Recording media, magnetic

The optimal material for magnetic recording media was, for many years, y-FejOs (maghemite). This form of FejOj, which has a defect-spinel crystal structure, can be prepared as small, elongated particles. The coercive field is produced within the required range by shape anisotropy (see Section 4.5.1). The process used to prepare small particles of 

The last step is a reoxidation to y-Fe20 at 250 °C. The particle dimensions vary from 0.25 to 0.75 pm in length, and 0.05-0.15 pm in width, with a coercive field of 20-24 kA/m and a saturation magnetisation of 370 kA/m. Since the Curie temperature is one of the highest amongst the ferrites ( 600°C), the temperature dependence of all the magnetic properties is quite small. 

The fabrication of magnetic recording tapes and discs is relatively simple a suspension of the magnetic particles is deposited on the plastic substrate, under an aligning magnetic field. The solvent is evaporated a dry binder remains to keep the particles strongly attached to the substrate. The tape is finally rolled to obtain a compact coating. 

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Table 2. Magnetic Properties of Common Magnetic Recording Media...

For applications, such as magnetic recording media, it is necessary to know how different parameters will affect the relaxation time in order to avoid spontaneous data erasure (caused by thermal fluctuations) on the lifetime of the device. Because of the ongoing effort to increase the information/volume ratio, it is of special importance to know how the dipolar interaction of densely packed nanoparticles will affect the relaxation time. 

A variety of nanomaterials have been synthesized by many researchers using anodic aluminum oxide film as either a template or a host material e.g., magnetic recording media (13,14), optical devices (15-18), metal nanohole arrays (19), and nanotubes or nanofibers of polymer, metal and metal oxide (20-24). No one, however, had tried to use anodic aluminum oxide film to produce carbon nanotubes before Kyotani et al. (9,12), Parthasarathy et al. (10) and Che et al. (25) prepared carbon tubes by either the pyrolytic carbon deposition on the film or the carbonization of organic polymer in the pore of the film. The following section describes the details of the template method for carbon nanotube production. 

Elongated iron particles may be superior particulate materials for magnetic recording media, but the problem associated with corrosion has not been completely overcome for long storage time. 

Chromium dioxide may also be used in combination with cobalt-modified iron oxides (see Section 5.1.2) in the production of magnetic recording media. The world production of Cr02 in 1995 amounted to 80001, ca. 11 % of the total consumption of magnetic pigments. Producers are BASF and Du Pont. 

TABLE 5 MAGNETIC PROPERTIES OF COMMON. MAGNETIC RECORDING MEDIA... 

Sliarroek, M.P. Paniculate Magnetic Recording Media A Review, IEEE Trans. 

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