We study the magnetic and electronic properties of Ni-intercalated ${\mathrm{NbSe}}_2$. We calculate the magnetic exchanges of ${\mathrm{Ni}}_x{\mathrm{NbSe}}_2$ ($x=1/3,1/4,$ and 1) and find that the out-of-plane magnetic coupling depends on the Ni connectivity: it is ferromagnetic when Ni atoms stack on top of each other and antiferromagnetic otherwise. Focusing on ${\mathrm{Ni}}_{0.25}{\mathrm{NbSe}}_2$, we identify a ground-state transition from a stripe antiferromagnetic phase with Kramers degeneracy to a ferromagnetic phase above a critical Coulomb interaction ${\mathrm{U}}_C$. Spin-orbit coupling lowers ${\mathrm{U}}_C$, aligns the easy axis along $z$, and stabilizes collinear antiferromagnetic and ferromagnetic states over the competing ${120}^{\circ }$ phase. Ni intercalation also strongly modifies the electronic structure, replacing the $\mathrm{\Gamma }$-point hole pocket of pristine ${\mathrm{NbSe}}_2$ with an electron pocket and shifting the Van Hove singularity away from the Fermi level, thereby suppressing potential instabilities. Finally, we investigate the altermagnetic phase in the broader class ${\mathrm{T}}_{0.25}{\mathrm{MX}}_2$, finding that spin-orbit effects induce orbital antiferromagnetism with weak ferromagnetism or ferrimagnetism depending on the Néel vector orientation. Our results demonstrate that Ni-intercalated ${\mathrm{NbSe}}_2$ provides a versatile platform to explore and tune multiple competing magnetic phases that lie close in energy.

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• Fermi surface
• Magnetic order
• Spin-orbit coupling
• Transition metal dichalcogenides