Magnetic structure of short-period CdTe/MnTe superlattices

Abstract

The magnetic properties of short-period superlattices consisting of zincblende MnTe (type-III antiferromagnet with Néel temperature of 67 K in bulk-like films) and CdTe are investigated by coherent Raman scattering (CRS) experiments 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 observing the paramagnetic (PMR) and antiferromagnetic resonances (AFMR) of localized d-electrons of Mn-ions and the spin-splitting of delocalized band carriers, respectively. Resonant CRS is particularly sensitive to Mn-ions located in regions with high expectation propabilities of electrons, i.e. near the interfaces between the CdTe quantum wells and MnTe barriers. Simultaneous observation of PMR and AFMR demonstrates that besides the antiferromagnetically coupled, also uncoupled Mn-spins exist in the interface regions. Their number is determined quantitatively by magnetization experiments. The observed free carrier spin-splitting energy is directly related to the local magnetization of magnetic ions within regions of high expectation probabilities of electrons. The data are analyzed within the framework of a mean-field analysis (MFA) which incorporates the electron–Mn-ion exchange as well as the Mn–Mn interion exchange interaction. The latter is represented by the individual nearest and next nearest neighbor exchange interactions, the coordination number of spins and their respective orientation. The phase transition temperature is substantially decreased due to the reduced dimensionality (less nearest neighbors) and due to strain which modifies the exchange integrals and bond angles.