Distribution of Thermal Stability Factor for Barium Ferrite Particles

The thermal stability factor (K_u V/k_BT, where K_u, V, k_B, and T are the magnetic anisotropy constant, particle volume, Boltzmann constant, and temperature, respectively), obtained from the dependence of remanence coercivity on time, is generally assumed to correlate with the signal decay rate. However, some data fail to explain the relation between the thermal stability factor and the signal decay rate, especially when Barium ferrite particles are used as magnetic particles in recording media. This study reveals that the distribution of the thermal stability factor is the key to explaining these phenomena. Cumulative distribution functions (CDFs) of the thermal stability factor for various Barium ferrite particles were measured, and a good correlation between the signal decay rate and the value of the 10th percentile in the CDF of the thermal stability factor was confirmed for each particle ensemble. This indicates that the measureable signal decay rate in a practical time period usually depends solely on the lower range of values for the thermal stability factor.