Effect of biaxial strain on the phase transitions of Ca(Fe1-xCox)2As2

Abstract

We study the effect of applied strain as a physical control parameter for the phase transitions of Ca(Fe1−xCox)2As2 using resistivity, magnetization, x-ray diffraction and 57 Fe Mössbauer spectroscopy. Biaxial strain, namely compression of the basal plane of the tetragonal unit cell, is created through firm bonding of samples to a rigid substrate, via differential thermal expansion. This strain is shown to induce a magneto-structural phase transition in originally paramagnetic samples; and superconductivity in previously non-superconducting ones. The magneto-structural transition is gradual as a consequence of using strain instead of pressure or stress as a tuning parameter.

$^{57}$Fe Mössbauer study of stoichiometric iron based superconductor CaKFe$_4$As$_4$: a comparison to KFe$_2$As$_2$ and CaFe$_2$As$_2$

“…Overall the linewidth increases by a few percent on cooling from room temperature to the base temperature. The observed spectral lines for CaKFe 4 As 4 are somewhat narrower than those in CaFe 2 As 2 [14,24] and KFe 2 As 2 (see below) single crystal measurements, and measurably sharper than the Mössbauer spectra lines in the substituted Ca(Fe 0.965 Co 0.035 ) 2 As 2 [40] that vary in the range of 0.28 -0.35 mm/s between room temperature and 5 K. This suggests that CaKFe 4 As 4 crystals used in this work are well ordered.…”