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

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Abstract
The pinning field Hp (the amount of the shift of the hysteresis loops) and the coercivity Hc 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 Hc increases sharply. The observed strong positive correlation between Hp and Hc, 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 Hp, although the sharp increase in Hc at very low temperatures remains to be explained.