# Non-collinear magnetic structure and anisotropic magnetoelastic coupling in cobalt pyrovanadate Co2V2O7

## TL;DR

This study reveals the complex non-collinear magnetic ground state and anisotropic magnetoelastic coupling in Co2V2O7, linking its magnetic structure to ferroelectricity and providing insights into its magnetic and structural properties.

## Contribution

The paper uncovers the non-collinear magnetic structure of Co2V2O7 and demonstrates its role in magnetoelectric coupling, supported by neutron diffraction and ab initio calculations.

## Key findings

- Co2V2O7 has a non-collinear magnetic ground state with a spin-chain-like structure.
- The non-collinear magnetic structure is more stable than ferromagnetic states at low temperature.
- Anisotropic magnetoelastic coupling is evidenced by opposite lattice parameter deviations below TN.

## Abstract

The Co2V2O7 is recently reported to exhibit amazing magnetic field-induced magnetization plateaus and ferroelectricity, but its magnetic ground state remains ambiguous due to its structural complexity. Magnetometry measurements, and time-of-flight neutron powder diffraction (NPD) have been employed to study the structural and magnetic properties of Co2V2O7, which consists of two non-equivalent Co sites. Upon cooling below the Ne\'el temperature TN = 6.3 K, we observe magnetic Bragg peaks at 2K in NPD which indicated the formation of long range magnetic order of Co2+ moments. After symmetry analysis and magnetic structure refinement, we demonstrate that Co2V2O7 possesses a complicated non-collinear magnetic ground state with Co moments mainly located in b-c plane and forming a non-collinear spin-chain-like structure along the c-axis. The ab initio calculations demonstrate that the non-collinear magnetic structure is more stable than various ferromagnetic states at low temperature. The non-collinear magnetic structure with canted up-up-down-down spin configuration is considered as the origin of magnetoelectric coupling in Co2V2O7 because the inequivalent exchange striction induced by the spin-exchange interaction between the neighboring spins is the driving force of ferroelectricity. Besides, it is found that the deviation of lattice parameters a and b is opposite below TN, while the lattice parameter c and stay almost constant below TN, evidencing the anisotropic magnetoelastic coupling in Co2V2O7.