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Register a new userSuppression of antiferromagnetic order and orthorhombic distortion in superconducting Ba(Fe0.961Rh0.039)2As2
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Neutron diffraction and high-resolution x-ray diffraction studies find that, similar to the closely related underdoped Ba(Fe[1-x]Cox)2As2 superconducting compounds, Ba(Fe0.961Rh0.039)2As2 shows strong evidence of competition and coexistence between superconductivity and antiferromagnetic order below the superconducting transition, Tc = 14 K. The transition temperatures for both the magnetic order and orthorhombic distortion are in excellent agreement with those inferred from resistivity measurements, and both order parameters manifest a distinct decrease in magnitude below Tc. These data suggest that the strong interaction between magnetism and superconductivity is a general feature of electron-doped Ba(Fe[1-x]TMx)2As2 superconductors (TM = Transition Metal).
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Inelastic neutron scattering measurements have been performed on underdoped Ba(Fe1-xCox)2As2 (x = 4.7%) where superconductivity and long-range antiferromagnetic (AFM) order coexist. The broad magnetic spectrum found in the normal state develops into a magnetic resonance feature below TC that has appreciable dispersion along c-axis with a bandwidth of 3-4 meV. This is in contrast to the optimally doped x = 8.0% composition, with no long-range AFM order, where the resonance exhibits a much weaker dispersion [see Lumsden et al. Phys. Rev. Lett. 102, 107005 (2009)]. The results suggest that the resonance dispersion arises from interlayer spin correlations present in the AFM ordered state.
Neutron and x-ray diffraction studies of Ba(Fe{1-x}Mn{x})2As2 for low doping concentrations (x <= 0.176) reveal that at a critical concentration, 0.102 < x < 0.118, the tetragonal-to-orthorhombic transition abruptly disappears whereas magnetic ordering with a propagation vector of (1/2 1/2 1) persists. Among all of the iron arsenides this observation is unique to Mn-doping, and unexpected because all models for stripe-like antiferromagnetic order anticipate an attendant orthorhombic distortion due to magnetoelastic effects. We discuss these observations and their consequences in terms of previous studies of Ba(Fe{1-x}TM{x})2As2 compounds (TM = Transition Metal), and models for magnetic ordering in the iron arsenide compounds.
Inelastic neutron scattering from superconducting (SC) Ba(Fe$_{0.926}$Co$_{0.074}$)$_2$As$_2$ reveals anisotropic and quasi-two-dimensional (2D) magnetic excitations close to textbf{Q}$_{texttt{AFM}}=({1}{2}/{1}{2})$ - the 2D antiferromagnetic (AFM) wave-vector of the parent BaFe$_2$As$_2$ compound. The correlation length anisotropy of these low energy fluctuations is consistent with spin nematic correlations in the $J_1$-$J_2$ model with $J_1/J_2 sim$ 1. The spin resonance at $sim$8.3 meV in the SC state displays the same anisotropy. The anisotropic fluctuations experimentally evolve into two distinct maxima only along the direction transverse to textbf{Q}$_{texttt{AFM}}$ above $sim$80 meV indicating unusual quasi-propagating excitations.
The evolution of 75As NMR parameters with composition and temperature was probed in the Ba(Fe1-xRux)2As2 system where Fe is replaced by isovalent Ru. While the Ru-end member was found to be a conventional Fermi liquid, the composition (x=0.5) corresponding to the highest Tc (20K) in this system shows an upturn in 75As 1/T1T below about 80 K evidencing the presence of antiferromagnetic (AFM) fluctuations. These results are similar to those obtained in another system with isovalent substitution BaFe2(As1-xPx)2 [Y. Nakai, T. Iye, S. Kitagawa, K. Ishida, H. Ikeda, S. Kasahara, H. Shishido, T. Shibauchi, Y. Matsuda, and T. Terashima, Phys. Rev. Lett. 105, 107003 (2010)] and point to the possible role of AFM fluctuations in driving superconductivity.
Zero-field (ZF) muon spin relaxation ($mu$SR) measurements have revealed static commensurate magnetic order of Fe moments in NdOFeAs below $T_{N} sim 135$ K, with the ordered moment size nearly equal to that in LaOFeAs, and confirmed similar behavior in BaFe$_{2}$As$_{2}$. In single crystals of superconducting (Ba$_{0.55}$K$_{0.45}$)Fe$_{2}$As$_{2}$, $mu$SR spectra indicate static magnetism with incommensurate or short-ranged spin structure in $sim$ 70 % of volume below $T_{N} sim$ 80 K, coexisting with remaining volume which exhibits superfluid-response consistent with nodeless gap below $T_{c}sim 30$ K.
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