Посилання:Phononic and magnetic excitations in the quasi-one-dimensional Heisenberg antiferromagnet KCuF₃ / V. Gnezdilov, J. Deisenhofer, P. Lemmens, D. Wulferding, O. Afanasiev, P. Ghigna, A. Loidl, A. Yeremenko // Физика низких температур. — 2012. — Т. 38, № 5. — С. 538-548. — Бібліогр.: 66 назв. — англ.
Підтримка:We like to thank M.V. Eremin and B. Lake for important
discussions. D.W. and P.L. acknowledges support
by B-IGSM and NTH “Contacs in Nanosystems”. We also
acknowledge support by the DFG via TRR80 and via LE
967/6-1 and the Swiss NSF through NCCR MaNEP.
The Raman-active phonons and magnetic excitations in the orbitally ordered, quasi-one-dimensional Heisenberg
antiferromagnet KCuF₃ are studied as a function of temperature in the range between 3 and 290 K in various
scattering configurations. The low-energy Eg and B1g phonon modes show an anomalous softening (~25%
and ~13%) between room temperature and the characteristic temperature TS = 50 K. In this temperature range a
freezing-in of F–
ion dynamic displacements is proposed to occur. In addition, the Eg mode at about 260 cm⁻¹
clearly splits below TS. The widths of the phonon lines above TS follow an activated behavior with an activation
energy of about 50 K. Our observations clearly evidence a reduction of the lattice symmetry below TS and indicate
a strong coupling of lattice, spin, and orbital fluctuations for T > TS. A strongly polarization dependent quasielastic
scattering is observed at temperatures above TN = 39 K due to magnetic-energy fluctuations. For temperatures
below TN a rich spectrum of additional modes is observed, with different lineshape, polarization and
temperatures dependence. We attribute them to longitudinal and transverse magnetic modes as well as to a continuum
of magnetic excitations.