No Evidence for “Small-Moment Antiferromagnetism” under Ambient Pressure in URu2Si2: Single-Crystal 29Si NMR Study

The still unidentified hidden order (HO) phase below T 0 = 17.5 K in the heavy-electron superconductor URu 2 Si 2 has been investigated by 29 Si NMR on a single crystal under external magnetic field H ext ∥ c -axis and ambient pressure P . For a previously proposed model of the small-moment antiferromagnetism (SMAF), in which tiny-moment antiferromagnetism (AF) under ambient P is ascribed to spatially homogeneous AF with an ordered moment µ SMAF = 0.02–0.04 µ B , splitting of the line would be expected on the basis of a scaling from the corresponding splitting in the P -induced AF. However, we observed at T = 4.5 K no splitting of the line. This clearly indicates that the SMAF model cannot describe the ambient- P properties. Below T 0 down to ∼14 K, the 29 Si NMR line shows additional broadening over the paramagnetic width. The additional contribution, however, disappears below ∼14 K, which indicates that the HO itself produces almost zero internal field at the 29 Si site along the c -axis at low temperat...

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