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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 ͑Cd, Mn͒Te͑͞Cd, Mn, Mg͒Te quantum well structures. As a responsible mechanism we suggest switching-on of the kinetic exchange for the conduction electrons with finite k vectors. Quantitative agreement between experimental data and calculations is achieved. PACS numbers: 75.30.Et, 71.70.Ej, 75.50.Pp, 78.20.Ls Semimagnetic or diluted magnetic semiconductors (DMS) are known for their giant magneto-optical effects originating in a strong sp-d exchange interaction between the band electrons and the magnetic (e.g., Mn) ions. Incorporation of semimagnetic layers in quantum-confined heterostructures opened new possibilities for the "spin splitting engineering" [1]. In this context, in addition to a magnetic field, temperature, and Mn molar fraction dependences, also the confinement energy and the size quantization became means of an effective tuning of the spin splittings. While a precise tuning of the spin splitting is of great significance for future-spin-dependent electronics, it is already now of obvious importance in, e.g., studies of samples with zero g-factor in the fractional quantum Hall regime [2]. Also, exciting physical phenomena have been reported recently for semimagnetic heterostructures: coherent spin excitations [3,4], magnetic polaron formation [5], and ferromagnetic hole alignment in p-type doped structures [6].For the electrons from the vicinity of the conduction band edge the exchange interaction with the localized d electrons of magnetic ions is described by the Hamiltonian:where the parameter of the s-d exchange interaction a is positive. In the case of the holes, the exchange energy has the same form but the parameter of p-d exchange interaction b , 0. In Eq. (1) s and r are the spin (total angular momentum in the case of the holes) and coordinate operators of a carrier, and S i and R i are the total spin and coordinate of the ith magnetic ion. A positive sign of a results from the direct (or potential) exchange of the conduction band electron with the d electrons of Mn ions. The negative sign of b is due to a dominant role of the kinetic exchange [7] which occurs because of possible transitions to virtual states in the d shell [8].A possibility of a modification of the exchange parameters under quantum-confined conditions has been recognized already with the first semimagnetic semiconductor quantum wells (QWs) studied. However, experimental evidences showing unambiguously such a modification of the exciton Zeeman splitting, i.e., of ͑a 2 b͒, have been found only recently [9]. A special design of the QW structures was crucial for the latter studies since one had to rule out effects related to a modification of magnetic properties at the magneti...

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The lattice parameters of the hexagonal unit cell, the atomic parameters, and the shift of the Raman active vibrations are measured of p-Bi,Te, under uniaxial and hydrostatic pressure. The structural investigations are performed by neutron diffraction, and the lattice vibrations are studied by Raman scattering. The results of the diffraction experiments constitute a direct experimental confirmation of the weak bonding between the sandwiches in this narrow gap semiconductor with sandwich structure. As a consequence, some Raman active phonon modes show a rather strong dependence upon uniaxial pressure up to Aa/Ap = 1.9 x 10-8cm-l/Pa. Die Gitterparameter der hexagonalen Einheitszelle, die Atompositionen und die Verschiebung der Raman-aktiven Gitterschwingungen von p-Bi,Te, unter uniaxialem und hydrostatischem Druck werden gemessen. Die strukturellen Untersuchungen werden mittels Neutronenbeugung durchgefuhrt, die Gitterschwingungen mit Ramanstreuung untersucht. Die Ergebnisse der Diffraktionsexperimente konstatieren einen direkten experimentellen Beweis fur die schwachen Bindungen zwischen den Sandwiches in diesem Schmalband-Halbleiter mit Sandwichstruktur. Als Konsequenz zeigen einige Raman-aktive Gitterschwingungen eine relativ starke Druckabhangigkeit der Anregungsfrequenzen, unter uniaxialem Druck bis zu AG/Ap = 1,9 x 10-8 cm-l/Pa. l) Rontgenring 8, D-8700 Wurzburg, FRG. 2, Present address: Siemens AG, Zentralbereich Technik, D-8000 Munchen 83. 9. 132 W. KULLMANN et al. Te'