Elastic and magnetic effects on the infrared phonon spectra on MnF
We measured the temperature-dependent infrared reflectivity spectra of MnF{sub 2} between 4 and 600 K. We show that the phonon spectrum undergoes a clear renormalization at T{sub N}. The ab initio calculation we performed on this compound accurately predicts the magnitude and the direction of the changes in the phonon parameters across the antiferromagnetic transition, showing that they are mainly induced by the magnetic order. In this material, we found that the dielectric constant is mostly from phonon origin. The large change in the lattice parameters with temperature seen by x-ray diffraction as well as the A{sub 2u} phonon softening below T{sub N} indicate that magnetic order induced distortions in MnF{sub 2} are compatible with the ferroelectric instabilities observed in TiO{sub 2}, FeF{sub 2} and other rutile-type fluorides. This study also shows the anomalous temperature evolution of the lower energy E{sub u} mode in the paramagnetic phase, which can be compared to that of the B{sub 1g} phonon seen by Raman spectroscopy in many isostructural materials. This was interpreted as being a precursor of a phase transition from rutile to CaCl{sub 2} structure which was observed under pressure in ZnF{sub 2}.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- DOE - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 1001317
- Report Number(s):
- BNL-94314-2010-JA; ISSN 1550-235X; R&D Project: LS001; KC0401030; TRN: US1100328
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 82, Issue 5; ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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