Strong tuning of magnetism and electronic structure by spin orientation.

To efficiently manipulate magnetism is a key physical issue for modern condensed matter physics, which is also crucial for magnetic functional applications. Most previous relevant studies rely on the tuning of spin texture, while the spin orientation is often negligible. As an exception, spin-orbit coupled $J_{\rm eff}$ states of $4d$/$5d$ electrons provide an ideal platform for emergent quantum effects. However, many expectations have not been realized due to the complexities of real materials. Thus the pursuit for more ideal $J_{\rm eff}$ states remains ongoing. Here a near-ideal $J_{\rm eff}$=$3/2$ Mott insulating phase is predicted in the family of hexachloro niobates, which avoid some common drawbacks of perovskite oxides. The local magnetic moment is nearly compensated between spin and orbital components, rendering exotic recessive magnetism. More interestingly, the electronic structure and magnetism can be strongly tuned by rotating spin axis, which is rare but crucial for spintronic applications.