טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentYagil Alon
SubjectMagnetic Imaging of Skyrmions in Thin Films
DepartmentDepartment of Physics
Supervisors Professor Michael Reznikov
Dr. Ophir Auslaender


Abstract

Skyrmions are nanometer-scale magnetic domains which can be attributed a nontrivial topological charge. Their size and stability make them leading candidates for high density magnetic memory storage. Skyrmions have been observed at low temperatures in certain bulk crystals with no inversion center. Recently, thin multistack films of Ir/Fe/Co/Pt have been shown to host magnetic skyrmions at ambient conditions. Furthermore, the properties of these films can be tuned by the thickness of the magnetic layers. In this work we explore the properties of the stray field from skyrmions, which is measurable using magnetic force microscopy. We show that a simple model of the skyrmion field as a dipole plus quadrupole field is sufficient to capture properties such as skyrmion size. We then apply this knowledge to probe the topological Hall effect. We show that topological Hall resistivity scales with the isolated skyrmion density over a wide range of temperature and magnetic field, confirming the impact of the skyrmion Berry-phase on electronic transport. While we establish qualitative agreement between the topological Hall resistivity and the topological charge density, our quantitative analysis shows much larger topological Hall resistivity than current theory predicts for the observed skyrmion density. Our results are fundamental for the skyrmion topological Hall effect in multilayers, where interfacial interactions, multiband transport, and non-adiabatic effects play an important role, and for skyrmion applications that rely on the topological Hall effect.