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Magnetoelastic-coupling-assisted first-order antiferromagnetic transitions in the corrugated honeycomb-lattice compounds $(Ca, Sr) {Mn}_{2} P_{2}$

Santanu Pakhira ^1,2,*, Liran Wang ², N. S. Sangeetha ³, Aashish Sapkota ⁴, Teslin R. Thomas³, Andreas Kreyssig ³, Frédéric Hardy², Anna E. Böhmer ³, Christoph Meingast² et al.

David C. Johnston ^4,5

¹Department of Physics, Maulana Azad National Institute of Technology Bhopal 462003, India
²Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
³Experimental Physics IV, Ruhr University Bochum, 44801 Bochum, Germany
⁴Ames National Laboratory, Iowa State University, Ames, Iowa 50011, USA
⁵Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA

^*Contact author: spakhira.phy@gmail.com

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Phys. Rev. B 112, 104443 – Published 29 September, 2025

DOI: https://doi.org/10.1103/x3t1-np4q

Abstract

Understanding the origin of unconventional magnetic order is a central theme in the research field of functional quantum materials for spin-dependent applications. In general, a paramagnetic (PM) to antiferromagnetic (AFM) transition is of thermodynamically second order in nature in the absence of a magnetic field. In the magnetically frustrated corrugated-honeycomb lattice compounds $(Ca, Sr) {Mn}_{2} P_{2}$ , electrical resistivity $ρ$ measurements in the $a b$ plane are reported to exhibit sharp discontinuities at the respective PM to AFM ordering temperatures $T_{N} = 69.5$ and 53 K, respectively, signifying the unusual first-order nature of the AFM transition. To reveal the origin of such anomalous transitions, high-resolution linear thermal-expansion measurements are reported for both ${CaMn}_{2} P_{2}$ and ${SrMn}_{2} P_{2}$ in the $a b$ plane and along the $c$ axis using capacitance dilatometry. The thermal expansion measurements show a sharp discontinuity in $Δ L / L$ at $T_{N}$ , yielding a diverging behavior in the thermal expansion coefficient $α (T)$ associated with strong magnetoelastic coupling, driving the first-order AFM transition in ${CaMn}_{2} P_{2}$ . However, this effect is weaker in ${SrMn}_{2} P_{2}$ , consistent with the magnetic entropy changes $S (T)$ obtained from the heat-capacity measurements. Temperature-dependent $a b$ -plane x-ray diffraction measurements for ${CaMn}_{2} P_{2}$ near its $T_{N}$ yield a volume thermal expansion coefficient consistent with literature data for other materials. The uniaxial pressure derivatives of $T_{N}$ in the two compounds are found to be respectively opposite in sign, presumably due to the different magnetic structures.

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Phys. Rev. B 112, 104443– Published 29 September, 2025

Vol. 112, Iss. 10 — 1 September 2025

Received 28 January 2025
Revised 10 July 2025
Accepted 3 September 2025

DOI: https://doi.org/10.1103/x3t1-np4q

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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Magnetoelastic-coupling-assisted first-order antiferromagnetic transitions in the corrugated honeycomb-lattice compounds $(Ca, Sr) {Mn}_{2} P_{2}$

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Magnetoelastic-coupling-assisted first-order antiferromagnetic transitions in the corrugated honeycomb-lattice compounds (Ca,Sr)Mn2P2

Abstract

Physics Subject Headings (PhySH)

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References (20)

Magnetoelastic-coupling-assisted first-order antiferromagnetic transitions in the corrugated honeycomb-lattice compounds $(Ca, Sr) {Mn}_{2} P_{2}$