Media for Magnetic Recording Beyond 100 Gbit/in. 2
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Media for Magnetic
Recording Beyond 100 Gbitin.2
H.J. Richter and S.D. Harkness IV Abstract The requirements for media for high-density magnetic recording are reviewed, particularly with respect to the emerging technology of perpendicular magnetic recording. It is discussed in general how suitable properties of the recording films can be achieved in practice. Several approaches to extend the thermal limit of magnetic recording technology are outlined. Keywords: film, magnetic properties, memory.
for perpendicular recording and “left” to “right” for longitudinal recording. The information is coded in the locations where the transition between opposing magnetizations occurs. As shown in Figure 2 (which illustrates longitudinal recording), the magnetization transition boundary needs to follow the given microstructure, as single-domain grains cannot be “cut” magnetically. The transition centers do not come to lie exactly where intended. These “misplacements” are unforeseeable and generally referred to as “transition jitter.” Transition jitter is the most dominant factor for noise in the medium. Figure 2 shows the idealized case of the grain size limit, in which the transition width is solely determined by the locations and distributions of the grains. Then, the transition width W is equal to the grain size D. For historical reasons, the transition width is described by a transition parameter, a, that is related to the transition width by a W/π. It has been shown that the medium signal-to-noise ratio (SNR) scales with SNR
Introduction This article focuses on recording media as they are used in hard disk drives in personal or laptop computers and in other applications. Traditionally, the demand for ever-increasing recording density was achieved by scaling, but fundamental physical mechanisms no longer allow simple scaling. To date, most magnetic storage devices use longitudinal recording, where the magnetization of the bits lies in the plane of the magnetic film. In contrast to longitudinal recording, the magnetization in perpendicular recording is in a direction normal to the film plane. It is generally accepted that perpendicular magnetic recording is advantageous for a further increase in the areal density, and it is anticipated that the recording industry will transition to this technology.
Fundamentals of Magnetic Recording, Scaling Aspects Figure 1 shows a sketch of the “heart” of a magnetic recording system for both longitudinal and perpendicular recording. For longitudinal recording, the write head consists of an electromagnet with a gap whose fringe field magnetizes the medium passing by it (see the article by McFadyen et al. in this issue). At readback, the magnetic field from the written magnetization pattern is sensed by a magnetoresistive transducer which changes its resistance in the presence of a magnetic field.
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For perpendicular magnetic recording, the writing is accomplished by the main pole (shown on the right in Figure 1). The write flux is sent through the magnetic layer, then through
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