[1] P C Hohenberg. Existence of long-range order in one and two dimensions. Phys Rev, 158, 383(1967).
[2] N D Mermin, H Wagner. Absence of ferromagnetism or antiferromagnetism in one- or two-dimensional isotropic Heisenberg models. Phys Rev Lett, 17, 1133(1966).
[3] V Berezinskiǐ. Destruction of long-range order in one-dimensional and two-dimensional systems possessing a continuous symmetry group. II. Quantum systems. Sov Phys JETP, 34, 610(1972).
[4] J M Kosterlitz, D J Thouless. Ordering, metastability and phase transitions in two-dimensional systems. J Phys C, 6, 1181(1973).
[5] J M Kosterlitz. The critical properties of the two-dimensional xy model. J Phys C, 7, 1046(1974).
[6]
[7]
[8] A Bedoya-Pinto, J R Ji, A K Pandeya et al. Intrinsic 2D-XY ferromagnetism in a van der Waals monolayer. Science, 374, 616(2021).
[9] B Huang, G Clark, E Navarro-Moratalla et al. Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit. Nature, 546, 270(2017).
[10] D Ghazaryan, M T Greenaway, Z Wang et al. Magnon-assisted tunneling in van der Waals heterostructures based on CrBr3. Nat Electron, 1, 344(2018).
[11] C Gong, L Li, Z L Li et al. Discovery of intrinsic ferromagnetism in two-dimensional van der Waals crystals. Nature, 546, 265(2017).
[12] Y J Deng, Y J Yu, Y C Song et al. Gate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2. Nature, 563, 94(2018).
[13] M Bonilla, S Kolekar, Y J Ma et al. Strong room-temperature ferromagnetism in VSe2 monolayers on van der Waals substrates. Nat Nanotechnol, 13, 289(2018).
[14] L Webster, J A Yan. Strain-tunable magnetic anisotropy in monolayer CrCl3, CrBr3, and CrI3. Phys Rev B, 98, 144411(2018).
[15]
[16] S Takei, Y Tserkovnyak. Superfluid spin transport through easy-plane ferromagnetic insulators. Phys Rev Lett, 112, 227201(2014).
[17] S K Kim, S B Chung. Transport signature of the magnetic Berezinskii-Kosterlitz-Thouless transition. SciPost Phys, 10, 068(2021).
[18] X Lu, R Fei, L Zhu et al. Meron-like topological spin defects in monolayer CrCl3. Nat Commun, 11, 4724(2020).
[19] M Augustin, S Jenkins, R F L Evans et al. Properties and dynamics of meron topological spin textures in the two-dimensional magnet CrCl3. Nat Commun, 12, 185(2021).