Using Raman scattering spectroscopy, we uncover a complex magnetic behavior of Nd2Ir2O7 , which stands out among magnetic pyrochlores by the lowest temperature of the all-in-all-out (AIAO) Ir moments ordering (TIrN=33~K) and the highest temperature at which AIAO order of rare-earth Nd ions is detected (TNd∗=15~K). Our findings suggest that in the temperature range between 15~K and 33~K, Nd magnetic moments exhibit strong fluctuations, possibly originating from spin ice behavior. This complex behavior emerges from the interplay of strong spin-orbit coupling, electronic correlations, and geometric frustration on two magnetic pyrochlore sublattices of Nd and Ir ions. The ordering of Ir magnetic moments is accompanied by an appearance of one-magnon Raman modes at 26.3 and 29.6 meV compatible with the AIAO order and of a broad mode at 14 meV, which could be associated with spinon continuum arising from Nd spin ice fluctuations. While two one-magnon excitations show minimal temperature evolution with decreasing temperature, the 14 meV mode shifts to higher frequencies as the temperature approaches a crossover to Nd AIAO order, broadens, and disappears below 15~K. An additional two-magnon excitation of the AIAO Nd order at around 33 meV appears in the spectra at low temperatures. These rather high energies of magnetic excitations of Nd moments make Nd2Ir2O7 a particularly attractive playground to study the rare-earth magnetism on the pyrochlore lattice.
@article{arxiv.2302.00579,
title = {Ramification of complex magnetism in Nd$_2$Ir$_2$O$_7$ observed by Raman scattering spectroscopy},
author = {Yuanyuan Xu and Yang Yang and Jérémie Teyssier and Takumi Ohtsuki and Yang Qiu and Satoru Nakatsuji and Dirk van der Marel and Natalia B. Perkins and Natalia Drichko},
journal= {arXiv preprint arXiv:2302.00579},
year = {2024}
}