Tuning the Magnetic Properties of FeCo Thin Films through the Magnetoelastic Effect Induced by the Au Underlayer Thickness

Abstract

Tuning the magnetic properties of materials is a demand of several technologies; however, our microscopic understanding of the process that drives the enhancement of those properties is still unsatisfactory. In this work, we combined experimental and theoretical techniques to investigate the handling of magnetic properties of FeCo thin films via the thickness-tuning of a gold film used as an underlayer. We grow the samples by the deposition of polycrystalline FeCo thin films on the Au underlayer at room temperature by a magnetron sputtering technique, demonstrating that the lattice parameter of the sub-20 nm thickness gold underlayer is dependent on its thickness, inducing a stress up to 3% in sub-5 nm FeCo thin films deposited over it. Thus, elastic-driven variations for the in-plane magnetic anisotropy energy, K u , up to 110% are found from our experiments. Our experimental findings are in excellent agreement with ab initio quantum chemistry calculations based on density functional theory, which helps to build up an atomistic understanding of the effects that take place in the tuning of the magnetic properties addressed in this work. The handling mechanism reported here should be applied to other magnetic films deposited on different metallic underlayers, opening possibilities for large-scale fabrication of magnetic components to be used in future devices.

Large Perpendicular Magnetic Anisotropy in Nanometer-Thick Epitaxial Graphene/Co/Heavy Metal Heterostructures for Spin–Orbitronics Devices

“…However, the calculated critical thicknesses for the MAE switch, n C , are notably smaller than the observed values. Let us recall that in the simulations, apart from ultrafine k -meshes larger than 70 × 70, we have employed a 12 layer thick HM buffer layer (see SI Section 8), which is much larger than those typically used in similar theoretical studies. ,− In order to ensure converged MAE values below 0.1 meV, we have also avoided the use of perturbative approaches (see SI Section 7). Still, further sources of inaccuracy could be ascribed to Co-HM intermixing at the interface, or to the particular moiré pattern between the Gr and Co unit cells or to the shape anisotropy (SA), which has been neglected so far.…”

Origin of the Large Perpendicular Magnetic Anisotropy in Nanometer-thick Epitaxial Graphene/Co/Heavy Metal Heterostructures

“…In the following, we rationalize the experimental findings by presenting DFT-derived magnetic anisotropy energies (MAEs) and orbital magnetic moments (OMMs) for ideal and defected Gr/Co n /HM heterostructures (see Figures 3(A employed a 12 layer thick HM buffer layer (see SM section ?? ), which is much larger than those typically used in similar theoretical studies 15,[30][31][32][33][34] , and, in order to ensure converged MAE values below 0.1 meV, we have also avoided the use of perturbative approaches (see SM section ??). Still, further sources of inaccuracy could be ascribed to Co-HM intermixing at the interface, or to the particular moiré pattern between the Gr and Co unit cells or to the shape anisotropy (SA), which has been neglected so far.…”

Spatial anisotropy of the quantum spin liquid system YbMgGaO4 revealed by ab initio calculations

“…The initial (unrelaxed) geometry was constructed making use of the experimental data, as reported in the [18]. Aiming to set up the disposition of Mg and Ga along the separating random alloy layers, we employ the special-quasirandom-structure (SQS) technique [38,39], which allows designing structural models with very small supercell for A 1−x B x binary alloys which mimic the behavior of realistic alloys. (A and B are atomic species, whereas x is the atomic concentration of B).…”