The results of a Fe-57 Mossbauer spectroscopy study between 2.0 and 294 K of superconducting Ba(Fe0.961Rh0.039)(2)As-2 are reported. The main component of the electric field gradient tensor at 294 K is shown to be positive and its increase with decreasing temperature is well described by a T-3/2 power-law relation. The shape of the Mossbauer spectra below the Neel temperature T-N = 55.5(1) K is shown to result from the presence of doping-induced disorder rather than of incommensurate spin-density-wave order. The measured hyperfine magnetic field reaches its maximum value at the critical temperature T-c = 14 K and then decreases by 4.2% upon further cooling to 2.0 K. This constitutes direct evidence of the coexistence of and competition between superconductivity and magnetic order. The extrapolated value of the Fe magnetic moment at 0 K is determined to be 0.35(1) mu(B). The Debye temperature of Ba(Fe0.961Rh0.039)(2)As-2 is found to be 357(3) K.
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This article is published as Wang, P., Z. M. Stadnik, J. Żukrowski, A. Thaler, S. L. Bud’ko, and P. C. Canfield. "Coexistence of antiferromagnetic ordering and superconductivity in the Ba (Fe 0. 961 Rh 0. 039) 2 As 2 compound studied by Mössbauer spectroscopy." Physical Review B 84, no. 2 (2011): 024509. DOI: 10.1103/PhysRevB.84.024509. Posted with permission.