Coexistence of commensurate and incommensurate antiferromagnetic ground states in CoxNbSe2 single crystal

In CoxNbSe2, crystal symmetry and cobalt site occupation drive the formation of two distinct magnetic phases. At x=1/4, the centrosymmetric structure (P63/mmc) promotes Co-Co interactions leading to the formation of an A-type antiferromagnetic structure phase with a transition temperature of TNA=169K. At x=1/3, the noncentrosymmetric structure (P6322) induces a lower-temperature magnetic phase with TNS=28K. We report the coexistence of both substructures within a superlattice, with a nuclear propagation vector of (1/3, 1/3, 0) relative to the host lattice. Single crystals of Co0.28NbSe2 exhibit both magnetic transitions, with TNA corresponding to the x∼1/4 phase and TNS corresponding to the x∼1/3 phase. Magnetic susceptibility and specific heat measurements confirm these transitions, although only the high-temperature TNA phase significantly affects resistivity. We successfully isolate each phase in powder samples, while single crystals with an intercalation ratio of x=0.28 display the coexistence of both phases in a single sample. Using single-crystal neutron diffraction, we solved the magnetic structure of the high-temperature centrosymmetric phase (TNA), and neutron powder diffraction revealed the double-q magnetic structure of the low-temperature noncentrosymmetric phase (TNS).