[Paper Review] Coupling between phonons and magnetic excitations in orthorhombic Eu_{1-x}Y_xMnO_3

J. Agostinho Moreira, A. Almeida+5 more|ArXiv.org|Mar 27, 2009

Magnetic and transport properties of perovskites and related materials3 citations

TL;DR

This study investigates spin-phonon coupling in orthorhombic Eu₁₋ₓYₓMnO₃ through temperature-dependent Raman spectroscopy, revealing that Y-doping induces structural distortions via cooperative Jahn-Teller and rotational effects. A pronounced frequency renormalization of the B1g symmetric MnO6 stretching mode at x=0.2 indicates dominant ferromagnetic interactions, with shifts persisting above the Néel temperature, providing strong evidence for dynamic spin-phonon coupling.

ABSTRACT

In this work we present a detailed study of the structural and lattice dynamic properties of Y-doped EuMnO3 ceramics (Eu1-xYxMnO3, with 0

Motivation & Objective

• To understand the structural and lattice dynamic properties of Y-doped EuMnO3 (Eu₁₋ₓYₓMnO₃) across varying Y-concentrations.
• To correlate structural distortions with Raman mode parameters in orthorhombic MnO₆ octahedra.
• To investigate the origin of anomalous phonon frequency shifts in relation to magnetic interactions.
• To provide evidence for spin-phonon coupling by analyzing temperature-dependent phonon behavior above the Néel temperature.

Proposed method

• Temperature-dependent Raman spectroscopy was used to probe lattice dynamics in Y-doped EuMnO₃ ceramics with x ≤ 0.55.
• Analysis of the B1g symmetric stretching mode of MnO₆ units revealed frequency shifts deviating from anharmonic behavior.
• Structural distortions were attributed to cooperative Jahn-Teller and rotational effects in the MnO₆ octahedra.
• The competition between ferromagnetic and antiferromagnetic interactions was inferred from phonon frequency renormalization trends.
• Phonon behavior above the Néel temperature was analyzed to detect coupling with dynamical magnetic fluctuations.
• Correlation between experimental phonon shifts and measured spontaneous magnetization was used to validate magnetic interaction dominance.

Experimental results

Research questions

• RQ1 How do Y-doping and structural distortions affect the lattice dynamics in orthorhombic Eu₁₋ₓYₓMnO₃?
• RQ2 What causes the observed frequency renormalization of the B1g MnO₆ stretching mode, particularly at x=0.2?
• RQ3 To what extent do ferromagnetic and antiferromagnetic interactions compete in determining phonon behavior?
• RQ4 Is there evidence of spin-phonon coupling in the paramagnetic phase above the Néel temperature?
• RQ5 How do the structural distortions (Jahn-Teller and rotational) correlate with the observed phonon anomalies?

Key findings

• The B1g symmetric stretching mode of MnO₆ units exhibits frequency shifts that deviate from pure anharmonic temperature dependence, depending on Y-concentration.
• At x=0.2, a pronounced frequency renormalization indicates a dominance of ferromagnetic over antiferromagnetic interactions.
• The observed frequency shifts persist above the Néel temperature, suggesting coupling with dynamical magnetic fluctuations.
• The structural distortions in MnO₆ octahedra arise from a cooperative interplay of Jahn-Teller and rotational effects.
• The correlation between phonon renormalization and measured spontaneous magnetization supports the existence of strong spin-phonon coupling.
• The results provide direct evidence for spin-phonon coupling in orthorhombic Eu₁₋ₓYₓMnO₃, particularly in the paramagnetic regime.