Magnetic influence on the frequency of the soft-phonon mode in the incipient ferroelectric EuTiO3

TL;DR

This study investigates how magnetic ordering influences the soft-phonon mode frequency in EuTiO3, revealing a coupling between magnetic spins and dielectric properties that affects phonon behavior under magnetic fields.

Contribution

It introduces a coupling model showing the soft-phonon mode frequency depends on Eu spin correlations and magnetic field, linking magnetism and dielectric response in EuTiO3.

Findings

Soft-phonon mode frequency varies with Eu spin correlations.

Magnetic field significantly alters phonon frequency.

Coupling model explains dielectric-magnetic interaction.

Abstract

The dielectric constant of the incipient ferroelectric EuTiO$_3$ exhibits a sharp decrease at about 5.5K, at which temperature antiferromagnetic ordering of the Eu spins simultaneously appears, indicating coupling between the magnetism and dielectric properties. This may be attributed to the modification of the soft-phonon mode, $T_{1\mu}$, which is the main contribution to the large dielectric constant, by the Eu spins(7$\mu_B$ per Eu). By adding the coupling term between the magnetic and electrical subsystems as $ -g\sum\limits_l {\sum\limits_{< {i,j}} {q_l^2}} \overrightarrow {S_i} \cdot \overrightarrow {S_j} $ we show that the variation of the frequency of soft-phonon mode depends on the spin correlation between the nearest neighbors Eu spins and is substantially changed under a magnetic field.