Magnetoelastic coupling in the organic radical β- p-NCC₆F₄CNSSN

Resonant ultrasound spectroscopy (RUS) was used to analyze the elastic and anelastic behavior associated with canted antiferromagnetic ordering at 36 K in the radical, β-p-NCC₆F₄CNSSN, 1. On cooling through the magnetic ordering transition there is anomalous elastic behavior away from the expected uniform stiffening with decreasing temperature, consistent with magnetoelastic coupling. The excess in the elastic stiffness follows the magnetic order parameter linearly below the magnetic ordering temperature. A much larger change in elastic properties is associated with short-range ordering between Tc and 150 K which appears to correlate with an excess heat capacity (and entropy). Thus it appears that the onset of long-range order to this spin canted system might only be a partial contribution to the whole phase transition.