Structural and magnetic properties of oxide films CoFeHfO: A possible candidate for all-oxide TMR junctions?

In search of a magnetic oxide, which is insensitive to oxygen at interfaces and thus appropriate as an electrode layer for tunneling junction applications, we prepared thin films of CoFeHfO by reactive DC-magnetron sputtering technique and investigated the relation between structural and magnetic properties. The results suggest that the films consist of two disorded phases, a Co(Fe)-rich and a HfO-rich. It was found that the degree of film homogeneity and thus the magnetic nature depends on preparation conditions such as film thickness and deposition rate. A second magnetic phase with a high saturation field, which is present in thicker films, could therefore be reduced by decreasing the film thickness. Consequently, the thinnest film (10 nm) is nearly single phased and exhibits an excellent uniaxial anisotropy with a coercive field H c of 16 Oe along the easy axis. Additionally, thermomagnetic measurements were carried out to understand annealing-induced effects. A clear improvement with increased saturation magnetisation ( M s = 695 emu/cm 3 ) and decreased H c was observed, which can be attributed to structural relaxation and phase separation caused by annealing.