Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Materials Science

Background:

• Spin-transfer-torque magnetic random access memory (STT-MRAM) offers non-volatility, high density, and low power consumption.
• CoFeB/MgO-based magnetic tunnel junctions (MTJs) are key components, exhibiting high tunnel magnetoresistance and perpendicular magnetic anisotropy (PMA).
• Experimental studies confirm the necessity of capping layers for strong PMA, but the underlying mechanism is not fully understood.

Purpose of the Study:

• Investigate the origin of perpendicular magnetic anisotropy (PMA) in MgO/CoFe/metallic capping layer structures.
• Elucidate the physical mechanism by which capping layers influence PMA.
• Provide insights for the development of nanoscale STT-MRAM.

Main Methods:

• Utilized a first-principles computation scheme to model MgO/CoFe/metallic capping layer structures.
• Analyzed the interfacial PMA contributions from both MgO/CoFe and CoFe/capping layer interfaces.
• Resolved magnetic anisotropy energy by layer and orbital to understand PMA variations.

Main Results:

• The computational results for PMA trends with different capping materials align well with experimental observations.
• Identified that interfacial PMA originates from both the MgO/CoFe and CoFe/capping layer interfaces.
• Attributed the variation in PMA to distinct hybridizations of d and p orbitals, mediated by spin-orbit coupling, influenced by the capping material.

Conclusions:

• The study clarifies the physical origin of PMA enhancement in CoFeB/MgO based MTJs due to capping layers.
• Demonstrated that interfacial effects and orbital hybridization are critical factors determining PMA.
• The findings offer significant benefits for the research and development of next-generation nanoscale STT-MRAM devices.