Dependence of the Growth Mode in Epitaxial FePt Films on Surface Free Energy

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• Epitaxial L1₀-ordered FePt thin films are crucial for magnetic recording and spintronics due to high perpendicular magnetic anisotropy (PMA).
• Controlling film growth mode is essential for achieving desired FePt properties.
• Distinguishing the roles of lattice mismatch and surface free energy in growth mode is challenging due to their correlation.

Purpose of the Study:

• To investigate the effect of surface free energy on the growth mode of FePt epitaxial films.
• To isolate the influence of surface free energy by using substrates with similar lattice constants.
• To correlate surface free energy with film morphology and magnetic properties.

Main Methods:

• Epitaxial growth of FePt films on MgO, NiO, and MgON substrates with similar lattice constants.
• Contact angle measurements to determine surface free energy of substrates.
• Characterization of film growth mode (3D island vs. 2D-like).
• Measurement of perpendicular magnetic anisotropy (PMA).

Main Results:

• FePt growth mode transitioned from 3D island on MgO to a more 2D-like mode on MgON and NiO.
• MgON and NiO exhibited higher surface free energy than MgO, correlating with the observed growth mode change.
• MgON promoted a flat FePt surface and enhanced PMA compared to SrTiO₃ (STO)/FePt.
• Tuning surface free energy allows control over FePt film flatness and PMA.

Conclusions:

• Surface free energy is a key parameter for controlling the growth mode and properties of FePt epitaxial films.
• Modifying substrate surface free energy offers a pathway to optimize FePt films for spintronics and magnetic recording.
• This approach enables flexible functional design of thin films with tailored magnetic properties.