Authors:András Kovács, Zi-An Li, Kiyou Shibata, and Rafal E. Dunin-Borkowski
Magnetic skyrmions are vortex-like spin structures that are of great interest scientifically and for applications in low-power magnetic memories. The nanometer size and complex spin structure require high-resolution and quantitative experimental methods to study the physical properties of skyrmions. Here, we illustrate how Lorentz TEM and off-axis electron holography can be used to study the spin textures of magnetic skyrmions in the noncentrosymmetric B20-type helimagnet FeGe as a function of temperature and applied magnetic field. By reversing the magnetic field inside the microscope, the switching mechanism of the skyrmion lattice at 240 K is followed, showing a transition of the skyrmion lattice to the helical structure before the anti-skyrmion lattice is formed.
Authors:Martial Duchamp, Vadim Migunov, Amir H. Tavabi, Adnan Mehonic, Mark Buckwell, Manveer Munde, Anthony J. Kenyon, and Rafal E. Dunin-Borkowski
Silicon oxide-based resistive switching devices show great potential for applications in nonvolatile random access memories. We expose a device to voltages above hard breakdown and show that hard oxide breakdown results in mixing of the SiOx layer and the TiN lower contact layers. We switch a similar device at sub-breakdown fields in situ in the transmission electron microscope (TEM) using a movable probe and study the diffusion mechanism that leads to resistance switching. By recording bright-field (BF) TEM movies while switching the device, we observe the creation of a filament that is correlated with a change in conductivity of the SiOx layer. We also examine a device prepared on a microfabricated chip and show that variations in electrostatic potential in the SiOx layer can be recorded using off-axis electron holography as the sample is switched in situ in the TEM. Taken together, the visualization of compositional changes in ex situ stressed samples and the simultaneous observation of BF TEM contrast variations, a conductivity increase, and a potential drop across the dielectric layer in in situ switched devices allow us to conclude that nucleation of the electroforming—switching process starts at the interface between the SiOx layer and the lower contact.