Ferroelastic altermagnetism

npj | quantum materials Article Published in partnership with Nanjing University https://doi.org/10.1038/s41535-025-00835-7 Ferroelastic altermagnetism Check for updates 1234567890():,; 1234567890():,; Rui Peng1,2, Shibo Fang2, Pin Ho3, Fanxin Liu1, Tong Zhou4 , Junwei Liu5 & Yee Sin Ang2 Combination of altermagnetism and ferroic orders, such as ferroelectric switchable altermagnetism [Phys. Rev. Lett. 134, 106801 (2025) and Phys. Rev. Lett. 134, 106802 (2025)], offers a powerful route to achieve nonvolatile switching of altermagnetic spin splitting. In this work, by synergizing altermagnetism and ferroelasticity, we propose the concept of ferroelastic altermagnets in which the ferroelastic crystal reorientation can drive multistate nonvolatile switching of the altermagnetic spin splitting via altermagnetoelastic effect. Using monolayers RuF4 and CuF2 as material candidates, we demonstrate 2-state and 3-state altermagnetic spin splitting switching as driven by ferroelastic strain states. Transport calculation shows that multistate spin conductivities can be ferroelastically encoded in ferroelastic altermagnets, thus suggesting the potential of ferroelastic altermagnets as nonvolatile nanomechanical spin switches. The proposed concept of ferroelastic altermagnetism enriches the emerging landscape of multiferroic altermagnetism and shall pave a way towards straintronicspintronic device applications. Together with ferromagnets (FM) and conventional antiferromagnets (AFM), altermagnets represent an emerging new family of collinear magnetic materials1–5. Altermagnets exhibit zero net magnetization like conventional AFM, but host nonrelativistic band spin splitting like FM. Such FM-AFM dichotomy endows altermagnets with the advantages of AFM such as robustness against external fields and compatible with ultrahighspeed device operation, while still exhibiting broken spin degeneracy of FM, which are critical for spin manipulation and information processing6–24. Altermagnets exhibit a plethora of intriguing physical phenomena such as spin current generation1,2, spin Hall effect6, spin Nernst effect7, anomalous Hall effect5, tunneling magnetoresistance effects6, and proximity effect25, which can be harnessed for various device applications. A large variety of altermagnets have been theoretically proposed3,4,17,26, and some of them have been experimentally confirmed27–30. The physics of altermagnets can be further enriched by multiferroicity. Multiferroics are singular materials that exhibit two or more ferroic orders among (anti)ferromagnetism, (anti)ferroelectricity and (anti) ferroelasticity31–39. For instance, the coupling between ferroelectricity and magn etism yields magnetoelectric effect where ferroelectric polarization and magnetization are coupled and can be mutually switched. Recent studies have unveiled the altermagnetic counterpart of magnetoelectric effect, namely the altermagnetoelectric effect [Fig. 1a] in which the altermagnetic spin splitting can be tuned by various forms of ferroelectric switching40–48, thus unveiling a route towards electrical-based nonvolatile switching of altermagnetism. The multiferroic integration of ferroelectricity and altermagnetism immediately raises the following question: Can altermagnetism be integrated with ferroelasticity49–53—magnetoelastic effect—to achieve nonvolatile nanomechanical deformation-induced switching of the altermagnetic spin splitting? Here we propose the concept of ferroelastic altermagnetism in which altermagnetism and ferroelasticity are synergized. As ferroelastic switching is equivalent to a rotation operation on the lattice, such lattice rotation changes the spin-momentum coupling in a ferroelastic altermagnet, thus enabling an altermagnetoelastic effect in which the altermagnetic spin splitting can be mechanically switched [Fig. 1b, c]. Using monolayers RuF4 and CuF2 as proof-of-concept, 2-state and 3-state nonvolatile switching of the altermagnetic spin splitting are demonstrated, respectively, via first-principles calculations. We further show that the multistate ferroelastic switching lead to nonvolatile switchable spin transport. These findings reveal a previously unexplored mechanism to achieve nonvolatile strain-based altermagnetic switching that enables multistate nonvolatile information encoding. Ferroelastic altermagnetism represents a mechanical multiferroic counterpart of the recently proposed ferroelectric altermagnetism40–45. In ferroelectric altermagnets, the reversal of electric polarization switches the altermagnetic spin splitting via internal electric-field control of the electronic structure, typically resulting in binary switching. In contrast, ferroelastic altermagnets utilize lattice reorientation to modify the altermagnetic symmetry, allowing multistate and mechanically driven nonvolatile control. Such strain-driven manipulation is particularly appealing for integrating altermagnetism into straintronic–spintronic platforms, where mechanical deformation can directly encode spin- 1 School of Physics, Zhejiang University of Technology, Hangzhou, China. 2Science, Mathematics and Technology (SMT) Cluster, Singapore University of Technology and Design (SUTD), Singapore, Singapore. 3Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Singapore. 4Eastern Institute for Advanced Study, Eastern Institute of Technology, Ningbo, Zhejiang, China. 5Hong Kong University of e-mail: ; ; Science and Technology, Hong Kong SAR, China. npj Quantum Materials | (2026)11:5 1 https://doi.org/10.1038/s41535-025-00835-7 Article Fig. 1 | Concept of ferroelastic altermagnetism. a Ferroelastic altermagnets arise in a material where altermagnetism and ferroelasticity are simultaneously present. Schematic diagram of b 2-state and c 3-state nonvolatile mechanical switching of the altermagnetic spin splitting in two-dimensional ferroelastic altermagnets. M is the mirror symmetry axis of the systems. dependent functionalities. Notice that the piezomagnetic effect describes the linear coupling between magnetization (M) and stress (σ), or conversely, between strain (ε) and a magnetic field (H), expressed as Mi = Qijkσjk or εjk = QijkHi2. In contrast, the magnetoelastic effect investigated in this work operates through a fundamentally different, nonlinear mechanism. Here, an applied stress does not primarily induce magnetization via a linear response but instead drives a ferroelastic phase transition, which in turn alters the altermagnetic order and the spin splitting, ultimately leading to the generation of spin currents with varying magnitudes and directions. Consequently, the relationship between stress and the altermagnetic order is nonlinear, governed by: F = Bijkl (MiMj) εkl, where F is free energy. monolayers RuF4 and CuF2 are confirmed by phonon and ab initio molecular dynamics simulations (Fig. S158). Under the octahedral crystal (...truncated)