Neutron scattering study on commensurate and incommensurate antiferromagnetic phases in UPd₂Si₂ under uniaxial stress

The nature of competition between incommensurate (IC) and commensurate (C) antiferromagnetic (AF) orders in UPd₂Si₂ was investigated by performing elastic neutron scattering experiments under uniaxial stress σ. It is found that applying σ along tetragonal [010] direction reduces the IC-AF order, and then stabilizes the C-AF order. The transition temperature from IC- to C-AF phases T_Nl is enhanced from 109 K (σ = 0) to 112.5 K at (0.8 GPa), while the onset of IC-AF transition T_Nh is unchanged from 132 K under σ. In addition, c-axis component q_z of the IC-AF modulation at 115 K also increases from 0.736 (σ = 0) to 0.747 (0.8 GPa). The magnitude of C-AF moment at 5 K is estimated to be 2.2 μ_B/U in the entire σ range presently investigated (σ ≤ 0.8 GPa). These features are similar to those obtained from the investigations using hydrostatic pressure p, indicating that applications of p and σ∥ [010] commonly induce the crystal strains which inherently affect a delicate balance of frustrated magnetic interactions between uranium 5f moments.