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 Hc 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 (Ms = 695 emu/cm 3 ) and decreased Hc was observed, which can be attributed to structural relaxation and phase separation caused by annealing.

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This paper shows results on structural and magnetotransport measurements for reactively sputtered amorphous oxide films (Co55Fe20Hf25)1 − xOx with x ⩽ 0.35 and their layered structures. A strong x-dependency was found to be related to microstructural changes caused by oxygen-induced chemical phase separation. For low x, Co–Co(Fe) pair-correlated atom clusters dominate and the films are soft ferromagnetic with excellent uniaxial magnetic anisotropy. Small coercivity Hc ≈ 1–4 Oe, enhanced magnetisation Ms ≈ 420 emu/cm3 and low resistivity ρ ≈ 10− 4 Ωcm were measured for these films, showing a good potential for application in magnetoelectronics. For large x, however, since Hf-O pair-correlated atom clusters are dominant, the films become granular-like superparamagnetic with a saturation field Hs>20 kOe and a remanence Mr/Ms ≈ 0. ρ is extremely high presumably due to Coulomb blockade effect. A large magnetoresistance was observed, being 30% (70 kOe) at 5 K and 10% at room temperature. This effect can be attributed to spin-dependent tunnelling among lateral separated Co-Co(Fe) clusters. The layered structure shows a small, but low-field magnetotunnelling effect.

Three kinds of Co-rich magnetic amorphous films of CoFeB, CoFeNiSiB, and CoFeHfO were prepared by magnetron sputtering and applied as soft ferromagnetic ͑FM͒ electrodes in tunneling magnetoresistance ͑TMR͒ devices. Initial results exhibit a large room-temperature TMR effect of approximately 50%. The high effect can be attributed to interfacial coherence between the amorphous barrier-electrode layers and, accordingly, suggests a high local spin polarization possibly associated with strong nearest-neighbor spin correlations of the magnetic atoms. The magnetotransport behavior may be governed by details of the local spin environment in magnetic amorphous electrodes due to their short electron mean-free path ͑ϳ3-5 Å͒. The annealing effect on TMR was found to be more pronounced due to the atomic cooperative structural relaxation and more thermally stable compared with the polycrystalline electrode junctions. Additionally, the use of the magnetic oxide electrode CoFeHfO has shown that the relevant FM electrode-barrier interface becomes insensitive to the oxygen, which simplifies the oxidation process used for the oxide barrier fabrication.

Electronic, lattice, and spin interactions at the interfaces between crystalline complex transition metal oxides can give rise to a wide range of functional electronic and magnetic phenomena not found in bulk. At hetero-interfaces, these interactions may be enhanced by combining oxides where the polarity changes at the interface. The physical structure between non-polar SrTiO3 and polar La1-xSrxMnO3(x=0.2) is investigated using high resolution synchrotron x-ray diffraction to directly determine the role of structure in compensating the polar discontinuity. At both the oxide-oxide interface and vacuum-oxide interfaces, the lattice is found to expand and rumple along the growth direction. The SrTiO3/La1-xSrxMnO3 interface also exhibits intermixing of La and Sr over a few unit cells.