Enhanced perpendicular magnetocrystalline anisotropy energy in an artificial magnetic material with bulk spin-momentum coupling

TL;DR

This paper demonstrates that breaking structural inversion symmetry in Co-Pt/Pd multilayers enhances perpendicular magnetocrystalline anisotropy energy, with first-principles calculations confirming the role of bulk spin-momentum coupling in this enhancement.

Contribution

It introduces the asymmetric CoPtPd multilayer as the first artificial magnetic material with bulk spin-momentum coupling, showing increased PMA due to symmetry breaking.

Findings

Asymmetric Co/Pd/Pt multilayers have larger PMA than symmetric ones.

First-principles calculations support the role of bulk spin-momentum coupling.

Symmetry breaking significantly enhances magnetic anisotropy energy.

Abstract

We systematically investigate the perpendicular magnetocrystalline anisotropy (MCA) in Co$-$Pt/Pd-based multilayers. Our magnetic measurement data shows that the asymmetric Co/Pd/Pt multilayer has a significantly larger perpendicular magnetic anisotropy (PMA) energy compared to the symmetric Co/Pt and Co/Pd multilayer samples. We further support this experiment by first principles calculations on the CoPt$_2$, CoPd$_2$, and CoPtPd, which are composite bulk materials that consist of three atomic layers in a unit cell, Pt/Co/Pt, Pd/Co/Pd, Pt/Co/Pd, respectively. By estimating the contribution of bulk spin-momentum coupling to the MCA energy, we show that the CoPtPd multilayer with the symmetry breaking has a significantly larger perpendicular magnetic anisotropy (PMA) energy than the other multilayers that are otherwise similar but lack the symmetry breaking. This observation thus provides an evidence of the PMA enhancement due to the structural inversion symmetry breaking and highlights the asymmetric CoPtPd as the first artificial magnetic material with bulk spin-momentum coupling, which opens a new pathway toward the design of materials with strong PMA.