In Situ and Operando TEM Studies on the Magnetic Textures in Permalloy

Understanding the generation, annihilation and propagation of magnetic structures with magnetic fields and spin currents are essential for the development of the next generation of spintronics devices. Here, we present our work on the spatially resolved magnetic domain imaging in Ni₈₀Fe₂₀/graphene using Lorentz -Transmission Electron Microscopy (LTEM) along with various <i>in-situ</i> and <i>operando</i> techniques [1]. To study the localized effects of NiFe (5 nm) – Graphene, nano-devices were fabricated on the electron transparent SiN window of a MEMS chip and subjected to the LTEM studies. In-plane magnetic fields were applied on the Ni₈₀Fe₂₀ to study the propagation of magnetic domain walls by continuously imaging the locations with NiFe and NiFe-graphene interface. The applied magnetic field on samples were varied by changing the strengths of the objective lens and appropriate sample tilt. The observations were backed with magnetization dynamics measurements using a flip-chip method for the measurement of bulk properties and micromagnetic simulations using Mumax³ for introducing different interfacial effects and studying the local changes to the magnetic microstructures caused by the introduction of Graphene.<br/>Magnetic textures generated in thin films are affected not just by the 2D interfaces but also by shape of the magnetic thin films since they allow for different pinning configurations and anisotropies. This was investigated by patterning Mulitiples NiFe(5 nm)/Pt (5 nm) rhombuses (with diagonals in the 500- 1000 nm range) using the focused ion beam to support the formation of a confined magnetic vortex. These NiFe/Pt rhombuses were connected through a 300 nm channel to allow for the use of operando spin-currents. Such a system was used to study the creation, evolution, and annihilation of magnetic vortices in the NiFe/Pt system. Spin current was pumped into the NiFe from the adjacent Pt layer by spin Hall effect. A pulsed charged current at a frequency of 100 kHz and 1% duty cycle was used to minimise localized heating effects. Modified Transport of Intensity Equations (MTIE) were used to estimate the direction of the magnetic field in the different shapes and their evolution with spin currents were studied.<br/>[1] E. Tyukalova<i> et al.</i>, "Challenges and Applications to Operando and In Situ TEM Imaging and Spectroscopic Capabilities in a Cryogenic Temperature Range," <i>Accounts of Chemical Research, </i>vol. 54, no. 16, pp. 3125-3135, 2021/08/17 2021, doi: 10.1021/acs.accounts.1c00078.<br/>[2] W. Lv<i> et al.</i>, "Electric-Field Control of Spin–Orbit Torques in WS2/Permalloy Bilayers," <i>ACS Applied Materials & Interfaces, </i>vol. 10, no. 3, pp. 2843-2849, 2018/01/24 2018, doi: 10.1021/acsami.7b16919.<br/>[3] H. Yang<i> et al.</i>, "Significant Dzyaloshinskii–Moriya interaction at graphene–ferromagnet interfaces due to the Rashba effect," <i>Nature Materials, </i>vol. 17, no. 7, pp. 605-609, 2018/07/01 2018, doi: 10.1038/s41563-018-0079-4.