Haruki Yamane

Differential type giant magnetoresistive memory using spin-valve film with a NiO pinning layer

The giant magnetoresistive (GMR) memory device of differential type is able to perform data readout without a magnetic field, and has many highly efficient properties, such as a nonvolatile, nondestructive readout, high-speed access, large output signal, and low electric power consumption. We have demonstrated data read/write of this memory by means of a spin-valve film with a NiO pinning layer. The spin-valve film was constructed of a multilayered structure [NiO/NiFeCo/Cu/NiFeCo], and exhibited the appropriate properties of a storage element, such as a MR ratio of 5%, a squareness ratio of unity, a writing field of 20 Oe, and a high corrosion resistance. The differential type memory device is constructed of a memory cell including two storage elements, in which the word currents of each element are in opposite directions. The information storage is performed by storing different resistance values in each element. The data readout of this memory is accomplished by sensing the differentiation of each eleme...

Annealing effects on multilayered Co/Pt and Co/Pd sputtering films

Effects of air annealing on magnetic properties and structures of multilayered Co/Pt and Co/Pd sputtering films were studied. The dual‐source rf magnetron sputtering method was employed in fabricating the films. The thicknesses of the Co layer and Pt layer of the Co/Pt films were 4.3 and 10.0 A, respectively: the total thickness was 4300 A. The thicknesses of Co layer and Pd layer of the Co/Pd films were 3.6 and 11.8 A, respectively: the total thickness was 5600 A. Residual magnetizations and coercivities of the Co/Pt and Co/Pd films increased with air‐annealing at 250–350 °C for 30 min to 2.5–3 kG and 2–3 kOe, respectively. The increases were observed only during air annealing, but not in vacuum annealing. Saturated magnetizations and intensities of the superlattice x‐ray peak decreased uniformly relative to annealing temperature.

Changes in film structure and increase in coercivity for Co/Pd multilayered films with atmospheric annealing

Co/Pd multilayered films exhibit large perpendicular magnetic anisotropy and have attracted attention as new materials for recording media and for other applications. The coercivity (Hc), however, is small in as‐sputtered films. We have found that Hc increased markedly with the atmospheric annealing at 300 °C to 2 kOe, and studied the change in film structure and reason of the increase in Hc with the annealing. The rf magnetron sputtering method was employed in fabricating the films. Film structure changes were observed by x‐ray diffraction, Auger electron spectroscopy, transmission electron microscopy, energy dispersive x‐ray spectrography, and atomic force microscopy. The increase in Hc was observed only in the atmospheric annealing, and not in the vacuum‐annealing. The internal structure of films after the atmospheric annealing at 300 °C consisted of columnar parts that had the multilayered structure that undertook vertical magnetization and column boundaries being surrounded by Co oxides. As a consequ...

Magnetic properties of multiple‐structure multilayered Co/Pd films

Co/Pt and Co/Pd multilayered films exhibit large perpendicular magnetic anisotropy and have attracted attention as new materials for magneto‐optical recording media and for applications in other areas. The coercivity and the squareness ratio of these films are small at thick films of 1000 A or more. We studied Co/Pd multiple‐structure multilayered films, consisting of periodic piles of Co/Pd multilayered film layers and Pd thin‐film layers in order to improve the magnetic characteristics. By adopting such multiple structures, a squareness ratio of unity, coercivity of 2.5 kOe, and residual magnetization of 1.5 kG were obtained at a thick film of 2000 A.

Annealing effects on Co/noble metal multilayer films

Abstract Co/noble metal (Pd, Au, etc.) multilayer films exhibit large perpendicular magnetic anisotropy. After annealing in air, the coercivities of Co/Pd multilayer films markedly increased as a result of the formation of Co oxides. On the other hand, for Co/Au multilayer films, the uniaxial magnetic anisotropy constant increased as the Co-Au interfaces became sharper.

