Tomohiro Takayama received his Ph.D from the Department of Advanced Materials Science at University of Tokyo in 2006. After serving as an assistant professor in the same department, he moved to Max Planck Institute for Solid State Research in Germany in 2013, where he worked as a group leader. In 2025, He joined MANA, NIMS. His research interest focuses on the development of novel quantum materials and the investigation of their electronic, magnetic and thermal properties.

van der Waals (vdW) magnets where magnetically active layers are stacked via vdW bonds have appeared as a platform for unconventional magnetic and electronic properties [1]. To data, most of vdW magnets comprise divalent or trivalent 3d ions, whereas incorporation of higher valent transition ions like 4d/5d elements is challenging. To overcome this point, we have synthesized cation-ordered vdW magnet ABX6 where A/B is divalent/tetravalent ion and X is halogen, respectively, such as Ni2+Pt4+I6. The A2+ and B4+ ions form a BN-type ordered pattern on a honeycomb lattice as depicted in Fig. 1. In a series of M2+PtI6 compounds (M = Fe, Co, Ni), we observed the appearance of antiferromagnetic order. We will discuss the synthesis and magnetism of these vdW magnets with a new architecture.

This work was done in collaboration with J. Gu, A. N. Yaresko, S. Bette, F. Orlandi, P. Manuel, and H. Takagi.

1. K. S. Burch, D. Mandrus, and J.-G. Park, Nature 563, 47 (2018). DOI:10.1038/s41586-018-0631-z