Magnetization Process of the n-type Ferromagnetic Semiconductor (In,Fe)As:Be Studied by X-ray Magnetic Circular Dichroism

摘要

In order to investigate the mechanism of ferromagnetic ordering in the newn-type magnetic semiconductor (In,Fe)As co-doped with Be, we have performedX-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD)studies of ferromagnetic and paramagnetic samples. The spectral line shapessuggest that the ferromagnetism is intrinsic originating from Fe atomsincorporated into the Zinc-blende-type InAs lattice. The magnetization curvesof Fe measured by XMCD were well reproduced by the superposition of a Langevinfunction representing superparamagnetic (SPM) behavior of nano-scaleferromagnetic domains and a T-linear function representing Curie-Weissparamagnetism even much above the Curie temperatures. The data at 20 K showed adeviation from the Langevin behavior, suggesting a gradual establishment ofmacroscopic ferromagnetism on lowering temperature. The existence of nano-scaleferromagnetic domains indicated by the SPM behavior suggests spatialfluctuations of Fe concentration on the nano-scale.