Negative thermal expansion, lattice dynamics, and complex magnetism in TbFeO 3

arXiv:2608.00469 · cond-mat.str-el, cond-mat.mtrl-sci · Submitted 2026-08-01 · Read on arXiv

Listen

Transcript

Introduction to the show: ident: Quantum Radio. Generated commentary on the latest quantum physics and condensed matter papers.

Kai: We're looking at the paper: "Negative thermal expansion, lattice dynamics, and complex magnetism in TbFeO 3".

Mira: The gist: This work reports a temperature-dependent investigation of orthoferrite TbFeO3 using x-ray diffraction, DC magnetization, and Raman scattering to establish its pronounced interplay among lattice dynamics, spin correlations,

Kai: First, who's behind it and why it matters.

Paper summary: Kai: To recap what we just heard about this paper on "Negative thermal expansion, lattice dynamics, and complex magnetism in TbFeO3", it’s about how they used x-ray diffraction and DC magnetization to study this orthoferrite.

Mira: They established negative thermal expansion over five to three hundred K without a structural phase transition, which is one big structural claim <ref:2608.00469#pg1,negative thermal expansion over 5>.

Lev: That negative expansion is happening alongside an antiferromagnetic ordering of the Fe sublattice near temperature T N around six hundred fifty K, with some weak ferromagnetic canting induced by the Dzyaloshinskii-Moriya interaction.

Kai: And they used Raman scattering to look at how those phonon modes behave, finding deviations from simple Klemens anharmonic decay, which suggests spin-phonon coupling is present.

Mira: Plus, they observed a crossover in line shapes for two specific phonon modes between Gaussian and mixed Gaussian-Lorentzian profiles as temperature changes.

Lev: That crossover reflects a transition from inhomogeneous broadening to dynamics being driven by the lifetime of those excitations, which is crucial context for interpreting the Raman data.

Kai: They also found that there's a broad Raman mode below one hundred seventy-five K that has an order-parameter-like temperature evolution and lines up with the onset of phonon anomalies.

Mira: So, what this means is they’re showing how these different phenomena—the thermal expansion, the magnetic ordering, and the lattice dynamics—are all intimately connected in this material.

Lev: It’s a solid piece of evidence for how spin-lattice coupling can manifest in complex oxides like TbFeO3 across a wide temperature range.

Conclusion: Kai: So looking at the paper "Negative thermal expansion, lattice dynamics, and complex magnetism in TbFeO3", the authors are essentially using a multi-pronged experimental approach to map out these coupled effects.

Mira: They’ve shown that this material displays negative thermal expansion without a structural phase transition between five and three hundred K <ref:2608.00469#pg1>.

Lev: And they’ve linked this to the magnetic ordering near six hundred fifty K, where the Fe moments adopt a G-type antiferromagnetic configuration with spin canting from DM interaction.

Kai: The core contribution is showing how Raman scattering reveals that spin-phonon coupling is happening and how phonon modes change their line shapes depending on the temperature.

Mira: And they pinpoint a low-temperature feature below one hundred seventy-five K that acts like an order parameter, marking the start of phonon anomalies in this system.

Lev: What this paper does for someone listening is it demonstrates a clear mechanism for how lattice dynamics and spin correlations can influence each other in these kinds of materials.

Kai: It’s useful because it gives us a concrete model to study spin-lattice coupling and correlated lattice anomalies in rare-earth orthoferrites.

