Heat Capacity Study Of Bafe2as2: Effects Of Annealing

Heat capacity, x-ray diffraction, and resistivity measurements on a high-quality BaFe2As2 sample show an evolution of the magnetostructural transition with successive annealing periods. After a 30-day anneal the resistivity in the (ab) plane decreases by more than an order of magnitude, to 12 mu Omega cm, with a residual resistance ratio similar to 36; the heat capacity anomaly at the transition sharpens, to an overall width of less than K, and shifts from 135.4 to 140.2 K. The heat capacity anomaly in both the as-grown sample and after the 30-day anneal shows a hysteresis of similar to 0.15 K, and is unchanged in a magnetic field mu H-0=14 T. The x-ray and heat capacity data combined suggest that there is a first-order jump in the structural order parameter. The entropy of the transition is reported.