Spin-phonon coupling in Sr and Ti incorporated 9R-BaMnO3

TL;DR

This study stabilizes the 9R phase of BaMnO3 through Sr and Ti doping, investigates its crystal and phonon properties, and reveals spin-phonon coupling evidenced by anomalous phonon behavior at low temperatures.

Contribution

It demonstrates a novel synthesis method for 9R BaMnO3 at ambient pressure and provides experimental evidence of spin-phonon coupling in doped BaMnO3.

Findings

Stable 9R phase achieved via doping at ambient conditions.

Antiferromagnetic transitions observed at 262 K and 200 K.

Anomalous phonon behavior indicating spin-phonon coupling.

Abstract

Materials having strong coupling between different degrees of freedom such as spin, lattice, orbital, and charge are of immense interest due to their potential device applications. Here, we have stabilized the 9R phase of BaMnO3, by Sr (Ti) doping in the Ba (Mn) site using solid-state route at ambient pressure, which otherwise requires high-pressure conditions to syntheize. Crsyatl structure, phonon spectra, and their evolution with temperature are investigated using x-ray diffraction and Raman spectroscopic techniques. Temperature-dependent magnetization data reveal an antiferromagnetic transition at around (TN =) 262 K and 200 K for Ba0.9Sr0.1MnO3 and BaMn0.9Ti0.1O3, respectively. No structural phase transition or lattice instabilities are observed in the measured temperature range (80 - 400 K) for both the compounds. We have observed anomalous behaviour of four different phonon modes involving Mn or O-vibrations at low temperatures which have been attributed to spin-phonon coupling.