Pressure effect on magnetism and valence in ferromagnetic superconductor Eu(Fe0.75Ru0.25)2As2

Eu(Fe0.75Ru0.25)2As2 is an intriguing system with unusual coexistence of superconductivity and ferromagnetism, providing a unique platform to study the nature of such coexistence. To establish a magnetic phase diagram, time-domain synchrotron Mössbauer experiments in 151Eu have been performed on a single crystalline Eu(Fe0.75Ru0.25)2As2 sample under hydrostatic pressures and at low temperatures. Upon compression the magnetic ordering temperature increases sharply from 20 K at ambient pressure, reaching ∼49 K at 10.1 GPa. With further compression, the magnetic order is suppressed and eventually collapses. Isomer shift values from Mössbauer measurements and x-ray absorption spectroscopy data at Eu L 3 edge show that pressure drives Eu ions to a homogeneous intermediate valence state with mean valence of ∼2.4 at 27.4 GPa, possibly responsible for the suppression of magnetism. Synchrotron powder x-ray diffraction experiment reveals a tetragonal to collapsed-tetragonal structural transition around 5 GPa, a lower transition pressure than in the parent compound. These results provide guidance to further work investigating the interplay of superconductivity and magnetism.

[1]  Y. Vohra,et al.  Microscopic phase diagram of Eu(Fe1−xNix)As2 ( x = 0,0.04) under pressure , 2021 .

[2]  Y. Yoshida,et al.  Coexisting spin resonance and long-range magnetic order of Eu in EuRbFe4As4 , 2019, Physical Review B.

[3]  T. Brueckel,et al.  Universal critical behavior in the ferromagnetic superconductor Eu(Fe0.75Ru0.25)2As2 , 2019, Physical Review B.

[4]  M. Kanatzidis,et al.  Pressure-temperature phase diagram of the EuRbFe4As4 superconductor , 2019, Physical Review B.

[5]  Qijin Chen,et al.  Unique crystal field splitting and multiband RKKY interactions in Ni-doped EuRbFe4As4 , 2019, Communications Physics.

[6]  A. Dai,et al.  Review of U-based Ferromagnetic Superconductors: Comparison between UGe2, URhGe, and UCoGe , 2019 .

[7]  K. Ishida,et al.  Review of U-based Ferromagnetic Superconductors: Comparison between UGe2, URhGe, and UCoGe , 2019, Journal of the Physical Society of Japan.

[8]  Xinyuan,et al.  Universal critical behavior in the ferromagnetic supercondutor , 2019 .

[9]  T. Kikegawa,et al.  New antiferromagnetic order with pressure-induced superconductivity in EuFe2As2 , 2018, Physical Review B.

[10]  Y. Vohra,et al.  Superconducting and magnetic phase diagram of RbEuFe4As4 and CsEuFe4As4 at high pressure , 2018, Physical Review B.

[11]  Farshad Nejadsattari,et al.  Mössbauer spectroscopy measurements on the 35.5 K superconductor Rb 1 -δ EuFe 4 As 4 , 2018 .

[12]  Y. Yoshida,et al.  Superconducting state in (Eu1-xCax)RbFe4As4 with 1144-type Structure , 2018 .

[13]  W. Bi,et al.  A compact membrane-driven diamond anvil cell and cryostat system for nuclear resonant scattering at high pressure and low temperature. , 2017, The Review of scientific instruments.

[14]  Yi Liu,et al.  RbEu (Fe 1 -x Ni x ) 4 As 4 : From a ferromagnetic superconductor to a superconducting ferromagnet , 2017, 1710.10895.

[15]  K. Shimizu,et al.  Divalent, trivalent, and heavy fermion states in Eu compounds , 2017 .

[16]  Si Wu,et al.  Superconductivity at 33 - 37 K in $ALn_2$Fe$_4$As$_4$O$_2$ ($A$ = K and Cs; $Ln$ = Lanthanides) , 2017, 1704.01488.

[17]  P. Gegenwart,et al.  Interplay of 4f and 3d moments in EuFe2As2 iron pnictides , 2017 .

[18]  M. Dressel,et al.  Europium-based iron pnictides: a unique laboratory for magnetism, superconductivity and structural effects , 2017, Reports on progress in physics. Physical Society.

[19]  Hao Yan,et al.  High-pressure synchrotron Mössbauer and X-ray diffraction studies: Exploring the structure-related valence fluctuation in EuNi 2 P 2 , 2016 .

