Ramification of complex magnetism in Nd$_2$Ir$_2$O$_7$ observed by Raman scattering spectroscopy

Yuanyuan Xu; Yang Yang; Jérémie Teyssier; Takumi Ohtsuki; Yang Qiu; Satoru Nakatsuji; Dirk van der Marel; Natalia B. Perkins; Natalia Drichko

arXiv · 2302.00579

Ramification of complex magnetism in Nd$_2$Ir$_2$O$_7$ observed by Raman scattering spectroscopy

Yuanyuan Xu·Yang Yang·Jérémie Teyssier·Takumi Ohtsuki·Yang Qiu·Satoru Nakatsuji·Dirk van der Marel·Natalia B. Perkins·Natalia Drichko

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Abstract

Using Raman scattering spectroscopy, we uncover a complex magnetic behavior of Nd$_2$Ir$_2$O$_7$ , which stands out among magnetic pyrochlores by the lowest temperature of the all-in-all-out (AIAO) Ir moments ordering ($T^\mathrm{N}_{\small\rm{Ir}}=33$~K) and the highest temperature at which AIAO order of rare-earth Nd ions is detected ($T^\mathrm{*}_{\small\rm{Nd}}$=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 Nd$_2$Ir$_2$O$_7$ a particularly attractive playground to study the rare-earth magnetism on the pyrochlore lattice.

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Yuanyuan Xu, Yang Yang, Jérémie Teyssier, Takumi Ohtsuki, Yang Qiu, Satoru Nakatsuji, Dirk van der Marel, Natalia B. Perkins, Natalia Drichko. 2023-02-01. Ramification of complex magnetism in Nd$_2$Ir$_2$O$_7$ observed by Raman scattering spectroscopy. https://arxiv.org/abs/2302.00579

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