Charge ordering and ferrimagnetism in the strongly correlated $\beta$-V$_2$PO$_5$ single crystal

TL;DR

This study reveals that $eta$-V$_2$PO$_5$ is a semiconductor exhibiting charge ordering, structural distortion, and ferrimagnetism, with insights from experiments and first principles calculations elucidating the underlying mechanisms.

Contribution

It provides a comprehensive analysis combining experimental and theoretical methods to understand charge ordering, structural transition, and ferrimagnetism in $eta$-V$_2$PO$_5$.

Findings

Charge ordering occurs with V$^{2+}$ and V$^{3+}$ ions.

Structural transition from tetragonal to monoclinic at 610 K.

Ferrimagnetic transition at 128 K with weak magnetic anisotropy.

Abstract

A combined study of transport, thermodynamic, neutron diffraction, nuclear magnetic resonance measurements and first principles calculation were performed for $\beta$-V$_2$PO$_5$ single crystal. It was shown to be a semiconductor with a band gap of 0.48 eV, undergoing a charge ordering (unusual V$^{2+}$ and V$^{3+}$) phase transition accompanied by a tetragonal to monoclinic structural distortion at 610 K and a paramagnetic to ferrimagnetic phase transition at 128 K with a propagation vector of $\textbf{k} = 0$. The easy axis is in the monoclinic $ac$ plane pointing 47(9)$^\circ$ away from the monoclinic $a$ axis. This collinear ferrimagnetic structure and anisotropic isothermal magnetization measurements suggest weak magnetic anisotropy in this compound. The first principles calculations indicate that the intra-chain interactions in the face-sharing VO$_6$ chains dominate the magnetic hamiltonian and identify the $\Gamma_5^+$ normal mode of the lattice vibration to be responsible for the charge ordering and thus the structural phase transition.