Studies Of Photoemission Electron Microscopy In Epitaxial Magnetic Heterostructure Films

As a newly evolving field,spintronics has become an important research area in both frontier physics theory and information technology.Magnetic multilayered films play a fundamental role in spintronic devices,becoming the focus of recent studies.Furthermore,the study with a focus on magnetic properties of multilayered films has attracted more and more interests,especially the magnetic domain structures dominated by surface and interface.Among methods for magnetic domain imaging in nano-scaled films,photoemission electron microscopy?PEEM?is sensitive to the spectroscopic information directly from the magnetic films and surfaces through photoemission process with variable excitation sources.Moreover,the breakthrough in deep ultra-violet laser technology makes it possible for PEEM to realize domain imaging without the limitation of synchrotron radiation facilities.In this dissertation,PEEM tech is used as the critical characterization method to carry out detailed studies on the magnetic contrast due to the photoemission process near Fermi level in epitaxial ferromagnetic or anti-ferromagnetic films.Primary contents and results are as follow:?1?The 177.3 nm deep ultraviolet laser with tunable polarizations was applied as excitation source connected to the PEEM/LEEM system,achieving a spatial resolution better than 20 nm.At the same time,the combined system of DUV-PEEM and MBE was completed,which provided the technical conditions for domain imaging in PEEM observation in magnetic films with epitaxial structure.?2?The magnetic domain structure of L1₀-FePt was directly observed in a?001?oriented surface using circular polarized DUV,and the spatial resolution was calculated to be 43.2 nm,which was at the same level as XMCD-PEEM.Furthermore,a stepped Cr seeding layer was applied to induce the formation of large-area epitaxial FePt films with?001?and?111?two orientations,where MLD with large asymmetry was observed in the transition area of two phases.The signal of MLD was 4.6 times larger than that of MCD.Detailed studies on the micro structure of the MLD area were performed by micro-LEED showing a transient state of FePt crystal structure with a FCT?111?orientation in the transition process of crystal structure from FCT?001?to FCC?111?.This novel structure indicated a twofold symmetry and a canted magnetization direction,giving a reasonable explanation of the MLD contrast.?3?Epitaxial IrMn₃ films were fabricated by molecular beam epitaxy.The contrast with a dependence of linear polarization was observed in?001?-oriented IrMn surface using UV light,and the origin due to antiferromagnetism of IrMn was confirmed,proving the feasibility of the threshold PEEM in antiferromagnetic domain imaging.Furthermore,similar experiment was performed on?111?-oriented IrMn surface,indicating a negligible MLD contrast.Therefore,the relationship between antiferromagnetic contact and crystal structure should be further explored.