Venue: Interplay between superconductivity and magnetism in EuFe2As2

Speaker: Prof. Zakir Hossain (IIT Kanpur, India)

Time: 16:00-17:00,  Mar 11,2013, Monday

Location: Dongsi-242,  Zijingang Campus, Zhejiang University, Hangzhou, China

Abstract:

Superconductivity in iron arsenide compounds is a subject of intense discussion in the scientific community. First iron-arsenide based high temperature superconductor was discovered in F-substituted LaOFeAs with a transition temperature at 26 K. Followed by this four more Fe-based series of compounds were found. Our main interest is in EuFe2As2 which has a very special place in AFe2As2 (A =Ba, Sr, Ca, Eu) series due to the large magnetic moment of Eu2+ (≈7μB) ions in this compound. This compound exhibits Spin density wave (SDW) transition associated with Fe-moments at 190 K and an antiferromagnetic ordering of Eu2+ ions at 19 K. The SDW transition can be suppressed or weakened either by applying hydrostatic pressure or by chemical pressure which induce superconductivity in this system. 50% potassium doping in EuFe2As2 leads to the suppression of SDW transition and gives rise to superconductivity below 33 K. 151Eu Mössbauer spectroscopy provide clear evidence that short range ordering of the Eu moments coexists with the superconducting state below 15 K. Superconducting transition temperature decreases for both under-doped and over-doped samples with maximum Tc for 50% K-doped sample and hence show a dome type T-x phase diagram similar to high Tc cuprates. Ni doping at iron site destroys the spin density wave and antiferromagnetic transition completely giving rise to ferromagnetism below 18 K. We also found evidence of double re-entrance type superconductivity in the EuFe2As2 system. These results will be presented in the perspective of the historical development of the field of superconductivity.