Mn local order in room temperature ferromagnetic Mn/ZnO multilayers

The local environment of Mn atoms in (ZnO30 A/Mnt)n multilayers (ML) has been studied by means of x-ray absorption spectroscopy at the Mn K edge. A series of ML has been prepared by sputtering with approximately constant total amount of Mn (300 A) while the Mn layer thickness (t) has been varied from 60 to 1 A (modifying consequently the number of Mn–ZnO interfaces) in order to study the Mn–Zn–O system. Variation of the Mn layer thickness (t) has been directly associated with changes in the Mn oxidation states within the sample series. Absorption spectroscopy results for films with t≤15 A indicate mostly MnO2 formation and no signal of Mn in the ZnO lattice is found. Conversely, films with t≥30 A present two different Mn environments, that have been related to the coexistence of rocksalt and wurtzite phases, formed by Zn1−xMnxO mixed solid solutions. The magnetic behaviour of samples is correlated with structural properties. That correlation strongly points towards substitutional Mn in the wurtzite phase as the origin of the observed ferromagnetism above room temperature.