Monolayer MXO as potential 2D altermagnets and half-metals: a first principles study.

Realizing novel two-dimensional (2D) magnetic states would accelerate the development of advanced spintronic devices and the understandings of 2D magnetic physics. In this paper, we have examined the magnetic and electronic properties of 20 dynamically stable and exfoliable MXO (M = Ti-Ni; X = S-Te; excluding CoTeO). It has been unveiled that [XO]-and [M]-crystal fields govern the M-3orbital splittings in MXO. The splittings further lead to the antiferromagnetic (AFM) orderings in TiSO/FeSO/FeSeO/MXO (M = V, Cr, Mn and Ni; X = S-Se) as well as the ferromagnetic orderings in TiSeO/TiTeO/FeTeO/CoSO/CoSeO through kinetic and superexchange mechanisms. Notably, all the AFM MXO are 2D altermagnets, and TiSeO/TiTeO/CoSO/CoSeO are 2D half-metals. In particular, the anisotropichoppings lead to the tunable altermagnetic splitting in TiSO/CrTeO, while the parity of V-3orbital contributes to the symmetry-protected altermagnetic splitting within VXO. These altermagnetic and half-metallic monolayer MXO provide promising candidates applied in low-dimensional spintronic devices. In addition, the potential 2D altermagnetic Weyl semimetal of FeSO/FeSeO, nodal-loop half-metal of TiSeO and half-semi metal of TiTeO facilitate to uncover novel low-dimensional topological physics. These theoretical results would expand the platform in particular for 2D altermagnets and nontrivial systems.