Enhanced Magnetic Viscosity At Low Temperatures In [Fe/Cr(0 0 1)](10) Multilayers

We report on magnetic aftereffect measurements in strongly and weakly antiferromagnetically (AFM)-coupled epitaxial [Fe/Cr(1 0 0)](10) and in epitaxial Fe(1 0 0), near the orientation transition (OT) between the easy and hard axes, studied at time scales up to 10(3) s and between 300 and 1.8 K. In strongly coupled multilayers, the relaxation is nearly logarithmic in time, has an intrinsic character, and the maximum relaxation rate is almost temperature independent down to 10 K and strongly increases below 10 K. The magnetic relaxation in Fe(0 0 1)films was, however, much faster at T > 10 K, but at lower temperatures it is nearly blocked making possible the observation of magnetization jumps of Barkhausen type. The unusual magnetic aftereffect in the Fe/Cr multilayers could be due to opening of relaxation channels through the Cr that separates the Fe layers. (C) 2007 Elsevier B.V. All rights reserved.