Large elastic softening in the one-dimensional magnetic material CsNiF3

The Young's modulus parallel to the linear chains in CsNiF₃ exhibits large precursor softening several hundred degrees above the region of measurable one-dimensional ferromagnetic correlations (30 K) and a rapid decrease below the three-dimensional antiferromagnetic ordering temperature (2.7 K). No such elastic anomaly is observed perpendicular to the chains. This elastic behavior shows the existence of large quadraticstrain dependences and anisotropy of the structural forces in CsNiF₃.