J. Phys. D: Appl. Phys. 46, 275002 (2013)
J. Zippel, M. Lorenz, A. Setzer, M. Rothermel, D. Spemann, P. Esquinazi, M. Grundmann, G. Wagner, R. Denecke, and A.A. Timopheev
Abstract
Ferromagnetic ordering is found for both undoped and Mn-doped zirconia (ZrO2 : Mn) thin films with 0 at% Mn 50 at% grown homoepitaxially on ZrO2 : Y2O3(0 0 1) substrates. Highly crystalline films show ferromagnetic saturation magnetization and coercive field at room temperature up to 1 emu cm−3 and 50mT, respectively. The Curie temperature is in all ferromagnetic samples above 300 K. Comparing optimum films with different Mn content, cubic ZrO2 :Mn films with about 25 at% Mn show reproducibly the highest magnetization, in relation to monoclinic and tetragonal films. In contrast, less crystalline films grown heteroepitaxially on LaAlO3(0 0 1) or under non-ideal conditions show negligible magnetic effects.
The fraction of paramagnetically active Mn atoms in a ZrO2 film with 27% Mn at 5K is only about 1/5 of the incorporated Mn atoms, corresponding well to the share of 20% Mn4+ in XPS. Magnetic trace impurities in the 100 ppm range cannot account for the observed effects. Our results indicate that the observed defect-induced magnetic ordering in nominally non-magnetic zirconia thin films requires a certain balance of overall crystallinity, dislocation density and film mosaicity.