Field modulation microcoils for magneto-optical recording

A magnetic field modulation (MFM) coil with a magnetic core, which can realize storage densities of 50-100 Gb/in² for use in advanced magneto-optical recording technology, is described. This MFM coil is made on a Si substrate utilizing thin-film technologies, namely, Si etching and fabrication of a magnetic multilayered core. Three holes are chemically etched in the Si substrate: two contact holes and one laser light hole. The magnetic core, consisting of CoFeSiB/SiO₂ multilayered film, is applicable to MFM coils. Whereas an air-core coil requires a high driving current, a magnetic core coil can be driven at a lower driving current. The inductance value of an air core coil is 20 nH, while that of a magnetic core is 31 nH. In comparison with the air coil, the magnetic flux can be more easily focused on one point in the case of the magnetic core coil because of the magnetic conduction of the magnetic layers. In conclusion, with the magnetic core coil, larger magnetic fields than those possible with the air core coil at the same current can be achieved, and efficiency is higher at a frequency of 100 MHz.