  GeMn granular thin films are a unique and promising material for spintronics
applications due to large positive magnetoresistance (MR). Previous studies on
GeMn have suggested that the large MR is related to nanospinodal decomposition
of GeMn into Mn-rich ferromagnetic nanoparticles and Mn-poor paramagnetic
matrix. However, its microscopic origin of the MR has not been clarified yet.
Here, using X-ray magnetic circular dichroism (XMCD), which is extremely
sensitive to the local magnetic state of each atom, we investigate the magnetic
properties of the nanoparticles and the matrix in GeMn separately. We find that
the MR ratio is proportional to the product of the magnetizations originating
from the nanoparticles and the matrix. This result indicates that
spin-polarized holes in the nanoparticles penetrate into the matrix and that
these holes undergo spin-disorder magnetic scattering by the paramagnetic Mn
atoms in the matrix, which induces the large MR.
