Evidence of precursor orthorhombic domains well above the electronic nematic transition temperature in Sr(Fe1-xCox)2As2

Raman scattering, synchrotron x-ray diffraction, specific heat, resistivity and magnetic susceptibility measurements were performed in Sr(Fe1-xCox)2As2 [x = 0.24(3)] single crystals with superconducting critical temperature Tc = 22 K and two additional transitions at 132 and 152 K observed in both specific heat and resistivity data. A quasielastic Raman signal with B2g symmetry (tetragonal cell) associated with electronic nematic fluctuations is observed. Crucially, this signal shows maximum intensity at Tnem 132 K, marking the nematic transition temperature. X-ray diffraction shows evidence of coexisting orthorhombic and tetragonal domains between Tnem and To 152 K, implying that precursor orthorhombic domains emerge over an extended temperature range above Tnem. While the height of the quasielastic Raman peak is insensitive to To, the temperature-dependence of the average nematic fluctuation rate indicates a slowing down of the nematic fluctuations inside the precursor orthorhombic domains. These results are analogous to those previously reported for the LaFeAsO parent oxypnictide [U.F. Kaneko et al., Phys. Rev. B 96, 014506 (2017)]. We propose a scenario where the precursor orthorhombic phase may be generated within the electronically disordered regime (Tnem) as long as the nematic fluctuation rate is sufficiently small in comparison to the optical phonon frequency range. In this regime, the local atomic structure responds adiabatically to the electronic nematic fluctuations, creating a net of orthorhombic clusters that, albeit dynamical for Tnem, may be sufficiently dense to sustain long-range phase coherence in a diffraction process up to To.Fil: Kaneko, Ulisses. Laboratorio Nacional de Luz Sincrotron;; BrasilFil: Piva, Mario. Universidade Estadual de Campinas; BrasilFil: Ramos de Jesus, Camilo Bruno. Universidade Estadual de Campinas; BrasilFil: Saleta, Martin Eduardo. Universidade Estadual de Campinas; Brasil. Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología; ArgentinaFil: Urbano, Ricardo. Universidade Estadual de Campinas; BrasilFil: Pagliuso, Pascoal G.. Universidade Estadual de Campinas; BrasilFil: Granado, Eduardo. Universidade Estadual de Campinas; Brasi

Incoherent electronic band states in Mn substituted BaFe2_{2}As2_{2}

Chemical substitution is commonly used to explore new ground states in materials, yet the role of disorder is often overlooked. In Mn-substituted BaFe$_{2}$As$_{2}$ (MnBFA), superconductivity (SC) is absent, despite being observed for nominal hole-doped phases. Instead, a glassy magnetic phase emerges, associated with the $S=5/2$ Mn local spins. In this work, we present a comprehensive investigation of the electronic structure of MnBFA using angle-resolved photoemission spectroscopy (ARPES). We find that Mn causes electron pockets to shrink, disrupting the nesting condition in MnBFA. Notably, we propose that electronic disorder, along with magnetic scattering, primarily contributes to suppressing the itinerant magnetic order in MnBFA. This finding connects the MnBFA electronic band structure properties to the glassy magnetic behavior observed in these materials and suggests that SC is absent because of the collective magnetic impurity behavior that scatters the Fe-derived excitations. Moreover, we suggest that Mn tunes MnBFA to a phase in between the correlated metal in BaFe$_{2}$As$_{2}$ and the Hund insulator phase in BaMn$_{2}$As$_{2}$.Comment: main 7 pages, 3 figures + supp 5 pages, 5 figure

Anisotropic magnetic excitations and incipient N\’eel order in \mathrm{Ba}{({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x})}_{2}{\mathrm{As}}_{2}

It is currently understood that high temperature superconductivity (SC) in the transition metal (M) substituted iron arsenides Ba(Fe1−xMx)2As2 is promoted by magnetic excitations with wave vectors (π,0) or (0,π). It is known that while a small amount of Co substitution lead to SC, the same does not occur for Mn for any value of x. In this work, magnetic excitations in the iron arsenides Ba(Fe1−xMnx)2As2(x=0.0,0.007,0.009,0.08) are investigated by means of resonant inelastic x-ray scattering (RIXS) at the Fe L3 edge, for momentum transfer q along the high symmetry Brillouin zone (π,0) and (π,π) directions. It is shown that with increasing Mn content (x), the excitations become anisotropic both in dispersion and lineshape. Both effects are detected even for small values of x, evidencing a cooperative phenomenon between the Mn impurities, that we ascribe to emerging Néel order of the Mn spins. Moreover, for x=0.08, the excitations along q∥(π,0) are strongly damped and nearly nondispersive. This result suggests that phases of arsenides containing local moments at the FeAs layers, as in Mn or Cr substituted phases, do not support high temperature SC due to the absence of the appropriate magnetic excitations

Physical properties of Sr2FeIrO6 and Sr1.2La0.8FeIrO6 double perovskites obtained by a new synthesis route

CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPERJ - FUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIROPrevious works on Sr2-xLaxFeIrO6 double perovskite (DP) series reported a possible ferromagnetic transition at T similar to 700 K for the x = 0.8 concentration, for which was observed the presence of spurious Fe2O3 phase. In order to prevent the formation of this impurity phase and check if this high temperature magnetic transition is intrinsic of the material, different synthesis routes became necessary. In this work, polycrystalline samples of Sr2-xLaxFeIrO6 (x = 0.0 and 0.8) have been synthesized by solid state reaction using a new heating treatment. The sample's properties were investigated by synchrotron x-ray powder diffraction (SXRD), transmission electron microscopy (TEM), magnetic susceptibility, specific heat and electrical resistivity, and compared with the previously reported results. The SXRD data revealed a structural transition induced by La to Sr substitution (I2/m P2(1)/n). Moreover, it was not detected the presence of Fe2O3 on the samples obtained by the new route, which might be related to the absence of high temperature magnetic ordering. The magnetometry results indicated the emergence of Ir4+ with La doping, being corroborated by specific heat measurements which suggest Fe3+/Ir5+ and Fe3+/Ir4+ configurations for x = 0.0 and 0.8 compounds, respectively. Temperature dependent electrical resistivity measurements showed that Sr2+ to La3+ substitution leads to a decrease of electrical resistivity, possibly associated with the increase in the number of Ir valence electrons. (C) 2016 Elsevier B.V. All rights reserved.Previous works on Sr2-xLaxFeIrO6 double perovskite (DP) series reported a possible ferromagnetic transition at T similar to 700 K for the x = 0.8 concentration, for which was observed the presence of spurious Fe2O3 phase. In order to prevent the formation of this impurity phase and check if this high temperature magnetic transition is intrinsic of the material, different synthesis routes became necessary. In this work, polycrystalline samples of Sr2-xLaxFeIrO6 (x = 0.0 and 0.8) have been synthesized by solid state reaction using a new heating treatment. The sample's properties were investigated by synchrotron x-ray powder diffraction (SXRD), transmission electron microscopy (TEM), magnetic susceptibility, specific heat and electrical resistivity, and compared with the previously reported results. The SXRD data revealed a structural transition induced by La to Sr substitution (I2/m P2(1)/n). Moreover, it was not detected the presence of Fe2O3 on the samples obtained by the new route, which might be related to the absence of high temperature magnetic ordering. The magnetometry results indicated the emergence of Ir4+ with La doping, being corroborated by specific heat measurements which suggest Fe3+/Ir5+ and Fe3+/Ir4+ configurations for x = 0.0 and 0.8 compounds, respectively. Temperature dependent electrical resistivity measurements showed that Sr2+ to La3+ substitution leads to a decrease of electrical resistivity, possibly associated with the increase in the number of Ir valence electrons.182459465CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPERJ - FUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIROCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPERJ - FUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIRO470.613/2012-2, 304649/2013-9, 442230/2014-12006/60440-0, 2007/50968-0, 2012/04870-7111.382/2013This work was supported by the Brazilian funding agencies CNPq (Grants No. 470.613/2012-2, 304649/2013-9, 442230/2014-1), FAPESP (Grants Nos. 2006/60440-0, 2007/50968-0, 2012/04870-7) and FAPERJ (Grant No. 111.382/2013). LNLS is acknowledged for concession of beamtime

Crystal structure, superconductivity and magnetism of the quasi-2D heavy fermion materials CeTIn[sub 5] (T = Co, Rh, Ir).

The crystal structure of the recently discovered heavy-fermion (HF) superconductor CeCoIn{sub 5} (T{sub c} = 2.3 K) has been determined by high-resolution neutron powder diffraction. It is tetragonal (space group P4/mmm), with lattice parameters a = 4.61292(9) {angstrom} and c = 7.5513(2) {angstrom} at ambient conditions. Whereas CeCoIn{sub 5} is isostructural with the HF aniferromagnet CeRhIn{sub 5} and the HF superconductor CeIrIn{sub 5}, its cell constants and its only variable positional parameter, zIn2, differ significantly from the corresponding ones of CeRhIn{sub 5} and CeIrIn{sub 5}. As a result, the distortions of the cuboctahedron [CeIn{sub 3}], which is the key structural unit in all three materials, are different in CeCoIn{sub 5} from the ones in CeRhIn{sub 5} and CeIrIn{sub 5}. The compounds CeCoIn{sub 5} and CeIrIn{sub 5}, which contain the most distorted (in one or another way) [CeIn{sub 3}] cuboctahedra exhibit superconductivity at ambient pressure below 2.3 K and 0.4 K, respectively. On the other hand, CeRhIn{sub 5}, in which [CeIn{sub 3}] cuboctahedra are the less distorted, and the cubic HF CeIn{sub 3} are antiferromagnets at ambient pressure with T{sub N} = 3.8 K and 10 K respectively; they become superconductors under pressure of 16 kbar and 25 kbar with T{sub c} = 2.1 and 0.2 K respectively

Low-temperature magnetic properties of GdCoIn5

A comprehensive experimental and theoretical study of the low temperature properties of GdCoIn5 was performed. Specific heat, thermal expansion, magnetization and electrical resistivity were measured in good quality single crystals down to 4He temperatures. All the experiments show a second-order-like phase transition at 30 K probably associated with the onset of antiferromagnetic order. The magnetic susceptibility shows a pronounced anisotropy below TN with an easy magnetic axis perpendicular to the crystallographic ɥ-axis. Total energy GGA+U calculations indicate a ground state with magnetic moments localized at the Gd ions and allowed a determination of the Gd-Gd magnetic interactions. Band structure calculations of the electron and phonon contributions to the specific heat together with Quantum Monte Carlo calculations of the magnetic contributions show a very good agreement with the experimental data. Comparison between experiment and calculations suggests a significant anharmonic contribution to the specific heat at high temperature (T≳100K).Fil: Betancourth Giraldo, Diana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Facio, Jorge Ismael. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Pedrazzini, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Jesus, Camilo B. R.. Universidade Estadual de Campinas; BrasilFil: Pagliuso, Pascoal G.. Universidade Estadual de Campinas; BrasilFil: Vildosola, Veronica Laura. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones No Nucleares. Gerencia Física (CAC). Departamento de Física de la Materia Condensada; ArgentinaFil: Cornaglia de la Cruz, Pablo Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Garcia, Daniel Julio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Correa, Víctor Félix. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentin