We have prepared ferromagnetic (FM) nanostructures to study high frequency magnetization dynamics in permalloy nanodisks using Lorentz transmission electron microscopy (TEM). The nanodisks were fabricated on thin silicon nitride membranes using three different fabrication methods: (a) lift-off, (b) ion beam etching (IBE) and (c) stencil lithography.

(a) In the first method, a bilayer of positive PMMA resist was used to create an undercut structure, which ensures a clean lift-off process. An additional offset electron beam exposure of the pattern was used to achieve a larger undercut. The result of the offset exposure was controlled by observing a cross-section of the developed bilayer resist using a scanning electron microscope (SEM) in snapshot mode to avoid melting.

(b) The second method involved the use of dry etching to etch a thin permalloy film using an Ar ion beam, while an electron-beam-patterned negative resist mask preserved the desired structure. Redeposition of etched material was found to construct fences at the edges of the structures. The fences, which could affect the magnetic properties of the nanodisks, were removed by using additional etching at a shallow angle.

(c) The third method, stencil lithography, makes use of nanostencils. Stencils (shadow masks) with nm-sized apertures milled in an identical SiN membrane using a focused ion beam. This method avoids the use of electron beam lithography, which is common in preparing nanodisk samples for TEM.

Results of the three fabrication methods were compared using SEM and Lorentz TEM. Magnetization dynamics in the nanodisks, which is important for the development of spintronics, will be studied with high spatial and temporal resolution in TEM using magnetic imaging with Lorentz TEM, off-axis electron holography and electron ptychography.