Phase diagram as a function of doping level and pressure in the Eu1−xLaxFe2

Abstract

We establish the phase diagram of Eu1−xLaxFe2As2 system as a function of doping level x and the pressure by measuring the resistivity and magnetic susceptibility. The pressure can suppress the spin density wave (SDW) and structural transition very efficiently, while enhance the antiferromagnetic (AFM) transition temperature TN of Eu 2+ . The superconductivity coexists with SDW order at the low pressure, while always coexists with the Eu 2+ AFM order. The results suggests that Eu 2+spin dynamics is disentangeld with superconducting (SC) pairing taken place in the two-dimensional Fe-As plane, but it can strongly affect superconducting coherence along c-axis.PACS numbers: 74.25. 74.25.Ha, Iron-based superconductors have attracted great attentions these years [1][2][3][4]. The parent compound undergoes structural and spin density wave (SDW) transitions. With chemical doping or high pressure, both structural and SDW transition can be suppressed and superconductivity emerges. AFe 2 As 2 (A=Ca, Sr, Ba, Eu) with the T hCr 2 Si 2 -type structure were widely investigated because it is easy to grow large size of high quality single crystals [5]. The maximum T C for the holedoped samples is about 38 K and for the Co doped samples the maximum T C is about 26 K [4,6]. Recently, superconductivity up to 49 K was discovered in rare earth doped CaFe 2 As 2 , it is the highest T C observed in 122 system [7][8][9][10]. EuFe 2 As 2 has the same structure as that of CaFe 2 As 2 [11]. EuFe 2 As 2 shows superconductivity around 31 K under the pressure of 3 GPa[12].The Eu122 system has an intriguingly outstanding issue regarding the interplay between the magnetism of large Eu +2 spins and the superconductivity. The doping on the Eu122 system has been achieved in two ways: direct electron doping on Fe-As layer, such as Co-doped Eu122, and doping induced by Eu replacement with rare earth atoms such as Eu 1−x La x Fe 2 As 2 . In the former case, a resistivity reentrance due to AFM order of Eu +2 spins was often observed [13][14][15][16], an indication of the effect of Eu 2+ spins on superconductivity. However, a clear understanding of such an effect has not been established due to lacking of systematic investigation. In the latter case, earlier results on Eu 1−x La x Fe 2 As 2 shows only gradual decrease of the spin density wave transition temperature, T SDW , of F e spins with increasing the La content. No superconducting transition was observed [17] and no information regarding of the role of Eu +2 spins has been * Corresponding author; Electronic address: chenxh@ustc.edu.cn provided.High pressure is confirmed to be good method to tune the phase competition of superconductivity and SDW in iron-pnicides superconductors. In this letter, we systematically investigate the superconductivity in La doped EuFe 2 As 2 system under ambient and high pressure by resistivity and magnetic susceptibility measurements. We obtain a complete phase diagram. obtained. It is found that one superconducting transition was observed in the highest doping level ...

Pressure effects on the superconducting properties of single-crystalline Co doped NaFeAs

“…Pressure was generated using a Be-Cu pressure cell with a Teflon cup which was filled with Daphene Oil 7373. The pressure applied in the resistivity measurement was determined by shifting the superconducting transition temperature of pure Sn [18]. The magnetic susceptibility was measured under pressures up to 6.1 GPa in a diamond anvil cell (DAC) made of Be-Cu alloy.…”

Europium-based iron pnictides: a unique laboratory for magnetism, superconductivity and structural effects

“…Indeed, additional phosphor substitution on Eu − 1 x Na x Fe 2 As 2 could even increase T c by 5 K [162]. This is in stark contrast to lanthanum substituted compounds [163][164][165][166]. Here, additional pressure induces superconductivity at lower critical temperatures compared to pure EuFe 2 As 2 under pres sure (figure 24) [166].…”

Hydrostatic pressure effects on the static magnetism in Eu(Fe0.925Co0.075)2As2

“…It is well established that the SDW transition of the Fe sublattice gets gradually suppressed with increasing doping level in hole-doped Eu 1− x K x Fe 2 As 2 19 and Eu 1− x Na x Fe 2 As 2 32 , in electron-doped Eu(Fe 1− x Co x ) 2 As 2 21, 24 , Eu(Fe 1− x Ir x ) 2 As 2 14, 33 , and Eu 1− x La x Fe 2 As 2 20 , as well as in isovalent-substituted Eu(Fe 1− x Ru x ) 2 As 2 30 and EuFe 2 (As 1− x P x ) 2 25, 26 , while the magnetic order of the Eu sublattice persists over the whole doping region. The magnetic ground state of the Eu 2+ moments displays a systematic change with increasing doping concentration, from the A-type AFM structure (with the spins lying in the ab planes) at low doping levels to the pure ferromagnetic structure (with the spins aligning along the c axis) at high doping levels 24 .…”