Magnetic Properties of FeAs Single Crystal

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O R I G I N A L PA P E R

Magnetic Properties of FeAs Single Crystal K.A. Ziq · A.F. Salem

Received: 5 November 2012 / Accepted: 1 December 2012 / Published online: 30 December 2012 © Springer Science+Business Media New York 2012

Abstract Magnetic measurements have been performed on FeAs single crystals and polycrystalline samples. Magnetic measurements revealed a very sharp spin-glass magnetic transition in self flux grown single crystal. The bifurcation point between zero field cooled (ZFC) and field cooled (FC) magnetization occurs at 130 K. Susceptibility of flux grown single crystals revealed ferromagnetic-type behavior in the temperature range 4–300 K, while single crystals grown by iodine transport vapor were non-magnetic revealed features associated with antiferromagnetic and spin wave characteristics. The shift in Raman lines reveled sharper peaks for the crystals grown by vapor transport method than that obtained for the flux grown crystals. The difference in the spectrum may indicate sharper distribution in the bonding strength between Fe and As ions in crystals grown by the iodine vapor transport method. Keywords Iron-based superconductors · Raman spectrum · Hysteresis loops

1 Introduction The discovery of superconductivity in LaFeAsO1−x Fx with Tc = 26 K by Hosono’s group has renewed interest in interplay between magnetism superconductivity and structural transition [1]. Soon after the discovery; the transition temperature reached mid 1950s K at ambient pressure in RFeAsO0.9 F0.1 (R = Nd, Sm) [2–6]. Moreover, superconductivity has been discovered in oxygen free Fe-based K.A. Ziq () · A.F. Salem Department of Physics, King Fahd University of Petroleum and Minerals, Dhahra 31261, Saudi Arabia e-mail: [email protected]

pnictide (Ba1−x Kx )Fe2 As2 —the 122 phase—with transition temperature close to 38 K [7]. The new Fe-based superconductors are characterized by FeAs sheets separated by barium atoms in the 122 phase; whereas for the 1111 phase the sheets alternate with LaO layers. The Fe-spins show ferromagnetic alignment along the b-axis and are antiferromagnetic alignment along the a- and c-direction. The magnetic moment associated with Fe-ion is relatively small (about 0.5μB indicating itinerant electron systems or frustrated localized spins. The parent material in both phases LaOFeAs and SrFe2 As2 are nonsuperconducting metallic; but shows anomalies in both resistivity and dc magnetic susceptibility that are commonly associated with spin density wave transition (T ∼ 150– 200 K) [8, 9]. Despite the intense research on the superconducting, magnetic and structural properties of the Fe-based superconductors, very little attention has been devoted to the precursor materials; namely FeAs single crystals. The crystalline structure of FeAs is MnP-type, it is distorted from hexagonal NiAs structure with lattice parameter: a = 5.440 Å, b = 6.026 Å, and c = 3.371 Å. The Fe-atoms nearly located in one plane and are surrounded by 6-(distorted octahedral) As atoms [10, 11], while in the superconducting state, the