S. Dey

The spin flop of synthetic antiferromagnetic films

The spin flop of synthetic antiferromagnetic pinned layers (SAF), under a magnetic field has been theoretically predicted and recently reported [J. G. Zhu and Y. Zheng, IEEE Trans. Magn. 34, 1063 (1998); J. G. Zhu, IEEE Trans. Magn. 35, 655 (1999)]. However, no experimental data have yet being reported to confirm the theoretical prediction. This article will provide direct experimental evidence to confirm the spin flop phenomenon in SAF layers. A spin valve, [CoFe/NiFe]/Cu/[CoFe(II)/Ru/CoFe(I)]/IrMn, was used to verify the spin flop in SAF layers. The exchange bias direction of CoFe(I)/IrMn was introduced by a magnetic annealing process at 225 °C with a field strength of Han(10 kOe) and the exchange bias direction was found parallel to the magnetic field. These samples serve as the reference for the remaining experiments. By magnetic annealing the reference samples at 225 °C with lower magnetic fields, we found that the magnetic field threshold for SAF spin flop is about 1 kOe. When the field is further i...

Pole tip recession studies of hard carbon‐coated thin‐film tape heads

Hard carbon coatings were deposited by cathodic arc and direct ion beam deposition techniques on thin‐film Al2O3–TiC heads and by the latter technique on thin‐film Ni–Zn ferrite heads. Functional accelerated tests were conducted against metal particle tapes in a linear tape drive. Ion beam carbon coatings on Ni–Zn ferrite and Al2O3–TiC heads substantially reduced the pole tip recession observed with uncoated heads. Cathodic arc carbon coated Al2O3–TiC heads performed better than uncoated heads, but were less effective than the ion beam coating. Pole tip recession increased only if carbon was removed from the pole tip. This suggests that coating effectiveness is determined by its adherence to the pole tip. In two‐wide pole tip heads, wear of the pole adjacent to the substrate was less than that of the other pole. Coatings withstood accelerated tests and may meet life time requirements of future heads.

Magnetic recording at a data rate of one gigabit per second

Magnetic recording at a data rate of 1 Gb/s was studied in detail. Dynamic flux response of the inductive write head under the write current excitation of 40 mA/sub o-p/ at 500 MHz was simulated by Finite Element Model (FEM). Results show that, while severe eddy current damping was observed at the yoke region, an efficient design in the apex region can significantly reduce the eddy current damping at the pole tips, thus rendering sufficient magnetic flux at 1 Gb/s. The effects of magnetic yoke and interconnect on the current rise time were also simulated by SPICE model and were compared with empirical results. A reasonable agreement was obtained, Dynamic coercivities in the media were also characterized. Finally, magnetic recording at 1 Gb/s has been demonstrated on media as high as 4000 Oe of VSM coercivity and with better than 10/sup -7/ of bit error rate.

Development of hard carbon coatings for thin-film tape heads

Major problems in thin-film recording heads are pole tip/gap recession in the inductive head and scratching/smearing, electrical short, electrostatic charge build up, and corrosion of the MR stripe in the MR heads. Wear of head structure can be minimized by depositing a hard carbon coating over the entire ABS including the head structure. In this study, we have deposited carbon coatings on Ni-Zn ferrite and Al/sub 2/O/sub 3/-TiC substrates and dummy heads by various deposition techniques and characterized for mechanical and tribological properties. Ion beam carbon coatings on Ni-Zn ferrite and cathodic arc carbon coatings on Al/sub 2/O/sub 3/-TiC heads exhibit most wear resistance compared to other coatings in a tape drive test.

Demonstration and characterization of 36 Gb/in/sup 2/ recording systems

We have successfully demonstrated recording at areal densities as high as 36 Gb/in/sup 2/ at data rates as high as 173 Mbits/s (21.6 MB/s) and at a Bit-Aspect-Ratio (BAR) of 7.3, using merged inductive-write/spin-valve-read heads on low noise thin film disks. Recording at a data rate of 590 Mbits/s (73.8 MB/s) has also been achieved at the corresponding linear density of 231 KBPI. Comparisons with previous areal density demonstrations have also been summarized.

Demonstration of 1 Gbit/sec magnetic recording using an integrated inductive write/GMR read head

1 Gbit/sec magnetic recording was demonstrated with integrated inductive write/GMR read heads on a thin film disk with a coercivity of 3200 Oe and an Mrt of 0.34 memu/cm/sup 2/ with a spinstand tester. The write heads were made with high moment materials on both P1 and P2 and a densely packed coil using conventional manufacturing processes, and the read heads were made of dual synthetic spin valve sensor used for the 36 Gbit/in/sup 2/ areal density demonstration. The interconnect between the head and pre-amplifier is a pair of twisted wires of about 2 inch length. The demonstration was done at the outer diameter of the disk rotating at 15000 RPM. With a modest 35 mA (0-P) write current, we achieved an overwrite of about 30 dB and an on track error rate of better than 10/sup -7/. BER test on a disk with a coercivity of 4000 Oe also showed very good results.

Study of thin-film media for linear densities beyond 500 KBPI

The linear density capability of thin-film media with a coercivity of about 2900 Oe and M/sub r/t ranging from 0.33 to 0.5 memu/cm/sup 2/ was studied with the advanced dual-spin valve heads used for the 14 Gbits/in/sup 2/ areal density demonstration. With a track error rate of 10/sup -7/ as the criterion, a linear density as high as 546 KFCI was achieved with the optimum head/medium design. Track edge noise was studied. Its effect on linear density design was examined, These results were used for designing the 14 Gbits/in/sup 2/ system.

26.5 Gb/in/sup 2/ areal-density longitudinal thin film media

A 26.5 Gb/in/sup 2/ areal-density demonstration was made using low-noise, thermally stable media and advanced dual-spin-valve heads. The demonstration was achieved at a linear density of 504 kbpi, a track density of 52.6 ktpi, and a data transfer rate of 230 Mb/s. The media had M/sub r/t of 0.40 memu/cm/sup 2/ and coercivity of 2500 Oe, and were composed of a dual-magnetic-layer structure with a five-element magnetic alloy. It was observed that smaller, uniform and isolated magnetic grains are critical to reducing the media noise and for designing ultra-high areal-density recording media that are thermally stable.

A small spot Kerr photometer system

A magneto‐optic small spot Kerr photometer device with a sampling spot size in the range of 4 μm is described. Key design features of the instrument include long working distance, large air‐core electromagnetic field coils, a sample holder which accommodates large samples, and a modulation detection scheme. Direct BH loops or the derivative, susceptibility signals can be obtained from a local area illuminated by the laser spot. The instrument can be used to obtain variations in magnetic properties across a large sample and is particularly suitable in wafer level testing in a manufacturing as well as research environment. Some studies done on soft magnetic films using this equipment are presented as examples of the versatility of the instrument.

Magnetics of NiFe and Ti composites-effect of annealing

The magnetic properties, retained stress, microstructure, and compositional profiles of Ti/NFe thin-film composites were studied as a function of annealing temperature up to 300 degrees C. Annealing of NiFe at 200 degrees C decreases the number of crystal defects and the internal stress. At 300 degrees C there is significant coarsening of microstructure. Annealing at 300 degrees C increases the retained tensile stress in the composite film by 50%, partly due to the microstructural changes in NiFe. Ni diffuses into Ti, depleting the Ni content of the NiFe layer. The NiFe magnetic properties show minor changes up to the annealing temperature of 200 degrees C, but show significant changes between 200 and 300 degrees C. >