Importance of In-Plane Anisotropy in the Quasi Two-Dimensional Antiferromagnet BaNi$_{2}$V$_{2}$O$_{8}$

TL;DR

This study investigates how in-plane anisotropy influences the magnetic phase diagram of the quasi two-dimensional antiferromagnet BaNi$_{2}$V$_{2}$O$_{8}$, revealing a crossover at a specific magnetic field and pressure effects.

Contribution

It demonstrates the significant role of in-plane anisotropy in the magnetic behavior of BaNi$_{2}$V$_{2}$O$_{8}$, including pressure-induced effects and deviations from ideal BKT behavior.

Findings

Identification of a crossover at 1.5 T magnetic field.

Pressure enhances in-plane anisotropy affecting $T_N$ and $H^{*}$.

In-plane anisotropy is relevant even at zero field and ambient pressure.

Abstract

The phase diagram of the quasi two-dimensional antiferromagnet BaNi$_{2}$V$_{2}$O$_{8}$ is studied by specific heat, thermal expansion, magnetostriction, and magnetization for magnetic fields applied perpendicular to $\mathbf{c}$. At $\mu_0H^{*}\simeq1.5$ T, a crossover to a high-field state, where $T_N(H)$ increases linearly, arises from a competition of intrinsic and field-induced in-plane anisotropies. The pressure dependences of $T_N$ and $H^{*}$ are interpreted using the picture of a pressure-induced in-plane anisotropy. Even at zero field and ambient pressure, in-plane anisotropy cannot be neglected, which implies deviations from pure Berezinskii-Kosterlitz-Thouless behavior.