Electronic and Magnetic Properties of Cation Ordered SrMnCrAsO.

Several different mechanisms of magnetoresistance (MR) have been observed in 1111 LnMnAsOF oxypnictides (Ln = lanthanide) as a result of magnetic coupling between the Mn and Ln. Such phases also exhibit interesting magnetic phase transitions upon cooling. SrMnCrAsO has been synthesized to investigate if it is possible to observe MR and/or magnetic phase transitions as a result of magnetic coupling between the Mn and Cr. SrMnCrAsO crystallizes in the tetragonal space group 4/ containing alternating MO and M'As layers, and neutron diffraction results demonstrate that the actual stoichiometry is SrMnCrAsO. Cation order is present between Mn and Cr, with Cr predominantly occupying the square planar MO site. Below 410 K, the magnetic moments of the Mn/Cr ions in the M'As sublattice exhibit G-type antiferromagnetic order. The Mn/Cr moments within the MO layer order below 167 K with a KNiF-type antiferromagnetic structure that simultaneously induces a spin flip of the magnetic moments in the M'As layers from a G-type to a C-type antiferromagnetic arrangement. The results demonstrate that the superexchange interactions are finely balanced in SrMnCrAsO. SrMnCrAsO is semiconducting, and there is no evidence of MR.