In this paper, the relationship between quality of sapphire crystal and growing parameters of SAPMAC (Sapphire growth technique with micro-pulling and shoulder-expanding at cooled center) method was discussed. Optimized temperature distribution and technique control were proposed by theoretical analysis, numerical simulation computation and experimental validation to obtain large size sapphire crystals. For aaxis crystallized direction, with 1.0-5.0mm/h growth velocity and 10-30K/h temperature decreasing speed, large sapphire single crystal (∅240mm×210mm, 27.5kg) having high optical quality was successfully grown. The absorption spectrum of standard samples was measured as well.

The hysteresis dynamics of a multidomain Potts lattice with nonzero domain wall width is simulated using kinetic Monte Carlo method. The remanence enhancement effect is investigated in detail taking into account full spin relaxation in the domain walls, whereas outside domain walls only spin reverse event is allowed. Significant enhancement of the remanence and weakening of the coercivity with increasing domain walls is revealed. While the dependence of the remanence and coercivity on domain size and domain wall width is established, the hysteresis area is found to be conserved against the two variables. The conservation property of the hysteresis area predicts that no excess energy is required for the spin relaxation inside the domain walls, thus the remanence enhancement. Finally, the theoretically predicted scaling relation on the remanence enhancement is confirmed with the present simulation.