Khalyavin, DD; Lovesey, SW; Manuel, P; Krüger, F; Rosenkranz, S; Allred, JM; Chmaissem, O; Khalyavin, DD; Lovesey, SW; Manuel, P; Krüger, F; Rosenkranz, S; Allred, JM; Chmaissem, O; Osborn, R; - view fewer (2014) Symmetry of reentrant tetragonal phase in Ba1−xNaxFe2As2: Magnetic versus orbital ordering mechanism. Physical Review B , 90 (17) , Article 174511. 10.1103/PhysRevB.90.174511.

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Abstract

Magnetostructural phase transitions in Ba1−xAxFe2As2 (A = K, Na) materials are discussed for both magnetically and orbitally driven mechanisms, using a symmetry analysis formulated within the Landau theory of phase transitions. Both mechanisms predict identical orthorhombic space-group symmetries for the nematic and magnetic phases observed over much of the phase diagram, but they predict different tetragonal space-group symmetries for the newly discovered reentrant tetragonal phase in Ba1−xNaxFe2As2 (x∼0.24–0.28). In a magnetic scenario, magnetic order with moments along the c axis, as found experimentally, does not allow any type of orbital order, but in an orbital scenario, we have determined two possible orbital patterns, specified by P4/mnc1′ and I4221′ space groups, which do not require atomic displacements relative to the parent I4/mmm1′ symmetry and, in consequence, are indistinguishable in conventional diffraction experiments. We demonstrate that the three possible space groups are, however, distinct in resonant x-ray Bragg diffraction patterns created by Templeton & Templeton scattering. This provides an experimental method of distinguishing between magnetic and orbital models.

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