Control of magnetoelastic coupling in Ni/Fe multilayers using He$^+$ ion irradiation

TL;DR

This paper demonstrates that He$^+$ ion irradiation can precisely tune and even reverse the magnetoelastic properties of Ni/Fe multilayers without damaging their structure, enabling advanced spintronic device applications.

Contribution

It introduces a novel method of controlling magnetoelastic coupling in multilayers through post-growth He$^+$ irradiation, allowing reversible tuning of magnetostriction.

Findings

Magnetostriction can be tuned and reversed by He$^+$ irradiation.

Irradiation does not alter the multilayer's polycrystalline structure.

Critical fluence reduces magnetostriction, achieving strain insensitivity.

Abstract

This study reports the effects of post-growth He$^+$ irradiation on the magneto-elastic properties of a $Ni$ /$Fe$ multi-layered stack. The progressive intermixing caused by He$^+$ irradiation at the interfaces of the multilayer allows us to tune the saturation magnetostriction value with increasing He$^+$ fluences, and even to induce a reversal of the sign of the magnetostrictive effect. Additionally, the critical fluence at which the absolute value of the magnetostriction is dramatically reduced is identified. Therefore insensitivity to strain of the magnetic stack is nearly reached, as required for many applications. All the above mentioned effects are attributed to the combination of the negative saturation magnetostriction of sputtered Ni, Fe layers and the positive magnetostriction of the Ni$_{x}$Fe$_{1-x}$ alloy at the intermixed interfaces, whose contribution is gradually increased with irradiation. Importantly the irradiation does not alter the layers polycrystalline structure, confirming that post-growth He$^+$ ion irradiation is an excellent tool to tune the magneto-elastic properties of magnetic samples. A new class of spintronic devices can be envisioned with a material treatment able to arbitrarily change the magnetostriction with ion-induced "magnetic patterning".