Antiferromagnetic order of ferromagnetically coupled dimers in the double pyrovanadate CaCoV$_2$O$_7$

Abstract

Magnetic properties of the pyrovanadate CaCoV2O7 have been studied by means of the bulk magnetization and neutron powder diffraction measurements. Magnetic susceptibility in the paramagnetic phase shows Curie-Weiss behavior with negative Weiss temperature Θ ≃ −22.5 K, indicating dominant antiferromagnetic interactions. At TN = 3.44 K, CaCoV2O7 shows antiferromagnetic order, accompanied by a weak net ferromagnetic moment of ∼ 0.05 µB/Co 2+ . Neutron powder diffraction confirms the formation of antiferromagnetic order below TN. It was further confirmed from the magnetic structure determination that the two Co 2+ ions in the adjacent edge-sharing octahedra have almost parallel (ferromagnetic) spin arrangement, indicative of a formation of a ferromagnetic spin dimer. The antiferromagnetic order is, in turn, stabilized by sizable inter-dimer antiferromagnetic interactions.