Antiferromagnetic order of ferromagnetically coupled dimers in the double pyrovanadate CaCoV2O7

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 ≃ −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/Co2+. Neutron powder diffraction confirms the formation of antiferromagnetic order below TN. It was further confirmed from the magnetic structure determination that the two Co2+ 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.