Edward S. Murdock

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.

Exchange coupling of radio frequency sputtered NiMn/NiFe and NiFe/NiMn bilayers

Exchange coupling of radio frequency sputtered NiMn/NiFe (NiMn on top) and NiFe/NiMn (NiMn at bottom) bilayers have been investigated. It was found that the exchange coupling field, Hex, is not only directly related with the annealing temperature and time, but also is greatly influenced by the thin film deposition conditions. It was demonstrated that successful antiferromagnetic-ferromagnetic bilayer preparation should avoid interfacial contamination, which could destroy the spin coupling at the interface. The NiFe/NiMn bilayers show a high exchange coupling field [307 Oe for NiFe(200 A)/NiMn(500 A)] bilayer with a high blocking temperature around 430 °C. Most important is that the coupling field was able to sustain its strength up to almost 270 °C before starting to decrease. X-ray diffraction reveals that the diffraction intensity of NiMn in as-deposited bilayers does not seem important to achieve a high exchange coupling field. Furthermore, the NiMn thickness dependence of the magnetic properties of Ni...

Electromigration-induced failure of single layered NiFe Permalloy thin films for a giant magnetoresistive read head

Electromigration-induced failures have been investigated in single layered NiFe Permalloy thin films, which are used in giant magnetoresistance (GMR) read heads in high-density magnetic recording disk drives. The time-to-failure and median-time-to-failure (MTTF, t50) of NiFe thin films were found to be strongly dependent on the applied current density, film thickness, and ambient temperature. The activation energy (ΔQ) of NiFe films derived from the “Black equation” was found to be 0.8 eV. The MTTF and standard deviation (σ) of a NiFe thin film electromigration test stripe with 10 nm thickness, 5 μm width, and 20 μm length were 3.74 and 1.74 h, respectively, at 160 °C ambient temperature. Typical electromigration failures such as “voids and cracks” were observed at the cathode or center region of NiFe film test stripes. These results suggest that the electromigration-induced failures are one of the crucial factors in determining the reliability of GMR spin-valve read heads used in high-density magnetic re...

Temperature variation of the magnetoresistance in cobalt-enhanced spin-valve structures

We have conducted a survey of the temperature variation of the magnetoresistance in a series of FeMn exchange-biased spin-valve structures. These permalloy-based samples were prepared in an ion-beam sputtering system and feature Co layers inserted at the interfaces with the Cu spacer layer to enhance the interfacial spin-dependent scattering. Typical values for the MR are 4.0% at 295 K and 8.4% at 8 K (sample with 15 A Co thickness). A control sample with no cobalt showed MR values of 1.3% and 4.3% for those same temperatures. Both the MR ratio and the un-normalized magnetoresistive change ΔR are plotted vs temperature. The MR ratio for the cobalt-enhanced samples exhibits nearly linear decrease with rising temperature. The sample with no cobalt exhibits a temperature variation deviating substantially from linearity, with an upward curvature. The temperature dependence for the MR in these spin valves is examined in the light of interchannel spin-mixing and intrachannel scattering.

Dependence of electromigration-induced failure lifetimes on NiFe thin-film thickness in giant magnetoresistive spin-valve read heads

The physical mechanisms responsible for the dependence of electromigration-induced failure lifetimes on NiFe thin film thickness in giant magnetoresistive spin-valve read heads have been studied to determine the maximum allowable current density. Based on measured median-times-to-failure, a maximum current density of about 1–2×108 A/cm2 was found to be safely used in 3–5 nm thick NiFe films. Grain size analyses using a transmission electron microscopy suggests that the longer lifetimes of thinner films are mainly due to the smaller number of grain boundaries and fewer triple points which result in less atomic flux divergence.

Transmission electron microscopy study of thermal effects on the free-layer reversal of a crossed-anisotropy spin valve

Transmission electron microscopy has been used to study the reversal of the free layer of a NiMn-pinned crossed-anisotropy spin valve as a function of applied field orientation and specimen temperature. By choosing the orientation of the applied field correctly it was possible to avoid the formation of domains in the reversal process. As the temperature was raised above room temperature, the mechanism remained qualitatively unchanged until temperatures of ≈200 °C were reached, beyond which irreversible behavioral change began to take place. From analysis of image sequences magnetoresistance characteristics have been constructed.

23.8 Gb/in.2 areal density demonstration

We have demonstrated 23.8 Gb/in.2 areal density using a merged read-write grant magnetoresistive head, with an oriented thin film medium tested with broadband electronics and enhanced EPR4 channels. The medium had high signal to noise ratio metrics that was robust unto temperatures as high as 75 °C. A unique aspect of the head design at such a narrow track width is the simultaneous enhancement of the transducer sensitivity while keeping product and system manufacturability in the forefront. The areal density was demonstrated at a track density of 45.8 k tracks/in., using photolithographically defined poles and linear density of 520 k bits/in.

Electromigration of magnetic thin films for predicting electrical-failured lifetime of GMR read heads

Summary form only given. Electromigration-induced failures of magnetic thin films have been investigated and analyzed to predict the electrical reliability of giant magnetoresistance (GMR) read heads. Magnetic thin films showed the larger failure lifetime (median time to failure, MTTF) compared to the high conductivity metallic thin films such as Cu and Al thin films under the same constant current biasing conditions. The increase of resistance due to void formation and increase of shunting current or interdiffusion paths due to hillock formation are considered to be serious potential problems in the degradation of the electrical reliability of GMR spin-valve heads.

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