In the past few years, magnetic two-dimensional (2D) materials and topological spin textures have become two of the hottest topics in the fields of material science and spintronics. Creating topological spin textures in 2D magnets naturally becomes very attractive, because one may take advantages of both to construct novel spintronic devices. In this dissertation, we investigated the structural and magnetic properties of several emerging 2D magnets and successfully observed topological spin textures in some of them.
First, we synthesized quasi-van der Waals (vdW) ferromagnet Fe0.26TaS2. Its critical behavior was systematically studied by measuring the magnetization around the ferromagnetic to paramagnetic phase transition temperature. The results reveal that the spin coupling inside Fe0.26TaS2 crystal is of the three-dimensional Heisenberg type with long-range magnetic interaction and that the exchange interaction decays with distance as J(r) ~ r −4.71.
Second, we synthesized vdW ferromagnet Fe5−δGeTe2 crystals and observed dipole skyrmions with unconventional helicity polarization in the nanoflake samples. We demonstrated that the short-range order of Fe split sites in Fe5−δGeTe2 results in a localized Dzyaloshinskii–Moriya interaction contribution, which breaks the degeneracy of the opposite helicities and leads to the helicity polarization. Moreover, the topological spin textures can persist up to nearly room temperature (~273 K). This work provides new insights into the skyrmion topology in 2D materials and reveals great potentials of Fe5−δGeTe2 for spintronic applications.
Third, we successfully synthesized Cr1/3TaS2 single crystals, a quasi-vdW helimagnet. We found that one-dimensional nontrivial magnetic solitons can be created below its Curie temperature. The coupling of the strong spin–orbit interaction from TaS2 and the chiral arrangement of the magnetic Cr ions evoke a robust Dzyaloshinskii-Moriya interaction. A magnetic helix having a short spatial period of ~25 nm was observed in Cr1/3TaS2 via Lorentz transmission electron microscopy. Moreover, chiral solitons can be created under an in-plane magnetic field, and the soliton confinement and discretization effects were also observed. Our work introduces a new paradigm to soliton physics and provides an effective strategy for seeking novel 2D magnets.
| Date of Award | Jul 3 2022 |
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| Original language | English (US) |
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| Awarding Institution | - Physical Sciences and Engineering
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| Supervisor | Xixiang Zhang (Supervisor) |
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