| 摘要 |
PURPOSE:To obtain a device which detects pulses induced on a magnetic head in discontinuous parts of an annular groove part and utilizes these pulses as a servo signal, by providing the annular discontinuous groove part in the peripheral direction on the surface of a nonmagnetic base material for magnetic disc and forming a ferromagnetic recording layer on all of the surface of the base material including groove part. CONSTITUTION:An annular discontinuous groove part 11 is provided on the surface of a nonmagnetic base material 10, and one groove 11b of this part 11 which has high frequency of discontinuity and the other groove 11a which has low frequency of discontinuity are provided a part corresponding to a magnetic recording part between them. The groove part 11 is formed by laser irradiation or wet or dry etching. A magnetic recording layer 12 is formed on all of the surface of a substrate 10 to obtain a magnetic disc 13. If a slider magnetic head 14 is deflected from the regular position to the side of the groove 11a or 11b, the quantity of magnetic flux is varied discontinuously on the boundary between the groove part 11 and a part 15, where no grooves are formed, to induce an impulsive voltage in a head 14. This impulsive signal is used as the servo signal and is detected by a frequency discriminating circuit. Thus, a high-precision write device of the servo signal is made unnecessary, and the information recording area of the magnetic disc is made wider than a conventional disc.
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