The focus of the work is on the epitaxial growth of Mn5Ge3 layers on Ge (001) via ultra-fast solid-state reaction between Mn and Ge using millisecond range FLA at the ambient pressure in continuous N2 flow. Epitaxial Mn5Ge3 layers were obtained both on Ge (001) and Ge (111) substrates by optimizing the fabrication parameters, Mn thickness (30 nm), FLA energy density (100-110 Jcm-2) and FLA duration time. The epitaxial relationship between the alloy film and substrate is the (100) plane of Mn5Ge3 along [001] direction parallel with the [100] direction of Ge (001) plane. It is notable that the hexagonal c axis of Mn5Ge3 on Ge (001) is parallel to the film surface plane, while the reported Mn5Ge3’s c axis on Ge (111) tends to be perpendicular to the film plane. In fact, using ultrafast-SPE the c-axis of Mn5Ge3 is always parallel to the sample surface. Mn5Ge3 films exhibit ferromagnetism which is demonstrated by the anomalous Hall effect up to the TC = 283±5 K. The films exhibit their in-plane magnetic easy axis along the hexagonal c-axis independent of the Mn5Ge3 film thickness. This provides a new avenue for the fabrication of Ge-based spin-injectors fully compatible with industrial CMOS technology.
The deeper understanding of the magnetic, structural and electrical properties of (100) epitaxial Mn5Ge3 grown on Ge (001) are presented by utilizing DFT calculation (by our collaborator M. Birowska) and various experimental methods. The Mn atoms in Mn5Ge3 occupy two distinct Wyckoff positions with fourfold (Mn1) and sixfold (Mn2) multiplicity. During cooling down to 100 K the Mn5Ge3 unit-cell shows remarkable structural deformation. The nearest distance d3 between Mn2-Mn2 atoms in the hexagonal a-b plane is shortened much faster than the nearest distance d1 between Mn1-Mn1 atoms along hexagonal c axis. The DFT calculations show that below critical distance d3 < 3.002 Å, the Mn2 atoms are AFM coupled while for d3 > 3.002 Å the coupling is FM. The FM coupling between Mn1 atoms weakly depends on the atomic distance d1. Moreover, there is a transition from collinear to noncollinear spin configuration at about 70±5 K. Simultaneously, at low temperature, the angular dependent magnetoresistance shows a switching from multi-fold component to twofold symmetry. The combination of different experimental techniques with theoretical calculations enabled us to conclude that the switching between non-collinear and collinear spin configurations and the variation of anisotropic magnetoresistance in Mn5Ge3 is due to the strain induced change of the magnetic coupling between Mn2-Mn2 atoms.
Finally, the effects of strain on the structural and magnetic properties of epitaxial Mn5Ge3 on Ge (111) substrate by applying ms-range FLA are investigated. The X-ray diffraction results demonstrate that during FLA process the formation of nonmagnetic secondary phases of MnxGey is fully suppressed and the in-plane tensile strain is enhanced. The temperature dependent magnetization indicates that after FLA the Curie temperature of Mn5Ge3 increases from 283±5 K to above 400 K. Further Monte Carlo simulations manifest that the change of the strain in Mn5Ge3 during ms-range FLA modifies the distance between adjacent Mn atoms in the hexagonal basal plane, which provokes the different ferromagnetic interaction between them. Consequently, the significant increase of Curie temperature is observed. This provides a good way to improve the Curie temperature of Mn5Ge3 which is promising to realize room-temperature operated Ge based spin-injectors.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:76315 |
| Date | 18 October 2021 |
| Creators | Xie, Yufang |
| Contributors | Helm, Manfred, Fischer, Inga Anita, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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