Abstract:Superconductivity (SC) and ferromagnetism (FM) are in general antagonistic, which makes their coexistence very rare. Following our recent discovery of robust coexistence of SC and FM in RbEuFe4As4 [Y. Liu et al., arXiv: 1605.04396 (2016)], here we report another example of such a coexistence in its sister compound CsEuFe4As4, synthesized for the first time. The new material exhibits bulk SC at 35.2 K and Eu 2+ -spin ferromagnetic ordering at 15.5 K, demonstrating that it is a new robust ferromagnetic supercon… Show more
“…The resistivity data shows the metallic behavior with convex curvature down to low- T . This behavior is also observed in other 122- and 1144-type superconductors 4–9,17,18 . The residual resistivity ratio, RRR = ρ 300 / ρ 0 , is 5.21, indicating the absence of strong scattering arising from impurities and/or grain boundaries, suitable for investigating their physical properties.…”
Section: Resultssupporting
confidence: 72%
“…On the other hand, Δr = r (La,Na) − r K = −0.34 Å, which is at the boundary between the 122-type and the 1144-type phases. Giving that (La,Na,K)Fe 2 As 2 forms the 122-type structure, one can conclude that the critical parameter which determines the real crystal structure is Δr , rather than Δa .Figure 6Plot of the difference between the ionic radius (VIII) of AE 2+ and A + ( Δr = r AE − r A ) and the difference (absolute value) between the a -axis lengths of AE Fe 2 As 2 ( AE 122) and A Fe 2 As 2 ( A 122) ( Δa = | a AE122 − a A122 |) for 122- and 1144-type Fe-based superconductors 4–9,17,18 . Yellow diamond shows (La,Na,K)Fe 2 As 2 .…”
Section: Discussionmentioning
confidence: 99%
“…Plot of the difference between the ionic radius (VIII) of AE 2+ and A + ( Δr = r AE − r A ) and the difference (absolute value) between the a -axis lengths of AE Fe 2 As 2 ( AE 122) and A Fe 2 As 2 ( A 122) ( Δa = | a AE122 − a A122 |) for 122- and 1144-type Fe-based superconductors 4–9,17,18 . Yellow diamond shows (La,Na,K)Fe 2 As 2 .…”
Section: Discussionmentioning
confidence: 99%
“…A large number of Fe-based superconductors (FeSCs) with various crystal structures have been reported, such as Ln FeAs(O,F) ( Ln corresponds to rare earth elements) — a 1111-type compound 1–3 , ( AE 1− x A x )Fe 2 As 2 ( AE = Ca, Sr, Ba, Eu, A = Na, K, Rb) — a 122-type compound 4,5 , AEA Fe 4 As 4 ( AE = Ca, Sr, Ba, Eu, A = Na, K, Rb) — a 1144-type compound 6–9 , A FeAs ( A = Li, Na) — a 111-type compound 10 , (Ca, Ln )FeAs 2 — a 112-type compound 11,12 , and perovskite Fe nictide 13 . The superconducting transition temperature ( T c ) reaches as high as ~55 K in bulk materials, and several reports have indicated that T c is close to 100 K in thin film samples 14,15 .…”
We synthesized a Fe-based superconductor (FeSC), (La,Na,K)Fe2As2, and characterized its superconducting properties. It was found that (La,Na,K)Fe2As2 has a 122-type (ThCr2Si2-type) structure with a space group I4/mmm (No. 139), identical to (Ba,K)Fe2As2 and (La,Na)Fe2As2 but distinct from so-called 1144-type FeSCs such as CaKFe4As4 and (La,Na)CsFe4As4. The results demonstrate that the formation of the 1144-type phase necessitates the large ionic radius mismatch among the so-called A-site constituent elements of the AFe2As2 formula. The lattice constants are a = 3.850(1) Å and c = 13.21(1) Å. The La, Na, and K ions occupy the same atomic site of Wyckoff position 1a. Electrical resistivity and magnetic susceptibility show the superconducting transition at 22.5 K. The transition temperature (Tc) of (La,Na,K)Fe2As2 is comparable with that of 122-type (La,Na)Fe2As2 and 1144-type (La,Na)AFe4As4 (A = Rb, Cs), while being more than 10 K lower than those of typical 122- and 1144-type FeSCs. The results suggest that the random distribution of La3+ and Na+ ions is the main reason for lower Tc in the AE = (La,Na) 122-type and 1144-type FeSCs.
