Magnetic structure and properties of centrosymmetric twisted-melilite K2CoP2O7

Abstract

Twisted-melilite dipotassium cobalt pyrophosphate (K₂CoP₂O₇, P4₂/mnm, #136), originally reported by Gabelica-Robert (1981), was synthesized in powder form by a standard solid-state reaction route. The magnetic properties of the material were studied by magnetometry and its magnetic structure determined using neutron powder diffraction for the first time. Below T_N = 11 K, the material adopts a G-type antiferromagnetic structure with moments aligned in the ab-plane (magnetic space group Pn′nm, #58.3.473). Ab initio calculations were performed to examine the isotropic magnetic spin exchange parameters as well as the preferred direction of magnetic moments due to spin–orbit coupling. The relationship between crystal structure geometry and the strength of the magnetic interactions was examined and compared to those of melilite-type Sr₂CoGe₂O₇.