Abstract
Local environments surrounding magnetic ions in Mn- or Cr-doped and hydrogenated amorphous Si films have been determined using extended x-ray absorption fine structure (EXAFS) method. These films are found to be ferromagnetic with high Curie temperatures above 250 K and therefore are of tremendous interest for practical spintronics applications. Our EXAFS results indicate that these material systems are nearly free of dopant clusters and oxides up to an unusually high dopant concentration of 20-22 at.%. As the dopant concentration increases, the saturation magnetization in the Cr-doped samples is decreased while that in the Mn-doped sample remains practically unchanged. Antiferromagnetic coupling of magnetic ions and enhancement of carrier-mediated ferromagnetism are proposed to account for the different concentration dependence of magnetization in the Cr- and Mn-doped samples. © 2010 The American Physical Society.