Abstract :
We have measured the specific heat of crystals of (Ca1−xSrx)3Ru2O7 using ac- and relaxation-time calorimetry. Special emphasis was placed on the characterization of the Néel ( T N = 56 K ) and structural ( T c = 48 K ) phase transitions in the pure, x = 0 material. While the latter is believed to be first order, detailed measurements under different experimental conditions suggest that all the latent heat (with L ∼ 0.3 R ) is being captured in a broadened peak in the effective heat capacity. The specific heat has a mean-field-like step at T N , but its magnitude ( Δ c P ∼ R ) is too large to be associated with a conventional itinerant electron (e.g. spin-density-wave) antiferromagnetic transition, while its entropy is too small to be associated with the full ordering of localized spins. The T N transition broadens with Sr substitution while its magnitude decreases slowly. On the other hand, the entropy change associated with the T c transition decreases rapidly with Sr substitution, and is not observable for our x = 0.58 sample.
