Tracking a hysteretic and disorder-broadened phase transition via the electromagnon response in improper ferroelectrics

TL;DR

This study uses terahertz spectroscopy to investigate how electromagnons reveal the nature of phase transitions in improper ferroelectrics, showing hysteresis and broadening effects due to disorder and alloying.

Contribution

It demonstrates that electromagnons can directly probe phase transition characteristics in improper ferroelectrics, including hysteresis and disorder effects, with new insights into alloying impacts.

Findings

Phase transition exhibits thermal hysteresis, confirming first-order nature.

Electromagnon energy increases with Zn alloying due to modified magnetic interactions.

Transition broadens under spin-disorder from alloying.

Abstract

We demonstrate that electromagnons can be used to directly probe the nature of a phase transition between magnetically ordered phases in an improper ferroelectric. The antiferromagnetic/paraelectric to antiferromagnetic/ferroelectric phase transition in Cu$_{1-x}$Zn$_{x}$O ($x=0, 0.05$) alloys was tracked via the electromagnon response using terahertz time-domain spectroscopy, on heating and cooling through the phase transition. The transition was found to exhibit thermal hysteresis, confirming its first-order nature, and to broaden under the influence of spin-disorder upon Zn substitution. The energy of the electromagnon increases upon alloying, as a result of the non-magnetic ions modifying the magnetic interactions that give rise to the multiferroic phase and electromagnons. We describe our findings in the context of recent theoretical work that examined improper ferroelectricity and electromagnons in CuO from phenomenological and first-principles approaches.