Magnetoresistive transducer for absolute position detection

In this paper a new method is presented for the measurement of absolute linear or angular position. The digital position information is recorded serially into one track of a suitable hard-magnetic medium. The stray field of this information layer determines the angular magnetisation distribution in a ferromagnetic (permalloy) detection strip which is positioned parallel to the track but with its plane perpendicular to the hard-magnetic layer. The bit pattern representing the position co-ordinate is regained by detection of the planar magnetoresistance effect in the sensor strip. Experiments have been performed using sensors with a resolution of 250 ¿m and 1 mm respectively and longitudinally recorded audio tape. Suitable sensor output signals could be measured without hysteresis

Investigation of the structure of recording head fields

Head fields of two recording heads (gap lengths 2.1 and 2.8 micrometer) have been measured with the help of a series of magnetoresistive transducers. The widths of these transducers are 1.9, 4.1 and 7.0 micrometer and they have been positioned in the gap field region very accurately using optical methods. The transducer outputs have been compared with computer simulated results. A systematic deviation between theoretical and experimental results may lead to the assumption that the surface of the recording head is magnetically inactive over a few tenths of a micrometer

Measurement system for two-dimensional magnetic field distributions, applied to the investigation of recording head fields

The system described is built around a very accurate positioner into which a sensitive transducer and the object of analysis is mounted. The properties of the applied magnetoresistive transducer are described. This transducer, a very narrow permalloy strip placed at the edge of a glass substratum, can be used to measure both components of the field distribution. The analysis of the measured results can be accomplished with the help of a computer simulation of the transducer response curves. The performance of the system is demonstrated by measurements on a number of ferrite heads and conclusions about the so called 'dead layer'-structures on these heads are given

Two-dimensional coding for probe recording on magnetic patterned media

The effect of intertrack intersymbol interference in a magnetic patterned medium is studied. A two-dimensional (2-D) channel code is proposed, dedicated to perpendicularly magnetized media without soft underlayer, which exhibit read pulses showing overshoot. Read pulse shapes were investigated using a magnetic-force microscope tip scanning the patterned medium row-by-row. To test different codes, a bit-detection simulation program was developed to generate large amounts of data on which bit error rates can be measured. Application of the 2-D channel code, which implies recording of particular dot positions with fixed bits ("ones", "zeros"), resulted in the elimination of 2-D worst-case bit patterns and a subsequent reduction of detected-bit errors. The accompanying redundancy of 22% is inevitable for this type of 2-D code

Two-dimensional data detection for probe recording on patterned media

The effect of intertrack intersymbol interference in a magnetic patterned medium is studied. A two-dimensional (2D) channel code is proposed, dedicated to perpendicularly magnetized media without soft underlayer, which exhibit read pulses showing overshoot. Read pulse shapes were investigated using a magnetic-force microscope tip scanning the patterned medium row-by-row. To test different codes, a bit-detection simulation program was developed to generate large amounts of data on which bit error rates can be measured. Application of the 2D channel code, which implies recording of particular dot positions with fixed bits ("ones", "zeros"), resulted in the elimination of 2D worst-case bit patterns and a subsequent reduction of detected-bit errors. The accompanying redundancy of 22% is inevitable for this type of 2D code

Analysis of side writing asymmetry

The side writing asymmetry of a recording head was investigated using an overwrite configuration that enhances the edge effects. The track profiles of the overwrite patterns were measured for analyzing the side writing performance of the head. Magnetic force microscope (MFM) images of the overwrite patterns were studied using fast Fourier transforms (FFT), and they confirmed the profiling results. We measured weak edge effects at good pole alignment. The experiments were performed with metal evaporated (ME) and metal particle (MP) tapes having magnetic layers between 50 and 300 nm

Comparison of recording properties of ME tape and thin MP tape with respect to overwrite behavior

Differences between the recording characteristics of thin MP and ME tape are studied. The effect of the thickness reduction of MP tape is also investigated. When thin MP tape (with thickness 140 nm) is compared with ME tape (with thickness 150 nm), we observe a better signal and overwrite response for the ME tape. Through simulations the influence of an easy axis out-of-plane and a different reversal mechanism in ME tape is related to overwrite behavio

Permalloy thin-film magnetic sensors

An introduction to the theory of the anisotropic magnetoresistance effect in ferromagnetic thin films is given, ending in a treatment of the minimalization of the free energy which is the result of the intrinsic and extrinsic anisotropies of the thin-film structure. The anisotropic magnetoresistance effect in long strips is reviewed. Attention is given to problems like the formation of domains and measures like biasing and linearization. The paper concludes with a description of some applications which are being developed by the authors: (1) an analyser for the stray field of recording heads; (2) a sensitive magnetometer; (3) an accurate absolute angle detector; and (4) an absolute (linear) position detector

Track edges in metal-evaporated tape and thin metal-particle tape

MFM images of tracks written in ME and MP tape have been obtained. The analysis of the images concentrated on the track edges. A track written with signals of 0.5 μm wavelength overwrites a part of a track written with a wavelength of 1 μm. The sharpness of the edges was derived from MFM results. It can be seen that the MP sample shows smaller changes in sharpness of the edge with an increasing write current than ME tape. In ME tape, the region between the λ=0.5 μm and the λ=1 μm parts of the track is much wider than the original λ=1 μm edge

Novel Profiling Model and Side Effects of Helical Scan Silicon Heads

Partial erasure of track edges was directly measured from triple-track patterns using a novel model to interpret the output profiles. The model is based on representing the read head as the sum of a reference width, wavelength independent, and two side reading effective widths that are wavelength dependent. We applied this technique to measure erase bands and side read widths of an advanced helical scan silicon head with 3.5-/spl mu/m pole width, in combination with metal particle tape with coercivity H/sub c/ = 135 kA/m. The good pole alignment of the head minimizes side effects and we report an erase band of 0.3 /spl mu/m for a 0.5-/spl mu/m wavelength track overwriting the edge of a track having the same wavelength