Investigating the Electronic and Magnetic Properties of Equiatomic Quaternary Heusler Alloys for Spintronics
Student: Eesha Andharia
Degree: Ph.D., August 2022
Major Professor: Dr. Bothina Manasreh
Research Area(s):
Microelectronics
Modeling and simulation
Background/Relevance

Magnetic Tunnel Junctions (MTJs) are a type of Spintronics devices that find wide application in MagneticRandomAccess Memory (MRAM).

TunnelMagnetoResistance (TMR) of these devices is the key parameter for testing the performance of these MTJs and it depends on high spinpolarization of the fixed Ferromagnetic electrode.
Innovation

Use of Quaternary Heusler Alloys (QHA) as a candidate material for the fixed Ferromagnetic electrode for improved TMR values even at Room Temperature (RT).
Approach
 Simulating quasiparticle bandstructure of QHAs using VASP code.
 Preserving the halfmetallicity of these QHAs in its 2D thinfilm form using Abinitio thermodynamics using Wein2k.
 Calculating the TMR values of QHA/MgO/CoFeB based MTJs using Micromagnetic simulations.
Key Results
 Optimization of crystal structure of QHA –CoFeMnSi using Wien2k code.
 For a Facecenteredcubic (FCC) crystal structure, the lattice parameters obtained using PBE functional within the framework of Density Functional Theory (DFT) are a=b=c=10.5962 Bohrs.
 Testing convergence with respect to overall Ecut_off (cutoff energy) , which is a product of RMT (Radius of Muffin Tin Orbital) and Kmax (Cutoff for the kinetic energy of plane waves) was 9.0 Ry.
 Convergence was also tested w.r.t Kmesh and was achieved for as high as 2000 Kpoints.
Conclusions

Optimization of lattice parameters and atomic positions obtained using Wien2k code.

Selfconsistentfield (scf) calculations have been undertaken using Wien2k code and the fermi energy Ef = 0.7643 eV.
Future Work

Undertaking GW calculations to obtain the Quasiparticle bandstructure of bulk and 2D QHAa – CoFeMnSi/Ge and CoFeCrSi/Ge.

Using Abinitio thermodynamics to study the surface stability of 2D QHAa.