Influence of quantum fluctuations on the spin-flop transition in hematite

Dannegger, Tobias and Hagymási, Imre and Rózsa, Levente and Nowak, Ulrich (2026) Influence of quantum fluctuations on the spin-flop transition in hematite. PHYSICAL REVIEW RESEARCH, 8 (2). -L022029. ISSN 2643-1564

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Abstract

Magnetic phase transitions between ordered phases are often understood on the basis of semiclassical spin models. Deviations from the classical description due to the quantum nature of the atomic spins as well as quantum fluctuations are usually treated as negligible if long-range order is preserved, and are rarely quantified for actual materials. Here, we demonstrate that a fully quantum-mechanical framework is required for a quantitatively correct description of the spin-flop transition in the insulating altermagnet hematite between the collinear antiferromagnetic and the weakly ferromagnetic spin-flop phase at low temperature. By applying both exact diagonalization and density-matrix renormalization group theory to the quantum Heisenberg Hamiltonian, we show how a quantum-mechanical treatment of an ab initio parametrized spin model can significantly improve the predicted low-temperature spin-flop field over a classical description when compared to measurements. Our results imply that quantum fluctuations have a measurable influence on selecting the ground state of a system out of competing ordered magnetic phases at low temperature. © 2026 authors. Published by the American Physical Society.

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