Materials for Future High Performance Magnetic Recording Heads
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déposition), sputtering, and ion beam déposition are becoming increasingly available and less expensive. Thèse methods will be used to fabricate future devices to incredibly accurate spécifications. There is a clear trend away from single- and multi-element bulk materials to thin film metastable materials and artificial structures whose properties can be controlled independently during fabrication. As the film thickness decreases the surface effects will contribute more to the material properties. The understanding and control of surfaces and interfaces in magnetic Systems is a new active area in the science of magnetism, and will lead to materials with combinations of properties now unavailable. The stability of the new structures (chemical, mechanical and thermal) will eventually détermine the applicability of new materials for magnetic recording heads. The various types of heads and the key challenges facing head developers are discussed by Lemke.5 This article describes some of the materials aspects of future thin film heads, including both inductive and magnetoresistive heads. Materials Requirements for Magnetic Heads Inductive Heads The properties of idéal core or pôle materials for inductive heads suitable for high density recording at high frequencies are listed in Table I. The head's ability to record on high coercivity média is directly proportional to the pôle material's saturation magnetization. A typical thin film head with 4 p,m thick NiFe pôles (4TTMS = 10 kG) and
gap g = 0.33 /nm can record optimum high density signais on today's commercial métal particle média (Hc = 1,500 Oe) if the gap depth is somewhat less than the pôle thickness.6 In longitudinal recording, increasing the linear density requires a corresponding réduction in the gap length. This in turn requires a higher record field in the smaller gap. 4 Significant increases in pôle thickness or réductions in gap depth are presently difficult to achieve. The use of pôle materials having higher 4irMs may be a solution to the problem. In reproducing perpendicular recording, the minimum wavelength dépends on the pôle thickness. Therefore, as the pôle gets thinner, a high magnetization pôle material is critical to achieve the required depth of recording. Head efficiency is proportional to the pôle permeability. High permeability over a wide frequency range is an obvious requirement for a high frequency head. Uniaxial induced anisotropy is essential to maintain the optimum domain structure and to keep permeability high over a wide frequency range. High resistivity reduces the permeability rolloff due to eddy current losses. However, high resistivity and uniaxial anisotropy may not be sufficient for high permeability at high frequency when pôles are thicker than the skin depth. A multilayer structure must be used, and the total required thickness realized by alternating magnetic material with an insulating spacer (Figure 2). The métal/ métal and metal/insulator interfaces, insulating materials, and structure stability now become critical issues. Dur
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