Exchange bias in self-organized nanopatterned Cr/Fe junctions

Abstract

We have investigated the exchange bias ͑EB͒ in ultrathin epitaxial Cr/Fe/Ag͑001͒ nanopatterned bilayers characterized by atomic-scale-tailored interfaces consisting of nanoripples aligned along the ͓100͔ Fe direction. Precisely measuring the magnetic anisotropy of the system, we quantitatively characterized the energetics of the magnetization reversal in terms of domain-wall propagation in the Fe layer and discussed the influence of the interface structure in determining the exchange bias and promoting the domain-wall processes. We found no influence of the relative orientation of the field-cooling direction with respect to the nanoripple orientation in determining the EB magnitude, but we observed that the anisotropic morphology generates characteristic spin frustrations affecting the energetics of different domain-wall processes.

Exchange bias anisotropy versus antiferromagnet thickness in uniaxial Cr/Fe bilayers

“…The EB unidirectional anisotropy pointed along the ͓100͔ Fe direction in the FC ʈ and along the ͓010͔ Fe direction in the FC Ќ case but with identical magnitude, in agreement with Ref. 20. A comparison between experimental and simulated coercivity H C and EB values for a broader ␣ range with respect to the one of Figs.…”

“…20,21 The experimental setup allows performing in situ magnetooptical Kerr effect ͑MOKE͒ with a resolution in external magnetic field H of Ϯ0.4 Oe, and features a variabletemperature sample holder goniometer with a Ϯ1°a zimuthal-angle resolution. The Cr/Fe/Ag͑001͒ bilayers described in this work were prepared and measured in situ according to the experimental procedures described in detail in Refs.…”

“…26,27 The deposition of a Cr overlayer preserves the MAE, only slightly modifying the magnitude of the various contributions. 20 This anisotropy affects the magnetization reversal mechanisms of the system as a function of the relative angle between the external field H and the anisotropy axes of the sample. The magnetization reversal, as will be shown in the next section, can proceed via one-step, two-step, or three-step processes that, respectively, involve the nucleation and propagation of 180°domain walls ͑DWs͒, 90°DWs, or both.…”

“…The physically relevant quantities, as long as this work is concerned, are the activation energy for a 90°DW E DW 90 and for a 180°DW E DW 180 . The magnetic anisotropy energy of the films can be written as 17,20,27 …”

“…20 We performed a best-fit procedure for the 4 nm case ͑the loops reported in Figs. 2 and 3͒ optimizing the anisotropy constants and J in Eq.…”