Origin of the large positive magnetoresistance in Ge1-xMnx granular thin films

TL;DR

This study reveals that the large positive magnetoresistance in GeMn granular thin films arises from spin-polarized holes in ferromagnetic nanoparticles scattering off paramagnetic Mn atoms in the matrix, elucidating its microscopic origin.

Contribution

The paper demonstrates that the MR in GeMn films is due to spin-polarized holes penetrating the matrix and causing spin-disorder scattering, clarified through XMCD analysis.

Findings

MR ratio is proportional to the product of nanoparticle and matrix magnetizations.

Spin-polarized holes cause spin-disorder scattering in the paramagnetic matrix.

XMCD reveals the separate magnetic states of nanoparticles and matrix.

Abstract

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.