**3. Structural characterization**

Thin film samples of Fe/MgO/Fe on MgO (100) substrates were characterized by XRD (miniflex Rigaku X-ray diffraction of 40 kV/40 mA) using CuKα radiation in θ–2θ geometry (**Figure 4**).

Surface morphologies of nanowires of Fe/MgO/Fe grown in the interior cylindrical space of CNTs were characterized by SEM/STEM in a previous study [12]. The SEM/STEM scan depicts a uniform composition.

X-ray absorption spectroscopy (XAS) measurements on thin films and nanowires of Fe/ MgO/Fe carried out at beamline 4UB at the National Synchrotron Light Source (NSLS) in

**Figure 4.** XRD of Fe/MgO/Fe/MgO (100) synthesized at several substrate temperatures and of pristine MgO (100).

Brookhaven National Laboratory (BNL) by the author revealed the existence of a missing shoulder at the Fe L<sup>3</sup> edge in the nanowire spectrum at 717 eV. At the Fe L<sup>2</sup> edge, the double peaks at 723.5 eV are of equal height for the nanowires and a leading peak in the film's spectra.
