Effect of nanoscale inhomogeneity on blocking temperature of ZnO:Co films fabricated by using nitrogen-mediated crystallization

Diluted magnetic semiconductors (DMS) have attracted interest for the potential applications of spintronic devices. The origin of the temperature dependence of their ferromagnetism has been debated and has not been concluded yet. A potential conclusion is that nanoscale inhomogeneity largely affects the temperature dependence of the magnetization in DMS even if the structure and compositions are not largely different. We examined this hypothesis by implementing nitrogen-mediated crystallization consisting of sputtering deposition of amorphous film and solid-phase crystallization by thermal annealing. A series of samples with different inhomogeneities were prepared by changing the annealing time. No significant changes in the composition and the structure were observed after annealing for various times, while significant enhancements were observed in the coercivity, blocking temperature, and grain size. These results provide clear understanding in the temperature dependence of the ferromagnetism in DMS and direct evidence of the potential conclusion on the long-lasting debate. Graphical abstract: (Figure presented.)