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.