Incommensurate-to-commensurate magnetic phase transition in SmIn3 observed by muon spin relaxation

Magnetic susceptibility and muon spin relaxation (μSR) measurements in the intermetallic cubic compound SmIn3 with a Γ8 crystalline-electric-field ground state are reported. Anomalies corresponding to successive phase transitions were observed in the magnetic susceptibility at TI - 16.5 K, TII - 15.1 K, and TIII - 14.7 K. A spontaneous local magnetic field was detected below TI using the μSR technique in zero applied field in contrast to the pure quadrupolar ordering scenario proposed in the phase between TI and TII. This result clearly indicates that the primary order parameters in all the ordered phases are magnetic. The local field distribution changes at around TII from a continuous broad one to a sharp one with decreasing temperature, suggesting that an incommensurate-to-commensurate magnetic phase transition takes place at this temperature. A possible magnetic structure in the ground state and the importance of multipolar interactions in the Γ8 subspace are discussed. (author)