The Growth and Characterisation of Mn2Au Thin Films and Heterostructures

Abstract

In this thesis, Mn2Au thin films and heterostructures are grown via molecular beam epitaxy. Mn2Au thin films are investigated on MgO (001) and Al2O3 (1102) substrates, and on Pt (111) seed layer grown on an Al2O3 (0001) substrate. The MgO (001) and Al2O3 (1102) substrate resulted in polycrystalline films, while the Al2O3(0001)/Pt (111) substrate and seed layer resulted in high crystalline quality Mn2Au (110) films. The films were characterised in-situ via reflection high energy electron diffraction, low energy electron diffraction; and ex-situ via θ − 2θ X-ray diffraction, azimuthal X- ray diffraction, reciprocal space maps, and X-ray reflectometry. The heterostructures used Al2O3(0001)/Pt (111) seed layers to grow Co (111)/Mn2Au (110) bilayers and Fe (110)/Mn2Au (110) bilayers which were structurally analysed using reflection high energy electron diffraction and θ−2θ X-ray diffraction, as-deposited and after annealing at 350 ◦ C and 500 ◦ C in an 800 mT applied magnetic field. Magnetic characterisation of the stacks was performed using room temperature vibrating sample magnetometry, both as-deposited and after the annealing cycles. The heterostructures were found to demonstrate exchange coupling between the Co (111)/Mn2Au layers as deposited, and the field cooling was unable to induce room temperature exchange bias in any of these. Heterostructures of the form Mn2Au (001)/Fe (001) was grown on an Al2O3 (1102)/Ta (001) substrate/seed layer along with one of the form Mn2Au (110)/Fe (110) grown on an Al2O3 (0001)/Pt (111) seed layer. These heterostructures were characterised structurally using reflection high energy electron diffraction, θ − 2θ X-ray diffraction, and azimuthal X-ray diffraction. The scope of the exchange coupling effect in these heterostructures was comprehensively investigated using room temperature vibrating sample magnetometry, both in their as-deposited state and after a field cooling cycle from 350 ◦ C to room temperature in an 800 mT applied magnetic field. The exchange coupling effect was also investigated using low temperature vibrating sample magnetometry measurements in the range of 5 K-270 K, after further field cooling in a 1 T applied field from 300 K-5 K.