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Autori: C R Rotundu, B Freelon, T R Forrest, S D Wilson, P N Valdivia, G Pinuellas, A Kim, J-W Kim, Z Islam, E Bourret-Courchesne, N E Phillips, and R J Birgeneau
Editorial: APS, Physical Review B, 82, p.144525, 2010.
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 Ohm cm, with a residual resistance ratio ~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 ~0.15 K, and is unchanged in a magnetic field mu_0H=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.
Cuvinte cheie: BaFe2As2, iron pnictide high temperature superconductors