The piezomagnetic effect refers to the induction of ferromagnet-like magnetization through the application of mechanical strain to a magnetically compensated system. It is regarded as the magnetic analogue of the piezoelectric effect, where strain induces electric polarization in dielectric materials. Although the phenomenon has been recognized for several decades, examples of piezomagnetism have been limited, with most studies attributing its origin to relativistic mechanisms, particularly spin–orbit coupling, which alters magnetic anisotropy under strain. More recently, however, it has been recognized that certain antiferromagnets can exhibit spin splitting in their electronic bands without relying on spin-orbit coupling. This development opens new opportunities, including the generation of spin currents under an applied electric field. These systems, which are distinct from conventional antiferromagnets, have been termed altermagnets. Their unique symmetry and band structures have garnered increasing attention, especially in relation to potential technological applications, including the prospect of unconventional piezomagnetism.

This study investigates the organic conductor κ-(BEDT-TTF)₂Cu[N(CN)₂]Cl, a strongly correlated material historically regarded as a conventional antiferromagnet but recently identified as a candidate altermagnet. We employ first-principles calculations in combination with effective Hubbard and Heisenberg models under monoclinic strain to evaluate their structural and electronic responses. Our analysis reveals that, in the altermagnetic insulating phase, a uniform magnetization emerges below the Néel temperature when strain is applied. This magnetization arises from the cooperative effects of strain-induced asymmetry in exchange interactions among parallel spins and thermal spin fluctuations, demonstrating that the piezomagnetic effect can occur in organic conductors where spin–orbit coupling is negligible. Furthermore, in the electron-doped altermagnetic metallic state, the presence of “s-wave”-type spin-split Fermi surfaces leads to a finite piezomagnetic response even at absolute zero. The study also demonstrates that both the applied strain amplitude and the multi-orbital character of the molecular dimers strongly influence the overall induced magnetization.

These findings reveal a new avenue for magnetic responses in organic conductors and underscore the potential of organic magnets as a versatile platform for future spintronics applications and the design of functional materials.

(Written by Makoto Naka on behalf of all the authors)

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