P. E. Oberg

Transverse recording using thin film recording heads

This paper presents the results of an investigation of a high density magnetic recording technique utilizing a thin film recording head and a transverse mode of recording on thin media. The significant results of this investigation are as follows. 1) Densities as high as 18 500 transitions per inch were experimentally written in a 300-A thick FeCr medium having an H c of 70 oersteds. 2) These densities were written with a thin film, vapor-deposited, recording head having a MATED-FILM® structure with a 0.4-mil etched gap. 3) Track widths of 1-mil on 2-mil centers were experimentally achieved. 4) Optical readout of a 0.2-mil wide transition (width of beam) region corresponding to 5000 transitions per inch was achieved using a laser beam and a linear motion transport system under ideal experimental conditions. 5) The magnetic field from the Neel wall separating recording domains was detected using a MATED-FILM Etched Gap head making this a possible readout method. Maximum achieved linear bit densities as a function of recording media coercivities are given.

Magnetoresistive magnetostriction monitoring

A monitor which is suitable for automatic control of magnetostriction of ferromagnetic alloy films is described. In operation, a glass substrate, upon which the monitor film is being deposited, is subjected to a low‐frequency periodic torsional stress. The film also is subjected to a high‐frequency alternating magnetic field which induces anisotropy in the film and also switches the state of magnetization. The periodic reversal of the applied stress and the related change of the strain induced anisotropy alters the magnetic switching characteristics of the film. Inductive sensing (pickup coil) and magnetoresistive sensing methods of the stress‐modulated switching characteristics are reported. A modified monitoring technique, utilizing a dc magnetic field transverse to the ac field mentioned above, is also described. This method allows the deposition of a magnetostrictive film at an elevated substrate temperature which results in a near zero magnetostrictive value at room temperature, while employing a nul...

Vapor-deposited thin-film recording heads

A vapor-deposited thin-film recording head and a unique reading technique are described. The head structure used for both write and read is similar to that of the Mated-Film memory element. Conventional longitudinal recordings at 4000 flux reversals per inch have been written with a thin-film head in 300-A-thick iron films having a coercivity of 80 Oe. Conventional longitudinal recordings up to 1600 flux reversals per inch in thin-film media and in oxide media have been sensed with the thin-film head. Although a one-turn sense line is used, flux amplification is obtained because the head magnetization, not the flux from the recording, is sensed. This also results in an output signal that is independent of recording media velocity.

Monitoring the Magnetostriction of Thin Films During Vacuum Deposition

A device has been constructed which monitors the magnetostriction of magnetic films prepared by vacuum deposition techniques. The substrate upon which the film is deposited is stressed mechanically during deposition, thereby applying alternate tensile and compressive states of strain to the depositing film. A localized alternating magnetic field is employed as an anisotropy orienting field and is used also to switch the state of magnetization of the film. The substrate is strained at a low repetition rate, and the depositing film is switched magnetically at a high rate. The periodic stress application to the film and the associated strain‐induced anisotropy modulate the flux reversal output; the resulting signal is detected by a pickup coil. The phase and amplitude of the modulated signal are a function of the magnetostriction and the corresponding film composition. The monitor is mounted in the vapor path so that a representative film element is deposited on the stressed substrate. Zero magnetostriction ...

Domain Studies in Thin Film Recording

An observation technique utilizing the longitudinal Kerr magneto‐optic effect was used in various studies of thin film recording. The semitransparent nature of the recording media allowed simultaneous observation of recorded domains and the write and read head gaps. Thin film heads were used to record in iron films having coercivities ranging from 60 to 160 Oe. The apparatus allowed quick determinations of maximum linear densities which were as high as 1550 flux reversals/cm. Recorded domain orientation with respect to the gap of a thin film read head was easily observed, and the corresponding output signals on an oscilloscope were photographed. The write‐read‐observe apparatus with a thin film read head was also helpful in detecting the magnetic field from Neel walls.

Analog Storage in Uniaxial Magnetic Films using Nonuniform Fields

Analog information storage characteristics have been produced in conventional Ni–Fe films having uniaxial anisotropy by the use of special magnetic operating fields. A directionally curved field applied in the hard‐axis direction induces a temporary angular distribution of magnetization directions across the film which, in conjunction with a uniform applied easy‐axis signal field, results in a proportionate net magnetization of the film. Various field‐shaping elements are described and experimental results are shown. Another proportional storage technique utilizing opposing, nonuniform magnetic fields in the easy direction is also described, and applications of analog elements are discussed.

Magnetoelastic Coefficient and Temperature Relationship in Thin Ni–Fe Films

Measurements of the magnetoelastic strain coefficient of nickel‐iron thin films on soda‐lime glass substrates have been made at temperatures from −40° to 200°C. The composition of the films ranged from 1% Ni rich to 1% Fe rich, with respect to the nonmagnetostrictive composition near 81% Ni, 19% Fe. Films with positive magnetostriction became less positive, and films with negative magnetostriction became less negative with a temperature increase. In some cases the magnetostriction changed from negative to positive when heated. The composition that displayed the least change in magnetostriction upon heating from −40° to 200°C is 0.1%. Fe‐rich as compared to the nonmagnetostrictive composition. Changes in the coercive force and the anisotropy field with temperature are also reported.

Rotating Commutator High‐Sensitivity Fluxmeter

A commutator driven by a 1800‐rpm motor switches and restores the state of a magnetic sample once each revolution. An overdamped ballistic galvanometer integrates the induced voltage and displays a flux change due to the applied switching pulse. Since there is one flux change per revolution, a large number of revolutions results in a large deflection due to the addition of all the flux changes. This fluxmeter has a sensitivity of 4.61 Mx‐turns/cm/min of operating time. With this fluxmeter it is possible to measure magnetization curves and hysteresis loops of very small magnetic samples. The experimental error in the flux measurement is 4%.