It is shown that a previously unknown class of magnetization patterns exists in planar structures which have the unique property that all the flux escapes from one surface with none leaving the other side. A simple case is a constant amplitude rotating vector magnetization where the sense of rotation dictates which surface has no flux. More complicated magnetization patterns are elucidated. The likelihood that the one-sided flux phenomenon occurs partially in the normal write, the contact-printing and the print-through processes of tape recording is discussed. It is concluded that significant improvements in tape recording performance would ensue if means could be found to enhance the effect.

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One-sided fluxes -- A magnetic curiosity?

The basic phenomena associated with the recording and reproduction of signals on magnetic recording media are described. Fields due to magnetized media and heads are reviewed along with their Fourier transforms. The playback-isolated voltage pulse and square-wave voltage spectrum are discussed in detail for various magnetization orientations. Descriptive models of the recording process are given for both longitudinal and vertical recording.

Fundamentals of the magnetic recording process

In planar structures, magnetization patterns exist that have the surprising property that all the external fringing field of flux emerges from one side of the structure, with precisely none appearing on the other side. In the last 25 years, this fact has led to a number of useful applications. More recently, the same concept has been found to hold for both cylindrical and spherical hollow structures, where all the fringing flux emerges either inside or outside the structure, with precisely none appearing on the other side. Again, this has led to a number of important practical applications. While many of the concepts have been published previously, this paper contains, for the first time, a uniform mathematical analysis of these one-sided flux configurations. Additionally, the paper reviews the principal applications of one-sided flux structures.

One-sided fluxes in planar, cylindrical, and spherical magnetized structures

Most of the technologically important aspects of magnetic recording are reviewed in a nonmathematical manner. After a discussion of recording media and heads, the fundamentals of the media magnetization and writing processes are considered. The factors limiting the bandwidth, distortion, and signal-to-noise ratio of audio, instrumentation, video, and digital recording machines are analyzed. The paper concludes with some predictions on the future of magnetic recording.

Tutorial review of magnetic recording

Publisher Summary This chapter discusses the preparation, structure, and properties of various recording materials—Fe oxides, Co-modified Fe oxides, barium ferrite, and chromium dioxide. It also discusses two types of hard films—metal films and oxide films. In digital recording, the functional parameter by which progress is most commonly judged is the bit density (the number of bits-per-unit-length of a track). To record and reproduce reliably at high density, it is required that each recorded bit be stored as a discrete transition of magnetization and that interference between neighboring transitions be minimized during writing, storage, and reading. This in turn, requires that the magnetic coating be thin, but to get a large signal from a thin coating implies the need for a reasonably high intensity of magnetization. The magnetization must not be too high, however, or demagnetization will be troublesome. To resist demagnetization and accidental erasure, the coercivity must be high but not so high that the writing and erasure heads have difficulty in switching the magnetization. Metal films can be made to have magnetic properties covering an extremely wide range. Continuous thin films made from the oxides of the ferromagnetic metals are unreactive and consequently their composition and properties are much more stable than those of the metal films. Because of the high temperatures involved in their preparation, oxide films are unsuitable for use with most flexible substrates. However, they adhere well to metals, glasses, and ceramics and are usually more wear resistant than are the metal films.

Chapter 7 Recording materials

Tape Noise in Audio Recording

This is the second of two papers. The first (I) [J. Acoust. Soc. 32, 1 (1960)] dealt with the general magnetic properties of recording tape. The present paper gives an analysis of hf biased recording based upon the anhysteretic properties of the tape as specified in I. Calculations of performance are compared with the results of absolute measurements carried out on a conventional recording machine and on large scale models. Satisfactory agreement is obtained when the theory is corrected to take into account a loss attributed largely to a dynamic form of demagnetization which takes place during recording. The corrected theory can be used to compare tape performance under a variety of operating conditions without reference to a particular test recorder. Attention is confined to recorded wavelengths which are large compared with coating thickness.

Eric D. Daniel

Papers

Tape Noise in Audio Recording

Determination of the Recording Performance of a Tape from Its Magnetic Properties

Audio Cassette Chromium Dioxide Tape