This Is AuburnElectronic Theses and Dissertations

Magnetism and Spin Dynamics in Emergent Two-Dimensional van der Waals Magnets




Alahmed, Laith

Type of Degree

Master's Thesis


Electrical and Computer Engineering

Restriction Status


Restriction Type

Auburn University Users

Date Available



The low Curie temperature of most two-dimensional (2D) van der Waals (vdWs) magnets makes it challenging to incorporate them into device applications. This thesis explores two intriguing materials: Fe5GeTe2, a 2D vdWs room temperature magnet, and Cu(1,3-bdc), a quasi-2D topological magnon insulator with low Curie temperature but peculiar magnetic properties. The materials were studied with various metrology, including X-ray diffraction, vibrating sample magnetometry, broadband FMR spectroscopy, thermal transport, etc. The magnetic measurements were performed with external magnetic fields applied in-plane and out-of-plane, and at different temperatures. We find that Fe5GeTe2 shows a record high Curie temperature of 332 K. Interestingly, for both magnets, a sizable Landé g-factor difference between the in-plane and out-of-plane cases was discovered, the Landé g-factor values deviate from g = 2, indicating a contribution of orbital angular momentum to the magnetic moment. The FMR measurements have revealed that Fe5GeTe2 has a damping constant comparable to Permalloy, and with reducing temperature, the linewidth has broadened. Our measurements not only demonstrate the room-temperature magnetization dynamics of Fe5GeTe2, but also provide evidence that Fe5GeTe2 transitions from ferromagnetic to ferrimagnetic at lower temperatures. In Cu(1,3-bdc), we have found that the interplay of topology, spin excitations, and orbital magnetism presents a playground for exploring topological spintronics. While the differences of in-plane and out-of-plane Landé g-factor (Δg) and saturation magnetization (ΔMs) in Cu(1,3-bdc) are well correlated at low temperatures, they diverge at higher temperatures (T>~4 K). Further theoretical analyses show that topological orbital moment induced by thermally excited spin chirality results in the g-factor anisotropy at higher temperatures. Our experiments have identified critical quantum phenomena in 2D magnets, highlighting them as ideal platforms for studying fundamental physics and building efficient spintronic devices.