Single Crystal Growth and Study of the Ferromagnetic Superconductor RbEuFe₄As₄

Abstract

RbEuFe 4 As 4 exhibits both superconducting order in the FeAs layers and ferromagnetic order in the Eu layers, providing a good platform to study the interaction and microscopic coexistence of these two traditionally incompatible orders. Growing high-quality RbEuFe 4 As 4 single crystals is essential to investigate these phenomena at a deeper level. Here we report the successful growth of the RbEuFe 4 As 4 single crystals with millimeter-size dimensions using a RbAs flux. The highquality crystals were characterized via resistivity, magnetization, and heat capacity measurements. Single crystal X-ray diffraction data refinements reveal almost regular FeAs 4 tetrahedra (As1− Fe−As1 = 108.60(7)°, As2−Fe−As2 = 109.01(8)°, and As1−Fe−As2 = 109.81(2)°) in RbEuFe 4 As 4 , providing structural support for the highest superconducting transition temperature (T c = 36.8 K) among all known AAeFe 4 As 4 (A = K, Rb, Cs; Ae = Ca, Sr, Eu) compounds. Our flux method using RbAs can also be employed to grow other desired transition metal compounds targeting the same crystal structure.

Superconducting and magnetic phase diagram of RbEuFe4As4 and CsEuFe4As4 at high pressure

“…The present measurements have been performed using polycrystalline samples which show somewhat broad transitions. Recently, single crystalline specimens 60 have been grown which show substantially sharper transitions. It would be particularly interesting to further examine the narrow pressure range around P c in such crystals in order to explore e.g., the influence of the FMS to SFM crossover on the upper critical field curve.…”

Anisotropic superconductivity and magnetism in single-crystal RbEuFe4As4

“…We evaluate the phase transitions occuring in singlecrystal RbEuFe 4 As 4 using zero-field specific heat measurements such as shown in Figure 2 [30]. A clear cusp in C/T at T m ∼ 15 K signals the magnetic transition whereas a step in C/T at T c ∼ 36.8 K is the signature of the superconducting transition.…”

Strongly fluctuating moments in the high-temperature magnetic superconductor RbEuFe4As4

“…For our calorimetry experiment, we mounted a small, platelet-shaped RbEuFe 4 As 4 single crystal, grown in RbAs flux 44 , onto a nanocalorimeter platform 45,46 using Apiezon grease, see Fig. 1.…”