Fizika Nizkikh Temperatur: Volume 47, Number 12 (December 2021), p. 1107-1118 ( to contents , go back )
Raman scattering study of the rare-earth binary ferroborate Nd0.75Dy0.25Fe3(BO3)4 single crystal
A. Yu. Glamazda1,2, V. P. Gnezdilov1,3, P. Lemmens3,4, G. A. Zvyagina1, and I. A. Gudim5
1B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine
Kharkiv 61103, Ukraine
2V. N. Karazin Kharkiv National University, Kharkiv 61022, Ukraine
3Institute for Condensed Matter Physics, TU-Braunschweig, Braunschweig 38106, Germany
4Laboratory for Emerging Nanometrology and International Graduate School of Metrology, TU-Braunschweig,
Braunschweig 38106, Germany
5L. V. Kirenskii Institute of Physics, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk 660036, Russia
Received July 8, 2021, published online October 25, 2021
We report comprehensive Raman scattering measurements on a single crystal of binary ferroborate Nd0.75Dy0.25Fe3(BO3)4 in the temperature range of 7–295 K with 532 nm (18797 cm–1) laser excitation. The performed analysis of the polarized Raman spectra revealed the bands assigned to phonon, magnetic, and electronic excitations. The temperature evolution of these quasiparticle excitations has allowed us to ascertain the intricate coupling and interplay between lattice, magnetic, and electronic degrees of freedom. Analysis of the measured Raman spectra made it possible to identify all A1 and Е phonon modes of predicted by the group-theoretical analysis. The splitting energies between the LO and TO components of the polar E phonons were determined. Below the magnetic ordering temperature of the Fe sublattice, TN, we have revealed a multiple peaked two-magnon excitation. Analyzing the temperature evolution of low-frequency modes in the spectra, we also identi-fied modes that are associated with electronic transitions between the crystal field levels of the Nd3+ ions with ground-state 4I9/2 and of the Dy3+ ions with ground-state 6H15/2 multiplets. In addition to the already known temperatures of magnetic transitions, analysis of the temperature behavior of low-frequency phonon and electronic excitations made it possible to establish a temperature T * = 100 K, presumably associated with local distortions of the crystal lattice. The presence of this temperature is confirmed by our ultrasonic study. A group of intense bands observed in the frequency range of 1700–2200 cm–1 has been associated with the mixed low-lying electronic Raman transitions 4I9/2→4I11/2 and the high-energy luminescence ones 4G5/2+2G7/2→4I9/2 for the Nd3+ ion.
Key words: ferroborates, Raman spectroscopy, luminescence.