Interlayer correlations and helical spin ordering in MnTe/CdTe multilayers (abstract)

Abstract

Mn-VI/II-VI superlattices belong to the family of artificial multilayered structures composed from zinc-blende II-VI semiconducting compounds and Mn chalcogenides using MBE and ALE. While all naturally existing crystals of MnTe have the NiAs (hexagonal) structure, the zinc-blende form is a fcc Heisenberg antiferromagnet with dominant nearest neighbor interactions. The magnetic properties of such frustrated systems are strongly influenced by lattice mismatch strain. For example, tensile strain produces an incommensurate helical antiferromagnetic phase with an in-plane axis. The strain and therefore helical period increases with thickness of CdTe, but in the presently studied samples is weak enough to allow investigation of the onset of incommensurate helical effects. In previously studied MBE-grown Mn-VI/Zn-VI systems, the nonmagnetic spacers were too thick to allow interlayer coupling. We report neutron diffraction studies of new MnTe/CdTe superlattices prepared by ALE with extremely thin CdTe spacers (from 2 to 6 monolayers). The results indicate the formation of spin helices, consistent with the tensile nature of strain in the MnTe layers. In addition, the widths of the AF diffraction peaks and the presence of satellite peaks clearly indicate that the magnetic interactions propagate through the CdTe spacers, introducing coherence between the helices in different MnTe layers. The nature of the interaction responsible for this transfer is not yet clearly understood. Some possible mechanisms are discussed.