Structural Properties and Recrystallization Effects in Ion Beam Modified B20-type FeGe Films

TL;DR

This study explores how ion irradiation and annealing can systematically modify the structural and magnetic properties of B20-phase FeGe films, with implications for skyrmion-based spintronic applications.

Contribution

It introduces a method to control disorder and recrystallization in FeGe films via ion irradiation and in-situ annealing, providing insights into the crystallization kinetics.

Findings

Ion irradiation creates amorphized regions that can host antiskyrmions.

Recrystallization can be controlled by annealing temperature.

Crystallization follows diffusion-controlled growth modeled by Johnson-Mehl-Avrami-Kolmogorov.

Abstract

Disordered iron germanium (FeGe) has recently garnered interest as a testbed for a variety of magnetic phenomena as well as for use in magnetic memory and logic applications. This is partially owing to its ability to host skyrmions and antiskyrmions -- nanoscale whirlpools of magnetic moments that could serve as information carriers in spintronic devices. In particular, a tunable skyrmion-antiskyrmion system may be created through precise control of the defect landscape in B20-phase FeGe, motivating developing methods to systematically tune disorder in this material and understand the ensuing structural properties. To this end, we investigate a route for modifying magnetic properties in FeGe. Specifically, we irradiate epitaxial B20-phase FeGe films with 2.8 MeV Au$^{4+}$ ions, which creates a dispersion of amorphized regions that may preferentially host antiskyrmions at densities controlled by the irradiation fluence. To further tune the disorder landscape, we conduct a systematic electron diffraction study with in-situ annealing, demonstrating the ability to recrystallize controllable fractions of the material at temperatures ranging from approximately 150$^{\circ}$ C to 250$^{\circ}$C. Finally, we describe the crystallization kinetics using the Johnson-Mehl-Avrami-Kolmogorov model, finding that the growth of crystalline grains is consistent with diffusion-controlled one-to-two dimensional growth with a decreasing nucleation rate.