UC San Diego

The Heusler/MgO-based magnetic tunnel junctions (MTJs) with perpendicular magnetic anisotropy (PMA) have attracted extensive interest because of their potential utilization in spin-transfer-torque magnetic random-access memory (STT-MRAM) with long retention time and low switching current. As a large family of intermetallic compounds, Heusler alloys offer fascinating magnetic properties due to their wide variety of element compositions. Nevertheless, the selection of promising Heusler compounds candidates for the application of p-MTJs with high stability and low energy consumption becomes a grand challenge. In this dissertation, we provided a systematic high-throughput computational design of Heusler/MgO heterostructures to search for promising structures with robust materials stability and large perpendicular magnetic anisotropy by employing a series descriptors such as formation energy, convex hull distance, magnetic ordering, lattice misfit, magnetic anisotropy constant, interfacial cleavage energy, spin polarization, and tunnel magnetoresistance (TMR).

In the first project, we focused on the full Heusler (X2YZ) and half Heusler (XYZ) compounds. By using a comprehensive screening over 40, 000 ternary Heusler compounds, 363 full Heusler compounds, and 134 half Heusler compounds were confirmed thermodynamically stable, where five full Heusler compounds and two half Heusler compounds were found promising for designing p-MTJs.

In the second project, we studied the origin of the large interfacial PMA in the Co2FeAl/MgO structure, by analyzing the layer-resolved and atomic-orbital-resolved Ki distributions. Later, the influences of the 26 capping layers on the Co2FeAl/MgO structure were further investigated. Our calculations indicated that adding Fe- and W-capping layers can significantly increase the Ki of the system.

In the third project, we performed a systematic high-throughput screening in selecting the quaternary Heusler/MgO heterostructures. 7 out of 3094 stable quaternary Heusler compounds were found feasible for future applications in the p-MTJs. Their phase stability was further confirmed by using the swapping method.

In the fourth project, we proposed a swapping method to predict the disordering effects in the quaternary Heusler (XX′YZ) compounds. By using the swapping method, we successfully verified the ordered structure of CoFeCrGe, the L21disordering in the CoMnCrAl, and the DO3 disordering in the CoFeMnGe, demonstrating the efficiency of our method.