Abstract
We present x-ray absorption near edge structure (XANES) and x-ray magnetic circular dichroism (XMCD) measurements performed at the Co $K$ and W ${L}_{2,3}$ edges, on amorphous Co-W alloy nanoparticles, and a comparison with those on a bulk Co${}_{3}$W alloy. A strong hybridization between the $4p$ and $3d$ orbitals in Co and the $5d$ band in W are observed, resulting in an induced magnetic moment in the W atoms. The orbital to spin moment ratio in W of all these Co-W systems is positive, suggesting a parallel orientation of the two moments. This is opposite to the expected antiparallel coupling for atoms with a less-than-half-filled $5d$ band, according to Hund's third rule. These findings are supported by calculations of the electronic density of states projected at the Co $3d$ and W $5d$ orbitals, as well as XANES spectra and XMCD signals at the Co $K$ and W ${L}_{2,3}$ edges in a Co${}_{3}$W system.
Highlights
Magnetic nanoparticles (NPs) have recently been the focus of much research because of their scientific and technological interest in diverse fields.[1,2] Extensive magnetic characterization of these particles has been carried out with the elementspecific x-ray magnetic circular dichroism (XMCD) technique
It is an important tool to study the magnetic anisotropy of these nanoparticles systems, e.g., to evaluate the contribution of the orbital moment to this anisotropy as a result of the symmetry breaking at the particle surface.[1,3,4,5,6,7,8]
Co-W hybridization and electronic transfer from W 5d to Co orbitals are determined by analysis of x-ray absorption near edge structure (XANES) measurements at the Co K and W L3 edges
Summary
Magnetic nanoparticles (NPs) have recently been the focus of much research because of their scientific and technological interest in diverse fields.[1,2] Extensive magnetic characterization of these particles has been carried out with the elementspecific x-ray magnetic circular dichroism (XMCD) technique. The effects of similar 3d−5d hybridization, in particular on 5d induced magnetic moments, have been previously studied both experimentally and theoretically in Fe/W multilayers[10] and bulk Co100−xIrx alloys,[11] to cite some examples of metallic systems. The structural disorder in transition metal alloys has been demonstrated to influence their electronic configuration.[14] for amorphous Fe-Zr and Co-Zr alloy films, the induced spin and orbital moments detected in Zr (a less-than half filled 4d element) are found to be parallel aligned, breaking down Hund’s third rule. The complete morphological, structural, and magnetic study of these Co-W NPs samples can be found in Ref. 9
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