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Suppression of the magnetic order in CeFeAsO: non-equivalence of hydrostatic and chemical pressure
Authors:
Philipp Materne,
Wenli Bi,
Esen Ercan Alp,
Jiyong Zhao,
Michael Yu Hu,
Anton Jesche,
Christoph Geibel,
Rhea Kappenberger,
Saicharan Aswartham,
Sabine Wurmehl,
Bernd Büchner,
Dongzhou Zhang,
Til Goltz,
Johannes Spehling,
Hans-Henning Klauss
Abstract:
We present a detailed investigation of the electronic properties of CeFeAsO under chemical (As by P substitution) and hydrostatic pressure by means of in-house and synchrotron Mössbauer spectroscopy. The Fe magnetism is suppressed due to both pressures and no magnetic order was observed above a P-substitution level of 40% or 5.2 GPa hydrostatic pressure. We compared both pressures and found that t…
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We present a detailed investigation of the electronic properties of CeFeAsO under chemical (As by P substitution) and hydrostatic pressure by means of in-house and synchrotron Mössbauer spectroscopy. The Fe magnetism is suppressed due to both pressures and no magnetic order was observed above a P-substitution level of 40% or 5.2 GPa hydrostatic pressure. We compared both pressures and found that the isovalent As by P substitution change the crystallographic and electronic properties differently than hydrostatic pressure.
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Submitted 2 May, 2018;
originally announced May 2018.
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Solitonic spin-liquid state due to the violation of the Lifshitz condition in Fe$_{1+y}$Te
Authors:
Ph. Materne,
C. Koz,
U. K. Rößler,
M. Doerr,
T. Goltz,
H. H. Klauss,
U. Schwarz,
S. Wirth,
S. Rößler
Abstract:
A combination of phenomenological analysis and Mössbauer spectroscopy experiments on the tetragonal Fe$_{1+y}$Te system indicates that the magnetic ordering transition in compounds with higher Fe-excess, $y\ge$ 0.11, is unconventional. Experimentally, a liquid-like magnetic precursor with quasi-static spin-order is found from significantly broadened Mössbauer spectra at temperatures above the anti…
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A combination of phenomenological analysis and Mössbauer spectroscopy experiments on the tetragonal Fe$_{1+y}$Te system indicates that the magnetic ordering transition in compounds with higher Fe-excess, $y\ge$ 0.11, is unconventional. Experimentally, a liquid-like magnetic precursor with quasi-static spin-order is found from significantly broadened Mössbauer spectra at temperatures above the antiferromagnetic transition. The incommensurate spin-density wave (SDW) order in Fe$_{1+y}$Te is described by a magnetic free energy that violates the weak Lifshitz condition in the Landau theory of second-order transitions. The presence of multiple Lifshitz invariants provides the mechanism to create multidimensional, twisted, and modulated solitonic phases.
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Submitted 26 October, 2015;
originally announced October 2015.
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Microscopic coexistence of superconductivity and magnetism in Ca1-xNaxFe2As2
Authors:
Philipp Materne,
Sirko Kamusella,
Rajib Sarkar,
Til Goltz,
Johannes Spehling,
Hemke Maeter,
Luminita Harnagea,
Sabine Wurmehl,
Bernd Buechner,
Hubertus Luetkens,
Carsten Timm,
Hans-Henning Klauss
Abstract:
We present a detailed investigation of the magnetic and superconducting properties of Ca1-xNaxFe2As2 single crystals with x = 0.00, 0.35, 0.50, and 0.67 by means of the local probe techniques Moessbauer spectroscopy and muon spin relaxation experiments. With increasing Na substitution level, the magnetic order parameter as well as the magneto-structural phase transition are suppressed. For x = 0.5…
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We present a detailed investigation of the magnetic and superconducting properties of Ca1-xNaxFe2As2 single crystals with x = 0.00, 0.35, 0.50, and 0.67 by means of the local probe techniques Moessbauer spectroscopy and muon spin relaxation experiments. With increasing Na substitution level, the magnetic order parameter as well as the magneto-structural phase transition are suppressed. For x = 0.50 we find a microscopic coexistence of magnetic and superconducting phases accompanied by a reduction of the magnetic order parameter below the superconducting transition temperature Tc. A systematic comparison with other 122 pnictides reveals a square-root correlation between the reduction of the magnetic order parameter and the ratio of the transition temperatures, Tc/TN, which can be understood in the framework of a Landau theory. In the optimally doped sample with Tc = 34 K, diluted magnetism is found and the temperature dependence of the penetration depth and superfluid density are obtained, proving the presence of two superconducting s-wave gaps
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Submitted 5 May, 2015;
originally announced May 2015.
