Temperature-dependent Raman and x-ray studies of the spin-ice pyrochloreDy2Ti2O7and nonmagnetic pyrochlore

Abstract

We present here temperature-dependent Raman, x-ray diffraction and specific heat studies between room temperature and 12 K on single crystals of spin-ice pyrochlore compound Dy 2 T i 2 O 7 and its non-magnetic analogue Lu 2 T i 2 O 7 . Raman data show a "new" band not predicted by factor group analysis of Raman-active modes for the pyrochlore structure in Dy 2 T i 2 O 7 , appearing below a temperature of T c =110 K with a concomitant contraction of the cubic unit cell volume as determined from the powder x-ray diffraction analysis. Low temperature Raman experiments on O 18 -isotope substituted Dy 2 T i 2 O 7 confirm the phonon origin of the "new" mode. These findings, absent in Lu 2 T i 2 O 7 , suggest that the room temperature cubic lattice of the pyrochlore Dy 2 T i 2 O 7 undergoes a "subtle" structural transformation near T c . We find anomalous red-shift of some of the phonon modes in both the Dy 2 T i 2 O 7 and the Lu 2 T i 2 O 7 as the temperature decreases, which is attributed to strong phonon-phonon anharmonic interactions.

Raman study of phonon modes in bismuth pyrochlores

“…This analysis would explain the trend, also present in the IR, of higher frequencies observed for the lighter B cation in BZN and BMN, than for BMT and BZT. However, based on Fischer's calculations, and the proximity of an F 2g mode to the E g mode in other pyrochlores, 10,[12][13][14][19][20][21][22]25,26,28,29 we have assigned the ϳ300 cm −1 feature in the Raman spectrum to the E g mode and one of the F 2g modes. The A 1g , and one of the F 2g modes of the ideal structure are assigned to bands at 530 cm −1 and 420 cm −1 , respectively.…”

“…The appearance of the additional Raman bands, which correspond to Raman-inactive modes of the ideal pyrochlore structure, confirms the displacive disorder of the A and OЈ sites in the bismuth pyrochlores. The Raman modes were assigned by reference to the Raman spectra of many other pyrochlores, [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] some of which include lattice-dynamical calculations, 12,27,28 and firstprinciples calculations. 11 In the literature, the lattice dynamical and ab initio calculations show an interesting difference.…”

“…Each mode was studied and assigned by first referencing the literature on diverse samples with structures close to the ideal pyrochlore structure. 10,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] Then, the bands were also compared to our ab initio calculations for Bi 2 Ti 2 O 7 and those in the literature for Cd 2 Nb 2 O 7 . 11 Table II shows the frequencies of the various observed modes for the four samples along with their assignment.…”

A lattice dynamical investigation of the Raman and the infrared frequencies of the Dy2Ti2O7 pyrochlore spin ice compound

“…For the information on phonons, charge carriers and spins, this geometrically frustrated pyrochlore Dy 2 Ti 2 O 7 (space group O h 7 ) had been studied experimentally for its infrared and Raman modes [3][4][5][6]. Fuentes et al [4] measured the Raman spectra but did not assign various modes.…”

Anomalous surface lattice dynamics in the low-temperature phase of Ba(Fe 1− x Co x ) 2 As 2

“…Another channel for phonon decay is associated with a strong spinphonon interaction, such that the change of spin structure may significantly renormalize the phonon energy and lifetime. Because the two phonon modes discussed here are in the As-Fe layer associated with the magnetic ions, spin-charge-lattice coupling should be included, caused by the modulation of the spin exchange integral by lattice vibrations (32)(33)(34)(35)(36). It should be pointed out that one cannot talk about spin-phonon interaction without the involvement of EPC (35,36) or spin-orbit coupling (37).…”