Principal Investigator Riccardo Comin
The ability to image the nanoscale structure of materials with tunable magnetic textures is pivotal for the development of low-power and nonvolatile data storage technologies. Soft X-ray imaging has emerged in the last decade as a powerful and accurate methodology to resolve the bulk domain structure of several magnetic materials -- magnetic multilayers, buried interfaces, or skyrmion lattices -- as well as nanoelectronic devices under operating conditions.
Soft X-ray imaging relies on two main requirements: (i) the ability to focus a collimated X-ray beam on a spot the size of a few tens of nm and (ii) the ability to scan the focused X-ray beam with nm precision. We have commissioned a new soft X-ray nanofocusing setup installed at beamline CSX-1 of the National Synchrotron Light Source II. The schematics of this setup are shown in Figure 1. A key element is the Fresnel zone plate (inset D), which acts as a diffractive phase mask to focus X-rays to a 70-nm spot at the sample, and is fabricated using e-beam lithographic tools. The beam spot can be moved with the aid of piezo-based nanopositioners (inset C), which translate the X-ray optics while keeping the sample in a fixed position. Diffracted X-rays are collected with a CCD camera in the far field (~30 cm from the sample). The resulting magnetic scattering intensity encodes local antiferromagnetic strength and can be acquired in less than a second. By scanning the X-ray beam across the sample, we are able to probe the spatial distribution of antiferromagnetic order.
We applied this new method to the study of antiferromagnetic rare earth NdNiO3. In particular, and for the first time, we unveil the inhomogeneous nature of the spin-ordered ground state. Furthermore, we identify the spatial distribution of antiferromagnetic domains and show that it follows a scale-free distribution. Our future focus is to extend our studies to the imaging of nanoscale magnetic textures in antiferromagnetic spintronic materials and devices, including in operando studies as a function of applied current.