Temperature‐Dependent Solid‐State Reactions With and Without Kirkendall Effect in Al₂O₃/ZnO, Fe₂O₃/ZnO, and Co_<i>X</i>O_<i>Y</i>/ZnO Oxide Thin Film Systems

Abstract

Abstract Temperature‐dependent solid‐state reactions and the occurrence of the Kirkendall effect are studied in thin film oxide systems applying optical reflection microscopy, X‐ray reflectivity, (scanning) transmission electron microscopy, grazing‐incidence X‐ray diffraction measurements, and SQUID magnetometry. The efficiency of the simultaneous application of different analytical methods for the precise selection and investigation of the most interesting samples is demonstrated first on the example of the Al 2 O 3 /ZnO system, for which the spinel formation after a solid‐state reaction and the formation of Kirkendall voids were already reported. The demonstrated methodology is then applied to study Fe 2 O 3 /ZnO and Co X O Y /ZnO film pairs. The investigations clearly demonstrate the temperature‐driven formation of a ferromagnetic spinel by a solid state reaction involving the Kirkendall effect in the Fe 2 O 3 /ZnO system, already after an annealing at 600 °C for 1 h. We also report on the solid state reaction in the Co X O Y /ZnO system after annealing at 700 °C for 1 h, however without the Kirkendall effect and without any evidence of ferromagnetism of the final state.