Importance of the Spin-Orbit Coupling for 3d-Ion Compounds: the Case of NiO

The orbital and spin moment of the Ni$\text{}^{2+}$ ion in NiO has been calculated at 0 K to be 0.54 μ$\text{}_{B}$ and 1.99 μ$\text{}_{B}$ respectively. Such large orbital moment, more than 20% of the total moment of 2.53 μ$\text{}_{B}$, proves the need for the "unquenching" of the orbital moment in compounds containing 3d ions. It turns out that the spin-orbit coupling is indispensable for description of magnetic and electronic properties of 3d-ion compounds.