Controlling the spin of metal atoms adsorbed on oxide surfaces: Ni on regular and defective sites of the MgO(001) surface

Abstract

We have analyzed the relative energy of nonmagnetic and magnetic low-lying electronic states of Ni atoms adsorbed on regular and defective sites of the MgO͑001͒ surface. To this end cluster and periodic surface models are used within density functional theory. For Ni atoms adsorbed on oxygen vacancies at low coverage, the interaction energy between the metal and the support is much larger than on regular sites. Strong bonding results in a diamagnetic adsorbed species and the energy required to reach the high-spin state increases. Moreover, a correlation appears between the low-spin to high-spin energy difference and the interaction energy hypothesizing that it is possible to prepare the surface to tune the high-spin to low-spin energy difference. Magnetic properties of adsorbed thin films obtained upon increasing coverage are more difficult to interpret. This is because the metallic bond is readily formed and dominates over the effect of the atoms directly bound to the vacancy.

First-principles calculations of the atomic and electronic structure ofFcenters in the bulk and on the (001) surface ofSrTiO3

“…The nature of defects in simple ionic oxides has been studied quite extensively, [5][6][7][8][9][10] including its effect on the magnetic moment of supported Ni atoms. 11 However, much less is known about the nature of point defects in less simple oxides. This is because in the case of covalent and semicovalent oxides-ABO 3 perovskites among them-their electronic structure exhibits an increased complexity which has hindered a proper characterization of these systems.…”

Adsorption energy and spin state of first-row transition metals adsorbed on MgO(100)

“…The low lying electronic states of Ni on MgO ͑100͒ have been studied in detail for Ni on basic sites of the perfect substrate 14 and for various oxygen vacancies point defects on the same surface. 15 In the later case, situations with different coverage were also discussed.…”

Effect of surface site on the spin state of first-row transition metals adsorbed on MgO: Embedded cluster model and hybrid density functional theory calculations

“…[27][28][29] On the other hand, the interaction of the transition-metal atoms with lowcoordinated anionic sites and with F S centers results in stronger adsorption energies. 22,37,[51][52][53][54][55] The effect is greater when the interaction takes place above the low-coordinated sites, whereas the effect on the electronic structure of the adsorbed atom is larger when the interaction takes place above the F S center; see Tables II and III. This may be explained by the following argument; the interaction above low-coordinated sites faces a smaller Pauli repulsion because the oxygen anion electron density is more delocalized and results in a larger value of the calculated adsorption energy.…”

“…In the case of Ni atoms adsorbed on oxygen vacancies at low coverage, the interaction energy between the metal and the support is much larger than on regular sites, resulting in a diamagnetic adsorbed species, and the energy required to reach the highspin state increases in opposition to the trend found for the first-row transition-metal atoms on the regular sites of the perfect MgO͑001͒ surface. 37 The fact that the interaction with different sites induces qualitatively different changes on the energy required to switch from low spin to high spin may have technological consequences and merits a more detailed study. This is the main goal of the present paper.…”