Sidney M. Rubens

Cube‐Surface Coil for Producing a Uniform Magnetic Field

A system of five, equally‐spaced, square coils which provides a uniform magnetic field over a considerable volume is described. The region of uniformity is easily accessible from outside the coils. The method used to design the system is discussed.

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...

Angular Dispersion and its Relationship with Other Magnetic Parameters in Permalloy Films

An experimental investigation has been made of the dispersion of the easy axis in Permalloy films deposited in an orienting field. The dispersion was studied as a function of the following parameters: reversible rotation limit H tr ; easy direction coercive force H c ; anisotropy field H k ; and hard direction hysteresis loop squareness ratio (M r /M s ) d , and coercive force (H cd ). Observations were made with a Kerr magneto-optic apparatus and with a 1000-cycle hysteresigraph. Angular dispersion of the easy axis, measured by the hysteresigraphic method, was found to increase with H c /H k . Reversible rotation limit was not found to decrease with increasing angular dispersion as predicted by theory, but rather to decrease more rapidly initially with increasing dispersion and then to increase again at larger dispersion. The initial effect is believed to be due to the influence of local variation of H k on the reversible rotation measurement. There is some indication that hard direction coercive force increases with increasing dispersion, but there seems to be no simple correlation between dispersion and hard direction hysteretic properties. Reversible rotation limit was found to be roughly proportional to coercive force in most films, except those which exhibit an unusual type of wall motion switching behavior.

High Sensitivity Ballistic Fluxmeter

The sensitivity of a ballistic galvanometer, used as a fluxmeter, can be considerably increased when it is employed for measuring flux changes which occur in a time which is much less than the damping time, in the case of a highly damped galvanometer, or the period of oscillation for a slightly damped one. This is accomplished by mechanically opening a switch in the galvanometer test coil circuit a short time after the flux change is completed thereby leaving the galvanometer either critically or lightly damped as desired. By use of this method gain in flux sensitivity of 56 has been obtained with a critically damped Leeds and Northrup Type 2290 galvanometer. With the critical damping resistance removed, the gain is 152. Such a ballistic fluxmeter is well suited for measuring the ferromagnetic properties of very small toroidal cores frequently employed in computers, etc.

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 ...

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.

Effect of a Transverse Field on Switching Rates of Magnetic Memory Cores

A ferromagnetic material having a rectangular hysteresis loop can be magnetized much easier if a magnetic field is applied transverse to the direction of remanence at the same time the remagnetizing pulse is applied. This effect, which has been observed in cores of ferrite, rolled Permalloy and vacuum‐deposited alloys, is shown to be compatible with the existing theories of domain wall motion. It forms the basis of an improved method of writing into magnetic memory cores in a digital computer.

A Double‐Yoke Plate Permeameter

A double‐yoke permeameter, with which both normal and ideal permeabilities of moderately large steel plates can be measured, is described. The technique for making these measurements is also given. The permeameter is suitable for measuring plates several feet long, up to a foot wide, and from ⅛″ to 1½″ thick; two approximately identical test plates are required.