Dipolar-octupolar Ising antiferromagnetism in Sm2Ti2O7: A moment fragmentation candidate

Over the past two decades, the magnetic ground states of all rare-earth titanate pyrochlores have been extensively studied, with the exception of Sm₂Ti₂O₇. This is, in large part, due to the very high absorption cross section of naturally occurring samarium, which renders neutron scattering infeasible. To combat this, we have grown a large, isotopically enriched single crystal of Sm₂Ti₂O₇. Using inelastic neutron scattering, we determine that the crystal field ground state for Sm³⁺ is a dipolar-octupolar doublet with Ising anisotropy. Neutron diffraction experiments reveal that Sm₂Ti₂O₇ orders into the all-in, all-out magnetic structure with an ordered moment of 0.44(7)μB below TN=0.35 K, consistent with expectations for antiferromagnetically coupled Ising spins on the pyrochlore lattice. Zero-field muon spin relaxation measurements reveal an absence of spontaneous oscillations and persistent spin fluctuations down to 0.03 K. The combination of the dipolar-octupolar nature of the Sm3+ moment, the all-in, all-out ordered state, and the low-temperature persistent spin dynamics make this material an intriguing candidate for moment fragmentation physics.