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.

The perovskite structure is very common in ceramics. In this thesis, eleven kinds of high-entropy ABO3 perovskites, with five equimolar atoms in B sites, were successfully synthesized by high-energy ball milling and conventional pressureless sintering. Six of them, compositions #S1, Sr(Zr0.2Sn0.2Ti0.2Hf0.2Mn0.2)O3, #S5, Sr(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, #B2, Ba(Zr0.2Sn0.2Ti0.2Hf0.2Ce0.2)O3, #B3, Ba(Zr0.2Sn0.2Ti0.2Hf0.2Y0.2)O3-x, #B5, Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, and #BS1, (Ba0.5Sr0.5)(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, can form a cubic homogeneous single phase, while the others showed a major cubic phase with different amount of secondary phases. Phase purity was verified by energy dispersive x-ray spectroscopy (EDS) mapping. Quench experiments were carried out to prove that composition #S1, Sr(Zr0.2Sn0.2Ti0.2Hf0.2Mn0.2)O3, is an entropy stabilized perovskite, which is also characterized in atomic and nanoscale by aberration-corrected scanning transmission electron microscopy (AC STEM), STEM high-angle annular dark-field (HAADF) images, and STEM annular bright-field (ABF) images. Goldschmidt's tolerance factor (t) was introduced to be a necessary, but not sufficient, condition to form a homogeneous single phase, while the revised Hume-Ruthery rule for high-entropy alloys (HEAs) can not extend to the case of high-entropy ABO3 perovskites. The successful synthesis of these high-entropy ABO3 perovskites reveals the possibility to create high-entropy cubic ceramics and to discover new materials in ABO3 perovskites family.