Recent Developments in Magnetic Recording Heads
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Recent Developments in Magnetic Recording Heads Atsushi Tanaka and Mitsumasa Oshiki Storage System Laboratories, Fujitsu Laboratories Ltd., Atsugi, 243-0197, Japan ABSTRACT Recently developed and future magnetic head technologies are reviewed. Scaling of dimensions brought about significant increases in recording densities in the last decade. On the recording head aspect, as the read head is narrowed, large improvements in sensitivity are required. Therefore, spin-valve read heads have been improved by introducing synthetic ferromagnetic pinned layers, a spin filter back layer and a specular scattering layer. The current perpendicular to plane (CPP) structure is now being adopted instead of the current in plane (CIP) structure which is the present magnetic head structure. Under heads with a CPP structure, tunneling magnetoresistance (TMR) devices and multilayer GMR are candidates. In CPP mode, we can make better use of “spintronics” or spin-dependent conduction phenomena because device character depends more directly on the spin-dependent electronic states of the materials. Future technologies of read head are also discussed. INTRODUCTION Information and communication systems increasingly handle huge amounts of data, placing heavy demands on hard disk storage capacity and performance. Figure 1 shows the development of areal recording densities for mobile disk drive products with magnetoresistive (MR) heads and giant magnetoresistive (GMR) spin-valve heads. High annual growth rates of 80% or more have been achieved in areal recording density during this period. Areal recording density is approaching 70 Gbit/in2 this year. Figure 1 also shows demonstrations made over several years at international magnetic conferences, including Intermag, MMM, and TMRC. These densities were achieved by combining advanced head technology with low-noise disk media [1-5]. The progress in developing spin-valve materials and high-sensitivity spin-valve read heads could enable us to achieve a continued increase in areal recording density in hard disk drives. In this paper recent developed GMR read head technologies are reviewed and promising future technologies of current-perpendicular-to-plane (CPP) are also mentioned.
GMR READ HEAD Figure 2 summarizes the evolution of the spin-valve structure we have developed. The spin-valve films are classified as follows: a) Bottom type spin-valve b) Bottom type synthetic ferrimagnetic spin-valve with back layer c) Bottom type double specular spin-valve The bottom type spin-valve film (Figure 2 (a)) has a simple structure consisting of four layers: a free layer, a Cu spacer layer, a pinned layer, and an antiferromagnet pinning layer. The resistance versus field R-H curve of the bottom type spin-valve in the early development stage is shown in Fig. 3(a). The film structure is Sub./Ta(5 nm)/NiFe(5)/ PdPtMn(25)/CoFe(3.5)/Cu(3.5)/ CoFe(5.5)/ NiFe(2.5). The MR ratio is ~ 6.0% [4]. For the bottom type synthetic ferromagnetic spin-valve, two magnetic layers antiferromagnetically couple to each other
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