Authors: Mingyu Xu | Juan Schmidt | M. A. Tanatar | R. Prozorov | Sergey L. Bud’ko | P. C. Canfield
Source: Physical review. B./Physical review. B (article, 2023-04-12)
Field: Materials Science — Electronic, Optical and Magnetic Materials

Superconductivity and magnetic and transport properties of single-crystalline <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mi>CaK</mml:mi><mml:mo>(</mml:mo><mml:mi>Fe</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>Cr</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:msub><mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mn>4</mml:mn></mml:msub><mml:msub><mml:mi>As</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math> Members of the $\mathrm{CaK}{({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x})}_{4}{\mathrm{As}}_{4}$ series have been synthesized by high-temperature solution growth in single-crystalline form and characterized by x-ray diffraction, elemental analysis, and magnetic and transport measurements. The effects of Cr substitution on the superconducting and magnetic ground states of ${\mathrm{CaKFe}}_{4}{\mathrm{As}}_{4}$ (${T}_{c}=35$ K) have been studied. These measurements show that the superconducting transition temperature decreases monotonically and is finally suppressed below 1.8 K as $x$ is increased from 0 to 0.038. For $x$-values greater than 0.012, signatures of a magnetic transition can be detected in magnetic measurements with the associated features in the transport measurements becoming detectable for $x\ensuremath{\ge}0.038$. The magnetic transition temperature increases in a roughly linear manner as Cr substitution increases. A temperature-composition ($T\ensuremath{-}x$) phase diagram is constructed, revealing a half-dome of superconductivity with the magnetic transition temperature, ${T}^{*}$, appearing near 22 K for $x\ensuremath{\sim}0.017$ and rising slowly up to 60 K for $x\ensuremath{\sim}0.077$. The $T\ensuremath{-}x$ phase diagrams for $\mathrm{CaK}{({\mathrm{Fe}}_{1\ensuremath{-}x}{T}_{x})}_{4}{\mathrm{As}}_{4}$ for $T=\text{Cr}$ and Mn are essentially the same despite the nominally different band filling; this is in marked contrast to $T=\text{Co}$ and Ni series for which the $T\ensuremath{-}x$ diagrams scale by a factor of 2, consistent with the different changes in band filling Co and Ni would produce when replacing Fe. Superconductivity of $\mathrm{CaK}{({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x})}_{4}{\mathrm{As}}_{4}$ is also studied as a function of magnetic field. A clear change in ${H}_{c2}^{\ensuremath{'}}(T)/{T}_{c}$, where ${H}_{c2}^{\ensuremath{'}}(T)$ is $d{H}_{c2}(T)/dT$, at $x\ensuremath{\sim}0.012$ is observed and probably is related to a change of the Fermi surface due to magnetic order. Coherence length and the London penetration depths are also calculated based on ${H}_{c1}$ and ${H}_{c2}$ data. Both of them as a function of $x$ show changes near $x=0.012$, again consistent with Fermi surface changes associated with the magnetic ordering seen for higher $x$-values. Physics ; Computer science Iron-based superconductors research ; Rare-earth and actinide compounds ; Corporate Taxation and Avoidance