Recent developments in the theory and materials for digital recording

There is ample evidence that further advancement in the state of the art of digital magnetic recording systems hinges to a large extent on the limitations imposed by the writing process, and in particular on the phenomena of recording demagnetization and asymmetric peak shift. To adequately handle these problems one must consider the dynamic interaction of the writing-demagnetization process self-consistently and integrally, instead of treating these processes as independent and unrelated. The evolution of our theoretical understanding of saturation recording is discussed, with particular emphasis on the iterative process which offers the greatest promise for the adequate treatment of the nonlinear writing-demagnetization phenomena. The results of the theoretical analysis are used to predict the desired properties of the recording materials for high bit packing densities, where recording demagnetizing is severely limiting system performance. Besides the well-known criteria of small thickness and relatively low remanence and high coercivity, a very narrow range of switching fields (steep-sided hysteresis loop) is also very desirable. In this regard the recent development of a superior gamma-ferric oxide coating is most exciting. It consists of nondendritic particles which can be well dispersed and aligned resulting in phenomenal orientation ratios, narrow range of switching fields, and superior recording performance.