Events

Department of Magnetic Reseach Seminar

The crystal structure and magnetism in van-der-Waals trihalides

dr Jiří Pospíšil

Wydział Matematyki i Fizyki Uniwersytetu Karola w Pradze w Czechach

Seminarium odbędzie się zdalnie w aplikacji Microsoft Teams. W celu wzięcia udziału w wydarzeniu należy dołączyć do zespołu Seminarium OBM.Można do niego dołączyć na stałe przy użyciu kodu dostępu ol7omod (dotyczy to osób posiadających konto w domenie intibs.pl, pozostałe osoby proszę o kontakt z prof. dr. hab.Adamem Pikulem, prof. INTiBS PAN ())

Streszczenie:

The van-der-Waals trihalides are a fascinating group of materials, where ferromagnetic order can be preserved down to the single-layer limit. We will present our recent results which show a tight connection between the dimorphic crystal structure with trihalides magnetism. Our particular interest is focused on compounds based on vanadium-VX3. The representative chromium-based triad, CrCl3, CrBr3, CrI3, is characterized by the low-temperature phase adopting the trigonal BiI3-type while the structure of the high-temperature phase is monoclinic of AlCl3 type (C2/m). The structural transition between the two crystallographic phases is of the first-order type with large thermal hysteresis in CrCl3 and CrI3. We studied crystal structures and structural phase transitions of vanadium-based counterparts VCl3, VBr3, and VI3 by measuring specific heat, magnetization, and X-ray diffraction as functions of temperature and observed an inverse situation1.
We will also show our comprehensive study of VI3 which is exceptional by extra distortion to the triclinic phase accompanied by the simultaneous order-to-order ferromagnetic transition2. To demonstrate the development of the magnetic structure of VI3, we measured angular dependences of the torque and magnetization with respect to the direction of the applied magnetic field within the “ac” plane perpendicular to and within the basal ab plane, respectively3. The p-T phase diagram is also unique when the external pressure 7.5 GPa enhances the TC twice4.
Another predicted class of materials preserving the 2D magnetism are 5f electron systems thanks to strong spin-orbit coupling. Within this scenario, we focused on 5f electron vdW material UI3. We have successfully prepared the first high-quality single crystals of this material. A single crystal study allowed us to reveal a complex magnetism and anisotropy. UI3 was predicted to host the ferromagnetic order in 2D limit with a high ordering temperature of over 100 K5.
1 M. Kratochvílová, et al., Journal of Physics: Condensed Matter 34, 294007 (2022).
2 P. Doležal, et al., Physical Review Materials 3, 121401(R) (2019).
3 A. Koriki, et al., Physical Review B 103, 174401 (2021).
4 J. Valenta, et al., Physical Review Materials 103, 054424 (2021).
5 S. J. Li, et al., Journal of Physics D Applied Physics 53, 185301 (2020).