Magnetic properties of disordered ferrite and ilmenite-hematite thin films

We have synthesized thin films of disordered zinc ferrite (ZnFe₂O₄) and ilmenite-hematite (FeTiO₃-Fe₂O₃) solid solution, the former and the latter of which are interesting from the viewpoints of magnetooptics and spintronics, respectively, by utilizing sputtering and pulsed laser deposition methods, and have explored their magnetic, magnetooptical, and electrical properties. Although ZnFe₂O₄ possesses a normal spinel structure as its stable phase, some of the Fe³⁺ ions occupy the tetrahedral as well as the octahedral sites in ZnFe₂O₄ of which the sputtered thin film is composed. Consequently, the as-deposited thin film manifests large magnetization even at room temperature although the magnetic phase transition temperature of the stable phase of ZnFe₂O₄ is as low as 10 K. Also, the thin film exhibits a cluster spin glass transition at a temperature as high as 325 K. Furthermore, the ZnFe₂O₄ thin films exhibit large Faraday effects at a wavelength of 400 nm or so. The ilmenite-hematite solid solution is one of the ferrimagnetic semiconductors. Most of the compositions possess Curie temperatures higher than room temperature, and the type of carrier can be tuned only by changing the composition. We have succeeded in synthesizing solid-solution thin films of various compositions grown epitaxially on sapphire substrates with a (0 0 0 1) plane, and have shown that the thin films are ferrimagnetic semiconductors.