Crystal structure and magnetic properties of Sr_4Mn_2NiO_9

摘要

The crystal structure of Sr_4Mn_2NiO_9 has been refined on single crystal. This phase belongs to the series A_(1+x)(A'_xB_(1-x))O_3 (x= 1/3) related to the 2H-hexagonal perovskite. The structure contains transition metals in chains of oxide polyhedra (trigonal prisms and octahedra); neighboring chains are separated from each other by the Sr atoms. The sequence of the face sharing polyhedra along the chains is two octahedra + one trigonal prism. Mn occupies the octahedra and Ni is disordered in the trigonal prism with approx =80 percent in the pseudo square faces of the prism and approx = 20 percent at the centre. This result has been confirmed by XANES experiments at Mn K and Ni K edges, respectively. Sr_4Mn_2NiO_9 is antiferromagnetic with a Neel temperature at T = 3 K. The Curie constant measured at high temperature is in good agreement with approx = 80 percent of the Ni~(2+) ions in the spin state configuration S=0.