Pe. Sulewski et Sw. Cheong, RAMAN-ACTIVE PHONONS OF THE SPIN-1 CHAIN ANTIFERROMAGNETS R2BANIO5 (R=GD AND Y), Physical review. B, Condensed matter, 50(1), 1994, pp. 551-554
We report Raman spectra of single-crystalline Gd2BaNiO5 and Y2BaNiO5,
concentrating on identification and assignment of the phonons at room
temperature. All nine of the expected Ramanactive phonons (3 A(g) + 1B
1g + 2B2g + 3B3g) are observed. The three Gd(Y) related modes of B2g,
A(g), and B3, symmetry are observed at 123(160), 175(233), and 204(269
) cm-1, respectively. The six O(1) vibrational modes of the Gd(Y) comp
ound occur at 183(184), 312(328), 335(340), 422(440), 518(540), and 56
2(584) cm-1, having B3g, B2g, B1g, B3g, A(g), and A(g) symmetries, res
pectively. A strong mode polarized along the Ni-O(2) chain axis at app
roximately 726(755) cm-1 in the Gd(Y) compound may arise from magnetic
excitations along the spin chains or from a Raman-forbidden, infrared
-allowed vibrational mode along the Ni-O(2) chains.