Fig. 2
From: Hedgehog spin-vortex crystal stabilized in a hole-doped iron-based superconductor
Resistance, magnetic susceptibility, and heat capacity of Co-doped and Ni-doped CaKFe4As4. a Temperature dependence of normalized resistance, R/R300K, of CaK(Fe1 − xNi x )4As4 single crystals demonstrating the suppression of the superconducting transition temperature, Tc, and the emergence of a kink-like feature labeled TN with increasing Ni content, x. The anomaly at TN appears clearly as a step in the derivative of resistance, dR/dT, and specific-heat, Cp, of x = 0.049 (upper left insets). In the magnified portion in the specific-heat inset, data from a x = 0.017 sample was subtracted to accentuate the step-like anomaly characteristic of a bulk, second-order transition at TN. The zero-field cooled (ZFC) volume magnetic susceptibility, 4πχ, (bottom right inset) demonstrates the suppression of Tc with increasing x and full superconducting shielding for x ≤ 0.049. The upper right inset shows a magnified view of Cp/T of the x = 0.049 sample around Tc. b Evolution of resistance and ZFC magnetic susceptibility in CaK(Fe1 − yCo y )4As4. Tc is suppressed by Co substitution and the kink-like feature at TN emerges in the resistance data similar to the effect of Ni substitution
