Y. Motomura

Magnetoresistance of non-coupled [NiFe/Cu/Co/Cu] multilayers

Abstract Non-coupled-type [NiFe/Cu/Co/Cu] multilayers prepared on Cr buffer layers showed enhanced magnetoresistance (MR) ratios and sharp field dependences. The effect of interface doping with impurity layers is systematically studied.

Shielded magnetoresistive head for high density recording

The fabrication process and the head material properties for shielded magnetoresistive heads with planarized lower shields using a tri-layered MR element are described in detail. Applying the etch-back process with low molecular weight polystyrene and CF/sub 4//O/sub 2/ reactive ion etching, the residual step height for a lower shield is dramatically decreased to less than 5% of the initial step height. The tri-layered MR element consists of an MR layer, a magnetic separation layer (MSL), and a soft adjacent layer (SAL). 40-nm thick Ni/sub 81/Fe/sub 19/ (wt.%) films were deposited by evaporation for use as an MR layer. Evaporated Ti MSL thickness was experimentally determined to be 20 nm. Amorphous Co/sub 82/Zr/sub 6/Mo/sub 12/ SAL films exhibited preferable magnetic properties as an SAL material. The fabricated shielded MR heads, using the tri-layered MR element with these NiFe, Ti, and CoZrMo films, provide superior capability to realize high recording density. >

Soft magnetic properties and heat stability for Fe/NiFe superlattices

Soft magnetic properties and heat stability were investigated for Fe/NiFe (91 wt.% Ni and 19 wt.% Fe) superlattice films. X-ray diffraction data show that the films have a textured BCC Fe [110]/FCC NiFe [111] stacking. Saturation magnetic flux density (B/sub s/) is the average of bulk Fe and NiFe values. Coercive field (H/sub c/) value and relative permeability ( mu ) depend on the thicknesses of both Fe and NiFe layers. Saturation magnetostriction constant ( lambda s) behavior is explained as the average of lambda s values for Fe, NiFe, and Fe-NiFe interdiffusion layers. In Fe/NiFe films with 8 approximately 16-nm, superlattice modulation wavelength and around 50% Fe-layer thickness ratio, large 15-kG B/sub s/ value, 3000- mu values, and very small lambda s values less than 5*10/sup -7/ were achieved. The soft magnetic properties and the superlattice periodicity are stable at up to 200 degrees C annealing temperature. Effective interdiffusivity values are 1.9*10/sup -24/ approximately 1.5*10/sup -21/ m/sup 2/ s/sup -1/ in the 200 approximately 400 degrees C temperature range, and are found to have an Arrhenius temperature dependence. Activation energy for the interdiffusion is estimated to be 0.84 eV. Extrapolating the effective interdiffusivity value to lower temperature, Fe/NiFe films appear rather stable at an operating temperature for hard disk drives. >

Magnetic Properties and Magnetoresistance Effect in Evaporated NiFeCo Films

The anisotropic magneto-resistance (MR) ratio and magnetic anisotropy field H<inf>k</inf> have been examined for (Ni<inf>0.82</inf>Fe<inf>0.18</inf>)<inf>100-x</inf>Co<inf>x</inf> and Ni<inf>82</inf>Fe<inf>18-x</inf>Co<inf>x</inf> evaporated films, both as-prepared and after annealing at 320°C for two hours, to evaluate their usefulness as MR head materials. The MR ratio of the (Ni<inf>0.82</inf>Fe<inf>0.18</inf>)<inf>100-x</inf>Co<inf>x</inf> is almost constant regardless of changes in the Co concentration. The MR ratio for the Ni<inf>82</inf>Fe<inf>18-x</inf>Co<inf>x</inf> films increases as the Co concentration increases, and after annealing the MR ratio rises up to 5% in the range of Co concentrations above 6 at%. The H<inf>k</inf> increases as the Co concentration is increased, and is not changed by annealing. The increase in the MR ratio for Ni<inf>82</inf>Fe<inf>18-x</inf>Co<inf>x</inf> films due to annealing is related to inhomogeneous strain and lattice defects. For Ni<inf>82</inf>Fe<inf>12</inf>Co<inf>6</inf> film, an MR ratio of 5.1% and an H<inf>k</inf> of 7.0 Oe were obtained, making such film suitable for application in MR heads.

