Dennis Elias Speliotis

Hard Magnetic Films of Iron, Cobalt, and Nickel

Thin films of Fe, Co, and Ni were prepared by vacuum deposition. The angle of incidence was varied from 0° to 80° for the explicit purpose of changing the anisotropy and producing very high coercivities. The film thicknesses, determined interferometrically, were in the range from 100 to 4000 A. X‐ray and electron diffraction examination revealed a highly faulted cubic structure for Fe and Ni, and a mixture of cubic and hexagonal phases for Co, with crystallite size ranging from 20 to 1000 A. Increasing the angle of deposition from the substrate normal had a pronounced effect on the magnetic properties of the films. The maximum effect was observed in Fe, where easy‐axis coercivity exceeded 1100 Oe at angles approaching 90°, while at normal incidence it was only 20 Oe. Next was Co with maximum coercivity of 1000 Oe and Ni with maximum coercivity of 350 Oe. This order is what would be expected on the basis of shape anisotropy of elongated particles formed on account of the oblique incidence of the vapor flux...

A correlation between magnetic properties and recording behavior in metallic chemically deposited surfaces

One of the most intriguing problems in understanding the recording behavior of thin metallic surfaces is to determine the extent to which this behavior depends on and correlates with the magnetic properties of the surface. From the point of view of demagnetization it is obvious that the recording surface with the best high density resolution is one that has zero moment; unfortunately, this surface also has zero signal. It is apparent from this limiting case that there exists at any given composition-subject to a minimum acceptable signal-to-noise ratio-an optimum moment for any particular recording density. Furthermore, the coercivity and the steepness of the sides of the hysteresis loop are also implicated in determining the ability of the surface to resist demagnetization and to match the writing transducer field gradient.

Very High Coercivity Chemically Deposited Co–Ni Films

Films of Co–Ni, varying in composition from 30% Co to 100% Co, and ranging in thickness from 250 to 2500 A, were prepared by chemical deposition. Small amounts of P were also included in the deposit. Their crystallographic and magnetic properties were studied as a function of composition and thickness. X‐ray diffraction revealed a hexagonal structure for the Co films, with increasing presence of a cubic phase as Ni was introduced. The hexagonal crystallites of the all‐Co films were randomly oriented, but in the Co–Ni films there was an increasing orientation of the hexagonal (002) and cubic (111) axes perpendicular to the substrate. The coercivity for a particular thickness increased as the Ni content of the films increased, reaching a peak of about 1300 Oe at 10% to 30% Ni depending on the thickness. Beyond this, the coercivity decreased rapidly to a value of 200 Oe as the Ni content of the films increased to 70%. In the Co films the coercivity decreases markedly with increasing thickness. This dependenc...

Correlation between magnetic and recording properties in thin surfaces

Correlation between the magnetic properties and the recording performance of magnetic recording surfaces is a subject under very active investigation by several researchers. In this paper we report the results of a study conducted in which each magnetic parameter and the thickness of a recording surface was varied independently, and their effect on recording performance was individually determined. The width at half the amplitude of the pulse readback from an isolated magnetization transition on a recording surface varies proportionally to the one-half power of the thickness, and inversely proportionally to the one-half power of the coercivity; it is essentially independent of the remanent magnetization of the recording surface for coercivities greater than 150 Oe, but become increasingly more dependent on the remanent magnetization for coercivities below 150 Oe. The pulse amplitude varies proportionally to the one-half power of the coercivity, the remanence, and the thickness of the recording surface.

An investigation of separation losses in high-speed, high-density recording tapes

The trend in digital tape recording is toward larger storage capacity and faster accessing, which necessitate packing information at greater densities on tapes moving at higher speeds. The losses that inevitably arise from the finite separation between the head and the moving tape become much more serious as the length of the magnetized regions in the tape is reduced and as the relative velocity of head and tape is increased. The purpose of this paper was to investigate experimentally the dependence of separation losses on bit density and head gap length, and to distinguish from the reading losses those losses introduced during the writing process. Briefly, results showed that, for the heads and tapes used in the experiment, virtually all the losses could be attributed to the reading process. Furthermore, writing with a wide gap head and reading back with the four heads established that the percentage reading losses as a function of separation were apparently the same whatever reading head was used.

Static Magnetization Reversal in Thin Films of Co–Ni–P

Electrodeposited films of Co–Ni–P containing 14% nickel and 1% phosphorus by weight and having thickness 0.05 to 0.2 μ showed the following magnetic properties—high coercivity (300–550 Oe), high ratio of remanent‐to‐saturation moment (∼0.90), steep‐sided hysteresis loops and isotropy in the film plane.The process of magnetization reversal was studied by using a sensitive Hall probe to measure and map the horizontal component of the flux above the surface of the film after increasing reverse fields has been applied. This technique was used since neither the Bitter pattern method nor the Kerr effect revealed the natural pattern of magnetization reversal. However, it was possible to introduce, deliberately, a small region of reversed magnetization by means of the field from a magnetic recording head and examine this region by all three methods. This provided a method of checking the interpretations of the Hall effect data.It was found that these films employ a unique mode of magnetization reversal. Initially...

Cobalt-Substituted γ-Fe 2 O 3 as a High-Density Recording Tape

In this study we investigated the recording performance of a surface composed of Co-substituted γ-Fe2O3 particles. These particles were cubic in shape with edge length of 500 to 1000 A, and coercivity of 500 to 600 Oe. This high coercivity is due primarily to the large magnetocrystalline anisotropy of the cobalt cation in the spinel lattice. The recording surface exhibited higher output, better dynamic range, and considerably smaller half-pulse width than typical acicular γ-Fe2O3 surfaces. Coercivity and squareness were found to decrease dramatically with increasing temperature, and with adverse consequences affecting recording performance. Heating a prerecorded tape to 150°C results in a 50 percent loss of signal; the conventional γ-Fe2O3 tapes experience no loss.