Grain boundary defects induced Tc increment in MnSi

TL;DR

This study shows that laser annealing can significantly increase the Curie temperature of MnSi thin films by controlling crystal size, enabling miniaturized ferromagnetic devices.

Contribution

It introduces a method to enhance Tc in MnSi via controlled laser annealing and microstructure engineering, which was not previously demonstrated.

Findings

Tc increased by a factor of 4, reaching 120 K

Crystallinity controlled by laser fluence and pulse number

Spatially localized crystallization achieved with high resolution

Abstract

The rapid advancement of digital technologies necessitates significant progress in functional materials, which are often derived from scarce elements and involve complex manufacturing processes. Additionally, the trend towards miniaturization in high-tech devices has heightened the demand for extremely small components with tailored functionalities. In the domains of ferromagnetic materials, the market is mostly dominated by rare-earth elements-based structures, which are also limited in abundance. In this work, we focus on the microstructure and properties of MnSi. It is a ferromagnetic material with a relatively low Curie temperature (TC) of 30 K. However, our study demonstrates that Tc can be increased by a factor of 4 through careful control of the crystal size. MnSi thin films were synthesized by combining two non-equilibrium techniques: magnetron sputtering and laser annealing. Laser annealing provoked the crystallinity evolution, by heat accumulation, of the barely crystallized films deposited by magnetron sputtering. The laser beam scanning parameters were adjusted to achieve different fluence values, pulse numbers, and pulse frequencies at each point of the film. Films with a crystal size of around 20 nm exhibited a TC of up to 120 K. These properties were obtained under conditions of low fluence and a high number pulse. Local laser impacts were applied to as-deposited samples, enabling spatially controlled crystallization. The interface between the poorly and well-crystallized regions was showcased using high-resolution transmission electron microscopy (HR-TEM). A spatial resolution of approximately 100 {\mu}m was achieved. These results demonstrate the strong potential of laser annealing as a versatile and promising approach for the fabrication of miniaturized devices.