C. Chien

Voltage-induced barrier-layer damage in spin-dependent tunneling junctions

The effect of a dc stress voltage on the junction resistance and magnetoresistance (MR) of spin-dependent tunneling (SDT) junctions with naturally oxidized barriers was investigated. There is a threshold voltage at which irreversible resistance change begins. Beyond this threshold, device resistance decreases gradually over a transition period prior to breakdown of the tunneling barrier. The onset voltage of irreversible resistance change is much higher than the optimum operating voltage of SDT heads having the precursor aluminum thicknesses here investigated (5–11 A). The MR ratio decreased with increasing stress voltage in a pattern similar to that of the junction resistance.

Low resistance spin dependent tunneling junctions with naturally oxidized tunneling barrier

We investigated the effect of aluminum thickness on RA (resistance area product) and MR ratio in spin-dependent tunnel junctions. Very low RA values below 40 /spl Omega/ /spl mu/m/sub 2/ and a maximum MR ratio of 6% were obtained in Ni/sub 81/Fe/sub 19//Al/sub 2/O/sub 3//Ni/sub 81/Fe/sub 19/ tunneling junctions fabricated using natural oxidation of aluminum. The MR ratio significantly increased with use of Co/sub 90/Fe/sub 10/ electrodes. Using natural oxidation of 6 /spl Aring/ aluminum, RA and MR ratio of these junctions are /spl sim/50 /spl Omega/ /spl mu/m/sup 2/ and /spl sim/28%, respectively. The MR ratio and the junction resistance strongly depend on the aluminum thickness. The optimum thickness of aluminum is 6-7 /spl Aring/ fur natural oxidation.

Spin-dependent tunneling junctions with parallel hard bias for read heads

We investigated the feasibility of a spin-dependent tunneling (SDT) read head with a parallel hard bias. In this scheme, the longitudinal biasing to the free layer is provided by fringe fields from a hard magnet which is fabricated over or under the free layer. A linear response to the applied field is achieved for a SDT junction biased with 400 A CoCrPt underneath. Thinner CoCrPt layers yield Barkhausen jumps in the free layer. Micromagnetic simulation indicates the bias field at the edge of the free layer is smaller than that which would result from an abutted magnet. The simulation results are similar to experimental data, and indicate that shielded devices with 400 A permanent magnet will provide stable transfer curves.

Comparison of semiclassical calculations to experiment for spin valve films grown on oxide surfaces

The physical properties of spin valve films grown on the surface of nano-oxide layers were studied as a function of Cu spacer layer thickness. In comparison to identical structures without the oxide surface, the films exhibited an increase in ΔR/R of 30% accompanied by a reduction of only 5% in resistance. Semiclassical calculations were preformed on these films with a close match to experiment. Assuming the oxide layer did not cause drastic changes in the properties of the other film layers, the specular reflection was changed to obtain a match with experiment. The increase in giant magnetoresistance response was achieved by increasing the specular reflection at the metal/oxide interfaces from 15% to 85%, indicating high efficiency for specular reflection at the nano-oxide interface.

Inductive write heads for greater than 60 Gb/in/sup 2/ demonstration

Sputter deposited FeRhN films with a B/sub s/ value of more than 20 kG were used as high moment flux enhancement layer in the write element in order to achieve a recording density of 63.2 Gb/in/sup 2/. This layer was disposed between write gap and upper portion of the top pole, which was made of Ni/sub 45/Fe/sub 55/ with a B/sub s/ of 16 kG. A 36 dB overwrite and nonlinear transition shift of less then -20 dB were obtained at this recording density. A finite element model was used to calculate the longitudinal field and field gradient at the medium location. The results suggested significant increases of both by incorporating the flux enhancement layer.

Laminated FeRhN films for high speed writers

High moment FeRhN nanocrystalline films were laminated by Co/sub 90/Zr/sub 9/Cr (CZC) amorphous films, in order to improve the anisotropy definition and high frequency permeability. The experimental results also showed improved soft magnetic properties, higher resistivity, and better magnetic properties on sloped surfaces.

Micromagnetic simulation of tunneling magnetoresistance junctions with parallel hard bias

Tunneling magnetoresistance (TMR) films and devices were simulated to understand the response of the free layer with a parallel hard bias. In order to determine the effect of the granular hard bias material micromagnetic simulation was used to model both the hard bias and TMR material. Minimizing hysteresis and Barkhausen jumps in the response of the device involves an optimization of the spacing between the free layer and the hard bias coupled with the shape of the device edges.