Mössbauer studies of the peculiar magnetism in parent compounds of the iron-based superconductors

Abstract

A review of the magnetism in the parent compounds of the iron-based superconductors is given based on the transmission Mössbauer spectroscopy of ⁵⁷Fe and ¹⁵¹Eu. It was found that the 3d magnetism is of the itinerant character with varying admixture of the spin-polarized covalent bonds. For the ‘122’ compounds, a longitudinal spin density wave (SDW) develops. In the case of the EuFe₂As₂, a divalent europium arranges in an anti-ferromagnetical order at a much lower temperature as compared with the onset of SDW. These two magnetic systems remain almost uncoupled one to another. For the non-stoichiometric Fe_1+xTe parent of the ‘11’ family, one has a transversal SDW and magnetic order of the interstitial iron with relatively high and localized magnetic moments. These two systems are strongly coupled one to another. For the ‘grand parent’ of the iron-based superconductors FeAs, one observes two mutually orthogonal phase-related transversal SDW on the iron sites. There are two sets of such spin arrangements due to two crystallographic iron sites. The FeAs exhibits the highest covalency among the compounds studied, but it has still a metallic character.

Keywords:

• iron-based superconductors
• magnetism
• Mössbauer spectroscopy

Acknowledgements

Dr. Paweł Zajdel, Division of Physics of Crystals, Institute of Physics, Silesian University, Katowice, Poland, is thanked for preparation of the Fe_1+xTe samples. J. K. acknowledges support by the SNSF (Project No. 140760) and FP7 Super-Iron Project.

Notes

A contribution to XVI National Conference on Superconductivity, Zakopane, Poland, 7–12 October 2013.

Additional information

Funding

Funding. This work was supported by the National Science Center of Poland [grant number DEC-2011/03/B/ST3/00446].