Enhanced spin-orbit coupling in tetragonally strained Fe-Co-B films

Area of Science:

• Materials Science
• Condensed Matter Physics
• Magnetism

Background:

• Epitaxial growth of thin films is crucial for advanced electronic devices.
• Tetragonal strain influences magnetic properties in alloys.
• Interstitial doping can modify material symmetry and electronic structure.

Purpose of the Study:

• To synthesize and characterize tetragonally strained Fe-Co-B alloys.
• To investigate the effect of interstitial boron on magnetic properties, particularly spin-orbit coupling (SOC).
• To explore methods for enhancing magnetocrystalline anisotropy and orbital magnetic moments.

Main Methods:

• Epitaxial film growth of Fe-Co-B on AuCu buffer layers.
• Stabilization of tetragonal strain (c/a ratios) via controlled boron doping.
• Ferromagnetic resonance (FMR) and X-ray magnetic circular dichroism (XMCD) measurements.
• First-principles calculations to understand atomic-level effects.

Main Results:

• Increased c/a ratio (1.013, 1.034, 1.02) with boron concentration (0, 4, 10 at.%) was achieved.
• Total orbital magnetic moment significantly increased with higher c/a ratios.
• Enhanced spin-orbit coupling (SOC) observed due to reduced crystal symmetry and interstitial boron.
• First-principles calculations confirmed B impurities in octahedral sites enhance orbital magnetic moments.

Conclusions:

• Interstitial boron doping effectively enhances SOC phenomena in Fe-Co-B alloys.
• Stabilizing anisotropic strain via 4 at.% B doping offers a route to tune magnetocrystalline anisotropy and orbital moment.
• Boron doping influences film microstructure, coercive field, and magnetic relaxation.