Defect-engineered room-temperature ferromagnetism in quasi-two-dimensional nitrided CoTa2O6

Thermal ammonolysis of quasi-two-dimensional (quasi-2D) CoTa2O6 yields the O2-/N3- and anionic vacancy-ordered Co2+Ta25+O6-xN2x/3 square(x/3) (x <= 0.15), which exhibits a transition from antiferromagnetism to defect-engineered above-room-temperature ferromagnetism. First-principles calculations reveal that the origin of ferromagnetism is a particular CoO5N configuration with N located at Wyckoff position 8 j, which breaks mirror symmetry about the ab plane. A pressure-induced electronic phase transition is also predicted at similar to 24.5 GPa, accompanied by insulator-to-metal transition and magnetic moment vanishing.