Superconducting FeSe studied by Mössbauer spectroscopy and magnetic measurements A. Błachowski 1 , K. Ruebenbauer 1 , J. Żukrowski 2 , J. Przewoźnik 2 , K. Wojciechowski 3 , Z.M. Stadnik 4 1 Mössbauer Spectroscopy Division, Institute of Physics, Pedagogical University , Cracow, Poland
Superconducting FeSe studied by Mössbauer spectroscopy
and magnetic measurements
A. Błachowski1, K. Ruebenbauer1, J. Żukrowski2, J. Przewoźnik2,
K. Wojciechowski3, Z.M. Stadnik4
1Mössbauer Spectroscopy Division, Institute of Physics,
Pedagogical University, Cracow, Poland
2Solid State Physics Department, Faculty of Physics and Applied Computer Science,
AGH University of Science and Technology, Cracow, Poland
3Department of Inorganic Chemistry, Faculty of Material Science and Ceramics,
AGH University of Science and Technology, Cracow,Poland
4Department of Physics, University of Ottawa, Ottawa, Canada
Fe-based Superconducting Families
~55K ~40K ~20K ~10K
Fe-Se phase diagram
The following phases form close to the FeSe stoichiometry:
1) tetragonal P4/nmm structure similar to PbO, called β-FeSe (or α-FeSe)
2) hexagonal P63/mmc structure similar to NiAs, called δ-FeSe
3) hexagonal phase Fe7Se8 with two different kinds of order, i.e., 3c (α-Fe7Se8) or 4c (β-Fe7Se8)
A tetragonal P4/nmm phase transforms into Cmma orthorhombic phase at about 90 K,
and this phase is superconducting with Tc≈ 8 K.
Crystal structure of -FeSe
Aim of this contribution is to answer two questions concerned with
1) is there electron spin density (magnetic moment) on Fe ?
2) is there change of electron density on Fe nucleus
during transition from P4/nmm to Cmma structure ?
Magnetic susceptibility measured upon cooling and subsequent warming in field of 5 Oe
- point A - spin rotation in hexagonal phase
- region B- magnetic anomaly
correlated with transition between orthorhombic and tetragonal phases
- point C- transition to the superconducting state
Change in isomer shift S
Change in electron density on Fe nucleus
S = +0.006 mm/s
ρ = –0.02 electron/a.u.3
Mössbauer spectra obtained in external magnetic field aligned withγ-ray beam
Hyperfine magnetic field is equal to applied external magnetic field.
Principal component of the electric field gradient (EFG) on Fe nucleus
was found as negative.
1. There is no magnetic moment on iron atoms in the superconducting FeSe.
2. The electron density on iron nucleus is lowered by 0.02 electron/a.u.3
during transition from tetragonal to orthorhombic phase.