Magnetic and superconducting properties of Ir-doped EuFe2As2

Abstract

The magnetic and superconducting properties of 14% Ir-doped EuFeAs are studied by means of dc and ac magnetic susceptibilities, electrical resistivity, specific heat and Eu and Fe Mössbauer spectroscopy (MS) measurements. Doping of Ir in EuFeAs 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 Eu Mössbauer data indicate that the Eu spins order magnetically below 18 K. 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 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 and out-of-plane susceptibility () show superconducting transitions with zero resistance and diamagnetism, respectively. But the in-plane susceptibility () 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.