Self-organized synthesis of patterned magnetic nanostructures with in-plane and perpendicular to the plane magnetization

TL;DR

This paper presents a laser-induced self-organization method to synthesize patterned magnetic nanoparticle arrays with controllable in-plane and out-of-plane magnetization orientations, based on residual strain effects.

Contribution

It introduces a cost-effective, non-epitaxial technique for fabricating magnetic nanoparticle arrays with tailored magnetization directions influenced by magnetostrictive strain.

Findings

Nanoparticle morphology and magnetic behavior characterized by microscopy.

Magnetization orientation depends on magnetostrictive properties and residual strain.

Demonstrates control over magnetic orientation in nanoparticle arrays.

Abstract

Patterned arrays of ferromagnetic nanoparticles of Co, Ni, and Fe_{\text{50}} Co_{\text{50}} have been synthesized from their ultrathin metal films on SiO_{\text{2}} substrate by nanosecond laser-induced self-organization. The morphology, nanostructure, and magnetic behavior of the nanoparticle arrays were investigated by a combination of electron, atomic force, and magnetic force microscopy techniques. Transmission electron microscopy investigations revealed a granular polycrystalline nanostructure, with the number of grains inside the nanoparticle increasing with their diameter. Magnetic force measurements showed that the magnetization direction of the Co and Ni nanoparticles was predominantly out-of-plane while those for the Fe_{\text{50}}Co_{\text{50}} alloy was in the plane of the substrate. This difference in behavior is due to the dominating influence of magnetostrictive energy on the magnetization as a result of residual thermal strain following fast laser processing. Since the magnetostriction coefficient is negative for polycrystalline Co and Ni, and positive for Fe_{\text{50}}Co_{\text{50}}, the tensile residual strain forces the magnetization direction of the negative magnetostriction materials out-of-plane and the positive magnetostriction materials in-plane. This demonstrates a cost-effective non-epitaxial technique for the fabrication of patterned arrays of magnetic nanoparticles with tailored magnetization orientations.