Thermal stability of information storage tapes prepared from very fine metal particles

The magnetic viscosity coefficient (Sv), the normalized magnetization decay for logarithmic time [ΔM/(Mr log t)], the thermal stability factor, and the anisotropy field (HA) distribution were studied for metal particulate (MP) tapes prepared from acicular very fine Fe-Co particles as a function of average crystallite size (D1 1 0). D1 1 0 values of Fe-Co particles varied from 10.6 to 14.3 nm. Sv increased as D1 1 0 decreased. In MP tape with a D1 1 0 value of 10.6 nm, a small proportion of particles had low HA values. In the reverse field of 0.5 kOe, the values of ΔM/(Mr log t) at 350 K and the thermal stability factor for MP tape with D1 1 0 value of 10.6 nm were approximately 0.39%/decade (∼3.1%/3 years) and 109, respectively. The result suggests that the critical value of D1 1 0 could be approximately 9 nm for MP tapes prepared from ultra-fine Fe-Co particles (aspect ratio ∼3.5) with the average HA of approximately 3.4 kOe.