Magnetic phase diagram of single crystals

Abstract

We have systematically measured resistivity, susceptibility and specific heat under different magnetic fields (H) in Eu1−xLaxFe2As2 single crystals. It is found that a metamagnetic transition from A-type antiferromagnetism to ferromagnetism occurs at a critical field for magnetic sublattice of Eu 2+ . The jump of specific heat is suppressed and shifts to low temperature with increasing H up to the critical value, then shifts to high temperature with further increasing H. Such behavior supports the metamagnetic transition. Detailed H-T phase diagrams for x=0 and 0.15 crystals are given, and possible magnetic structure is proposed. Magnetoresistance measurements indicate that there exists a strong coupling between local moment of Eu 2+ and charge in Fe-As layer. These results are very significant to understand the underlying physics of FeAs superconductors. The discovery of superconductivity [1, 2,3,4] in ironpnicitides LnF eAsO 1−x F x (Ln=La, Sm, Ce and Pr) has generated much interest for extensive study on such iron-based superconductors, which is the second family of high-T c superconductors except for the high-T c cuprates. The magnetic ordering of the rare earth ions Ln 3+ at low temperature has been observed by neutron scattering [5,6,7] except for the spin density wave arose from F e 2+ . The coupling between Ln 3+ and Fe 2+ has been found above ordering temperature for local moment of rare earth ions Ln 3+ [5]. These results indicate that the coupling between spins of rare earth ions and Fe 2+ ions seems to be one important ingredient to understand magnetic properties at low temperatures. It is well known that spin density wave (SDW) is suppressed, while superconductivity emerges with doping [8,9,10,11,12]. However, no evidence is given for how to couple between SDW and magnetic ordering of rare earth ions Ln 3+ , and effect of magnetic ordering of Ln 3+ on superconductivity. Therefore, the coupling between the SDW from F e 2+ and magnetic ordering of rare earth ions Ln 3+ should be a very interesting issue. It maybe shed light to understand the underlying physics in Fe-As compounds.EuFe 2 As 2 is one of parent compounds with T hCr 2 Si 2 -type structure. It shows a SDW transition around 190 K, and an antiferromagnetic transition of Eu 2+ ions occurs at T N ∼20 K [13]. Superconductivity at ∼ 30 K can be achieved by K or Na doping [14,15]. This compound is believed to be more complicated than other parent compound due to the large local moment of Eu 2+ ions. Similar to electron-type N d 2−x Ce x Cu 2 O 4−δ [16,17,18,19,20,21], the interaction between magnetic moments of Fe 2+ and Eu 2+ may lead to rich physical phenomena, and these maybe shed light to the mechanism of superconductivity in these materials. In this paper, we have studied magnetic transition by resistivity, susceptibility and specific heat in Eu 1−x La x Fe 2 As 2 single crystals. The magnetic structure of Eu 2+ ions is found to be strongly dependent on external magnetic field. A metamagnetic transition from A-type antiferromagnetism to ferro...

Phase diagram as a function of doping level and pressure in the Eu1−xLaxFe2Zhang1, Ying2, Yan3 et al. 2012Phys. Rev. B12190View full textAdd to dashboardCite

“…For the parent compound, two anomalies in resistivity are observed at 188 K and 20 K, respectively. They arise from the SDW/structural transitions and the AFM order of local moments for Eu 2+ ions [17]. The resistivity anomaly arose from the the SDW/structural transition is gradually suppressed with increasing the doping x, while the anomaly around 20 K due to the antiferromagnetic transition of Eu 2+ ions nearly does not change by varying the La doping.…”

“…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.…”

“…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.…”

High-resolution angle-resolved photoemission spectroscopy study of the electronic structure ofEuFe2As2

“…1͒. [26][27][28][29][30] To reach a comprehensive picture of the complex electronic structure in the SDW state of iron pnictides and reveal the manifestation of various magnetic orderings on the electronic structure, we have performed the ARPES measurements of EuFe 2 As 2 single crystals. Two hole Fermi pockets around ͑0,0͒ and two electron pockets around ͑ , ͒ are observed in the high-temperature paramagnetic ͑PM͒ state.…”

Spin-dependent conductivity of iron-based superconductors in a magnetic field

“…5. From the behavior of this curve and estimations it follows that the condition ξ(H)/L N (F) ≥ 1 is violated in the fields higher than about 2 kOe: where λ B and R L are the de Broglie wavelength and the Larmor radius, respectively, for LaO(F)FeAs the Fermi velocity of which is v F ≈ 10 7 cm/s [19]. Thus, in fields higher than 2 kOe the behavior of magnetoresistance in contact with N (F) area, about 0.2 µ in thickness, at 1 mA and T < T c could qualitatively obey the following pattern:…”