Epitaxial ferri(ferro)magnetic Fe3−xZnxO4 thin films (x=0–0.9) were prepared using a pulsed-laser deposition technique. The electrical conductivity and magnetic properties of Fe3−xZnxO4 thin film were systematically modulated for the entire range of Zn substitution. Anomalous Hall coefficient measurements revealed the presence of spin-polarized carriers at room temperature. Valence band spectra obtained by hard x-ray photoemission spectroscopy revealed that the density of states near the Fermi level was reduced with an increasing Zn concentration of x. These results indicate that this system will serve as a tunable ferromagnetic semiconductor with a strong electron correlation.

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We have performed hard X-ray photoemission spectroscopy combined with magnetic circular dichroism (MCD-HXPES) for 10-nm-thick Fe3-xZnxO4 (x = 0,0.5) thin films. For the Fe3-xZnxO4 (x = 0,0.5) thin films, a clear MCD signal was obtained in the Fe 2p core-level photoemission without any surface treatments. This result shows that MCD-HXPES has a large probing depth for both electronic and magnetic states, and indicates a potential application of MCD-HXPES to various magnetic materials and spintronics devices.

We have constructed a field effect transistor structure composed of the sustainable oxide semiconductor ͑Fe, Zn͒ 3 O 4 with high Curie temperature and ferroelectric Pb͑Zr, Ti͒O 3 . Electric field control of ͑Fe 2.5 Zn 0.5 ͒O 4 channel resistance was achieved in the heterostructures though modulation of their carrier concentration. The results will lead to the significant development of sustainable oxide semiconductor spintronics devices working at room temperature.Field effect control of transition metal oxides with strongly correlated oxide in heterostructures offer to opportunities create next generation functional electrics devices, 1 such as electrically tunable colossal magnetoresistance devices, 2,3 ferromagnet, 4 and high T C superconductor 5 with controlling interactions between charge with spin. Another aspect of oxide is "sustainability," namely, a strategy for the use of elemental natural resources with environmental friendliness, which is an indispensable for the development of advanced materials and devices concerning our global environment. Among them, Fe-based oxides with spinel structures ͑spinel ferrites͒ exhibit ferrimagnetism with a very high Curie temperatures exceeding 800 K, which are industrially used for making recording media as an insulating ferrimagnet. The solid solution system of spinel ferrite, Fe 3−x Zn x O 4 ͑0 Ͻ x Ͻ 1͒, is a good candidate not only as a magnetic semiconductor with high T C ͑Refs. 6 and 7͒ but also as a an sustainable electromagnetic material. Their component, namely, Fe 2 O 3 and ZnO, have abilities concerning sustainability from the point of view on rich natural resource and environmental friendliness. For example, the Clarke number of Fe is the fourth and Zn is alterative element for rare In. Moreover, the powders of Fe 2 O 3 and ZnO are widely used for cosmetic applications. These are high advantages in comparison with other spin related field effect devices.Here, we report fabrication of ferroelectric field effect transistor ͑FET͒ structure based on sustainable strongly correlated ͑Fe, Zn͒ 3 O 4 ͑FZO͒ oxide semiconductor and their electrical transport properties.The FZO/PZT heterostructure for a bottom-gate FET was prepared on a Nb͑1 wt %͒-doped SrTiO ͑Nb-STO͒ ͑100͒ single crystal substrate by pulsed-laser deposition ͑PLD͒ technique. A Nb-STO͑100͒ substrate was used as a bottom electrode. A PZT layer was deposited as a ferroelectric gate insulator by PLD at oxygen pressure ͑P O2 ͒ of 6.0 Pa and substrate temperature ͑T s ͒ of 550°C. The thickness of PZT was fixed to 300 nm. A FZO as a channel layer was deposited on a PZT layer by PLD at P O2 of 1.0ϫ 10 −3 Pa and T s of 320°C during the deposition. The deposited thickness ͑d͒ of FZO was set to 20 nm. Finally, Au as a top electrode was prepared by thermal deposition technique. The channel size was 200ϫ 500 m. The ferroelectric property was evaluated by using a dielectric polarization measurement system. For the physical properties of FZO thin films, Hall resistance was measured at room temperature under a magnet...