Antiferromagnetic structure and electronic properties ofBaCr2As2andBaCrFeAs2

Abstract

The chromium arsenides BaCr2As2 and BaCrFeAs2 with ThCr2Si2 type structure (space group I4/mmm; also adopted by '122' iron arsenide superconductors) have been suggested as mother compounds for possible new superconductors. DFT-based calculations of the electronic structure evidence metallic antiferromagnetic ground states for both compounds. By powder neutron diffraction we confirm for BaCr2As2 a robust ordering in the antiferromagnetic G-type structure at TN = 580 K with µCr = 1.9 µB at T = 2 K. Anomalies in the lattice parameters point to magneto-structural coupling effects. In BaCrFeAs2 the Cr and Fe atoms randomly occupy the transition-metal site and G-type order is found below 265 K with µ Cr/Fe = 1.1 µB.57 Fe Mössbauer spectroscopy demonstrates that only a small ordered moment is associated with the Fe atoms, in agreement with electronic structure calculations with µFe ∼ 0. The temperature dependence of the hyperfine field does not follow that of the total moments. Both compounds are metallic but show large enhancements of the linear specific heat coefficient γ with respect to the band structure values. The metallic state and the electrical transport in BaCrFeAs2 is dominated by the atomic disorder of Cr and Fe and partial magnetic disorder of Fe. Our results indicate that Néel-type order is unfavorable for the Fe moments and thus it is destabilized with increasing iron content.

Is BaCr2As2 symmetrical to BaFe2As2Richard1, Roekeghem2, Lv3 et al. 2017Phys. Rev. B193120View full textAdd to dashboardCite

“…For instance, the magnetic ordering is different in the two systems. BaCr 2 As 2 shows a G-type ordering, and a Néel temperature of 580 K has been reported [25], with Cr spins pointing along the c-axis in EuCr 2 As 2 [26]. In contrast, BaFe 2 As 2 orders antiferomagnetically around 140 K with spins aligned inside the Fe plane in a bi-collinear structure [27].…”

Observation of a remarkable reduction of correlation effects in BaCr 2 As 2 by ARPES

“…The details of the single crystal synthesis, characterisation, and physical properties of the samples are described elsewhere. 21 The ARPES experiments were carried out at the UE 112-PGM2b beamline of the synchrotron facility BESSY (Berlin) using the 1 3 ARPES end station that is equipped with a Scienta R4000 energy analyser. All measurements were performed at a temperature of 1 K. The photon energies were varied from 50 to 110 eV using both horizontal and vertical polarisations.…”

Itinerant G-type antiferromagnetic order inSrCr2As2

“…The theory also indicated stronger Cr-As covalency than occurs in the Fe-As compounds. BaCr 2 As 2 undergoes G-type antiferromagnetic (AFM) ordering below a transition temperature T N = 580(10) K with moments aligned along the c axis [22]. ARPES measurements indicate reduction in electron correlation effects involving the nominally 3d 4 Cr +2 cations where the band renormalization is smaller than in BaFe 2 As 2 [23,24].…”

“…The ordered magnetic moment, µ = 1.9(1) µ B /Cr, is significantly reduced compared to its localized-moment value (4 µ B /Cr 2+ ) due to the itinerant character brought about by the spin-dependent hybridization [21] between the Cr 3d and the As 4p orbitals. This suggests that Cr as a dopant is a stronger scatterer compared to Co or Ni dopants and may explain why superconductivity has not been observed in Cr-doped BaFe 2 As 2 [21,22].…”