Magnetic structure of short-period CdTe/MnTe superlattices

The magnetic properties of short-period superlattices consisting of zincble nde MnTe (type-III antiferromagnet with Neel temperature of 67 K in bulk-li ke films) and CdTe are investigated by coherent Raman scattering (CRS) expe riments as well as SQUID-magnetometry as a function of temperature (1.6-150 K) and magnetic field (0-7 T). In CRS the magnetization is probed by obser ving the paramagnetic (PMR) and antiferromagnetic resonances (AFMR) of loca lized d-electrons of Mn-ions and the spin-splitting of delocalized band car riers, respectively. Resonant CRS is particularly sensitive to Mn-ions loca ted in regions with high expectation propabilities of electrons, i.e. near the interfaces between the CdTe quantum wells and MnTe barriers. Simultaneo us observation of PMR and AFMR demonstrates that besides the antiferromagne tically coupled, also uncoupled Mn-spins exist in the interface regions. Th eir number is determined quantitatively by magnetization experiments. The o bserved free carrier spin-splitting energy is directly related to the local magnetization of magnetic ions within regions of high expectation probabil ities of electrons, The data are analyzed within the framework of a mean-fi eld analysis (MFA) which incorporates the electron-Mn-ion exchange as well as the Mn-Mn interion exchange interaction. The latter is represented by th e individual nearest and next nearest neighbor exchange interactions, the c oordination number of spins and their respective orientation. The phase tra nsition temperature is substantially decreased due to the reduced dimension ality (less nearest neighbors) and due to strain which modifies the exchang e integrals and bond angles. (C) 1998 Elsevier Science B.V. All rights rese rved.