Absence of ferromagnetism in single-phase wurtzite Zn1−xMnxO polycrystalline thin films

This paper reports on the magnetic properties of Zn1−xMnxO with Mn concentrations from 5% to 25%. The polycrystalline films, deposited by pulsed laser deposition on c-oriented sapphire and mica substrates, were first characterized by x-ray diffraction, absorption, and fluorescence, as well as by photoelectron and optical spectroscopy. Except for the highest Mn content films, all films are single-phase wurtzite, with Mn in tetrahedral coordination. Films with 25% Mn show traces of other crystal phases with spinel or perovskite structure. Their magnetization was then measured in function of applied magnetic field in the range −5 to 5 T and temperature in the range 1.8 to 300 K. All single-phase films exhibit paramagmetic behavior in the whole temperature range. Ferri- or ferromagnetic behavior (involving only a small proportion of the total magnetization) is found only in samples with other phases or in the sapphire substrates. The paramagnetic susceptibility increases with the Mn content. However, the decr...