Effect of exchange reduction on the temperature dependence of the depinning field of domain walls

Recent experimental data suggest that for some 2:17 type magnets, the coercive field exhibit non-monotonic temperature dependence. As the temperature is increased, the switching field increases, attains a maximum, and then decreases. We study the effect of a reduction of the exchange for the spins in the pinning boundaries on the temperature dependence of the coercive field. In our model the pinning boundary consists of periodic arrays of faces of pyramids. Simulation results of non-monotonic temperature dependence of the depinning field is found, in agreement with experimental observation. We speculate that the pinning potential can change from repulsive to attractive as the temperature is increased. The location of the domain wall is also changed.