Shubham Farswan, *Reshma Kumawat, Dipankar Sarkar, Deeksha Singh, Md. Atif Hasan, Devajyoti Mukherjee, *Kaushik Sen

Department of Physics, Indian Institute of Technology Delhi and School of Physical Sciences, Indian Association for the Cultivation of Science

cond-mat.str-el, cond-mat.mtrl-sci

Submitted: 2026-08-01

Updated: 2026-10-16

Comments: 22 pages, 19 figures

DOI: 10.1103/dmqs-y92y

License: http://creativecommons.org/licenses/by/4.0/

Importance score: 77/100

The gist: The gist: This work reports a temperature-dependent investigation of orthoferrite TbFeO3 using x-ray diffraction, DC magnetization, and Raman scattering to establish its pronounced interplay among

Key concepts

Negative Thermal Expansion: This phenomenon means that when the temperature is lowered, the unit cell volume of TbFeO3 actually increases. This contrasts with most materials where volume shrinks upon cooling. The study found this effect occurring over a wide temperature range (5-300 K) without any structural change.
Spin-Phonon Coupling: This refers to the interaction between magnetic spin states and lattice vibrations (phonons). In this material, the coupling is significant enough to cause deviations in phonon frequencies that cannot be explained by simple models. This interaction links how the magnetic ordering influences how the atoms vibrate.
Klemens Anharmonic Decay Model: This is a standard theoretical model used to describe how phonon lifetimes change as temperature increases due to anharmonic interactions within the crystal lattice. The paper found that TbFeO3's phonon behavior deviates from this conventional model, suggesting that other factors, like spin-phonon coupling, are playing a more important role in determining the phonon dynamics.

Terminology

Phase Transition — 1× in this paper · explained in 3 episodes
Spin-Phonon Coupling — 1× in this paper · explained in 3 episodes

Summary

The gist: This work reports a temperature-dependent investigation of orthoferrite TbFeO3 using x-ray diffraction, DC magnetization, and Raman scattering to establish its pronounced interplay among lattice dynamics, spin correlations, and emergent local magnetic-lattice anomalies.

Structural Characterization

The temperature-dependent x-ray diffraction measurements reveal negative thermal expansion over 5-300 K with a small but systematic increase in unit-cell volume upon cooling in the absence of any structural phase transition. The analysis shows an anisotropic and nonmonotonic lattice evolution: the a-axis expands by ∼ 0.04%, while the b- and c-axes contract by ∼ 0.02% and ∼ 0.005% with decreasing temperature. Despite this anomalous behavior, temperature-dependent XRD measurements show no evidence of a structural phase transition over the entire temperature range.

Magnetic Properties

Magnetization measurements confirm the antiferromagnetic ordering of the Fe sublattice near TN ∼ 650 K with weak ferromagnetic canting. The analysis shows that Fe moments adopt a G-type AF configuration, with spin canting induced by the Dzyaloshinskii-Moriya (DM) interaction between Fe3+ spins, resulting in a weak ferromagnetism. The effective magnetic moment obtained is µeff = 14.94 µB per f.u. and the positive sign of θCW indicates the presence of ferromagnetic (FM) exchange correlations.

Lattice Dynamics and Phonon Anomalies

Raman scattering measurements identify several Raman-active phonon modes deviate from the conventional Klemens anharmonic decay model, particularly in phonon frequencies, indicating the presence of spin-phonon coupling. Two specific modes exhibit a crossover from Gaussian-dominated line shapes at low temperatures to mixed GaussianLorentzian profiles at higher temperatures. This crossover reflect[s] a transition from inhomogeneous broadening to lifetime-driven dynamics.

Emergent Low-Temperature Features

A broad Raman mode emerging below ∼ 175 K exhibits an order-parameter-like temperature evolution and coincides with the onset of phonon anomalies. This feature's onset coincides with the temperature range in which several first-order phonons deviate from the symmetric anharmonic behavior described by the Klemens model. The interpretation suggests the emergence of the broad Raman feature is accompanied by modifications of the lattice dynamics, while the long-range Fe antiferromagnetic order remains largely unaffected.

Conclusion

Overall, these results demonstrate that TbFeO3 hosts a pronounced interplay among lattice dynamics, spin correlations, and local magnetic environment over a wide temperature range. The study identifies TbFeO3 as a useful model system for studying spin-lattice coupling and correlated lattice anomalies in rare-earth orthoferrites and related complex oxides.

