Moriaki Fuyama

Exchange coupling between ferromagnetic fcc Ni81Fe19 and antiferromagnetic bcc CrMnPt films

We studied an antiferromagnetic CrMnPtx [(Cr:Mn≂1:1) in atomic percent] film for an exchange‐biased layer, focusing especially on the relationships between the exchange coupling properties of the CrMnPtx (top)/Ni81Fe19(bottom) films and the character of its CrMnPtx film. The best Pt content to obtain a large exchange coupling of the CrMnPtx film was 5.0–8.0 at. %. Typically, the exchange coupled 50 nm CrMnPt5−8/40 nm Ni81Fe19 films exhibited a relatively large exchange coupling field of ∼22 Oe and a high blocking temperature of ∼380 °C. Besides, the CrMnPt5−8 film deposited on the Ni81Fe19 film had a considerably high resistivity of ∼300–350 μΩ cm. These large exchange coupling and high resistivity values were obtained only when the α‐phase with a disordered bcc structure was stabilized in the CrMnPtx film by the underlying fcc Ni81Fe19 film. The Pt within the CrMnPtx film might localize the Mn magnetic moment. As to why the CrMnPtx film having the Pt content of 5.0–8.0 at. % could give the Ni81Fe19 film ...

Transferred Charge in the Active Layer and EL Device Characteristics of TFEL Cells

The relationship between transferred charge in the active layer of a thin-film electroluminescent (TFEL) cell and EL device characteristics has been investigated electrically. Making use of a charge density-voltage characteristic measuring system based on a Sawyer-Tower circuit, a general formula for the input power density was found to be given by twice the product of the frequency, the threshold voltage of the active layer, and the transferred-charge density. From this formula, the luminous efficiency could be estimated, once the dependence of the luminance upon the frequency and the transferred charge density was found. At a frequency smaller than the inverse of twice the luminous decay time, e.g. 500 Hz in the ZnS:Mn case, the luminance was found to be proportional to the product of frequency and transferred charge density. Hence, the luminous efficiency becomes constant with a value 2–2.5 times larger than that for 5 or 1 kHz drive conditions.

Magnetic exchange coupling for bilayered Ni81Fe19/NiO and trilayered Ni81Fe19/NiFeNb/NiO films

Exchange coupling between a ferromagnetic film and an antiferromagnetic NiO film was investigated. Bilayered ferromagnetic Ni81Fe19/antiferromagnetic NiO films had a large exchange coupling field and blocking temperature of about 200 °C. In trilayered Ni81Fe19/ferromagnetic (Ni81Fe19)100−xNbx/NiO films, a way could be developed to control the exchange coupling field at a small value by increasing the Nb of the intermediate film. The most important factor in the control seemed to be that the numbers of magnetic Fe and Ni atoms of (Ni81Fe19)100−xNbx, which contributed to the exchange coupling between (Ni81Fe19)100−xNbx and NiO, varied with the existence of nonmagnetic Nb at their interface. From experimental results with other trilayered Ni81Fe19/ferromagnetic (Ni100−xFex)93Nb7/NiO films, it was ascertained that the exchange coupling field seemed to be independent of the magnetic moment of the ferromagnetic film although unidirectional anisotropy constant was proportional to it. As for blocking temperature,...

Dielectric properties of rf‐sputtered Y2O3 thin films

Yttrium oxide (Y2O3) thin films were deposited on indium‐tin‐oxide(ITO)‐coated glass substrates by the radio‐frequency‐sputtering method using an Y2O3‐sintered target. The relative dielectric constant er and the dielectric strength EBD of the Y2O3 films were studied. It was found that er and EBD have a maximum value and a minimum value, respectively, at 1.3 Pa when the pressure of the sputtering gas, Ar+10% O2, is varied from 0.67 to 9.3 Pa. The x‐ray diffraction study showed that the Y2O3 films deposited at 1.3 Pa are predominantly oriented along the 〈332〉 direction and their grain size is the smallest. Ion mass analysis showed impurity diffusion from ITO in the films deposited at 1.3 Pa. Furthermore, the dielectric properties of the Y2O3 films deposited at 1.3 Pa are related to the structural properties, such as the 〈332〉 orientation, grain size, and impurity diffusion.

Spin-valve heads utilizing antiferromagnetic NiO layers

Spin-valve heads utilizing antiferromagnetic NiO layers as the pinning layers were investigated. Advantages of using NiO are (1) superior corrosion resistance, (2) relatively high blocking temperature and (3) reduction in the heat generation due to current shunting. Spin-valve films of a structure of NiO/NiFe/Cu/NiFe show large /spl Delta//spl rho///spl rho/ (approximately 4%) and good sensitivity. Thin Co layers inserted between NiFe and Cu improve both /spl Delta//spl rho///spl rho/ and the thermal stability. To explore the feasibility of spin-valves with NiO, unshielded sensors with hard bias structure having longitudinally magnetized permanent magnets were fabricated. Irregular response in the transfer curves can be suppressed when the permanent magnet strength M/sub r/t is 0.5 memu/cm/sup 2/ or more. The linear response region of the spin-valve sensor was optimized by adjusting the thickness of the pinned layers and the sensor height. Finally, by incorporating these results a shielded spin-valve head with a track width of 2.4 /spl mu/m, a gap length of 0.3 /spl mu/m and a sensor height of 0.7 /spl mu/m was fabricated The response was noise-free and the output obtained with a small sense current of 0.41 mA was approximately 1 mVp-p, demonstrating a high sensitivity of a spin-valve head utilizing NiO.

