Unveiling Lattice Dynamics and a Hidden Structural Transition in the 2D Ferromagnet AgVP2Se6 via Raman Spectroscopy
Abstract
Transition-metal chalcophosphates (TMCs) are two-dimensional (2D) van der Waals materials supporting a broad range of electronic and magnetic properties. Among quaternary TMCs, AgVP2Se6 is a rare ferromagnet (FM) with a triangular V sublattice, in contrast to the antiferromagnetic (AFM) zigzag chains of the sulfide AgVP2S6. Prior Raman studies of AgVP2Se6 have been performed far above the Curie temperature (TC), preventing studies of spin-phonon coupling. Here, we report polarization-resolved, temperature-dependent Raman and magneto-Raman spectroscopy of AgVP2Se6 single crystals grown by chemical vapor transport (CVT) and flux methods, across the FM transition, complemented by density functional theory (DFT) calculations of phonon, optical and magnetic properties. Cryogenic Raman spectra resolve up to thirty peaks, while angle-resolved measurements enable their symmetry assignment. Spectral differences between CVT- and flux-grown crystals are traced back to the presence of different interlayer stacking domains in these samples. Temperature- and field-dependent Raman spectra remain largely unchanged across TC, suggesting weak spin-phonon coupling. However, pronounced spectral alterations near 100 K suggest a potential structural phase transition. Our DFT calculations further reconcile the large discrepancy between the transport activation gap (≈ 0.325 eV) and optical absorption edge (≈ 2.14 eV), attributing the former to a transition to the V-d upper Hubbard band that is optically dark but thermally accessible. We also suggest a theoretical explanation of the qualitative difference (reproduced by DFT calculations) between the magnetic properties of the sulfide and selenide. These results provide key information regarding the lattice dynamics of AgVP2Se6 and will guide future applications in spin-based electronics.
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BibTeX
@misc{pham2026unveiling,
title = {{Unveiling Lattice Dynamics and a Hidden Structural Transition in the 2D Ferromagnet AgVP$_2$Se$_6$ via Raman Spectroscopy}},
author = {Thi Hai Yen Pham and Po-hao Chang and Aidan C. Malloy and Seng Huat Lee and Zhiqiang Mao and Maria F. Munoz and Riccardo Torsi and Angela R. Hight Walker and Igor Mazin and Patrick M. Vora},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.33116},
eprint = {2609.33116},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.33116},
}
RIS
TY - UNPB
TI - Unveiling Lattice Dynamics and a Hidden Structural Transition in the 2D Ferromagnet AgVP_2Se_6 via Raman Spectroscopy
AU - Thi Hai Yen Pham
AU - Po-hao Chang
AU - Aidan C. Malloy
AU - Seng Huat Lee
AU - Zhiqiang Mao
AU - Maria F. Munoz
AU - Riccardo Torsi
AU - Angela R. Hight Walker
AU - Igor Mazin
AU - Patrick M. Vora
PY - 2026
DA - 2026/09/27
PB - arXiv
DO - 10.48550/arxiv.2609.33116
UR - https://arxiv.org/abs/2609.33116
AB - Transition-metal chalcophosphates (TMCs) are two-dimensional (2D) van der Waals materials supporting a broad range of electronic and magnetic properties. Among quaternary TMCs, AgVP_2Se_6 is a rare ferromagnet (FM) with a triangular V sublattice, in contrast to the antiferromagnetic (AFM) zigzag chains of the sulfide AgVP_2S_6. Prior Raman studies of AgVP_2Se_6 have been performed far above the Curie temperature (T_C), preventing studies of spin-phonon coupling. Here, we report polarization-resolved, temperature-dependent Raman and magneto-Raman spectroscopy of AgVP_2Se_6 single crystals grown by chemical vapor transport (CVT) and flux methods, across the FM transition, complemented by density functional theory (DFT) calculations of phonon, optical and magnetic properties. Cryogenic Raman spectra resolve up to thirty peaks, while angle-resolved measurements enable their symmetry assignment. Spectral differences between CVT- and flux-grown crystals are traced back to the presence of different interlayer stacking domains in these samples. Temperature- and field-dependent Raman spectra remain largely unchanged across T_C, suggesting weak spin-phonon coupling. However, pronounced spectral alterations near 100 K suggest a potential structural phase transition. Our DFT calculations further reconcile the large discrepancy between the transport activation gap (≈ 0.325 eV) and optical absorption edge (≈ 2.14 eV), attributing the former to a transition to the V-d upper Hubbard band that is optically dark but thermally accessible. We also suggest a theoretical explanation of the qualitative difference (reproduced by DFT calculations) between the magnetic properties of the sulfide and selenide. These results provide key information regarding the lattice dynamics of AgVP_2Se_6 and will guide future applications in spin-based electronics.
ER -