Xuelian Huang

Structural and magnetic studies of Cu-doped ZnO films synthesized via a hydrothermal route

Highly-textured n-type ZnO:Cu films with room-temperature ferromagnetism have been hydrothermally grown in aqueous solution at 90 °C using PLD-derived ZnO seed layers on different substrates (quartz, silicon, glass and sapphire). The crystallinity of the ZnO seed layers on different substrates plays an important role in the microstructure of the subsequently grown ZnO:Cu films. Better crystallinity and texture of the seed layers is favourable to the growth of continuous films. Thick Zn0.98Cu0.02O films (ca. 1.2 μm) exhibit high value of magnetic moment (0.40 μB per Cu), comparable to the previously reported value of thin films, indicating that thick ZnO:Cu films with high magnetization can be synthesized via this hydrothermal route. The incorporation of hydrogen into the ZnO lattice plays a dominant role in ferromagnetism in this ZnO:Cu system.

High-Coercivity in

Hematite particles (α-Fe₂O₃) were synthesized by oxidation of Fe₃O₄ nanoparticles through heat treatment in the atmosphere of 95% N₂ plus 5% O₂. This method can result in an effective fabrication of high-coercivity α-Fe₂O₃ particles. The Morin transition of the as-prepared α-Fe₂O₃ particles was detected to be 265 K, and a coercivity of 6.2 kOe could be observed at room temperature. The magnetic properties at different temperatures of the as-produced α-Fe₂O₃ particles were studied.

\alpha\hbox{-}{\rm Fe}_{2}{\rm O}_{3}

Magnetite Fe3O4 (ferrite) has attracted considerable interest for its exceptional physical properties: It is predicted to be a semimetallic ferromagnetic with a high Curie temperature, it displays a metal-insulator transition, and has potential oxide-electronics applications. Here, we fabricate a high-magnetization (> 1 Tesla) high-resistance (~0.1 Ω·cm) sub-nanostructured (grain size < 3 nm) Fe3O4 film via grain-size control and nano-engineering. We report a new phenomenon of spin-flipping of the valence-spin tetrahedral Fe3+ in the sub-nanostructured Fe3O4 film, which produces the high magnetization. Using soft X-ray magnetic circular dichroism and soft X-ray absorption, both at the Fe L3,2- and O K-edges, and supported by first-principles and charge-transfer multiple calculations, we observe an anomalous enhancement of double exchange, accompanied by a suppression of the superexchange interactions because of the spin-flipping mechanism via oxygen at the grain boundaries. Our result may open avenues for developing spin-manipulated giant magnetic Fe3O4-based compounds via nano-grain size control.

Formed After Annealing From

Highly textured manganese zinc ferrite (Mn0.7Zn0.3Fe2O4) films have been successfully fabricated on glass substrates by pulse laser deposition at relatively low temperatures. Investigations indicated that the strain, which is induced by high deposition rate and the difference of thermal coefficient between the film and glass substrate, is attributed to the growth of textured structure. Growth of highly textured cobalt ferrite film was also achieved using the same method. This work provided a possible technique for fabricating high quality ferrite films on glass substrates.