Coupled Phonons, Magnetic Excitations and Ferroelectricity in AlFeO3: Raman and First-principles Studies

TL;DR

This study investigates the interplay of phonons, magnetic excitations, and ferroelectricity in AlFeO3 through Raman spectroscopy and first-principles calculations, revealing strong spin-phonon coupling and magnetic transition effects.

Contribution

It provides new insights into spin-phonon coupling and magnetic-induced phonon renormalization in AlFeO3 using combined experimental and theoretical approaches.

Findings

Strong spin-phonon coupling observed near Tc ~ 250 K.

Two-magnon Raman scattering appears below Tc.

Weak anomalies indicating a magnetically driven ferroelectric transition at ~ 100 K.

Abstract

We determine the nature of coupled phonons and magnetic excitations in AlFeO3 using inelastic light scattering from 5 K to 315 K covering a spectral range from 100-2200 cm-1 and complementary first-principles density functional theory-based calculations. A strong spin-phonon coupling and magnetic ordering induced phonon renormalization are evident in (a) anomalous temperature dependence of many modes with frequencies below 850 cm-1, particularly near the magnetic transition temperature Tc ~ 250 K, (b) distinct changes in band positions of high frequency Raman bands between 1100-1800 cm-1, in particular a broad mode near 1250 cm-1 appears only below Tc attributed to the two-magnon Raman scattering. We also observe weak anomalies in the mode frequencies at ~ 100 K, due to a magnetically driven ferroelectric phase transition. Understanding of these experimental observations has been possible on the basis of first-principles calculations of phonons spectrum and their coupling with spins.