Highly spin-polarized materials and devices for spintronics^∗

Area of Science:

• Materials Science and Engineering
• Condensed Matter Physics
• Spintronics

Background:

• Spintronics performance relies on current spin polarization.
• Highly spin-polarized current sources are crucial for advanced spintronic devices.
• Co-based full-Heusler alloys and spin filtering devices (SFDs) are promising candidates.

Approach:

• Fabricated multilayer structures using magnetron sputtering and microfabrication techniques.
• Investigated Co2Cr1-x Fex Al (CCFA(x)) and Co2FeSi1-x Alx (CFSA(x)) Heusler alloys.
• Utilized X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) for structural analysis.
• Developed SFDs with Co-ferrite ferromagnetic barriers prepared via surface plasma oxidation.

Key Points:

• Achieved giant tunnel magnetoresistance (TMR) of up to 390% at 5 K using Co2FeSi0.5Al0.5 (CFSA(0.5)) Heusler alloy electrodes, corresponding to 0.81 spin polarization.
• Demonstrated a strong spin filtering effect with -124% inverse TMR at 10 K using a Co-ferrite (CFO) barrier, indicating 77% spin filtering efficiency.
• Established a correlation between TMR and the crystalline structure (L21 vs. B2) of CFSA films.

Conclusions:

• Co-based Heusler alloys, particularly CFSA(0.5), are effective sources for highly spin-polarized currents.
• Co-ferrite exhibits a significant spin filtering effect, making it suitable for SFDs.
• Structural properties critically influence the performance of both Heusler alloy-based MTJs and Co-ferrite SFDs.