Measurement of orbital asymmetry and strain in Co90Fe10/Ni multilayers and alloys: Origins of perpendicular anisotropy

TL;DR

This study investigates the origins of perpendicular magnetic anisotropy in Co90Fe10/Ni multilayers using spectroscopic and diffraction techniques, revealing that orbital moment asymmetry, not strain, primarily drives the anisotropy.

Contribution

It demonstrates the direct link between orbital moment asymmetry and perpendicular anisotropy, and isolates interface effects by comparing multilayers with alloys.

Findings

Orbital moment asymmetry correlates with anisotropy.

Strain does not significantly influence anisotropy.

Interface effects are key to understanding anisotropy differences.

Abstract

We use broadband ferromagnetic resonance spectroscopy and x-ray diffraction to investigate the fundamental origin of perpendicular anisotropy in Co90Fe10/Ni multilayers. By careful evaluation of the spectroscopic g-factor, we determine the orbital moment along the out-of-plane and in-plane directions. For the multilayers, we find a direct relationship between the orbital moment asymmetry and the perpendicular anisotropy, consistent with the theory of Bruno [P.Bruno, Phys. Rev. B, 39, 865 (1989)]. A systematic x-ray diffraction study revealed the presence of a trigonal strain as high as 0.7 % in some samples. However, we found no direct correlation between the strain and the anisotropy, indicating that the anisotropy is not dominated by magnetoelastic effects. In order to further study the interface structure on the anisotropy, we prepared a set of equivalent alloy samples. The strain in the alloy samples was comparable to that of the multilayer samples; however the orbital moment asymmetry in the alloy samples showed a very different trend allowing us to isolate the effect of the interfaces in the multilayers.