Metamagnetic transition in EuFe2As2single crystals

We report the measurements of the anisotropic magnetization and magnetoresistance (MR) on single crystals of EuFe 2 As 2 , a parent compound of ferro-arsenide high-temperature superconductor. Apart from the antiferromagnetic (AFM) spin density wave (SDW) transition at 186 K associated with Fe moments, the compound undergoes another magnetic phase transition at 19 K due to AFM ordering of Eu 2+ spins ( J = S =7/2). The latter AFM state exhibits metamagnetic (MM) transition under magnetic fields. Upon applying magnetic field with H ∥ c at 2 K, the magnetization increases linearly to 7.0 μ B f.u. −1 at μ 0 H =1.7 T and then remains at this value for saturated Eu 2+ moments under higher fields. In the case of H ∥ ab , the magnetization increases step-like to 6.6 μ B f.u. −1 with small magnetic hysteresis. An MM phase was identified with the saturated moments of 4.4 μ B f.u. −1 . The MM transition accompanies negative in-plane MR, reflecting the influence of Eu 2+ moments ordering on the electrical conduction of FeAs layers. These results were explained in terms of spin-reorientation and spin-reversal based on an A-type AFM structure for Eu 2+ spins. The magnetic phase diagram has been established.