Signatures of magnetostriction and spin-phonon coupling in magnetoelectric hexagonal 15R-BaMnO3

TL;DR

This study reveals strong spin-phonon coupling and magnetostriction effects in 15R-BaMnO3, demonstrated through Raman spectroscopy, magnetic measurements, and structural analysis, highlighting their role in the material's magnetoelectric behavior.

Contribution

It provides the first detailed experimental evidence of spin-phonon coupling and magnetostriction in 15R-BaMnO3 using Raman spectroscopy and complementary techniques.

Findings

Renormalization of Raman spectrum at specific temperatures

Appearance of new Raman modes in magnetic phases

Anomalous phonon shifts linked to lattice distortions

Abstract

Spin-phonon coupling, the interaction of spins with surrounding lattice is a key parameter to understand the underlying physics of multiferroics and engineer their magnetization dynamics. Elementary excitations in multiferroic materials are strongly influenced by spin-phonon interaction, making Raman spectroscopy a unique tool to probe these coupling(s). Recently, it has been suggested that the dielectric and magnetic properties of 15R-type hexagonal BaMnO3 are correlated through the spin-lattice coupling. Here, we report the observation of an extensive renormalization of the Raman spectrum of 15R-BaMnO3 at 230 K, 280 K, and 330 K. Magnetic measurements reveal the presence of a long-range and a short-range magnetic ordering in 15R-BaMnO3 at 230 K and 330 K, respectively. The Raman spectrum shows the appearance of new Raman modes in the magnetically ordered phases. Furthermore, an additional Raman phonon appears below ~ 280 K, possibly arising from a local lattice-distortion due to the displacement of Mn-ions, that exhibits anomalous shift with temperature. The origin of the observed renormalization and phonon anomalies in Raman spectra are discussed based on the evidences from temperature- and magnetic-field-dependent Raman spectra, temperature-dependent x-ray diffraction, magnetization, and specific heat measurements. Our results indicate the presence of magnetostriction and spin-phonon coupling in 15R-BaMnO3 thus suggesting that the optical phonons are strongly correlated to its magnetoelectric properties.