Perpendicular magnetic anisotropy and magneto-optical properties of (Co–Tb)/Pd multilayers

Abstract The perpendicular magnetic anisotropy (PMA) and magneto-optical properties of sputtered RE–TM (Co–Tb)/Pd multilayered films were studied. Thick CoTb layers with high Tb concentration were observed to be amorphous. Like in the crystalline Co/Pd multilayered films, perpendicular magnetic anisotropy was observed only for (Co–Tb)/Pd multilayers with thin magnetic layer. The magnetic layer thickness range, over which the easy magnetization axis is perpendicular to the film plane, is much broader for (Co–Tb)/Pd multilayers than that for Co/Pd multilayered films. Kerr rotation angles were found to decrease with increasing Tb concentration.

Fabrication and magneto-optical properties of perpendicular magnetic CoPt nanostructures formed by surface agglomeration of Ag

The magneto-optical (MO) properties of perpendicular magnetic Co80Pt20 nanostructures formed by the surface agglomeration of Ag were investigated under polar Kerr measurement conditions. A ZnO intermediate thin layer on a Ru underlayer promoted the Ag agglomeration to form the nanostructures and improved the perpendicular magnetic properties. The magnetic nanostructures consisting of CoPt layers and Ag fine grains had two magnetic regions with different coercivities. The antiparallel magnetic alignment between the CoPt layers on the Ag grains and on the Ru underlayer produced an increase in the Kerr rotation angle at a low magnetic applied field. This was explained by MO phase reversal in the CoPt layer on the Ag grains. The MO behaviors (enhancement and phase reversal of Kerr rotation) of the CoPt nanostructures are attributed to the influence of surface plasmon polaritons excited at the Ag grains.

Sensitive giant magnetoresistive sensor using AC bias magnetic field

A new sensitive magnetic sensor was developed by utilizing the giant magnetoresistance effect of spin-valve film. The sensor element was composed of a spin-valve layer patterned to a micro size, and a bias current layer which generates a square wave AC magnetic field. High sensitivity was attained using only the edge part of the step shape MR loop.

Magneto-Optical Enhancement in Cavity Structure Consisted of Perpendicular Antiferromagnetically Coupled CoPt Layers

Magneto-optical properties of a stacked-layer structure with perpendicular antiferromagnetically coupled CoPt layers have been investigated under the polar Kerr measurement condition. The stacked layer included an optical cavity that was basically composed of a [CoPt/ZnO/CoPt] trilayer inside the film. It also acted as a magneto-optical cavity under the residual magnetization condition. The enhancement of the residual Kerr rotation was observed by the antiparallel magnetization alignment of the CoPt layers. The enhanced residual rotation angle in the AF sample was greater than the saturation angle of a 5-nm-thick CoPt single film. Moreover, by the finite-difference time-domain simulation, in this system, we demonstrated that a large enhancement of the magneto-optical effect can be anticipated by adopting a two-dimensional photonic crystal structure.

Tantalum-chromium alloy films as contact materials for a capacitor using Sr{sub 0.9}Bi{sub 2.1}Ta{sub 2}O{sub 9} for ferroelectric memories

Tantalum-chromium (Ta-Cr) alloy films have been examined as contact materials for ferroelectric memories. Ta-Cr films were prepared by dual-source radio frequency (rf)-magnetron sputtering and with a film composition that was varied by control of rf power applied to the targets. Three types of films were obtained by the controlling film composition. Films with no or low levels of added Cr had high resistivity and a {beta}-Ta structure. Films with intermediate levels of added Cr had high resistivity and an amorphous structure. Films with high levels of pure Cr had low resistivity and a bcc-Cr structure. Amorphous Ta-69%Cr and crystalline Ta-74%Cr alloy films were highly stable despite changes in thermal and oxidation conditions, maintaining a constant resistivity even after annealing at 700 C in an oxygen atmosphere. The high oxidation resistance of these films has been attributed to the chromic scale surface barrier layer.