Origin of Ising magnetism in Ca3Co2O6 unveiled by orbital imaging

The one-dimensional cobaltate Ca$${}_{3}$$3Co$${}_{2}$$2O$${}_{6}$$6 is an intriguing material having an unconventional magnetic structure, displaying quantum tunneling phenomena in its magnetization. Using a newly developed experimental method, $$s$$s-core-level non-resonant inelastic x-ray scattering ($$s$$s-NIXS), we were able to image the atomic Co $$3d$$3d orbital that is responsible for the Ising magnetism in this system. We can directly observe that corrections to the commonly accepted ideal prismatic trigonal crystal field scheme occur in Ca$${}_{3}$$3Co$${}_{2}$$2O$${}_{6}$$6, and it is the complex $${d}_{2}$$d2 orbital occupied by the sixth electron at the high-spin Co$${}_{\,\text{trig}\,}^{3+}$$trig3+ ($${d}^{6}$$d6) sites that generates the Ising-like behavior. The ability to directly relate the orbital occupation with the local crystal structure is essential to model the magnetic properties of this system.