Programme

P.62 -- Posters, VCTP-51

Date: Thursday, 6 August 2026

Time: 09:30 - 10:30

Synthesis and structural stability investigation of Fe$_3$GeTe$_2$ van-der-Waals ferromagnet

T. L. Phan* (1), N. H. Tiep (1), T. H. Nguyen (2), N. T. Dang (3), N. N. Hieu (3)

(1) Faculty of Engineering Physics and Nanotechnology, VNU University of Engineering and Technology, 144 Xuan Thuy, Cau Giay, Hanoi, Vietnam; (2) Division of Physics, School of Engineering and Techonology, Nha Trang University, Khanh Hoa 650000, Viet Nam; (3) Institute of Research and Development, Duy Tan University, Da Nang, Viet Nam

Fe$_3$GeTe$_2$ (FGT) is known as a layered van-der-Waals (vdW) ferromagnet that has recently attracted much interest of the scientific and technological community due to its intriguing magnetic properties and potential applications in spintronic devices. This work presents the synthesis of a bulk FGT sample using solid-state reactions. Powder X-ray diffraction (XRD) confirmed the as-prepared FGT crystallizing in the P63/mmc hexagonal structure. Its structural stability was then examined under air exposure and mechanical milling. As a result, upon prolonged exposure to ambient air, the initially single-phase FGT gradually degraded, leading to the formation of secondary phases. Mechanical ball milling for durations ranging from one to 30 minutes also caused rapidly structural deconstruction and phase transformation, as evidenced by significant changes in the XRD patterns. Such results demonstrate that FGT is highly sensitive to both environmental and mechanical factors. To understand the origin of this behavior, density functional theory (DFT) calculations were performed. The calculated phonon spectra of FGT monolayers on metal substrates exhibit no negative frequencies, proving their intrinsic dynamical stability; free-standing FGT layers could be unstable. The discrepancy between the theoretical prediction and experimental observations suggests that the degradation of FGT is likely driven by extrinsic factors, such as oxidation, defect formation, strain accumulation, and mechanically induced structural disorder, which are not taken into account in the idealized DFT model. Our results highlight the importance of environmental and processing conditions in determining the practical stability of FGT, thereby providing valuable guidance for its handling, fabrication, and potential applications in next-generation electronic devices.

Presenter: Phan L. Long