Giant Magnetic Anisotropy of Co, Ru, and Os Adatoms on MgO (001) Surface

Abstract

Large magnetic anisotropy energy (MAE) is desirable and critical for nanoscale magnetic devices. Here, using ligand-field level diagrams and density functional calculations, we well explain the very recent discovery [I. G. Rau et al., Science 344, 988 (2014)] that an individual Co adatom on a MgO (001) surface has a large MAE of more than 60 meV. More importantly, we predict that a giant MAE up to 110 meV could be realized for Ru adatoms on MgO (001), and even more for the Os adatoms (208 meV). This is a joint effect of the special ligand field, orbital multiplet, and significant spin-orbit interaction, in the intermediate-spin state of the Ru or Os adatoms on top of the surface oxygens. The giant MAE could provide a route to atomic scale memory.

Giant magnetic anisotropy of heavyp-elements on high-symmetry substrates: a new paradigm for supported nanostructures

“…The MAEs of Bi-Ge, Bi-In and Bi-Sn are comparable to the largest MAE reported for d-element dimers [51]. To our knowledge, the MAE of the Bi-Tl dimer of 203 meV is the largest value ever reported for the supported dimers, and this MAE value is very close to the record-breaking MAE value of an Os adatom on MgO [29]. Note also from table 1 that the MAE value increases along with the increasing atomic number of element X for X in the same group.…”

“…Recently much progress has been made in designing structures with desired MAE [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42]. Among these systems, an osmium adatom on MgO(100) was reported to have a record-breaking MAE of 208 meV [29]. Lately, an increasing number of investigations focused on supported transition-metal-dimers, and found that specific dimers on substrates could form vertical structures.…”

Ferromagnetism in the unusual low-valence layered material LaSrNiRuO 4

“…We first did a constrained LSDA+U calculation, assuming the Ni + S = 1/2 but Ru 2+ S = 0 states with the doubly occupied 3z 2 − r 2 , xz and yz orbitals of the Ru 4d. In many cases, this type of calculations can find several orbitally polarized metastable solutions, in addition to the ground state [22][23][24]. Unfortunately, however, the present constrained LSDA+U calculation turns out not to stabilize the Ru 2+ S = 0 state, and it converges exactly to the Ni + S = 1/2 and Ru 2+ S = 1 FM insulating ground state.…”

Magnetocrystalline anisotropy of Fe and Co slabs and clusters onSrTiO3by first-principles

“…Nevertheless, the arguments put forward are rather general and could be very useful in the design of atomic-scale devices with optimized magnetic anisotropy. Note however, that if the nonsphericity of the Coulomb and exchange interaction [32] starts to play a dominant role in the electronic structure of the system, then orbital polarization effects arise [33,34] and our analysis of the MCA based on a perturbation treatment of the SOC only non longer applies, and more complex scenarii can occur as in the case of the giant magnetic anisotropy of single adatom on MgO [35].…”