Effect of antiferromagnetic grain size on exchange-coupling field of Cr70Al30/Fe19Ni81 bilayers

Abstract

The exchange-coupling mechanism of Cr70Al30/Fe19Ni81 bilayer films was investigated in terms of the crystallographic orientation, the interface roughness, and the grain size. The exchange-coupling field Hex appears when the Cr70Al30 layer is thick enough to accommodate an antiferromagnetic domain wall. The value of Hex was found to increase with decreasing the grain size in association with the [110] orientation. This tendency can be explained by considering the exchange-coupling field evaluated from the random field approximation.

A new paradigm for exchange bias in polycrystalline thin films

“…Hence, a decrease of H ex with the AF grain size is observed. These data and the quality of the fits mean that we can now explain the apparently irreconcilable data of Takano et al [36] and Uyama et al [37]. Fig.…”

“…For example Takano et al [36] reported a decrease in H ex with increasing AF grain size (D) in NiFe/CoO bilayers following H ex p1/D. Uyama et al [37] observed a decrease in H ex with increasing grain size above 50 nm but also observed the well-known broad peak in the variation of H ex with t AF . Again for large grain sizes an approximate 1/t AF variation was observed.…”

Multiple antiferromagnet/ferromagnet interfaces as a probe of grain-size-dependent exchange bias in polycrystalline Co/Fe50Mn50

“…A simple geometric calculation based on the occurrence of ffiffiffiffi ffi N p uncompensated spins in a cubic grain with a total of N spins [49] leads to an inverse grain size dependence as do more sophisticated models [23,50]. The functional form H E ¼ B/d grain ÀA, where A and B are positive constants and d grain is the average grain size, describes experimental data on CoO/NiFe [23] and CrAl/ NiFe [51] rather well. In the CoO/NiFe case A % 0, while for CrAl/NiFe, and in our case, A is clearly nonzero.…”

“…The solid lines show the very-reasonable fits to this form with the parameters given in the caption. Nonzero values of A, which clearly occur in this case, have been ascribed to inter-grain coupling [51] although the origin is not completely clear. H C decreases with increasing grain size, albeit with a much weaker dependence than H E .…”

Size Dependence of Structures and Properties of Magnetic Materials

“…[293]) and H e and T B are sizedependent, which is emphasized in this section. Besides, H e and T B are also functions of AFM orientation (compensated versus uncompensated AFM surface [298][299][300][301][302][303] and in-plane versus out-of-plane AFM spins [298,299,302]), of FM/AFM interface disorder (roughness [299,301,302,[304][305][306], crystallinity [307,308], grain size [309,310], of interface impurity layers [311]), and of strain effect [312][313][314], of stoichiometry [293] or of presence of multiple phases [315] and so forth.…”