Inverse magnetostriction effect on magnetoresistive response for evaporated NiFe and NiFeCo films

The relations between inverse magnetostriction energy e and magnetoresistive (MR) response have been investigated for Ni82Fe18 films and Ni82Fe12Co6 films that have about twice the uniaxial anisotropy energy as the NiFe films. To obtain films with various e values (50–800 J/m3), internal stress σ for the films is changed by the deposition conditions and film thickness control. The σ is measured by the bending method. The σ changes for both films are related to microstructure differences. Hysteresis or Barkhausen jump is observed for the NiFe films with absolute e value ‖e‖ more than 120–130 J/m3, and for the NiFeCo films with ‖e‖ more than 300–330 J/m3. The threshold ‖e‖ values are on the same order of magnitude as the calculated uniaxial anisotropy for each film. To obtain smooth MR response, it is very important to reduce the ‖e‖ to less than the uniaxial anisotropy energy value, by deposition conditions and film thickness control.

Dynamic magnetization changes in laminated Permalloy films

Laminated soft magnetic films separated by nonmagnetic interlayers have edge-curling walls (ECWs) at the pattern edge. The authors have investigated dynamic magnetization changes near the ECW in strip-shaped laminated Permalloy films. Observation results obtained by scanning Kerr effect microscope at 10 MHz show the unique magnetization behavior-that is, inactive (weak Kerr signal) regions at the strip edges and magnetization change peaks inside the inactive regions. The edge region is observed as the inactive region under an excitation field smaller than the switching field in the ECW. According to the magnetization change calculation, the peak appears because the magnetization near the ECW shows a different behavior depending on the external field direction. Further examination shows that the ratio of the active region width in the actual strip width is changed by the layer configuration. >

Offtrack characteristics of shielded magnetoresistive head

The shielded magnetoresistive (MR) head offtrack profile shows a wide output plateau which follows the conventional offtrack roll off curve. The authors investigated the origin of the unique offtrack characteristics and their influence on crosstalk signal-to-noise-ratio (SNR), based on experimental and magnetic calculation results. In the measurement, 8- mu m track-width MR heads, consisting of a pair of 100- mu m shields and a trilayered MR element between shields, were used. The plateau width is close to the shield width. The output in the plateau region is the sum of the contributed outputs from individual tracks under the shield. Therefore, this output can severely reduce the crosstalk SNR when the MR head includes several tracks under the shield. Magnetic calculation shows that the magnetic flux from the recorded track to the MR element through the shields can produce the output at the plateau region. Further examination shows that crosstalk SNR is improved by increasing the shield thickness and/or by decreasing the shield width. Therefore, to realize high track density, shield optimization is important. >

Preparation of ferrite thin film flexible disks and their read/write characteristics

A flexible disk of continuous ferrite thin film has been prepared. Ferrite thin film media have been formed on flexible polyimide substrates through direct radio frequency (RF) sputtering deposition of Co, Cu doped Fe 3 O 4 films. The D -6 dB density for the ferrite thin film, 18 K-FRPI, which is significantly higher than the 7 K-FRPI value for conventional media, was obtained with a 1.0 μm gap length ferrite head.

Magnetic Domains in Single-Pole Magnetic film Heads and Recording Characteristics

Domain structures in the main pole films of single-pole heads were studied, including microscopic domain observations and measurements of domain inclination angles ¿ (between the easy axis direction and the track width direction), and the effects of domain structures on recording using Co-Cr media investigated. Although isolated readback voltages were larger for large angles ¿, other characteristics, noise in particular, were better for smaller ¿. It was concluded that small inclination angles ¿ are necessary for high density, high fidelity recording.