The research team led by Prof. Yuan at East China Normal University has reported the discovery of two-dimensional room-temperature ferromagnetism in Ta0.67V0.33Se2. The related findings have been published online in Physical Review B under the title "Signature of room-temperature two-dimensional ferromagnetism in Ta0.67V0.33Se2."
Magnetic two-dimensional materials are an important area in the exploration of new-dimensional topological properties. In two-dimensional materials, the screening effect is suppressed, making it easier to externally control magnetism through various mechanisms, including the use of stress, intercalation, and electromagnetic fields. To date, many interesting physical phenomena have been discovered in two-dimensional magnets, laying the foundation for diverse applications. These phenomena include the observation of the quantum anomalous Hall effect in MnBi2Te4, as well as non-reciprocal magnetoacoustic effects and two-dimensional spin waves exhibited in CrI3 or CrCl3. Numerous prototype spintronic devices have also made experimental breakthroughs, opening up promising possibilities for future applications.
In previous studies, two-dimensional ferromagnetic materials typically exhibited low Curie temperatures, which affected the observation and control of low-dimensional magnetism. In this study, the researchers successfully synthesized the two-dimensional room-temperature van der Waals magnet Ta0.67V0.33Se2 and found that it exhibited room-temperature ferromagnetism in both bulk and few-layer forms. Single crystals of Ta0.67V0.33Se2 were prepared using chemical vapor transport, and their chemical composition, crystal structure, and phonon dynamics were characterized by energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy, respectively. At approximately 60 K, the reversal of the Hall sign and the peak in the longitudinal resistance suggest the presence of a temperature-induced Lifshitz phase transition. Magnetization measurements in the bulk also showed similar anomalous peaks around 60 K, indicating a strong coupling between electrical and magnetic properties. The magnetization measurements confirmed the existence of long-range magnetic order at room temperature. Furthermore, significant hysteresis curves observed in Nano-MOKE experiments on samples of varying thickness indicate that room-temperature ferromagnetism is present in Ta0.67V0.33Se2 regardless of thickness.
This work received strong support and assistance from several teachers and teams, including Qingyuan Jin, Xiaolei Zhang, Hao Shen, Hai-Bo Yang, Xueliang Shi, and Lin Sun from East China Normal University, Yongfeng Mei, Jizhai Cui, and Cheng Zhang from Fudan University, and Shengli Zhang and Ying Li from Xi'an Jiaotong University. The project was funded by National Key R&D Program of China, Shanghai Pilot Program for Basic Research , the National Natural Science Foundation of China. Prof. Yuan is the corresponding author of the paper, with Yuhan Du, a PhD student of the 2024 cohort, and Yuanji Ma, a master's student of the 2020 cohort, as co-first authors.
More information: https://doi.org/10.1103/PhysRevB.110.184427
