Thermodynamics of a frustrated quantum magnet on a square lattice

TL;DR

This study investigates the magnetic properties and phase transitions of a frustrated quantum magnet on a square lattice, revealing a potential spin-nematic phase near saturation due to geometric frustration and quantum fluctuations.

Contribution

First experimental evidence of a quantum phase possibly related to a spin-nematic state in a $J_1$-$J_2$ square lattice antiferromagnet.

Findings

Dimensionality reduction in magnetization scaling indicating frustration

Emergence of a fluctuating quantum phase near saturation below 150 mK

Identification of phase transitions depending on magnetic field orientation

Abstract

We report the magnetic and calorimetric measurements in single crystal samples of the square lattice $J_{1}-J_{2}$ quantum antiferromagnet BaCdVO(PO$_4$)$_2$. An investigation of the scaling of magnetization reveals a "dimensionality reduction" indicative of a strong degree of geometric frustration. Below a characteristic temperature of $T^{\ast}\simeq150$~mK we observe the emergence of an additional strongly fluctuating quantum phase close to full magnetic saturation. It is separated from the magnetically ordered state by first- and second-order phase transitions, depending on the orientation of the applied magnetic field. We suggest that this phase may indeed be related to the theoretically predicted spin-nematic state.