Magnetoelectric Behavior from $S=1/2$ Asymmetric Square Cupolas

TL;DR

This study combines experimental measurements and theoretical modeling to understand the magnetoelectric behavior of a quasi-two-dimensional square cupola material, revealing phase transitions and predicting new phenomena driven by Dzyaloshinskii-Moriya interactions.

Contribution

It introduces a spin model with Dzyaloshinskii-Moriya interactions that explains observed anomalies and predicts new magnetoelectric phases in the material.

Findings

Magnetization curves are well reproduced by the model.

Anomalies are explained by magnetoelectric phase transitions.

A hidden phase and additional responses are predicted under magnetic fields.

Abstract

Magnetoelectric properties are studied by a combined experimental and theoretical study of a quasi-two-dimensional material composed of square cupolas, Ba(TiO)Cu$_4$(PO$_4$)$_4$. The magnetization is measured up to above the saturation field, and several anomalies are observed depending on the field directions. We propose a $S$=1/2 spin model with Dzyaloshinskii-Moriya interactions, which well reproduces the full magnetization curves. Elaborating the phase diagram of the model, we show that the anomalies are explained by magnetoelectric phase transitions. Our theory also accounts for the scaling of the dielectric anomaly observed in experiments. The results elucidate the crucial role of the in-plane component of Dzyaloshinskii-Moriya interactions, which is induced by the noncoplanar buckling of square cupola. We also predict a `hidden' phase and another magnetoelectric response both of which appear in nonzero magnetic field.