Characterisation of manganese alloy antiferromagnetic materials for property screening and for heterostructure effects

Faster, more efficient electronic devices are in constant demand in computing. Increasing climate change pressure makes energy efficiency paramount in modern technology. Current materials research includes investigation into spintronics to reduce energy usage and increase switching speed in memory technology. To increase device density, antiferromagnetic materials, with zero magnetization meaning resistance to external magnetic fields, are used. Antiferromagnetic spin orbit torque devices are considered excellent candidates for spintronic memory bits. Antiferromagnetic materials are explored in this thesis using ab-initio density functional theory to predict material properties, including structural, electronic and magnetic properties like magnetocrystalline anisotropy. Properties of several Mn-alloy collinear L10 and noncollinear L12 and D019 antiferromagnets were calculated. The magnetocrystalline anisotropy energy calculated for noncollinear antiferromagnets is restricted to specific high symmetry planes. Calculations show Mn-Ir alloys’ immense magnetocrystalline anisotropy with 4.187 meV/FU and 6.26 meV/FU for L10 and L12 Mn-Ir, indicating these Mn-Ir alloys are materially and energetically efficient antiferromagnets for use in spintronic devices.
We investigate straining effects on D019 materials, finding distinct structural and magnetic property changes under ±6% (001) planar expansion strain. Weyl points appear consistently, shifting within D019 strained materials, by 0.22 eV in Mn3Ge. This consistency maintains the electron mobility, maintaining switching speeds. We determine Weyl points are conserved in D019 antiferromagnets Mn3Ge and Mn3Sn.
We determined interface effects on D019 noncollinear antiferromagnets, including charge density changes, projected density of states, structural effects and electronic properties, characterising surfaces and platinum interfaces. We calculate Mn3Ga surface magnetic moments cant significantly, to 44.66◦ , and platinum interface charge transfer of 1.795 e for Sn in Mn3Sn, indicating major charge polarization at the interface. We see changes to manganese density of states by 0.4 eV at platinum interfaces, likely due to heterostructure straining. We conclude significant charge transfer helps stabilise interfaces magnetically, resulting in altered conductivity.