Comparison of Young's modulus and specific heat anomalies at the magnetic transition in α′-NaV2O5

We have measured Young's modulus (using a vibrating reed technique) and the specific heat (using ac calorimetry) on the same crystals of α′-NaV₂O₅ at its T_c=34 K magnetic phase transition. Both properties exhibit large, unsymmetrical, and sample-dependent anomalies. While the specific heat results suggest tricritical behavior of the transition, large fluctuation effects are observed in the modulus above T_c. Fits of the modulus in terms of the specific heat, entropy, and free energy suggest that fluctuations are strongly stress- and sample-dependent.