Phase imaging of magnetic nanostructures using resonant soft x-ray holography

Abstract

We demonstrate phase imaging by means of resonant soft x-ray holography. Our holographic phase-contrast method utilizes the strong energy-dependence of the refractive index at a characteristic x-ray absorption resonance. The general concept is shown by using a Co/ Pd multilayer sample which exhibits random nanosized magnetic domains. By tuning below the Co Ledge resonance, our quantitative and spectroscopic phase method allows high-contrast imaging of nanoscale electronic and magnetic order while increasing the probing depth and decreasing the radiation dose by an order of magnitude. The complex refractive index is quantitatively obtained through the interference between resonant and nonresonant scattering.

Magnetic imaging by x-ray holography using extended references

“…The image reconstructions can indeed have different global amplitude and phase if the slit is not uniformly illuminated. Whilst the origin of the color reversal remains less clear, it has been reported by Scherz et al [16] that a phase change may arise from an inappropriate determination of the centre of symmetry, loss of high-q information due to the limited size of the CCD, or loss of low-q information due to the beamstop. The shadowing from the beamstop can be reduced by a simple modification of the design.…”

“…3(d). The resolution of the imaging can be estimated by taking into account the typical width of a domain wall in CoPt multilayer films (< 10 nm) [16,17], By fitting the measured intensity profile with a hyperbolic tangent of the form I = I 0 tanh[2(x − x 0 )/w] + I C [18], where x 0 is the center position of the domain wall, w is its width and, I 0 and I C are intensity offset values, we obtain a width of the domain boundary w ≈ 30 ± 10 nm in both directions. This value is of the order of the sample period (∼30 nm), and is thus limited by the maximal acceptance angle of the CCD camera.…”

Coherent Resonant Soft X-ray Scattering Study of Magnetic Textures in FeGe

“…Moreover, a topological winding number of the magnetically ordered system can be directly determined from the polarization-dependent (or dichroic) soft X-ray diffraction pattern alone [16]. Dichroic resonant soft X-ray scattering can be successfully combined with coherent diffraction approaches such as iterative phase retrieval [17][18][19], Fourier transform holography-based methods [20][21][22][23], and ptychography [24,25] for the lensless real-space imaging of local magnetic moment at the scale from a few tens of nanometers to a few microns. Lensless approaches allow the use of various sample environments, which confers a significant advantage compared to zone-plate-based magnetic transmission X-ray microscopy.…”

Exploring the limits of soft x-ray magnetic holography: Imaging magnetization reversal of buried interfaces (invited)

“…In addition, the technique can image deeply buried magnetic systems and, as a pure photon-based technique (photon-in/ photon-out), can be used in applied magnetic fields. Up to now, soft x-ray holography has focused on [nonmagnetic/ magnetic] n multilayers with perpendicular magnetic anisotropy, [5][6][7][8][9][10] using Pt (Refs. [5][6][7]10) and Pd (Refs.…”

“…8 and 9) as nonmagnetic layers, and Co (Refs. [5][6][7][8]10) and CoNi (Ref. 8) as magnetic layers, with relatively large (5-60 nm) effective magnetic thicknesses for both remanence [5][6][7][8]10 and fielddependent 6,9,10 measurements.…”