Studies of nanomagnetism using synchrotron-based x-ray photoemission electron microscopy (X-PEEM)

Abstract

As interest in magnetic devices has increased over the last 20 years, research into nanomagnetism has experienced a corresponding growth. Device applications from magnetic storage to magnetic logic have compelled interest in the influence of geometry and finite size on magnetism and magnetic excitations, in particular where the smallest dimensions reach the important magnetic interaction length scales. The dynamical behavior of nanoscale magnets is an especially important subset of research, as these phenomena are both critical for device physics and profoundly influenced by finite size. At the same time, nanoscale systems offer unique geometries to promote and study model systems, such as magnetic vortices, leading to new fundamental insights into magnetization dynamics. A wide array of experimental and computational techniques have been applied to these problems. Among these, imaging techniques that provide real-space information on the magnetic order are particularly useful. X-ray microscopy offers several advantages over scanning probe or optical techniques, such as high spatial resolution, element specificity and the possibility for high time resolution. Here, we review recent contributions using static and time-resolved x-ray photoemission electron microscopy to nanomagnetism research.

Emergent reduced dimensionality by vertex frustration in artificial spin ice

“…The exact mechanism of island moment reversal (via coherent rotation or more complex intermediate states 25 ) is unclear, but by slowly cooling below room temperature, we can drive the arrays into their thermalized ground state. This sort of sample allows us to study both the ground state and thermal fluctuations about the ground state using photoemission electron microscopy with x-ray magnetic circular dichroism contrast (XMCD-PEEM) 26,27 . Measurements of the island moment configurations at T = 160 K indicate that the arrays are static at that temperature and are close to their predicted ground state, as depicted in Fig.…”

Magnetic imaging with full-field soft X-ray microscopies

“…Fig. 3 shows the schematics of an X-ray PEEM instrument [31]. In most of these instruments, the low-energy secondary electrons generated in the primary X-ray absorption process are used for imaging, leaving the sample through the surface and being guided through a high-resolution electron optics column onto the imaging detector.…”

Single-Particle Phenomena in Magnetic Nanostructures

“…Photoemission electron microscopy (PEEM) combines photoelectron spectroscopies with microscopic techniques. PEEM was initially developed with UV sources, but later synchrotron-based X-ray sources were exploited due to the greater element specificity that it offers with soft X-rays [209]. Synchrotron sources offer a multitude of techniques among which excellent chemical and magnetic contrast is available using X-ray magnetic circular dichroism (XMCD).…”

“…However, the soft X-ray excitation means that the kinetic energy distribution can be broadened and increases chromatic aberration. This can compromise the resolution to limit it to around 50-100 nm [209]. Since the photoelectrons are mainly secondary in nature, chemical information is available since core level states can be probed and chemical mapping is possible.…”