“…The resistivity data shows the metallic behavior with convex curvature down to low- T . This behavior is also observed in other 122- and 1144-type superconductors 4–9,17,18 . The residual resistivity ratio, RRR = ρ 300 / ρ 0 , is 5.21, indicating the absence of strong scattering arising from impurities and/or grain boundaries, suitable for investigating their physical properties.…”
Section: Resultssupporting
confidence: 72%
“…On the other hand, Δr = r (La,Na) − r K = −0.34 Å, which is at the boundary between the 122-type and the 1144-type phases. Giving that (La,Na,K)Fe 2 As 2 forms the 122-type structure, one can conclude that the critical parameter which determines the real crystal structure is Δr , rather than Δa .Figure 6Plot of the difference between the ionic radius (VIII) of AE 2+ and A + ( Δr = r AE − r A ) and the difference (absolute value) between the a -axis lengths of AE Fe 2 As 2 ( AE 122) and A Fe 2 As 2 ( A 122) ( Δa = | a AE122 − a A122 |) for 122- and 1144-type Fe-based superconductors 4–9,17,18 . Yellow diamond shows (La,Na,K)Fe 2 As 2 .…”
Section: Discussionmentioning
confidence: 99%
“…Plot of the difference between the ionic radius (VIII) of AE 2+ and A + ( Δr = r AE − r A ) and the difference (absolute value) between the a -axis lengths of AE Fe 2 As 2 ( AE 122) and A Fe 2 As 2 ( A 122) ( Δa = | a AE122 − a A122 |) for 122- and 1144-type Fe-based superconductors 4–9,17,18 . Yellow diamond shows (La,Na,K)Fe 2 As 2 .…”
Section: Discussionmentioning
confidence: 99%
“…A large number of Fe-based superconductors (FeSCs) with various crystal structures have been reported, such as Ln FeAs(O,F) ( Ln corresponds to rare earth elements) — a 1111-type compound 1–3 , ( AE 1− x A x )Fe 2 As 2 ( AE = Ca, Sr, Ba, Eu, A = Na, K, Rb) — a 122-type compound 4,5 , AEA Fe 4 As 4 ( AE = Ca, Sr, Ba, Eu, A = Na, K, Rb) — a 1144-type compound 6–9 , A FeAs ( A = Li, Na) — a 111-type compound 10 , (Ca, Ln )FeAs 2 — a 112-type compound 11,12 , and perovskite Fe nictide 13 . The superconducting transition temperature ( T c ) reaches as high as ~55 K in bulk materials, and several reports have indicated that T c is close to 100 K in thin film samples 14,15 .…”
We synthesized a Fe-based superconductor (FeSC), (La,Na,K)Fe2As2, and characterized its superconducting properties. It was found that (La,Na,K)Fe2As2 has a 122-type (ThCr2Si2-type) structure with a space group I4/mmm (No. 139), identical to (Ba,K)Fe2As2 and (La,Na)Fe2As2 but distinct from so-called 1144-type FeSCs such as CaKFe4As4 and (La,Na)CsFe4As4. The results demonstrate that the formation of the 1144-type phase necessitates the large ionic radius mismatch among the so-called A-site constituent elements of the AFe2As2 formula. The lattice constants are a = 3.850(1) Å and c = 13.21(1) Å. The La, Na, and K ions occupy the same atomic site of Wyckoff position 1a. Electrical resistivity and magnetic susceptibility show the superconducting transition at 22.5 K. The transition temperature (Tc) of (La,Na,K)Fe2As2 is comparable with that of 122-type (La,Na)Fe2As2 and 1144-type (La,Na)AFe4As4 (A = Rb, Cs), while being more than 10 K lower than those of typical 122- and 1144-type FeSCs. The results suggest that the random distribution of La3+ and Na+ ions is the main reason for lower Tc in the AE = (La,Na) 122-type and 1144-type FeSCs.
“…Since the first report of high-T c superconductivity in LaFeAs(O,F) at 26 K in 2008, hundreds of new layered iron pnictide superconductors have been discovered, with all of them formed by the typical Fe 2 As 2 layers stacking with various types of blocking layers [1][2][3][4][5][6][7][8][9][10]. Among them, the 1111-type SmFeAs(O,F) still holds the highest T c around 55 K in bulk materials after 8 years [11].…”
The complex interplay between different order parameters in correlated systems can be finely tuned by mechanical pressure giving access to a variety of distinct phases and thereby providing new functionalities. This review addresses the challenges in the state‐of‐the‐art theoretical simulations of pressure‐induced phenomena on a few representative examples of correlated systems that are currently in the focus of on‐going contemporary research. These include organic charge‐transfer multiferroics, unconventional iron‐based superconductors, frustrated quantum magnets, and candidate systems for Kitaev physics. All these systems show pronounced structural response to moderate pressures or even structural transitions to new phases which can be successfully addressed from first principles. The simulation techniques and general trends in pressure effects are discussed for each material class.
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