).
• An intense, energy and momentum broadened magnetic band of scattering was observed.
• This scattering band corresponds to kinematically allowed two-magnon processes, indicating enhanced anharmonic excitations.

Conclusions:

• The noncollinear, orthogonal spin arrangement in RbFe2Fe3F6 enhances anharmonic excitations.
• Neutron spectroscopy provides detailed insights into the spin dynamics of charge-ordered magnets.
• The findings contribute to the understanding of complex magnetic phenomena in materials with competing interactions.