Coexistence of antiferromagnetic ordering and superconductivity in the Ba(Fe0.961Rh0.039)(2)As-2 compound studied by Mossbauer spectroscopy

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

Coexistence of antiferromagnetic ordering and superconductivity in the Ba(Fe0.961Rh0.039)(2)As-2 compound studied by Mossbauer spectroscopy

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.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.</p

Magnetic field induced structural changes in magnetite observed by resonant x-ray diffraction and Mössbauer spectroscopy

International audienceWhen a magnetic field is applied to a single crystal of magnetite at 124 K > T > 50 K, the monoclinic c M axis, which is the easy magnetization axis, switches to one of the 100 cubic directions, nearest to the direction of the magnetic field, and the phenomenon known as an axis switching (AS) occurs. A global symmetry probe, resonant x-ray scattering, and a local probe, Mössbauer spectroscopy, are used to better understand the mechanism of axis switching. The behavior of three subsystems ordered below the Verwey transition temperature T V , i.e., lattice distortion, an orbital, and charge orderings, was observed via resonant x-ray scattering as a function of an external magnetic field. This was preceded by calculation of selected peak intensities using the FDMNES code. The Mössbauer spectroscopy studies confirmed that the magnetic field triggers electronic rearrangements and atomic displacements. The structure observed after the process of axis switching is very similar to the one obtained after cooling below T V with the magnetic field applied along one of the initial 100 cubic directions and distinct from the cooling in the absence of a magnetic field. From all the experimental observations of the phenomenon done so far, it is clear that AS starts from the fluctuations between octahedral iron orbitals that ultimately lead to the Verwey transition, but also to the higher-temperature trimeron dynamics. Therefore, further observation of the axis switching may be a key point to the understanding of a majority of strongly correlated electronic behavior in magnetite as well as in other transition metal oxides