Magnetic properties of single atoms of Fe and Co on Ir(111) and Pt(111)

Abstract

In using the fully relativistic versions of the Embedded Cluster and Screened Korringa-KohnRostoker methods for semi-infinite systems the magnetic properties of single adatoms of Fe and Co on Ir(111) and Pt(111) are studied. It is found that for Pt(111) Fe and Co adatoms are strongly perpendicularly oriented, while on Ir(111) the orientation of the magnetization is only out-of-plane for a Co adatom, for an Fe adatom it is in-plane. For comparison also the so-called band energy parts of the anisotropy energy of a single layer of Fe and Co on these two substrates are shown. The obtained results are compared to recent experimental studies using e.g. the spin-polarized STM technique.PACS numbers: 73.20. At, 72.10.Fk, 75.30.Hx, 73.20.Hb The potential application in non-volatile data storage devices is one of the driving forces behind research into magnetic nanostructures. In state-of-the-art hard disk drives a collection of a few hundred of single-domain particles (grains) are used to hold one bit of information. If materials can be manufactured which exhibit sufficiently large anisotropies and thermal stabilities it may become possible to store one bit in a single grain [1]. Such storage devices will require magnetic structures of precise atomic arrangement, as -if in addition the lateral dimensions of grains are further reduced -the influence of the perimeter atoms becomes increasingly important [2,3] and, as is known, from previous studies the magnetic properties of each atom in a nanostructure are highly influenced by its local environment [1,2,3,4].Using Scanning Tunneling Microscopy structures can be precisely tailored and their magnetic properties determined. In recent Scanning Tunneling Spectroscopy experiments [3,5] it has become possible to measure not only the Lande g-factor of individual atoms but also their magnetic anisotropy. The findings suggest that the anisotropy energy of a single atom may eventually be large enough to use the magnetic state of an atom as a storage unit, pushing the ultimate limit for data storage density even further. Since the magnetic properties of small clusters and single adatoms differ strongly from those of bulk systems and even monolayers -e.g. showing a much enhanced magnetic anisotropy energy -they do not only generate interest for their technological relevance but also from a fundamental point of view.In this paper we present a study of the magnetic moments and the angular dependent band energy part of the magnetic anisotropy energy of single atoms of Fe and Co, which -in order to investigate the influence of different substrates -have been deposited on Pt(111) and Ir(111). The calculations have been performed by means of the Embedded Cluster Method (ECM), a scheme based on the fully relativistic Screened Korringa-Kohn-Rostoker (SKKR) method, in which we can treat impurities embedded into a two-dimensional translationally invariant semi-infinite host. This approach makes use of multiple scattering theory in which the electronic structure of a cluster of embedded atoms...

Magnetocrystalline anisotropy energy of Co and Fe adatoms on the (111) surfaces of Pd and Rh

“…We should point out that our setup differs considerably from that used in previous calculations 4,31,32,34 of the magnetic anisotropy of supported nanostructures. Most of these calculations are based on a KKR Green's-function approach, a local exchange-correlation functional, a complete neglect of relaxation of the adsorbate/substrate complex, and the use of the magnetic force theorem for calculating the magnetic anisotropy energy.…”

“…4,21,[30][31][32][33][34][35] With the exception of our recent work 30 and the work by Shick and Lichtenstein 35 and by Balashov et al, 21 all these calculations are based on a Green's-function approach within the screened fully relativistic Kohn-Korringa-Rostocker ͑KKR͒ method, an idealized geometry propagating the bulk structure of the substrate, the local-density approximation, and the use of the magnetic force theorem. 4,21,[31][32][33][34][35] In our recent assessment of the impact of the different approximations, we have demonstrated that the most important step is the description of the adsorbate/ substrate complex. Calculations based on the assumption of an idealized bulklike geometry essentially attempt to cure a defect of the SDFT ͑missing orbital dependence of the exchange field͒ by artificially minimizing adatom/support hybridization.…”

Spin polarization of platinum (111) induced by the proximity to cobalt nanostripes

“…They treated Co in different configurations and environments, like Co 075407-6 overlayers on Pt(111) 35 , Co nano wires attached to Pt(111) step edges 36,37 and isolated Co adatoms on bare Pt(111) surfaces. 38,39 Even though these configurations have different coordination numbers of underlying Pt atoms per Co atom, they show consistently an induced spin moment M spin of the nearest-neighbor Pt atoms in the range from 0.1 to 0.3 μ B , which is about 1 order of magnitude larger than the orbital moments M orb . Therefore the total induced magnetic moment M Pt of Pt atoms is mainly determined by the spin moment M spin .…”

A theoretical STM study of Con/Pt(111)

“…The magnetic properties (spin and orbital moments, magnetic anisotropy energy) of a free surface of Co adlayers or of Co clusters on Pt(111) were already studied extensively in the past [22][23][24]. However, viewed as sample system in an STM experiment, the situation becomes less straight forward, since as already was mentioned a tip with a lead has to be included.…”