Field-induced spin reorientation and giant spin-lattice coupling inEuFe2As2

Abstract

We have studied a EuFe 2 As 2 single crystal by neutron diffraction under magnetic fields up to 3.5 T and temperatures down to 2 K. A field induced spin reorientation is observed in the presence of a magnetic field along both the a and c axes, respectively. Above critical field, the ground state antiferromagnetic configuration of Eu 2+ moments transforms into a ferromagnetic structure with moments along the applied field direction. The magnetic phase diagram for Eu magnetic sublattice in EuFe 2 As 2 is presented. A considerable strain (∼0.9%) is induced by the magnetic field, caused by the realignment of the twinning structure. Furthermore, the realignment of the twinning structure is found to be reversible with the rebound of magnetic field, which suggested the existence of magnetic shape-memory effect. The Eu moment ordering exhibits close relationship with the twinning structure. We argue that the Zeeman energy in combined with magnetic anisotropy energy is responsible for the observed spin-lattice coupling.PACS numbers: 74.70. Xa, 75.30.Kz, 75.80.+q The recent discovery of iron pnictide superconductors has triggered extensive research on their physical properties and mechanism of high temperature superconductors [1][2][3]. All iron pnictides are found to be of layered structure in nature. For undoped iron pnictides, the chains of parallel Fe spins within the FeAs layers couple antiferromagnetically in the ab plane of the orthorhombic lattice with an antiparallel arrangement along the c axis [4][5][6]. This antiferromagnetic (AFM) order in the parent compounds is likely due to a spin-densitywave (SDW) instability caused by Fermi surface nesting [7]. Similar to the high T c cuprate superconductors, the undoped iron pnictides are not superconducting under ambient pressure and show an antiferromagnetic SDW order. Upon carrier doping, the magnetic order is suppressed and superconductivity emerges concomitantly [8,9]. EuFe 2 As 2 is a peculiar member of the iron arsenide AFe 2 As 2 family since the A site is occupied by Eu 2+ , which is an S-state (orbital angular momentum L = 0) rare-earth ion possessing a 4f 7 structure with the total electron spin S = 7/2. Here we report a single crystal neutron diffraction measurement on EuFe 2 As 2 under a magnetic field up to 3.5 T. The spin reorientation of Eu moments is observed upon an applied magnetic field parallel to both a and c axes of the orthorhombic structure, while the Fe SDW order persists at high magnetic fields. Interestingly, the application of a magnetic field changes the twinning population in EuFe 2 As 2 and the redistribution of the domain population is found to be associated with the evolution of the magnetic order of Eu moments, which indicates the existence of a giant spin-lattice coupling effect. A single crystal of EuFe 2 As 2 was grown by the Sn-flux method [10]. It was in shape of a platelet with approximate dimensions of 5 × 5 × 1 mm 3 . Single crystal neutron scattering measurements were performed on the thermal neutron two-axis diffractometer...

Anomalous in-plane magnetoresistance in a EuFe2As2single crystal: Evidence of strong spin-charge-lattice coupling

“…7,8 Works on EuFe 2 As 2 single crystals revealed that the Fe and Eu spins form long-range AFM order below 190 and 19 K, respectively. 9 Furthermore, the application of an external magnetic field will induce a magnetic phase transition in EuFe 2 As 2 with the Eu moments changing from AFM to FM arrangement, 10 while the AFM SDW order of Fe is found to be robust and it persists in the investigated field range up to 3 T. 11 The superconductivity can be achieved by applying high pressure or doping on any site in EuFe 2 As 2 . [12][13][14][15][16][17][18][19][20][21] Given the fact that a large in-plane electronic anisotropy exists in the AFM phase, [22][23][24] it is significant to understand the relationship between magnetism and electrical property of iron pnictide system.…”

Coexistence of superconductivity and ferromagnetism in P-dopedEuFe2As2

“…EuFe 2 As 2 exhibits a spin density wave (SDW) transition in the Fe sublattice concomitant with a structural phase transition at 190 K. In addition, Eu 2+ moments order in an A-type antiferromagnetic (AFM) structure at 19 K (ferromagnetic layers ordered antiferromagnetically along the c axis) [19][20][21]. Superconductivity can be achieved in this system by substituting Eu with K or Na (Refs.…”

Anisotropic magnetic order of the Eu sublattice in single crystals of EuFe2−xCoxAs

“…22). 24 In addition, neutron diffraction measurements 23 suggested a canted AFM (C-AFM) structure of the Eu 2+ moments in EuFe 2 As 2 at intermediate magnetic fields.…”