Influence of Thermal Gradient and Cooling Rate on Writability in Heat-Assisted Magnetic Recording

We analyze the influence of thermal gradient and cooling rate on writability in 4 Tbpsi shingled heat-assisted magnetic recording employing a stochastic calculation. We separate the bit error rate bER for each grain column in 2 bits of data and focus on the mean magnetization reversal number per unit time 𝑁- for the medium in the recording direction during writing. We introduce the medium writing temperature 𝛥𝑇med and time 𝜏med, which are temperature and time ranges, respectively, where the 𝑁- value is larger than 1 ns-1. We also introduce the Curie temperature variation time 𝜏Tc and the field end temperature 𝑇end. The 𝜏med and 𝜏Tc values are functions of the cooling rate, which is the product of the thermal gradient and the linear velocity. In contrast, the 𝑇end value is a function of the thermal gradient only. When the writing field is small, write-error and erasure-before-write are mainly dominant, and the bER value is determined by the 𝜏med and 𝜏Tc values, respectively. When the writing field is large, erasure-after-write is mainly dominant, and the bER value is determined by the 𝑇end value in addition to the 𝜏Tc value.