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Interplay of magnetism and superconductivity in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ single crystals probed by muon spin rotation and ${}^{57}$Fe Mössbauer spectroscopy
Authors:
Til Goltz,
Sirko Kamusella,
Hirale S. Jeevan,
Philipp Gegenwart,
Hubertus Luetkens,
Philipp Materne,
Johannes Spehling,
Rajib Sarkar,
Hans-Henning Klauss
Abstract:
We present our results of a local probe study on EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ single crystals with $x$=0.13, 0.19 and 0.28 by means of muon spin rotation and ${}^{57}$Fe Mössbauer spectroscopy. We focus our discussion on the sample with $x$=0.19 viz. at the optimal substitution level, where bulk superconductivity ($T_{\text{SC}}=28$ K) sets in above static europium order (…
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We present our results of a local probe study on EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ single crystals with $x$=0.13, 0.19 and 0.28 by means of muon spin rotation and ${}^{57}$Fe Mössbauer spectroscopy. We focus our discussion on the sample with $x$=0.19 viz. at the optimal substitution level, where bulk superconductivity ($T_{\text{SC}}=28$ K) sets in above static europium order ($T^{\text{Eu}}=20$K) but well below the onset of the iron antiferromagnetic (AFM) transition ($\sim$100 K). We find enhanced spin dynamics in the Fe sublattice closely above $T_{\text{SC}}$ and propose that these are related to enhanced Eu fluctuations due to the evident coupling of both sublattices observed in our experiments.
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Submitted 30 June, 2014;
originally announced June 2014.
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Magnetic order and spin dynamics in La2O2Fe2OSe2 probed by 57Fe-Moessbauer, 139La-NMR, and muon spin relaxation spectroscopy
Authors:
M. Günther,
S. Kamusella,
R. Sarkar,
T. Goltz,
H. Luetkens,
G. Pascua,
S. -H. Do,
K. -Y. Choi,
H. D. Zhou,
C. G. F. Blum,
S. Wurmehl,
B. Büchner,
H. -H. Klauss
Abstract:
We present a detailed local probe study of the magnetic order in the oxychalcogenide La2O2Fe2OSe2 utilizing 57Fe Moessbauer, 139La NMR, and muon spin relaxation spectroscopy. This system can be regarded as an insulating reference system of the Fe arsenide and chalcogenide superconductors. From the combination of the local probe techniques we identify a non-collinear magnetic structure similar to S…
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We present a detailed local probe study of the magnetic order in the oxychalcogenide La2O2Fe2OSe2 utilizing 57Fe Moessbauer, 139La NMR, and muon spin relaxation spectroscopy. This system can be regarded as an insulating reference system of the Fe arsenide and chalcogenide superconductors. From the combination of the local probe techniques we identify a non-collinear magnetic structure similar to Sr2F2Fe2OS2. The analysis of the magnetic order parameter yields an ordering temperature TN = 90.1 K and a critical exponent of beta = 0.133, which is close to the 2D Ising universality class as reported in the related oxychalcogenide family.
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Submitted 17 October, 2014; v1 submitted 1 April, 2014;
originally announced April 2014.
