Three dimensional spin configuration in an exchange coupled Fe/NiO(100) system is investigated using a combination of photoemission electron microscopy and magnetic linear- and circular dichroism spectroscopy in the soft-x-ray range. By comparing the experimental image contrasts with a cluster model calculation including the crystal symmetry, we have successfully determined the spin configuration of the bulk antiferromagnetic NiO substrate. The easy axes of the outermost ferromagnetic Fe film and the ferromagnetic interface corresponding to the three kinds of spin axes of the antiferromagnetic NiO substrate have been assigned. We also observe that the magnetic field amplitude required for magnetization reversal depends on these initial easy axes directions. These findings are strongly related to the mechanism of exchange bias phenomena.
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