Abstract: Artificial spin ice (ASI), a two-dimensional array consisting of coupled nanomagnets, offers the possibility to create designer geometric frustration. The geometric frustration gives rise to rich exotic phases, such as spin liquid and magnetic monopole defects.

In the first part of my talk, I will present how we control the magnetic phase transition from an antiferromagnetic to ferromagnetic coupling by modifying the geometry of artificial spin array. In addition, we designed a dimer Kagome ASI, in which a dimer nanomagnets is used as a building block, to generate strongly antiferromagnetic order in the system. We can manipulate different types of antiferromagnetic couplings by tuning geometric parameters of the Kagome lattice.

Next, I will discuss our current work with exfoliated van der Waals (vdW) Fe₃GeTe₂ ​“sheet.” VdW materials have layered crystal structures, giving rise to strong intra-layer interaction and weak inter-layer van der Waals interaction. Magnetic VdW materials exhibit rich non-trivial spin textures, for instance, merons, Bloch and Néel skrymions, which is dependent of structure and elemental compositions. Therefore, these types of materials are potential candidates for future low-dimensional spintronic applications.  We explored magnetic-field- and temperature-dependent behaviors of magnetic domains in Fe₃GeTe₂. The Néel labyrinth stripe domains and skyrmion lattice were created by manipulation of magnetic field. The order of the skyrmion lattice displays thermally hysteretic behavior. Furthermore, we also found that the surface oxidation layer promotes the formation of skyrmions without the need of a magnetic field.