| Summary: | We have explored the use of coherent resonant x-ray scattering as a powerful
technique to study, characterize and reconstruct magnetic domains for
antiferromagnetic (AFM) and ferromagnetic (FM) thin films. This method
is capable of high-resolution imaging (as it is not limited by optical aberrations),
is able to probe buried interfaces and is operational in the presence
of other fields. Here we report the first experimental observation of x-ray
speckle patterns generated by AFM domains. Resonant x-ray scattering
was performed on LaFe0₃ thin films possessing two types of domains with
their AFM orientations perpendicular to each other. X-ray magnetic linear
dichroism (XMLD) at the FeL₃ absorption edge has been exploited in order
to give rise to modulations of the scattering amplitudes according to domain
distributions, resulting in magnetic speckle.
We also report resonant x-ray scatterng in the transmission geometry
from FM domains of Co/Pt multilayers. Magnetic x-ray circular dichroism
(MXCD) has been utilized with the contrast arising from the dependence of
scattering amplitude on magnetization direction of FM domains, which are
oriented normal to the surface (i.e. parallel of antiparallel to photon helicity)
due to the perpendicular interfacial anisotropy provided by the broken
symmetry at the Co-Pt interface. By tuning the energy to the CoL₃ edge,
magnetic speckle is very clearly demonstrated. We have analytically shown
that upon reversal of magnetic contrast (tuning of the scattering energy to
either of the two crystal field split peaks of the FeL₃ edge in the first experiment,
and changing the photon helicity in the second experiment) changes in
speckle patterns will be observed solely arising from the interference between
roughness and/or pinhole scattering with magnetic scattering.
We have developed a new reconstruction technique, upon extension of
Fourier transform iterative algorithms previously utilized in other reconstruction
tasks, capable of reconstructing AFM and FM magnetic structure from
resonant x-ray scattering intensity measurements. This technique is shown
to be very successful upon application to noisy simulated data. Using this
method, experimental speckle data from the F M domains of the Co/Pt multilayer
have been inverted resulting in magnetic domains showing a remarkable
similarity to the worm-domain structure of the actual domain distribution
imaged using magnetic force microscopy (MFM). This, to our knowledge,
has been the first reconstruction of magnetic domains from experimental
data. Moreover, direct (non-iterative) reconstruction of FM domains has
been shown to be possible upon using small pinholes and/or rough samples
with roughness scale comparable to the size of domains.
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