Antiferromagnetic ordering of Fe/Ru(0001)

The structural, electronic, and magnetic properties of the Fe/Ru(0001) system were determined by using the local-density total-energy full-potential linearized augmented-plane-wave energy-band method. Structurally, Fe atoms are found to occupy the hcp sites on the Ru(0001) substrate. Compared with the average of their bulk values, the nearest Fe-Ru distance contracts about 6% for the paramagnetic case but expands 1% for the ferromagnetic and the antiferromagnetic configurations, indicating the strong effect of magnetism and the lattice geometry. As the result of the strong overlayer-substrate hybridization, the Fe atoms, which are coupled ferromagnetically in the case of the corresponding free-standing Fe monolayer, favor antiferromagnetic coupling for Fe/Ru(0001). The predicted antiferromagnetic coupling appears to explain the observation by Liu and Bader that Fe overlayers on Ru(0001) are magnetically dead when the number of Fe layers is less than 2.