Large Thermo-Spin Effects in Heusler Alloy-Based Spin Gapless Semiconductor Thin Films

Area of Science:

• Spintronics
• Condensed Matter Physics
• Materials Science

Background:

• Heusler alloys are promising for spintronic applications due to their high Curie temperature and spin polarization.
• Spin gapless semiconductors (SGSs) offer tunable properties for advanced electronic devices.

Purpose of the Study:

• Investigate the temperature-dependent anomalous Nernst effect (ANE) and longitudinal spin Seebeck effect (LSSE) in CoFeCrGa thin films.
• Compare the performance of these films with bulk materials and other magnetic systems.
• Understand the underlying mechanisms governing ANE and LSSE in these heterostructures.

Main Methods:

• Fabrication of CoFeCrGa thin films on MgO substrates.
• Measurement of ANE and LSSE coefficients across a range of temperatures.
• Utilized radio frequency transverse susceptibility and broad-band ferromagnetic resonance.
• Correlated LSSE signal with magnetic anisotropy and Gilbert damping.

Main Results:

• The MgO/CoFeCrGa (95 nm) film showed an ANE of ≈1.86 μV K⁻¹ at room temperature, vastly exceeding bulk CoFeCrGa.
• The LSSE coefficient for the MgO/CoFeCrGa (95 nm)/Pt (5 nm) heterostructure was ≈20.5 nV K⁻¹ Ω⁻¹, double that of La₀.₇Sr₀.₃MnO₃.
• Both ANE and LSSE showed identical temperature dependences, peaking at ≈225 K due to magnon scattering and population effects.
• Extrinsic skew scattering was identified as the dominant mechanism for ANE.

Conclusions:

• CoFeCrGa thin films demonstrate superior ANE and LSSE properties compared to bulk and some established materials.
• The temperature dependence of ANE and LSSE is linked to magnon dynamics.
• Established a correlation between LSSE, magnetic anisotropy, and Gilbert damping.
• Findings are crucial for developing efficient Heusler alloy-based spin caloritronic nanodevices.