Magnetization process of the layered diluted ferromagnetic semiconductor $(\mathrm{Ba},\mathrm{K}){(\mathrm{Zn},\mathrm{Mn})}_2{\mathrm{As}}_2$ studied by x-ray magnetic circular dichroism

The layered 122-type diluted ferromagnetic semiconductor $(\mathrm{Ba},\mathrm{K}){(\mathrm{Zn},\mathrm{Mn})}_{2}{\mathrm{As}}_{2}$ has attracted much attention both for its high Curie temperature up to $\ensuremath{\sim}230$ K and for the independent control of charge-carrier and spin concentrations through doping K and Mn atoms at the Ba and Zn sites, respectively. In order to unveil the nature of the ferromagnetism in $(\mathrm{Ba},\mathrm{K}){(\mathrm{Zn},\mathrm{Mn})}_{2}{\mathrm{As}}_{2}$, its magnetization process has been studied by x-ray magnetic circular dichroism (XMCD) at the Mn ${L}_{2,3}$ edge in a wide range of temperature and magnetic field. The average magnetization of the Mn atoms as a function of magnetic field ($M\text{--}H$ curves) at various temperatures could be successfully explained by a mixture of paramagnetic (PM), superparamagnetic (SPM), and ferromagnetic (FM) components as previously reported for GaMnAs, revealing the complex nature of the ferromagnetism in $(\mathrm{Ba},\mathrm{K}){(\mathrm{Zn},\mathrm{Mn})}_{2}{\mathrm{As}}_{2}$. The average magnetization of the SPM clusters of different sizes and the FM regions were found to be small compared to those in GaMnAs, which we attribute to the antiferromagnetic interaction between nearest-neighbor Mn atoms in $(\mathrm{Ba},\mathrm{K}){(\mathrm{Zn},\mathrm{Mn})}_{2}{\mathrm{As}}_{2}$ on the basis of recent theoretical predictions.