Kinetic Exchange between the Conduction Band Electrons and Magnetic Ions in Quantum-Confined Structures

We provide an experimental evidence and a theoretical substantiation for a strong reduction of the $s-d$ exchange interaction between electrons and Mn-ion spins with increasing degree of the confinement in nanostructures of diluted magnetic semiconductors. By spin-flip Raman scattering a strong (up to $25\%$) reduction of the exchange parameter is observed in $(\mathrm{Cd},\mathrm{Mn})\mathrm{Te}/(\mathrm{Cd},\mathrm{Mn},\mathrm{Mg})\mathrm{Te}$ quantum well structures. As a responsible mechanism we suggest switching-on of the kinetic exchange for the conduction electrons with finite $\mathbf{k}$ vectors. Quantitative agreement between experimental data and calculations is achieved.