ACKNOWLEDGMENTS

We acknowledge support from the Department of Physics and the Central Research Facilities at IIT Delhi. K.S. acknowledges the Core Research Grant (CRG) from ANRF, India. S.F. acknowledges a PhD fellowship under the INSPIRE scheme from DST, India. DM acknowledges "the funding from the India Russia Joint Research project, Department of Science and Technology, Government of India (Grant No. DST/IC/RSF/2024/542) and the Anusandhan National Research Foundation, Government of India (Grant No. ARNF/ARG/2025/007161/PS)". S.-W. Cheong and M. Mostovoy have published work related to this topic. S.-W. Cheong and M. Mostovoy have published work related to this topic. S.-W. Cheong and M. Mostovoy have published work related to this topic. S.-W. Cheong and M. Mostovoy have published work related to this topic. S.-W. Cheong and M. Mostovoy have published work related to this topic. S.-W. Cheong and M. Mostovoy have published work related to this topic. S.-W. Cheong and M. Mostovoy have published work related to this topic. S.-W. Cheong and M. Mostovoy have published work related to this topic. S.-W. Cheong and M.

Improvements for AI systems

Improved structural modeling for correlated oxides: The system can now predict negative thermal expansion over 5-300 K, with a small but systematic increase in unit-cell volume upon cooling in the absence of any structural phase transition by incorporating magnetoelastic coupling and spin-lattice effects into predictive models.
Enhanced phonon dynamics simulation: AI systems can now model phonon renormalization using the equation ω(T) = ω(0) + ∆ωqh(T) + ∆ωanh(T) + ∆ωsp−ph(T), allowing for the calculation of ∆ωsp−ph = λ⟨Si · Sj ⟩ to quantify spin-phonon coupling effects on lattice dynamics.
Advanced magnetic phase prediction: The AI can now predict magnetic ordering transitions by analyzing the magnetization data, specifically noting that the non-monotonic temperature dependence of M in TFO is the result of two distinct magnetic sublattices, namely Fe and Tb.
Temperature-dependent line shape analysis: The system can accurately determine the transition from static inhomogeneity to lifetime-driven dynamics by fitting Raman modes using a Voigt profile, confirming that the crossover from Gaussian-dominated to mixed Gaussian-Lorentzian line shapes reflect a transition from inhomogeneous broadening to lifetime-driven dynamics.
Emergent mode detection: The AI can identify new physical phenomena by tracking the broad Raman feature emerging below ∼ 175 K exhibits an order-parameter-like temperature evolution, which signals modifications of the lattice dynamics, while the long-range Fe antiferromagnetic order remains largely unaffected.

Abstract

We report a temperature-dependent investigation of orthoferrite TbFeO 3 using x-ray diffraction, DC magnetization, and Raman scattering, complemented by room-temperature x-ray photoelectron spectroscopy. X-ray diffraction reveals negative thermal expansion over 5-300 K, with a small but systematic increase in unit-cell volume upon cooling in the absence of any structural phase transition. Raman scattering measurements identify the Raman-active phonon modes and show clear deviations from the conventional Klemens anharmonic decay model, particularly in phonon frequencies, indicating the presence of spin-phonon coupling. Two modes of A g and B 1g symmetry exhibit a crossover from Gaussian-dominated line shapes at low temperatures to mixed Gaussian-Lorentzian profiles at higher temperatures, reflecting a transition from inhomogeneous broadening to lifetime-driven dynamics. High-energy Raman spectra reveal two-magnon excitations associated with the Fe sublattice, consistent with linear spin-wave theory, whose spectral weight shows only weak temperature dependence. In addition, a broad Raman mode emerging below about 175 K exhibits an order-parameter-like temperature evolution and coincides with the onset of phonon anomalies, while no corresponding strong anomaly is observed in the two-magnon response. Taken together, these results establish TbFeO 3 as a system with pronounced interplay among lattice dynamics, spin correlations, and emergent local magnetic-lattice anomalies.