Nurul Amin

NiMn‐pinned spin valves with high pinning field made by ion beam sputtering

Spin valves of film layer structure, Ta/NiMn/NiFe/Co/Cu/Co/NiFe/Ta/Substrate were fabricated by ion beam sputtering. Optimization of the processes of deposition and posthermal treatment yields highly (111) oriented spin valve films with a giant‐magnetoresistance ratio of above 4% and pinning field of 650 Oe. This is the strongest pinning field ever observed. It stays constant up to 180 °C, then decreases to zero at a blocking temperature of 380 °C. These spin valves are highly thermally stable and, thus, suitable for the application of high density recording heads.

Temperature dependence of giant magnetoresistance properties of NiMn pinned spin valves

The giant magnetoresistance response of NiMn pinned spin valves was studied at elevated temperature. Top spin valve films were made by ion beam sputtering and thermally treated to induce the strong unidirectional pinning field in the pinned layer. Both δR and δR/R decrease linearly with temperature. The sheet resistance of the spin valves also increases linearly with temperature. The exchange coupling between pinned layer and free layer decreases slightly and the coercivity of the free layer increases slightly. The temperature dependence of the exchange pinning field is unique in NiMn spin valves. The pinning field has a weakly increasing temperature dependence up to 200 °C, then decreases to zero at the blocking temperature of 380 °C. Samples with different thickness NiMn layers show different temperature dependencies. However, the blocking temperature is unchanged. The pinning fields of NiMn, FeMn, IrMn, and NiO spin valves were also measured up to 200 °C; NiMn pinned spin valves show the least dependen...

Exchange tab stabilized readback transducers for areal densities exceeding 20 Gb/in/sup 2/

We present results from a high-density giant magnetoresistive magnetic recording reader using exchange bias stabilization. This novel reader design approach reduces the amount of parasitic resistance, as the sense current is not delivered through high resistivity permanent magnets. Heads were demonstrated to deliver areal densities in excess of 24 Gb/inch/sup 2/. The electrical performance of these heads, in particular, amplitude sensitivity, microtrack profiles and areal density capability are presented. Reader film properties and manufacturability of this approach are discussed in detail.

Magnetic coercivity of Fe3O4 particle systems

Magnetic coercivity and squareness of various Fe3O4 particle systems have been investigated as a function of particle size and packing density. It has been found that these particle systems, exhibiting considerable deviations from spherical symmetry, have magnetic coercivities and squareness which are almost independent of packing density.

Giant magnetoresistance properties of patterned IrMn exchange biased spin valves

Giant magnetoresistance (GMR) responses were studied in micron-sized IrMn pinned spin valve stripes. As the stripe height is decreased both the pinning field and free layer bias field increase while the GMR ratio stays almost constant. The free layer coercivity becomes zero for the shortest stripe while the pinned layer coercivity drops slightly at high aspect ratio. The pinned layer switching field is enhanced in the patterned films, indicating a strong magnetostatic coupling between the free and pinned layer that was further simulated micromagnetically.

Analysis of Electromagnetic Fields Generated by a Spin-Torque Oscillator

Electromagnetic fields generated by spin-torque nano-oscillators have been theoretically investigated. The study is conducted on a specific magnetic device with an in-plane magnetization rotation driven by spin transfer torque. Under the macrospin approximation, analytic solutions of the electromagnetic fields can be obtained. The electromagnetic fields have been analyzed and characterized in the near field and far regimes. In the far field, the electromagnetic fields resemble those of an electric dipole. However, the radiating fields are too weak to be detected, given the small size of the spin-torque oscillator. In the near field, the magnetic dipole field from the rotating magnetization and a radiating E-field are detectable over a reasonable range. This implies that the spin-torque oscillators can be used as a magnetic field or an electric field source in a short-range communication system.

Magnetization in a spin valve head mapped by an MFM tip

We have mapped the magnetization distribution in a spin valve head by monitoring its magneto-resistance /spl delta/R, while scanning the sample surface with an MFM tip. We find that conventional tips give enhanced response at two edges of the sensor. In comparison, mapping with horizontally magnetized tips shows no such artifacts. This is because conventional tips produce in-plane magnetic field components in all radial directions, thus the response /spl delta/R does not simply correspond to local magnetization. In contrast, horizontally magnetized tips produce fields along a single direction. Therefore, mapping of /spl delta/R renders the approximately single-domain magnetization in our spin valve films.

Magnetic behavior of layered films of submicronic Fe3O4 particles

A special aggregate of six glass slides, glued together, has been prepared. Each side of each slide contained a thin layer (∼0.2 μm) of dispersed Fe3O4 particles of mean diameter ∼0.17 μm prepared by reduction of α‐Fe2O3 particles. Magnetization measurements on the above aggregate have been carried out at 300 K as a function of the angle between the direction of the magnetic field and the plane of the slide aggregate as it is rotated along the long axis of symmetry. The angular dependence of the coercivity and the ratio of the remanent to saturation magnetization imply that magnetic‐moment reversals in this system are likely to be incoherent fanning rotations.

Some magnetic properties of submicronic Fe3O4 particles

Nearly spherical Fe3O4 particles of narrow size distribution with the average diameter between 0.07 and 0.60 μm have been prepared by H2 transformation of α‐Fe2O3 particles produced from homogeneous precipitation of ferric salt solutions. The magnetic behavior of these particles has been investigated as a function of temperature between 300 and 900 K in magnetic fields up to 7 kOe. The coercive force Hc has been found to be proportional to Mr/N and Mns, where Mr is the remanent magnetization, Ms is the saturation magnetization, N is the effective self‐demagnetization constant, and n is a power index. The implication of these results is briefly discussed.

Tempertature dependence of GMR properties of ion beam sputtered NiMn exchange biased spin valves

WEDNESDAY AFTERNOON, JANUARY 7,1998 173 CONCOURSE, 2:30 TO 530 Session DP EXCHANGE BIASING I (POSTER SESSION) Kantaro Takano, Chair University of California at San Diego, CMRR, 9300 Gilman Drive, La Jolla, CA 92037