Transition to collapsed tetragonal phase in CaFe2As2 single crystals as seen by 57Fe Mossbauer spectroscopy

Abstract

Temperature dependent measurements of 57Fe Mossbauer spectra on CaFe2As2 single crystals in the tetragonal and collapsed tetragonal phases are reported. Clear features in the temperature dependencies of the isomer shift, relative spectra area and quadrupole splitting are observed at the transition from the tetragonal to the collapsed tetragonal phase. From the temperature dependent isomer shift and spectral area data, an average stiffening of the phonon modes in the collapsed tetragonal phase is inferred. The quadrupole splitting increases by ~25% on cooling from room temperature to ~100 K in the tetragonal phase and is only weakly temperature dependent at low temperatures in the collapsed tetragonal phase, in agreement with the anisotropic thermal expansion in this material. In order to gain microscopic insight about these measurements we perform ab initio density functional theory calculations of the electric field gradient and the electron density of CaFe2As2 in both phases. By comparing the experimental data with the calculations we are able to fully characterize the crystal structure of the samples in the collapsed-tetragonal phase through determination of the As z-coordinate. Based on the obtained temperature dependent structural data we are able to propose charge saturation of the Fe - As bond region as the mechanism behind the stabilization of the collapsed-tetragonal phase at ambient pressure.

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Cited by in corpus (10)

• Preserved entropy and fragile magnetism
• Trends in pressure-induced layer-selective half-collapsed tetragonal phases in the iron-based superconductor family $AeA$Fe${}_4$As${}_4$
• Wavefunctions, electronic localization and bonding properties for correlated materials beyond the Kohn-Sham formalism
• Ab-initio perspective on structural and electronic properties of iron-based superconductors
• ${}^{57}$Fe Mössbauer study of stoichiometric iron based superconductor CaKFe${}_4$As${}_4$: a comparison to KFe${}_2$As${}_2$ and CaFe${}_2$As${}_2$
• The collapsed tetragonal phase as a strongly covalent and fully nonmagnetic state: persistent magnetism with interlayer As-As bond formation in Rh-doped Ca${}_{0.8}$Sr${}_{0.2}$Fe${}_2$As${}_2$
• Mössbauer spectroscopy study of magnetic fluctuations in superconducting RbGd${}_2$Fe${}_4$As${}_4$O${}_2$
• Electronic Correlations and Absence of Superconductivity in the Collapsed Phase of LaFe${}_2$As${}_2$
• Study of the rare earth effects on the magnetic fluctuations in RbLn${}_2$Fe${}_4$As${}_4$O${}_2$ (Ln = Tb, Dy and Ho) by Mössbauer spectroscopy
• Observation of the Dirac Dispersions in Co-doped CaFe2As2