Intermultiplet transitions and long-range order in Sm-based pyrochlores

We present bulk and neutron scattering measurements performed on the isotopically enriched ¹⁵⁴Sm₂Ti₂O₇ (titanate) and ¹⁵⁴Sm₂Sn₂O₇ (stannate) samples. Both compounds display sharp heat capacity anomalies, at 350 mK and 440 mK, respectively. Inelastic neutron scattering measurements are employed to solve the crystalline electric field (CEF) excitations scheme, which includes transitions between the ground and first excited J multiplets of the Sm³⁺ ion. In order to further validate those results, the single-ion magnetic susceptibility of the compounds is calculated and compared with the experimental static susceptibility measured in low applied magnetic fields. We show that the inclusion of intermultiplet transitions in the crystal field analysis is fundamental to the understanding of the intermediate and, more importantly, low temperature magnetic behaviour of the Sm-based pyrochlores. Finally, the heat capacity anomally is shown to correspond to the onset of an all-in-all-out long-range order in the stannate sample, while in the titanate a dipolar long-range order can be only indirectly infered.