Investigating the competition between ferroelectric ordering and quantumfluctuations is essential to tailor the desired functionalities of mixed ferroelectric and incipient ferroelectric systems, like, (Ba,Sr)TiO3 and (Eu,Ba)TiO3. Recently, it has been shown that suppression of quantum fluctuations increases ferroelectric ordering in (Eu,Ba)TiO3 and since these phenomena are coupled to crystallographic phase transitions it is essential to understand the role of phonons. Here, we observe that the unusual temperature dependence of phonons in BaTiO3 gets suppressed when Ba 2+ is replaced by Eu 2+ . This manifests in a decrease in the cubic-to-tetragonal (i.e., para-to-ferroelectric) phase transition temperature (by 150 K) and a complete suppression of tetragonality of the lattice (at room temperature by 40% replacement of Ba 2+ by Eu 2+ ). We have quantified the anharmonicity of the phonons and observed that the replacement of Ba 2+ by Eu 2+ suppresses it (by 93%) with a resultant lowering of the ferroelectric ordering temperature in the EuxBa1-xTiO3. This suggests that tuning phonon anharmonicity can be an important route to novel ferroelectric materials.

Coupling of material properties provides new fundamental insights and possibilities toward multifunctional devices. The spinel structures display strong coupling between different order parameters, as a consequence, exhibiting many fascinating properties like multiferroicity, superconductivity etc. Here, we have investigated structural, magnetic, and vibrational properties of mixed-spinel CoMn2O4, stabilized in distorted tetragonal structure as evidenced from X-ray diffraction measurements. Magnetization measurements reveal two ferrimagnetic phase transitions at 185 K and 90 K. Raman scattering measurements reveal the renormalization of phonon parameters for a few phonon modes at low temperatures, arising from spin-phonon coupling. The obtained value for λS2 is ~ 2 cm-1. The strength of the spin-phonon coupling (λ) is estimated according to the spins involved in corresponding lattice vibrations and discussed.

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 latticedistortion 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.

Here we have investigated the role of electron phonon coupling on the Raman spectrum of narrow bandgap semiconductors APd3O4 (A = Ca, Sr) and hole-doped system Sr0.85Li0.15Pd3O4. Four Raman active phonons are observed at room temperature for all three compounds as predicted by factor group analysis. The lowest energy phonon (∼190/202 cm−1) associated with Pd vibrations is observed to exhibit an asymmetric Fano-like lineshape in all the three compounds, indicating the presence of an interaction between the phonon and the electronic continuum. The origin of the electronic continuum states and electron–phonon coupling are discussed based on our laser power- and temperature-dependent Raman results. We have observed an enhanced strength of electron–phonon coupling in Sr0.85Li0.15Pd3O4 at low temperatures which can be attributed to the metallicity in this doped compound.

No abstract