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We report a possible coexistence of nontrivial topology and antiferromagnetism in the newly discovered compounds EuCdBi2, with magnetic Eu layer locating above and below Bi square net. The X-ray diffraction on single crystals and powder indicats that this 112-type material crystalizes in space group of I4/mmm, the same as SrMnBi2 and EuMnBi2. Our combined measurements of magnetization, electrical transport and specific heat consistently reveal antiferromagnetic (AFM) transition of Eu2+ moments at TN = 20 K. The Eu moments are not saturated under a field of 7 T at 1.8 K. The anisotropic susceptibility suggests the Eu moments lie in the ab plane, and a metamagnetic (MM) transition is observed near 1 T below TN. Large positive magnetoresistance (MR) present for both H ‖ ab and H ‖ c, which are considered to contain part contributions from Dirac bands. Hall measurements show the electron-hole compensation effect is prominent above 100 K, with a crossover of Hall resistance from negative to positive values at ∼150 K. The fitted mobility of electrons is as high as 3250 cm2 V−1 S−1 at 1.8 K. Interestingly, the rapid increase of carrier density and suppression of mobility appear at around TN, indicating non-negligible interaction between Eu moments and electron/hole bands. EuCdBi2 may provide a new platform to investigate the interplay of topological bands and antiferromagnetic order.

In this study, we measure the in-plane transport properties of high-quality Ba(Fe0.914Co0.086)2As2 single crystals. Signatures of vortex unbinding Berezinskii–Kosterlitz–Thouless (BKT) transition are shown from both the conventional approach and the Fisher–Fisher–Huse dynamic scaling analysis, in which a characteristic Nelson–Kosterlitz jump is demonstrated. We also observe a non-Hall transverse signal exactly at the superconducting transition, which is explained in terms of guided motion of unbound vortices.

We report electrical and magnetic measurements of an optimally doped Eu(Fe _0.88 Ir _0.12 ) _2 As _2 crystal which shows superconductivity at T _sc = 22 K and magnetic ordering of the Eu ^2+ spins below 20 K. The results suggest that the Eu ^2+ spins lie flat ferromagnetically in the ab plane at T ^ab _m = 20 K, and then tilt toward the c -axis at T ^tilt _m = 17.4 K. The isothermal magnetization loop at low temperatures shows both ferromagnetic behavior and superconducting characteristics, unambiguously demonstrating the coexistence of ferromagnetism and superconductivity. The upper critical field measured is remarkably reduced, as compared to other Fe-based superconductors with the same T _sc , and it exhibits abnormal temperature dependence featured by the existence of an inflection point around T ^ab _m , where the anisotropy ratio γ (≡ H ^∥ ^ab _c2 / H ^∥ ^c _c2 ) shows a minimum value smaller than 1.0. These observations can be explained by a ferromagnetic exchange field of ∼30 T which tilts its direction toward the c -axis below T ^tilt _m . The strong internal field, much higher than the intrinsic lower critical field expected, leads to the absence of Meissner state, which is confirmed by the magnetic measurements under ultra-low fields.