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Competing Antiferromagnetic Phases in Multiferroic Wurtzite Transition-Metal Chalcogenides

Antiferromagnetic (AFM) spintronics offers a pathway toward electrically controllable spin-based devices beyond ferromagnets. Here, we identify wurtzite MnX (X = S, Se, Te) as a family of multiferroic materials hosting competing AFM phases, including altermagnetic, where nonrelativistic spin splitting can be controlled by ferroelectric polarization. Using density-functional theory and atomistic spin-model calculations, we show that all pristine MnX compounds stabilize a stripe type collinear AFM ground state, contrary to earlier predictions of an altermagnetic ground state, with the magnetic order governed by frustrated Heisenberg and biquadratic exchange interactions. We further demonstrate that Cr doping drives a transition to an A-type AFM phase that breaks Kramers spin degeneracy and realizes a g-wave altermagnetic state with large nonrelativistic spin splitting near the Fermi level. Importantly, this spin splitting can be deterministically reversed by polarization switching, enabling electric-field control of altermagnetic electronic structure without reorienting the Neel vector or relying on spin-orbit coupling. The close energetic proximity of the stripe AFM to a noncollinear all-in-all-out configuration indicates that wurtzite MnX lies near a topological magnetic phase with finite scalar spin chirality, which may be stabilized by modest perturbations such as temperature, strain or chemical tuning. The distinct magnetic phases exhibit symmetry selective linear and non-linear Hall responses, providing direct transport signatures of altermagnetism and polarization control. Together, these results establish doped wurtzite MnX as a promising platform for altermagnet-ferroelectric multiferroics and electrically AFM spintronics.