  Thermal ammonolysis of quasi-two-dimensional (quasi-2D) CoTa2O6 yields the
O2-/N3- and anionic vacancy ordered Co2+Ta5+2O6-xN2x/3$\Box$x/3 (x $\leq$ 0.15)
that exhibits a transition from antiferromagnetism to defect engineered above
room-temperature ferromagnetism as evidenced by diffraction, spectroscopic and
magnetic characterizations. First-principles calculations reveal the origin of
ferromagnetism is a particular CoON configuration with N located at Wyckoff
position 8j, which breaks mirror symmetry about ab plane. A pressure-induced
electronic phase transition is also predicted at around 24.5 GPa, accompanied
by insulator-to-metal transition and magnetic moment vanishing.
