We held a seminar featuring a lecture by Dr. Charles Menil from Université Paris Sciences et Lettres.

Title：Magnetic memory and hysteresis in ferromagnetic Weyl semi metal Co3Sn2S2
Speaker：Charles Menil 氏
Affiliation：  Laboratoire de Physique et d’Étude des Matériaux, (ESPCI - CNRS - Sorbonne Université), Université Paris Sciences et Lettres, 75005, Paris, France
Date：2025/4/9th（Wed）16:00～  (JST)
Venue：Online

Co₃Sn₂S₂, a ferromagnetic Weyl semimetal with Co atoms on a Kagome lattice has generated much recent attention. From electronic properties, it serves as a platform for exploring Weyl fermion physics with broken time reversal symmetry [1]. From magnetic properties, experiments have identified a temperature scale below the Curie temperature, associated with a, still debated, secondary magnetic phase [2,3].
After introducing key properties of Co₃Sn₂S₂, I will present magnetization measurements that reveal a memory effect which can be erased by applying a large magnetic field. We attributed this effect to a small secondary spin population with a coercive field significantly larger than that of the majority spins. Additionally, the shape of magnetization hysteresis curves can be understood through a surprisingly simple model in which the demagnetizing field plays a crucial role in defining a threshold between two distinct hysteresis regimes. By combining the effects of demagnetizing fields and memory, our results imply that the temperature scale below the Curie temperature is not a thermodynamic phase transition, but a crossing point between metastable boundaries. [4]

[1] Liu, E., Sun, Y., Kumar, N. et al. Giant anomalous Hall effect in a ferromagnetic kagome
lattice semimetal. Nature Phys 14, 1125 1131 (2018). https://doi.org/10.1038/s41567 018
0234 5
[2] Guguchia, Z., Verezhak, J.A.T., Gawryluk, D.J. et al. Tunable anomalous Hall conductivity through volume wise magnetic competition in a topological kagome magnet. Nat Commun 11, 559 (2020). https://doi.org/10.1038/s41467 020 14325 w
[3] Lachman, E., Murphy, R.A., Maksimovic, N. et al. Exchange biased anomalous Hall effect driven by frustration in a magnetic kagome lattice. Nat Commun 11, 560 (2020). https://doi.org/10.1038/s41467 020 14326 9
[4] Menil, C., Leridon, B., Cavanna, A. et al. Magnetic memory and distinct spin populations in ferromagnetic Co3Sn2S2. npj Quantum Mater. 10, 23 (2025). https://doi.org/10.1038/s41535 025 00739 6