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Microscopic Coexistence of Magnetism and Superconductivity in charge compensated Ba1-xKx(Fe1-yCoy)2As2
Authors:
Til Goltz,
Veronika Zinth,
Dirk Johrendt,
Helge Rosner,
Gwendolyne Pascua,
Hubertus Luetkens,
Philipp Materne,
Hans-Henning Klauss
Abstract:
We present a detailed investigation of the electronic phase diagram of effectively charge compensated Ba1-xKx(Fe1-yCoy)2As2 with x/2 = y. Our experimental study by means of x-ray diffraction, Mössbauer spectroscopy, muon spin relaxation and ac susceptibility measurements on polycrystalline samples is complemented by density functional electronic structure calculations. For low substitution levels…
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We present a detailed investigation of the electronic phase diagram of effectively charge compensated Ba1-xKx(Fe1-yCoy)2As2 with x/2 = y. Our experimental study by means of x-ray diffraction, Mössbauer spectroscopy, muon spin relaxation and ac susceptibility measurements on polycrystalline samples is complemented by density functional electronic structure calculations. For low substitution levels of x/2 = y \< 0.13, the system displays an orthorhombically distorted and antiferromagnetically ordered ground state. The low temperature structural and magnetic order parameters are successively reduced with increasing substitution level. We observe a linear relationship between the structural and the magnetic order parameter as a function of temperature and substitution level for x/2 = y \< 0.13. At intermediate substitution levels in the range between 0.13 and 0.19, we find superconductivity with a maximum Tc of 15 K coexisting with static magnetic order on a microscopic length scale. For higher substitution levels x/2 = y \> 0.25 a tetragonal non-magnetic ground state is observed. Our DFT calculations yield a signifcant reduction of the Fe 3d density of states at the Fermi energy and a strong suppression of the ordered magnetic moment in excellent agreement with experimental results. The appearance of superconductivity within the antiferromagnetic state can by explained by the introduction of disorder due to non-magnetic impurities to a system with a constant charge carrier density. Our experimental study by means of x-ray diffraction, Mössbauer spectroscopy, muon spin relaxation and ac susceptibility measurements on polycrystalline samples is complemented by density functional electronic structure calculations.
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Submitted 4 February, 2014;
originally announced February 2014.
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Structural and electronic phase diagrams of CeFeAsO1-xFx and SmFeAsO1-xFx
Authors:
Hemke Maeter,
Jorge Enrique Hamann Borrero,
Til Goltz,
Johannes Spehling,
Andrej Kwadrin,
Agnieszka Kondrat,
Louis Veyrat,
Guillaume Lang,
Hans-Joachim Grafe,
Christian Hess,
Günter Behr,
Bernd Büchner,
Hubertus Luetkens,
Chris Baines,
Alex Amato,
Norman Leps,
Rüdiger Klingeler,
Ralf Feyerherm,
Dimitri Argyriou,
Hans-Henning Klauss
Abstract:
We have studied the structural and electronic phase diagrams of CeFeAsO1-xFx and SmFeAsO1-xFx by a detailed analysis of muon spin relaxation experiments, synchrotron X-ray diffraction, Mössbauer spectroscopy, electrical resistivity, specific heat, and magnetic susceptibility measurements (Full abstract in the main document).
We have studied the structural and electronic phase diagrams of CeFeAsO1-xFx and SmFeAsO1-xFx by a detailed analysis of muon spin relaxation experiments, synchrotron X-ray diffraction, Mössbauer spectroscopy, electrical resistivity, specific heat, and magnetic susceptibility measurements (Full abstract in the main document).
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Submitted 25 October, 2012;
originally announced October 2012.
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Ferromagnetism and superconductivity in P-doped CeFeAsO
Authors:
A. Jesche,
T. Förster,
J. Spehling,
M. Nicklas,
M. de Souza,
R. Gumeniuk,
H. Luetkens,
T. Goltz,
C. Krellner,
M. Lang,
J. Sichelschmidt,
H. -H. Klauss,
C. Geibel
Abstract:
We report on superconductivity in CeFeAs1-xPxO and the possible coexistence with Ce- ferromagnetism (FM) in a small homogeneity range around x = 30% with ordering temperatures of T_SC = T_C = 4K. The antiferromagnetic (AFM) ordering temperature of Fe at this critical concentration is suppressed to T^N_Fe ~ 40K and does not shift to lower temperatures with further increase of the P concentration. T…
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We report on superconductivity in CeFeAs1-xPxO and the possible coexistence with Ce- ferromagnetism (FM) in a small homogeneity range around x = 30% with ordering temperatures of T_SC = T_C = 4K. The antiferromagnetic (AFM) ordering temperature of Fe at this critical concentration is suppressed to T^N_Fe ~ 40K and does not shift to lower temperatures with further increase of the P concentration. Therefore, a quantum-critical-point scenario with T^N_Fe -> 0K which is widely discussed for the iron based superconductors can be excluded for this alloy series. Surprisingly, thermal expansion and X-ray powder diffraction indicate the absence of an orthorhombic distortion despite clear evidence for short range AFM Fe-ordering from muon-spin-rotation measurements. Furthermore, we discovered the formation of a sharp electron spin resonance signal unambiguously connected with the emergence of FM ordering.
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Submitted 12 July, 2012; v1 submitted 29 June, 2012;
originally announced June 2012.