Orbital magnetism in Fe, Co, and Ni

The spin and orbital contributions to the magnetic moments of Fe, Co, and Ni are calculated from first principles, using the linear muffin-tin orbitals method with the spin-orbit coupling treated at each variational step. In these calculations the spin and orbital moments agree with previously reported results obtained from spin-polarized Dirac calculations. When Hund’s second rule is accounted for in the band Hamiltonian by adding an additional term for orbital polarization, the orbital moments agree better with experiment and the trends in the experimental orbital moments across the series can be explained. Specifically, the maximum orbital moment for Co is shown to occur because of its hcp equilibrium crystal structure.