Magnetic Structure and Electromagnetic Properties of LnCrAsO with a ZrCuSiAs-type Structure (Ln = La, Ce, Pr, and Nd)

We report the synthesis, structure, and electromagnetic properties of Cr-based layered oxyarsenides Ln­CrAsO (Ln = La, Ce, Pr, and Nd) with a Zr­CuSiAs-type structure. All Ln­CrAsO samples showed metallic electronic conduction. Electron doping in La­CrAsO by Mn-substitution for the Cr sites gave rise to a metal–insulator transition. Analysis of powder neutron diffraction data revealed that La­CrAsO had G-type antiferromagnetic (AFM) ordering, i.e., a checkerboard-type AFM ordering in the CrAs plane and antiparallel spin coupling between the adjacent CrAs planes, at 300 K with a large spin moment of 1.57 μB along the c axis. The magnetic susceptibility of La­CrAsO was very small (on the order of 10–3 emu/mol) and showed a broad hump at ∼550 K. First-principles density functional theory calculations of La­CrAsO explained its crystal structure and metallic nature well, but could not replicate the antiparallel spin coupling between the CrAs layers. The electronic structure of La­CrAsO is discussed with regard to those of related compounds La­FeAsO and La­MnAsO.