SPICE Workshop on Chiral Phonons, July 29th - 31st 2025
Jonas Fransson
Recent experiments suggest that the conditions for ferromagnetic order in, e.g., magnetite, can be modified by adsorption of chiral molecules. Especially, the coercivity of magnetite was increased by nearly 100 %, or 20 times the earth magnetic flux density, at room temperature. The coercivity was, moreover, demonstrated to increase linearly with temperature in a finite range around room temperature. Based on these results, a mechanism is proposed for providing the necessary enhancement of the magnetic anisotropy. It is shown that nuclear vibrations (phonons) coupled to ferromagnetic spin excitations (magnons) absorb the thermal energy in the system, thereby diverting the excess energy that otherwise would excite magnons in the ferromagnet. This energy diversion, not only restores the ferromagnetic order but also enhances its stability by increasing the anisotropy energy for magnon excitations. The coupling between phonons with magnons is enabled by chirality due to the lack of inversion symmetry.
Relevant literature:
• Non-classical Temperature Dependence of Chirality-Induced Magnetization and Its Implications for RNA’s Homochirality, Y. Kapon, L. Brann, S. Yochelis, J. Fransson, D. D. Sasselov, Y. Paltiel, and S. F. Ozturk, arXiv:2412.05720
• Chiral Phonons Enhance Ferromagnetism, J. Fransson, Y. Kapon, L. Brann, S. Yochelis, D. D. Sasselov, Y. Paltiel, and S. F. Ozturk, J. Phys. Chem. Lett. 16, 2001, (2025).
• Vibrationally Induced Magnetism in Supramolecular Aggregates, J. Fransson, J. Phys. Chem. Lett. 14, 2558 (2023).
• Mircoscopic theory for coupled atomistic magnetization and lattice dynamics, J. Fransson, D. Thonig, P. F. Bessarab, S. Bhattacharjee, J. Hellsvik, and L. Nordström, Phys. Rev. Materials, 1, 074404 (2017).