Oxidation-induced spin reorientation in Co adatoms and CoPd dimers on Ni/Cu(100)

Abstract

Ultrasmall magnetic clusters and adatoms are of strong current interest because of their possible use in future technological applications. Here, we demonstrate that the magnetic coupling between the adsorbates and the substrate can be significantly changed through oxidation. The magnetic properties of Co adatoms and CoPd dimers deposited on a remanently magnetized Ni/Cu(100) substrate have been investigated by x-ray absorption and x-ray magnetic circular dichroism spectroscopy at the Co L 2,3 edges. Using spectral differences, pure and oxidized components are distinguished, and their respective magnetic moments are determined. The Co adatoms and the CoPd dimers are coupled ferromagnetically to the substrate, while their oxides, Co-O and CoPd-O, are coupled antiferromagnetically to the substrate. Along with the spin reorientation from the pure to the oxidized state, the magnetic moment of the adatom is highly reduced from Co to Co-O. In contrast, the magnetic moment of the dimer is of similar order for CoPd and CoPd-O.

Quantum size effects of small, size-selected and deposited CoRh clusters on Ni

“…The fine structure of the alloy clusters can be assigned to an increased chemical reactivity towards oxygen rather than resulting from alloying Co with Rh. This can be inferred from the shown Co 1 -O spectrum [28], representing the oxidized Co 1 adatom and thus, clearly correlating the side peak to the presence of oxygen. Even a broadening on the low photon energy side, in CoO bulk, layer and nanoparticles [30-32] seen by a small peak at 776.6 eV, is visible.Similar oxidation effects have been reported already for size selected CoPd and CoPt alloy clusters on Ni [28,29].…”

“…This can be inferred from the shown Co 1 -O spectrum [28], representing the oxidized Co 1 adatom and thus, clearly correlating the side peak to the presence of oxygen. Even a broadening on the low photon energy side, in CoO bulk, layer and nanoparticles [30-32] seen by a small peak at 776.6 eV, is visible.Similar oxidation effects have been reported already for size selected CoPd and CoPt alloy clusters on Ni [28,29]. The fully oxidized Co 1 -O sample was prepared in [28] by introducing a waiting time of 60 min.…”

“…Different signal to noise ratios in figure 2 correspond mainly to the change of the Co content of the individual cluster species. At the bottom, the measured and well known Co 1 adatom spectrum is presented [28,29]. The main peak of the Co L 3 -edge at 778.0 eV (left dashed line) exhibits no fine structure in contrast to the alloy clusters.…”

“…Even a broadening on the low photon energy side, in CoO bulk, layer and nanoparticles [30-32] seen by a small peak at 776.6 eV, is visible.Similar oxidation effects have been reported already for size selected CoPd and CoPt alloy clusters on Ni [28,29]. The fully oxidized Co 1 -O sample was prepared in [28] by introducing a waiting time of 60 min. between the magnetization of the Ni film and the deposition of the Kr buffer layer.…”

“…While the left line does not fit for all species, the right perfectly matches. The Co 1 -O spectrum was already published in [28]. adatom, respectively.…”