Anisotropic magneto-elastic coupling in the quasi-2D Ising magnet Li2FeSiO4 and thermodynamic signature of low-energy orbital excitations
Abstract
The relevance of spin, lattice and orbital degrees of freedom in the quasi-2D Ising-like magnet Li2FeSiO4 is demonstrated by thermal expansion and specific heat measurements supported by numerical studies. By means of thermodynamic and Grüneisen analysis, we separate the orbital signatures and quantify the energy gap and its pressure dependence from the experimental data as Δ∼ 300 − 350 K and ∂ ln Δ/∂ pc ≈ −4.6 %/GPa). Both values excellently agree with the theoretical DFT predictions. The thermal expansion anomalies associated with the onset of long-range magnetic order imply significant magneto-elastic coupling and are used to determine the anisotropic uniaxial strain dependencies of TN. They are dominated by the in-plane (i.e., c axis) response (∂ ln TN )/∂ pc ≃ 15 %/GPa while the (negative) a axis and (positive) out-of-plane (b axis) pressure dependencies are much smaller. Short-range magnetic order extends well above TN but is not driven by the same energy scale as TN as evidenced by the observation of non-monotonic in-plane distortion, sign-change of the Grüneisen parameter, and failure of Grüneisen scaling.
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BibTeX
@misc{hergett2026anisotropic,
title = {{Anisotropic magneto-elastic coupling in the quasi-2D Ising magnet Li$_2$FeSiO$_4$ and thermodynamic signature of low-energy orbital excitations}},
author = {Waldemar Hergett and Kevin Ackermann and Sven Spachmann and Martin Jonak and Mahmoud Abdel-Hafiez and Hend Shahed and Michael Merz and Maurits W. Haverkort and Rüdiger Klingeler},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.35341},
eprint = {2610.35341},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.35341},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Anisotropic magneto-elastic coupling in the quasi-2D Ising magnet Li_2FeSiO_4 and thermodynamic signature of low-energy orbital excitations
AU - Waldemar Hergett
AU - Kevin Ackermann
AU - Sven Spachmann
AU - Martin Jonak
AU - Mahmoud Abdel-Hafiez
AU - Hend Shahed
AU - Michael Merz
AU - Maurits W. Haverkort
AU - Rüdiger Klingeler
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2610.35341
UR - https://arxiv.org/abs/2610.35341
AB - The relevance of spin, lattice and orbital degrees of freedom in the quasi-2D Ising-like magnet Li_2FeSiO_4 is demonstrated by thermal expansion and specific heat measurements supported by numerical studies. By means of thermodynamic and Grüneisen analysis, we separate the orbital signatures and quantify the energy gap and its pressure dependence from the experimental data as Δ∼ 300 − 350 K and ∂ ln Δ/∂ p_c ≈ −4.6 %/GPa). Both values excellently agree with the theoretical DFT predictions. The thermal expansion anomalies associated with the onset of long-range magnetic order imply significant magneto-elastic coupling and are used to determine the anisotropic uniaxial strain dependencies of T_N. They are dominated by the in-plane (i.e., c axis) response (∂ ln T_N )/∂ p_c ≃ 15 %/GPa while the (negative) a axis and (positive) out-of-plane (b axis) pressure dependencies are much smaller. Short-range magnetic order extends well above T_N but is not driven by the same energy scale as T_N as evidenced by the observation of non-monotonic in-plane distortion, sign-change of the Grüneisen parameter, and failure of Grüneisen scaling.
ER -