Thermal Stability of Data Storage Tapes Prepared from Ultrafine Particles

摘要

The reverse field dependence of the normalized magnetization decay and the effect of the ratio of the fluctuation field (H_f) to coercivity (H_c) on the temperature coefficient of coercivity {α(H_c)} were studied for advanced data storage tapes prepared from ultrafine acicular metal particulate (MP) composite and hexagonal platelet Ba-ferrite (BF) particles. The mean volume of particles (V_(phy)) for these tapes varied from approximately 2000-5000 nm~3. The effects of the degree of particle orientation (OR) on the normalized magnetization decay and activation volume (V_(act)) were also studied for advanced MP tapes. The values of H_f were not constant, but were largely dependent on the reverse field for ultrafine MP and all of BF tapes. In comparison to MP and BF tapes with approximately same V_(phy), the normalized magnetization decay and H_f of BF tapes were much larger than that of MP tapes. The smaller the V_(phy) was, the larger the normalized magnetization decay became. The value of α(H_c), which is important for the thermal stability of high-density recording media, increased as the ratio H_f/H_c increased for both tapes. In MP tape with a larger V_(phy) (5300 nm~3), increasing the OR was found to decrease the normalized magnetization decay. However, OR values had little effect on the normalized magnetization decay of advanced MP tape with a smaller V_(phy) (1700 nm~3) and it was difficult to decrease the irreversible susceptibility that is affected significantly the normalized magnetization decay. These may be attributed to the existence of a few particles approaching the theoretical superparamagnetic limit. The value of V_(act) in the low reverse field, which is a major factor affecting media noise, decreased as OR increased regardless of V_(phy). To decrease the normalized magnetization decay, it is particularly important to originate in decreasing H_f and increase H_c that related to the anisotropy field and distribution for advanced MP and BF tapes with very small V_(phy).