Magnetic and superconducting properties of Ir-doped EuFe₂As₂

Abstract

The magnetic and superconducting properties of 14% Ir-doped EuFe 2 As 2 are studied by means of dc and ac magnetic susceptibilities, electrical resistivity, specific heat and 151 Eu and 57 Fe Mössbauer spectroscopy (MS) measurements. Doping of Ir in EuFe 2 As 2 suppresses the Fe spin density wave transition and in turn gives rise to high temperature superconductivity below 22.5 K with a reentrant feature at lower temperature. Magnetization and 151 Eu Mössbauer data indicate that the Eu + 2 spins order magnetically below 18 K. 57 Fe MS studies show a line broadening in the absorption spectra below 18 K due to transferred hyperfine field from the magnetically ordered Eu sublattices. A pronounced λ-shape peak in the specific heat supports a second-order phase transition of Eu + 2 magnetic ordering with a strong ferromagnetic component, as confirmed by the magnetic field dependences of the transition. For a single crystal, the in-plane resistivity ρ ( ) ab and out-of-plane susceptibility ( χ c ) show superconducting transitions with zero resistance and diamagnetism, respectively. But the in-plane susceptibility ( χ ab ) does not show any diamagnetic shielding against external fields. The observed non-zero resistance in the temperature range 10-17.5 K, below the superconducting transition temperature, suggests the possible existence of a spontaneous vortex state in this superconductor.

μSRand neutron diffraction investigations on the reentrant ferromagnetic superconductorEu(Fe0.86Ir0.14<

“…The polycrystalline sample of Eu(Fe 0.86 Ir 0.14 ) 2 As 2 was prepared by the solid state reaction method [26,27] starting with the high purity elements (Eu: 99.9%, Fe: 99.999%, Ir: 99.99%, and As: 99.999%) in stoichiometric ratio. Fine pieces of Eu were mixed with Fe, Ir and As powders, pelletized and sealed in an evacuated quartz tube and fired at 900 • C for 30 h. After the first firing the sample was thoroughly ground and again pelletized and sealed in evacuated quartz tube.…”

Strongly fluctuating moments in the high-temperature magnetic superconductor RbEuFe4As4

“…EuFe 2 As 2 which show a singularity [16][17][18][19] . The variation of the specific heat in the vicinity of the phase transition, the specific heat can be expressed 20 as C = a ± |t| −α +b(t).…”

Electronic structure and H−T phase diagram of Eu(Fe1−xRhx)<

“…The specific heat of a Type-II superconductor in field has a reduced jump height, which may push it beyond our detection limit even in low or zero field in doped EuFe 2 As 2 . We note that no specific heat jump at T c has been observed in Ir-doped and P-doped Eu-122 either 33,34 , likely for the same reasons. Unfortunately, this makes it difficult to confirm that the observed superconductivity is an intrinsic, bulk property.…”