Antiferromagnetic transition inEuFe2As2: A possible parent compound for superconductors

Abstract

Ternary iron arsenide EuFe2As2 with ThCr2Si2-type structure has been studied by magnetic susceptibility, resistivity, thermopower, Hall and specific heat measurements. The compound undergoes two magnetic phase transitions at about 200 K and 20 K, respectively. The former was found to be accompanied with a slight drop in magnetic susceptibility (after subtracting the Curie-Weiss paramagnetic contribution), a rapid decrease in resistivity, a large jump in thermopower and a sharp peak in specific heat with decreasing temperature, all of which point to a spin-density-wave-like antiferromagnetic transition. The latter was proposed to be associated with an A-type antiferromagnetic ordering of Eu 2+ moments. Comparing with the physical properties of the iso-structural compounds BaFe2As2 and SrFe2As2, we expect that superconductivity could be induced in EuFe2As2 through appropriate doping. [18,19,20] EuFe 2 As 2 is another member of the ternary iron arsenide family, [21] however, only few work was performed on this material. Mössbauer and magnetic susceptibility studies [22] indicated that EuFe 2 As 2 experienced two magnetic transitions. The first one around 200 K was due to the AFM transition in the iron sublattice. The second one at 19 K arose from the AFM ordering of Eu 2+ magnetic moments. No other physical properties of EuFe 2 As 2 have been reported. In order to assess the potential of inducing superconductivity in this compound, we have carried out a systematic study of the physical properties of EuFe 2 As 2 . We found that the transition at about 200 K was accompanied by a rapid decrease in resistivity, a large jump in thermopower and a sharp peak in specific heat. In addition, a slight drop in magnetic susceptibility was observed after subtracting the Curie-Weiss paramagnetic contribution of Eu 2+ magnetic moments. These properties are quite similar with those of BaFe 2 As 2 and SrFe 2 As 2 , suggesting that EuFe 2 As 2 is another possible parent compound in which superconductivity may be found by proper doping. Polycrystalline samples of EuFe 2 As 2 were synthesized from stoichiometric amounts of the elements as reported previously [21]. Fresh Eu grains, Fe powders and As grains were mixed in a ratio of 1:2:2, sealed in an evacuated quartz tube and sintered at 773 K for 12 hours then 1073 K for another 12 hours. After cooling, the reaction product was thoroughly ground in an agate mortar and pressed into pellets under a pressure of 2000 kg/cm 2 in an argon-filled glove-box. The pellets were annealed in an evacuated quartz tube at 1123 K for 12 hours and furnace-cooled to room temperature. The EuFe 2 As 2 samples were obtained as black powders, which is stable in air.

Superconductivity at 34.7 K in the iron arsenide Eu0.7Na0.3Fe2As2

“…It is seen that all main peaks can be indexed by the ThCr 2 Si 2 tetragonal structure with a = 3.8978Å and c = 12.2623 Å. It is noted that the lattice parameter values are a = 3.9104 Å and c = 12.1362 Å for the undoped compound EuFe 2 As 2 [18]. Clearly Na-doping leads to an apparent decrease in the a-axis lattice and an increase in the c-axis lattice.…”

“…The Eu in EuFe 2 As 2 is divalent and similar to alkaline earth elements in chemical properties. EuFe 2 As 2 exhibits a clear anomaly in resistivity near 200 K [18], which is similar to BaFe 2 As 2 and SrFe 2 As 2 . This suggests that EuFe 2 As 2 is another promising parent compound in which superconductivity may be realized by appropriate doping.…”

Superconductivity and ferromagnetism in EuFe2(As1−xPx)2

“…EuFe 2 As 2 , first synthesized in late 1970s, [15] is a unique "122" compound which shows both SC in the FeAs-layers upon appropriate doping, and long-range magnetic ordering in the Eu sublattice. It was found that the undoped parent compound undergoes antiferromagnetic (AFM) ordering in the Fe sublattice at 200 K, followed by another AFM ordering in the Eu sublattice at 20 K. [16,17,18,19] The two subsystems are hardly coupled, as evidenced from optical [20] and photoemission [21] studies. The magnetic structure of the latter AFM order had been proposed to be of A-type, [17,22] in which Eu 2+ spins algin ferromagnetically in the basal planes but antiferromagnetically along the c-axis, which was then confirmed by the magnetic resonant x-ray scattering [23] and neutron diffraction [24] experiments.…”

Superconducting Properties of Polycrystalline Ba2Ti2Fe2As4O

“…1 shows the temperature dependence of field-cooled (FC) and zero-field-cooled (ZFC) dc magnetic susceptibility under magnetic field H=10 Oe. The susceptibility becomes negative below ∼21 K. Further, the shielding volume fraction of 90% is given by the ZFC data and the magnetic expelling fraction of 2.1% by the FC curve at 2 K, assuming theoretical density of 5.97 g/cm 3 . This suggests that the superconducting transition is of bulk nature and this material is a type-II superconductor with strong flux pinning.…”

“…Scientists have discovered FeSC in several systems, sush as LaFeAsO(1111) [1], BaFe 2 As 2 (122) [2] [3], LiFeAs(111) [4], FeSe(11) [5] and KFe 2 Se 2 (122*) [6]. Recently, we successfully designed and synthesized a new oxypnictide Ba 2 Ti 2 Fe 2 As 4 O with superconducting transition temperature T c ∼22 K [7].…”