Influence of Bi3+ substitution on spin-phonon coupling in La0.7Sr0.3MnO3 Manganites: A Raman spectroscopy study
Anita D. Souza, Shamima Hussain, Sudhindra Rayaprol, Nishkala KR, Vikash Mishra, Mamatha D. Daivajna
Abstract
• To understand the role of Bi 3+ on lattice dynamics and magnetic ground state in La 0.7- x Bi x Sr 0.3 MnO 3 ( x = 0.0 – 0.70) series, Raman spectroscopy was carried out. • The Raman spectra of ferromagnetic La 0.7 Sr 0.3 MnO 3 (i.e., x = 0.0) show rhombohedral symmetry ( D 3 d 6 ), but Bi 3+ substituted samples (i.e., x ≥ 0.30) show the phonon modes corresponding to orthorhombic ( D 2 h 16 ) symmetry. • Phonon modes were theoretically calculated using Quantum expresso code, which matched the observed results. • The variation in the Raman spectra with Bi 3+ substitution suggests a strong influence of lattice distortion on the electrical and magnetic behavior corresponding to structure-property correlation. • Softening of phonon modes across the magnetic ordering temperature indicating the spin-phonon coupling of the system. Interesting structural and physical properties observed in La 0.7- x Bi x Sr 0.3 MnO 3 are attributable to the Bi 3+ concentration ( x ). In order to understand the role played by Bi 3+ substitution in influencing lattice dynamics and magnetic ground state, we carried out Raman spectroscopy studies on a series of La 0.7- x Bi x Sr 0.3 MnO 3 ( x = 0.0 – 0.70) samples. As the Bi 3+ concentration increases from x = 0.0 to 0.30, the magnetic ground state transforms from dominantly ferromagnetic metallic to the coexistence of ferro and antiferromagnetic phases. Correspondingly a significant increase in the number of Raman modes has been noticed, which specifies a transition in the crystal structure. The Raman spectra of ferromagnetic La 0.7 Sr 0.3 MnO 3 (i.e., x = 0.0) has been accounted for considering the rhombohedral symmetry ( D 3 d 6 ). Whereas for Bi 3+ substituted samples (i.e., x ≥ 0.30), the Raman spectra show the phonon modes corresponding to orthorhombic ( D 2 h 16 ) symmetry. To compare with experimental values, theoretical Raman modes were calculated using Quantum Espresso code. The variation in the Raman spectra with Bi 3+ substitution suggests a strong influence of lattice distortion on the electrical and magnetic behavior, highlighting a strong structure-property correlation in the system. Additionally, phonon modes show softening across the magnetic ordering temperature indicating the spin-phonon coupling of the system. The the theortical frame work using Balkanski model confirms the above conclusion.