Temperature dependence of the pinning field and coercivity of NiFe layers coupled with an antiferromagnetic FeMn layer

The pinning field H_p (the amount of the shift of the hysteresis loops) and the coercivity H_c of the samples of the form glass/Ta 120 A/(Cu 100 A)/NiFe 75 A/FeMn 150 A/Ta 50 A increase almost linearly with decreasing temperature down to 20 K, below which H_c increases sharply. The observed strong positive correlation between H_p and H_c, seems to be reasonably explained by a combination of a newly developed model in which a directional distribution of the pinning field caused by a random distribution of the crystalline orientations in the antiferromagnetic FeMn layer is taken into account and Hoffmann's ripple theory in which the local anisotropy is assumed to be proportional to H_p, although the sharp increase in H_c at very low temperatures remains to be explained.