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The electronic structures of AgNi1-xCoxO2 (0 ≤ × ≤ 1) delafossite oxides have been investigated by employing photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS) in the soft X-ray regime of synchrotron radiation. The Ag 3d core-level PES spectra shift toward the higher binding energy with increasing x, in agreement with the metallic nature for low values of x and the insulating nature for high values of x in AgNi1-x CoxO2. Further, the Ag 3d core-level PES spectra become more asymmetric with decreasing x, which reflects the larger number of electron-hole pairs in the Ni-rich regime. Valence-band PES spectra reveal that the band width of the occupied Ni 3d states is broader than that of the Co 3d states, implying the larger Ni 3d-O 2p hybridization than the Co 3d-O 2p hybridization. The Co and Ni 2p XAS spectra show that Co ions are in the low-spin Co3+ states for all x, while Ni ions are in the Ni2+ - Ni3+ mixed-valent states. The Ni3+ component increases with x. [ABSTRACT FROM AUTHOR]

This work focuses on magnetic tunnel junctions with a MgO barrier layer made by RF-sputtering and radical oxidation. In case of RF-sputtered MgO, its crystal orientation, MR and RA values very sensitively depend on the chamber atmosphere. The MR ratio of 97% in radical oxidized MgO is obtained at 0.4 V, which is slightly higher than RF-sputtered MgO. Also, its RA is smaller than that of RF-sputtered MgO. These improved MgO properties are originated from the improvement of the crystal orientation of MgO(200) and the decrease of OH component within the MgO barrier. In addition, the breakdown voltage in radical oxidized MgO is higher than that of RF-sputtered MgO at the same MgO thickness. [ABSTRACT FROM AUTHOR]

Toggle switching mode MRAM is tested and characterized with respect to the free- and pinned-layer material and thickness. With magnetization curves, we were able to find the optimum thickness combinations of free-layer and spacer materials. For CoFeB where the intrinsic anisotropy field (Hi) is about 20-30 Oe, one needs to have a reasonably high exchange coupling field (Hex) to ensure large switching margin. In case of an NiFe/Ru/NiFe free-layer, Hi is usually much smaller than Hex, so that further decrease of Hex between two magnetic layers is needed. The pinned-layer roughness and thickness are other factors to be optimized to reduce the toggle switching field. High cell aspect ratio ≥3.0 helps to minimize the switching distribution and enhance the switching stability. [ABSTRACT FROM AUTHOR]

The dependence of the switching field distribution of magnetic random access memory cells on film roughness, saturation magnetization, film thickness, and cell aspect ratio is discussed. We found that a flat interface between the tunnel oxide and the magnetic film is very important in suppressing switching field variation For free-layer materials, NiFe, CoNiFe, CoFeB, and lamellar structures are examined. By trying various compositions of these materials, we have improved switching characteristics with small saturation magnetization and small thickness. Good results with laniellar structures suggest that the suppression of the grain growth in the ferromagnetic layer is another effective way to get enhanced switching characteristics. [ABSTRACT FROM AUTHOR]

Dependence of magnetic tunnel junction (MTJ) properties on seed layer, surface treatment and magnetic materials was investigated to improve TMR ratio. Roughness of tunnel oxide layer generated from seed layer roughness reduces TMR ratio as well as PA product owing to locally reduced oxide layer thickness. Crystallinity of seed layer is found to be important to enhance TMR ratio. Surface treatment with ion beam etching on a pinned layer Improves tunnel oxide uniformity providing higher TMR ratio. Also, highly polarized magnetic material increases TMR ratio but the effect of surface treatment is quite different depending on pinned layer material. [ABSTRACT FROM AUTHOR]