Coexistence of superconductivity and magnetism in CaK(Fe\(_{1-x}\)Ni\(_x\))\(_4\)As\(_4\) as probed by \(^{57}\)Fe Mössbauer spectroscopy

• Published in: arXiv.org
• Main Authors: Bud'ko, Sergey L, Kogan, Vladimir G, Prozorov, Ruslan, Meier, William R, Xu, Mingyu, Canfield, Paul C
• Format: Paper
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 16.10.2018
• Subjects: Hyperfine structure; Iron; Magnetic moments; Magnetism; Mossbauer spectroscopy; Nickel; Order parameters; Specific heat; Spectrum analysis; Spin density waves; Superconductivity; Temperature dependence; Transition temperature
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1810.07084

Temperature dependent \(^{57}\)Fe M\"ossbauer spectroscopy and specific heat measurements for CaK(Fe\(_{1-x}\)Ni\(_x\))\(_4\)As\(_4\) with \(x\) = 0, 0.017, 0.033, and 0.049 are presented. No magnetic hyperfine field (e.g. no static magnetic order) down to 5.5 K was detected for \(x\) = 0 and 0.017 in agreement with the absence of any additional feature below superconducting transition temperature, \(T_c\), in the specific heat data. The evolution of magnetic hyperfine field with temperature was studied for \(x\) = 0.033 and 0.049. The long-range magnetic order in these two compounds coexists with superconductivity. The magnetic hyperfine field, \(B_{hf}\), (ordered magnetic moment) below \(T_c\) in CaK(Fe\(_{0.967}\)Ni\(_{0.033}\))\(_4\)As\(_4\) is continuously suppressed with the developing superconducting order parameter. The \(B_{hf}(T)\) data for CaK(Fe\(_{0.967}\)Ni\(_{0.033}\))\(_4\)As\(_4\), and CaK(Fe\(_{0.951}\)Ni\(_{0.049}\))\(_4\)As\(_4\) can be described reasonably well by Machida's model for coexistence of itinerant spin density wave magnetism and superconductivity [K. Machida, J. Phys. Soc. Jpn. {\bf 50}, 2195 (1981)]. We demonstrate directly that superconductivity suppresses the spin density wave order parameter if the conditions are right, in agreement with the theoretical analysis.