Origin of the large positive magnetoresistance of GeMn granular thin films

Wakabayashi, Yuki*; Akiyama, Ryota*; Takeda, Yukiharu   ; Horio, Masafumi*; Shibata, Goro*; Sakamoto, Shoya*; Ban, Yoshisuke*; Saito, Yuji  ; Yamagami, Hiroshi; Fujimori, Atsushi*; Tanaka, Masaaki*; Oya, Shinobu*

GeMn (GeMn) granular thin films are a unique and promising material for spintronic applications owing to their large positive magnetoresistance (MR). The microscopic origin of the MR has not yet been clarified. Here, we develop a method to separately investigate the magnetic properties of the nanoparticles and the matrix, utilizing the extremely high sensitivity of X-ray magnetic circular dichroism (XMCD) to the local magnetic state of each atom. 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 the spin-polarized holes in the nanoparticles penetrate into the matrix and that these holes undergo first order magnetic scattering by the paramagnetic Mn atoms in the matrix, which induces the large MR.