(a) Spin-polarization in vacuum above Fefcc (red) and Hofcc (orange) atoms for two selected tip-atom distances, from DFT calculations. (b) Magnetic coupling parameters for Fe–Fe, Fe–Ho and Ho–Ho pairs on hcp sites, obtained from the magnetic force theorem. The inset shows a more narrow window for the coupling strength J for a better view on the smallest values. (c) Local density of states (LDOS) for isolated Fefcc (red) and Hofcc (orange) atoms, showing the location of the 3d and 4f states with respect to the Fermi energy of platinum. Positive or negative values indicate majority or minority spins, which is also indicated by the grey up or down arrows.