Analysis of unswitched grains in thermally assisted magnetic recording

A simplified model of thermally assisted magnetic recording was used to study the influence of thermal gradients and the average grain size in recording media. The signal to noise ratio (SNR) peaked for thermal gradients between 10 and 20K/nm and increased as the average grain size was reduced. However, the number of unswitched grains in written bits increased for smaller grains, limiting the increase in SNR. Exchange coupling decreased the probability of a grain remaining unswitched, but increased the magnetic cluster size, although the transition noise remained unaffected until the exchange coupling strength exceeded 0.8erg/cm².