NIO STRUCTURE-EXCHANGE ANISOTROPY RELATION IN THE NI81FE19/NIO FILMS AND THERMAL STABILITY OF ITS NIO FILM

We studied an antiferromagnetic (AF) NiO film for an exchange‐biased layer, focusing especially on the relationships between the exchange coupling properties of the Ni81Fe19(top)/NiO(bottom) films and the character of its NiO film. Among the variable sputtering conditions, our experimental data showed that the dominant factor determining the exchange coupling properties was the Ar pressure during the NiO film preparation. Better exchange coupling properties resulted when the NiO film was deposited at low Ar pressure which was attributed to: (i) the smooth surface of the NiO film and (ii) the presence of relatively large particle sizes within it. The former was thought to bring about not only an increase in the number of unidirectional exchange coupled Ni81Fe19/NiO spins, but also the appearance of exchange paths having large local exchange anisotropies. The latter was thought to produce an increase in the AF clusters with a particle volume larger than KeiA/KAFi, where Kei, A, and KAFi are local unidirecti...

Single-pole/TMR heads for 140-gb/in/sup 2/ perpendicular recording

Single-pole writers and tunneling magnetoresistive (TMR) readers for 140-Gb/in/sup 2/ perpendicular recording were fabricated and their recording performance was tested. Data erasure, which is observed as write instability in a repeated read-write operation, can be suppressed by combining a laminated pole and low throat height. Fe-Co/Ni-Cr laminated film was used to reduce the remanent magnetization of the main pole after patterning. Narrow track writers with a 120-nm-wide trapezoidal pole showed a good write ability of 30 dB or more in overwrite for media with high coercivity of up to 7 kOe. Also, negligibly small skew writing was confirmed. TMR heads with a sensor width of 85 nm and a head resistance of 250 /spl Omega/ showed approximately 30 dB of head signal-to-noise ratio (SNR). A potentially higher SNR with a higher operating voltage was suggested from a measured output versus sensing current curve. Calculations showed that the side reading was suppressed in a side-shielded design. A 10% amplitude width of the microtrack profile of a 100-nm-wide reader was reduced from 198 to 162 nm by applying the side shields.

Design and read performance of GMR heads with NiO

GMR heads with NiO/NiFe/Co/Cu/NiFe films have been designed, fabricated, and their read performance was tested. Calculations showed that output was reduced significantly when the exchange coupling field on the pinned layer was smaller than 200 Oe due to tilting of the magnetization of the pinned layer. When the pinned layer of NiFe(1 nm)/Co(1 nm) was used, the coupling field from NiO was 360 Oe which would be large enough to ensure the full output. The readback waveform of the fabricated head was noise-free and well biased. The obtained output was about six times as large as that of conventional AMR head. When the sensing current was increased, the output increased linearly up to the current density of 20 MA/cm/sup 2/, while the peak asymmetry was not affected much by the current. The output increased linearly with the read width, except for small dead zones at both of the track. The microtrack profile was symmetric, reflecting the symmetric magnetization configuration of the free layer without the medium field.

Spin-Valve Films Using Exchange-Coupled CrMnPt/Co Structure

Spin-valve films using CrMnPt/Co structure were investigated. The exchange coupling field (Hex) applied on 3 nm thick Co pinned layers was increased by annealing from 190 Oe to 320-380 Oe. The annealing treatment necessary for the enhancement of the Hex was typically 230/spl deg/C, 1 hr. The annealing distorted the crystal lattice of the CrMnPt films, which is likely to enhance the Hex. The blocking temperature was 320/spl deg/C. The resistivity of the CrMnPt films was as high as 300 /spl mu//spl Omega/cm resulting in low current shunting to antiferromagnetic layers in spin-valve films.

TiO2 / SiO2 Multilayer Insulating Films for ELDs

Dielectric properties and the optical energy gap of TiO 2 /SiO 2 multilayer films prepared by sputtering were measured. The thickness ratio, TiO 2 /SiO 2 , was fixed at 1/3, and TiO 2 monolayer thickness, dt, was varied from 0.3 to 60 nm. The peak of the maximum charge density, which is the product of the dielectric constant and the breakdown field strength, was observed at dt=1 nm. The optical energy gap was constant for dt>2 nm, and increased as dt dropped below 2 nm