Chapter 7: Nanomaterials for Information Storage

7.1 Introduction

Magnetic recording is the central technology of information storage. A large part of the interest in nanoscaled magnetic films is stimulated by their applications to information storage. In recent decades, the recording areal density has been increasing at the rate of about a factor of 10 every 10 years. With the introduction of magnetoresistive (MR) reading head technology in 1991, this rate increased to a compounded annual growth rate of 60% (Yogi and Nguyen, 1992; Kryder, et al., 1996; Lembeth, et al., 1996). In the last two years this rate has further increased to more than 100% compounded annual growth rate mainly due to the application of giant magnetoresistive (GMR) technology combined with nanostructured, supersmooth magnetic recording media.

This recording areal density advancement has been realized almost exclusively through the reduction of the recorded data bit size. The areal density of the first rigid disk manufactured by IBM in 1957 (RAMAC 350) was 2 kbit/in ², in which the magnetic particles were 1 2 ?m in size and were made of ?-iron oxide ( ?-Fe ₂O ₃). The recorded bit size was on the order of hundreds of microns. The areal density of the current state of the art laboratory demonstration recording systems are surpassed 35 Gb/in ² by the end of 1999 using nanostructured magnetic alloy thin film media, with recorded bit width well below half micron.

One...