title: Ferromagnetic behaviour of Fe-doped ZnO nanograined films.
abstract: The influence of the grain boundary (GB) specific area s GB on the appearance of ferromagnetism in Fe-doped ZnO has been analysed. A review of numerous research contributions from the literature on the origin of the ferromagnetic behaviour of Fe-doped ZnO is given. An empirical correlation has been found that the value of the specific grain boundary area s GB is the main factor controlling such behaviour. The Fe-doped ZnO becomes ferromagnetic only if it contains enough GBs, i.e., if s GB is higher than a certain threshold value s th = 5 × 10(4) m(2)/m(3). It corresponds to the effective grain size of about 40 μm assuming a full, dense material and equiaxial grains. Magnetic properties of ZnO dense nanograined thin films doped with iron (0 to 40 atom %) have been investigated. The films were deposited by using the wet chemistry "liquid ceramics" method. The samples demonstrate ferromagnetic behaviour with J s up to 0.10 emu/g (0.025 μB/f.u.ZnO) and coercivity H c ≈ 0.03 T. Saturation magnetisation depends nonmonotonically on the Fe concentration. The dependence on Fe content can be explained by the changes in the structure and contiguity of a ferromagnetic "grain boundary foam" responsible for the magnetic properties of pure and doped ZnO.
authors.affiliation: Karlsruher Institut für Technologie, Institut für Nanotechnologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany ; Institute of Solid State Physics, Russian Academy of Sciences, Ac. Ossipyan str. 2, 142432 Chernogolovka, Russia ; Max-Planck-Institut für Intelligente Systeme, Heisenbergstrasse 3, 70569 Stuttgart, Germany ; National University for Research and Technology "MISiS", Leninsky prospect 4, 119991 Moscow, Russia.
authors.forename: Boris B
authors.initials: BB
authors.lastname: Straumal
authors.forename: Svetlana G
authors.initials: SG
authors.lastname: Protasova
authors.forename: Andrei A
authors.initials: AA
authors.lastname: Mazilkin
authors.forename: Thomas
authors.initials: T
authors.lastname: Tietze
authors.forename: Eberhard
authors.initials: E
authors.lastname: Goering
authors.forename: Gisela
authors.initials: G
authors.lastname: Schütz
authors.forename: Petr B
authors.initials: PB
authors.lastname: Straumal
authors.forename: Brigitte
authors.initials: B
authors.lastname: Baretzky
keywords: Fe; ZnO; ferromagnetism; grain boundaries