Non-stoichometry and the magnetic structure of Sr ₂ CrO ₃ FeAs

Abstract

The iron arsenide Sr2CrO3FeAs with the tetragonal Sr2GaO3CuS-type structure was synthesized and its crystal structure re-determined by neutron powder diffraction. In contrast to previous X-ray crystallographic studies, a mixed occupancy of chromium and iron was found within the FeAs 4/4 layer (93 ± 1%Fe : 7 ± 1%Cr). We suggest that the partial Cr-doping at the Fe site is the reason for the absence of a spin-density-wave anomaly and superconductivity in this compound. Additional experiments via neutron polarization analysis revealed short-range spin correlations below ∼100 K and long-range antiferromagnetic ordering below TN = 36 K with a magnetic propagation vector of q = ( 1 2 , 1 2 , 0). The Cr 3+ -ions form a collinear magnetic structure of the C-type in the magnetic space group CP mma (a = a − b, b = a + b, c = c), where Cr 3+ions occupy the 4g (0, 1 4 , z) Wyckoff position. The magnetic moments are aligned along the orthorhombic a -axis. At 3.5 K, an ordered magnetic moment of 2.75 ± 0.05 µB for the Cr 3+sublattice was refined.This paper is dedicated to Dr Klaus Römer on the occasion of his 70th birthday.

Structural chemistry of superconducting pnictides and pnictide oxides with layered structures

“…None of them shows magnetic ordering of the iron substructure or any kind of structural distortion at low temperatures. Neutron diffraction experiments with Sr 2 CrO 3 FeAs revealed antiferromagnetic ordering of the chromium atoms and an intrinsic doping of about 7% chromium into the iron layer [63]. This may be a reason for the absence of superconductivity, because Crdoping has proven to be poisonous to superconductivity in 122-type iron arsenides [64].…”

Electronic band structure and Fermi surface of new low-temperature Ni-based superconductors: 3.3K (Ni2P2)(Sr4Sc2O6) and 2.7K (Ni2As2)(Sr4Sc2O6) from first principles

“…So, superconductivity was found in (Fe 2 P 2 )(Sr 4 Sc 2 O 6 ) at 17K [15] and in (Fe 2 As 2 )(Sr 4 V 2 O 6 ) at 37K-46K [16,17]. Thus, this family opened up new guidelines for the development of [15,18], Cr [18][19][20], V [16,17], and Mg-Ti [21,22] has been prepared. Another remarkable feature of these perovskite-like oxide blocks is high structural flexibility: their thickness can be controlled according to the composition and synthesis conditions.…”

Electronic, magnetic properties and chemical bonding in layered oxychalcogenides Ca4Fe2Cu2S2O6 and Ca4Fe2Cu2Se2O6 from first principles calculations

“…The remarkable feature of the oxide blocks (A 4 M 2 O 6 ) of these materials is their high chemical flexibility to a large variety of constituent elements, and a set of related oxypnictides A 4 M 2 Fe 2 Pn 2 O 6 (where M are Sc, Ti, V, Cr, Mg-Ti, Al-Ti, and A are Ca, Sr or Ba) has been prepared [9][10][11][12][13][14][15][16][17][18][19][20].…”