Successful defence of  Abhay Kant Srivastava

Congratulations to Abhay Kant Srivastava!

Title: "Investigations of Anti-Skyrmions and Néel Skyrmions using Lorentz Transmission Electron Microscopy"

Abstract

Magnetic skyrmions are topologically stable magnetization whirls that can be found in magnetic systems with broken inversion symmetry. In this thesis, I focus on two different compounds Mn1.4Pt0.9Pd0.1Sn and PtMnGa that host anti-skyrmions and Néel skyrmions, respectively. For the Mn1.4Pt0.9Pd0.1Sn, the stabilization and thickness dependence of anti-skyrmions is studied using Lorentz Transmission Electron Microscopy (LTEM). Systematic measurements were performed at different temperatures and magnetic fields to generate the phase diagram, which revealed that the anti-skyrmion stability window varies little with thickness. The thickness independence stability of anti-skyrmions is attributed to the Dzyaloshinskii-Moriya interaction resulting from the D2d symmetry of the underlying crystal structure. For the compound PtMnGa, a detailed investigation of its crystal structure is performed. Observations revealed that its crystal structure is non-centrosymmetric (group C3v), in contrast with the centrosymmetric structure that has been assumed for more than 30 years and, thus, fulfills the criteria of hosting Néel skyrmions, which is discovered using the LTEM measurements. It is shown that skyrmions in this compound can be stabilized even at zero field after proper field cooling procedures. The thickness dependence of the skyrmion and cycloidal state is also investigated. Finally, it is shown that skyrmions in this compound are robust against in-plane magnetic fields of up to 1 T.