Abstract
The influence of coercivity hc and retentivity Br of the recording medium has been studied by numerous authors in the field of magnetic recording. In 1946 Camras1 considered the demagnetizing field of a bar magnet comprising the record medium and concluded that the reproduced voltage was proportional to Br for long wavelengths and to Hc for short wavelengths. In 1947 Kornei2 observed that a medium of high values of Hc/Br gave better high-frequency response, while Holmes3 concluded that in sound recording the ratio Hc/Br should be greater than 0.1 and less than 1. Wetzel4 also expressed a view similar to that of Camras on Hc and Br and presented data supporting it in 1948. Begun5 pointed out in 1949 that Hc was the most important factor in magnetic recording although he stated in 19556 that high Hc does not add materially to the medium's capability of retaining a short-wavelength signal unless Br can be increased at the same time. In 1953 Daniel7 reached the conclusion that as the wavelength approaches zero the playback voltage becomes proportional to 1/(1 + Br/Hc), while McGuigan8 pointed out that the area recorded on the medium at the time of writing spreads out over an area larger than the area directly under the pole tip of the head, and that the extent of this spreading depends on Hc of the medium, without specifying how.