Magnetization process of the -type ferromagnetic semiconductor (In,Fe)As:Be studied by X-ray magnetic circular dichroism

Sakamoto, Shoya*; Anh, L. D.*; Hai, P. N.*; Shibata, Goro*; Takeda, Yukiharu   ; Kobayashi, Masaki*; Takahashi, Yukio*; Koide, Tsuneharu*; Tanaka, Masaaki*; Fujimori, Atsushi*

In order to investigate the mechanism of ferromagnetic ordering in the new -type magnetic semiconductor (In,Fe)As codoped with Be, we have performed X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD) studies. The spectral line shapes suggest that the ferromagnetism is intrinsic, originating from Fe atoms incorporated into the zinc-blende-type InAs lattice. The magnetization curves of Fe measured by XMCD were well reproduced by the superposition of a Langevin function representing superparamagnetic (SPM) behavior of nanoscale ferromagnetic domains and a -linear function representing Curie-Weiss paramagnetism even much above the Curie temperatures. The data at 20 K showed a deviation from the Langevin behavior, suggesting a gradual establishment of macroscopic ferromagnetism on lowering temperature. The existence of nanoscale ferromagnetic domains indicated by the SPM behavior suggests spatial fluctuations of Fe concentration on the nanoscale.