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Destabilization of local magnetic anisotropy in heavy-fermion compounds

Ewan Scott ^1,* and Michal Kwasigroch ^1,2

¹Department of Mathematics, University College London, Gordon Street, London WC1H 0AY, United Kingdom
²Trinity College, Cambridge CB2 1TQ, United Kingdom

^*Contact author: ewan.scott.18@ucl.ac.uk

Phys. Rev. Research 7, 043225 – Published 1 December, 2025

DOI: https://doi.org/10.1103/7zsl-4497

Abstract

The local magnetic anisotropy of a typical crystalline compound is usually attributed to the combined effect of crystal electric fields and spin-orbit coupling. We show that this simple local picture is transformed in heavy-fermion compounds by the development of coherent electron scattering from local spin degrees of freedom. Provided the dominance of the coherence energy scale over the magnetic energy scale is strong enough, the fractionalization and delocalization of the spins destabilizes their single-ion anisotropy by generating an opposing anisotropy in the exchange. Experimentally, this can manifest as competing splittings in the Curie-Weiss constants and effective moments. We show that in the presence of orthorhombic or tetragonal symmetry, the destabilization of the anisotropy can result in either ferromagnetic or antiferromagnetic order that is perpendicular to the high-temperature easy axis. In the absence of destabilization, we show that the order is more likely to be antiferromagnetic. In agreement with our theory, we also observe that the temperature at which the anisotropy of the uniform magnetic response changes tracks the coherence energy scale in a wide range of actinide and lanthanide compounds.

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Phys. Rev. Research 7, 043225– Published 1 December, 2025

Vol. 7, Iss. 4 — December - December 2025

Received 3 October 2024
Revised 3 August 2025
Accepted 26 September 2025

DOI: https://doi.org/10.1103/7zsl-4497

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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Destabilization of local magnetic anisotropy in heavy-fermion compounds

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