[20]  W. Bi,et al.  Magnetism of europium under extreme pressures , 2016 .

[21]  V. Prakapenka,et al.  DIOPTAS: a program for reduction of two-dimensional X-ray diffraction data and data exploration , 2015 .

[22]  Changfeng Chen,et al.  Pressure induced valence change of Eu in EuFe2As2 at low temperature and high pressures probed by resonant inelastic x-ray scattering , 2014 .

[23]  H. Ebert,et al.  Hyperfine splitting and room-temperature ferromagnetism of Ni at multimegabar pressure. , 2013, Physical review letters.

[24]  Brian H. Toby,et al.  GSAS‐II: the genesis of a modern open‐source all purpose crystallography software package , 2013 .

[25]  S. Sinogeikin,et al.  BX90: a new diamond anvil cell design for X-ray diffraction and optical measurements. , 2012, The Review of scientific instruments.

[26]  R. Hennig,et al.  Synchrotron x-ray spectroscopy studies of valence and magnetic state in europium metal to extreme pressures , 2012, 1203.3387.

[27]  Y. Vohra,et al.  Structural phase transitions in EuFe2As2 superconductor at low temperatures and high pressures , 2011, Journal of physics. Condensed matter : an Institute of Physics journal.

[28]  J. Karpinski,et al.  Interplay between magnetism and superconductivity in EuFe2−xCoxAs2studied by57Fe and151Eu Mössbauer spectroscopy , 2011, 1107.5271.

[29]  T. Terashima,et al.  Phase diagram of pressure-induced superconductivity in EuFe 2 As 2 probed by high-pressure resistivity up to 3.2 GPa , 2011, 1103.4209.

[30]  I. Felner,et al.  57Fe and 151Eu Mössbauer spectroscopy and magnetization studies of Eu(Fe0.89Co0.11)2As2 and Eu(Fe0.9Ni0.1)2As2 , 2011 .

[31]  Zhongxian Zhao,et al.  Valence Change of Europium in EuFe 2 As 1.4 P 0.6 and Compressed EuFe 2 As 2 and Its Relation to Superconductivity , 2010 .

[32]  Y. Vohra,et al.  Anomalous compressibility effects and superconductivity of EuFe2As2 under high pressures , 2010, Journal of physics. Condensed matter : an Institute of Physics journal.

[33]  T. Terashima,et al.  EuFe2As2 under High Pressure: An Antiferromagnetic Bulk Superconductor , 2009, 0904.2618.

[34]  M. Nicklas,et al.  Evidence for a reentrant superconducting state in EuFe2AS2 under pressure , 2008, 0808.2026.

[35]  A. Sefat,et al.  Influence of the rare-earth element on the effects of the structural and magnetic phase transitions in CeFeAsO, PrFeAsO and NdFeAsO , 2008, 0811.0589.

[36]  M. Torrent,et al.  Compression curves of transition metals in the Mbar range: Experiments and projector augmented-wave calculations , 2008 .

[37]  Jiangping Hu,et al.  Spin and lattice structures of single-crystalline Srfe2As2 , 2008, 0807.1077.

[38]  Z. Ren,et al.  Antiferromagnetic transition in EuFe 2 As 2 : A possible parent compound for superconductors , 2008, 0806.2591.

[39]  R. Prozorov,et al.  Coexistence of ferromagnetism and superconductivity in ErRh4B4 single crystals probed by dynamic magnetic susceptibility , 2007, 0707.0029.

[40]  M Newville,et al.  ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT. , 2005, Journal of synchrotron radiation.

[41]  W. Sturhahn,et al.  CONUSS and PHOENIX: Evaluation of nuclear resonant scattering data , 2000 .

[42]  H. Hesse,et al.  Pressure and temperature dependence of the Eu valence in EuNi2Ge2 and related systems studied by Mössbauer effect, X-ray absorption and X-ray diffraction , 1997 .

[43]  O. Fischer,et al.  Superconductivity in the RexMo6S8 , 1993 .

[44]  O. Fischer,et al.  Superconductivity in the RE x Mo 6 S 8 , 1993 .

[45]  I. Felner,et al.  Eu valency and recoil-free fraction in EuCo2Si2-xGex , 1989 .

[46]  L. C. Gupta,et al.  ESCA studies of some mixed-valence rare-earth intermetallics , 1981 .