Anisotropic magnetic and superconducting properties of pure and Co-doped CaFe$_2$As$_2$ single crystals

TL;DR

This study investigates the anisotropic magnetic and superconducting properties of pure and Co-doped CaFe$_2$As$_2$ single crystals, revealing suppression of SDW order and emergence of superconductivity upon doping.

Contribution

It provides detailed measurements of magnetic susceptibility, resistivity, and heat capacity, demonstrating the transition from SDW order to superconductivity with Co doping in CaFe$_2$As$_2$.

Findings

Pure CaFe$_2$As$_2$ shows SDW and structural transition at 170 K.

Co doping suppresses SDW and induces superconductivity at 17 K.

Incommensurate SDW order is indicated by Mössbauer spectra.

Abstract

We report anisotropic dc magnetic susceptibility $\chi(T)$, electrical resistivity $\rho(T)$, and heat capacity $C(T)$ measurements on the single crystals of CaFe$_{2-x}$Co$_x$As$_2$ for $x$ = 0 and 0.06. Large sized single crystals were grown by the high temperature solution method with Sn as the solvent. For the pure compound with $x$ = 0, a high temperature transition at 170 K is observed which is attributed to a combined spin density wave (SDW) ordering and a structural phase transition. On the other hand, for the Co-doped samples for $x$ = 0.06, the SDW transition is suppressed while superconductivity is observed at $\simeq$17 K. The superconducting transition has been confirmed from the magnetization and electrical resistivity studies. The $^{57}$Fe M\"ossbauer spectrum in CaFe$_2$As$_2$ indicates that the SDW ordering is incommensurate. In the Co-doped sample, a prominent paramagnetic line at 4.2 K is observed indicating a weakening of the SDW state.