DFT-NEGF Simulation Study of Co2FeAl-MgO-Co2FeAl Magnetic Tunnel Junctions Under Biaxial Strain

• Published in: IEEE transactions on magnetics Vol. 58; no. 5; pp. 1 - 6
• Main Authors: Noh, Seongcheol, Sanvito, Stefano, Shin, Mincheol
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.05.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Anisotropy; Axial stress; Compressive properties; Co₂FeAl; Current density; Damping; Density functional theory; density functional theory - nonequilibrium Green’s function (DFT-NEGF); Green's functions; Heusler; Heusler alloys; Lattice parameters; Lattices; magnetic tunnel junction (MTJ); Magnetic tunneling; Magnetism; Magnetoresistance; magnetoresistive random access memory (MRAM); Magnetoresistivity; Metallicity; Metals; Orbits; Polarization (spin alignment); Random access memory; Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA); spin and molecular electronics algorithm on a generalized atomic orbital landscape (SMEAGOL); spintronic; Strain; Strain analysis; Tensile strain; Thermal stability; Tunnel junctions; Tunneling magnetoresistance; Voltage
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/TMAG.2022.3158549

Conventional spin-transfer torque-based magnetoresistive random access memory (STT-MRAM) with CoFeB electrodes has great potential as universal memory. However, state-of-the-art STT-MRAM technology has encountered the issues such as high writing current density and low thermal stability for scaling down to <inline-formula> <tex-math notation="LaTeX">1\times </tex-math></inline-formula> nm. Heusler alloy has been suggested as an alternative to resolve these problems by significantly reducing the Gilbert damping constant while preserving approximately 100% spin polarization. In particular, <inline-formula> <tex-math notation="LaTeX">L2_{1} </tex-math></inline-formula>-ordered Co 2 FeAl (CFA)-based magnetic tunnel junction (MTJ) exhibits outstanding half-metallicity and perpendicular magnetorcystalline anisotropy characteristics arising from Co(Fe)-O orbital hybridization at the interface. In this work, we investigate the biaxial strain effects of CFA-based MTJ by adjusting in-plane lattice constants from −4% to +4%. Our density functional theory - nonequilibrium Green's function (DFT-NEGF) calculations present that FeAl-O interfaced MTJ shows a converged tunneling magnetoresistance (TMR) ratio under compressive strain while Co 2 -O interfaced MTJ shows strain-sensitive TMR ratio under both compressive and tensile strain. The difference in the current-density trends for the two types of MTJs is mainly attributed to the additional state arising from Fe-O bonding. Our results emphasize the careful control of straintronic techniques on CFA-MTJs.