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

TL;DR

This study reveals that CaCoV$_2$O$_7$ exhibits antiferromagnetic order with ferromagnetically coupled dimers, confirmed by neutron diffraction, highlighting complex magnetic interactions in this pyrovanadate compound.

Contribution

The paper reports the discovery of antiferromagnetic order with ferromagnetic dimers in CaCoV$_2$O$_7$, providing detailed magnetic structure analysis using neutron diffraction.

Findings

Antiferromagnetic order appears below 3.44 K.

Co$^{2+}$ ions form ferromagnetic dimers.

Inter-dimer interactions stabilize the order.

Abstract

Magnetic properties of the pyrovanadate CaCoV$_2$O$_7$ 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 $\Theta \simeq -22.5$ K, indicating dominant antiferromagnetic interactions. At $T_{\rm N} = 3.44$ K, CaCoV$_2$O$_7$ shows antiferromagnetic order, accompanied by a weak net ferromagnetic moment of $\sim 0.05$~$\mu_{\rm B}/{\rm Co}^{2+}$. Neutron powder diffraction confirms the formation of antiferromagnetic order below $T_{\rm N}$. 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.