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SEM (a) and AFM (b) images of the Co-oxide NP film. (c) Hysteresis loops of Fe/Co-oxide bilayers measured at selective temperatures upon field cooling. (d) Temperature dependence of the coercivity, H c, and the exchange bias, H eb.
(a) Schematic illustration of the effective interface coupling that leads to negative or positive EB, i.e., parallel coupling (J 1 > 0) of SFe and SCo at T < 200 K, and antiparallel coupling (J 2 < 0) of SFe and SSG at T > 200 K. (b) Field cooling dependence of hysteresis loops at 300 K. (c) Cooling field dependence of the relaxation behavior, M TRM(t), measured at 300 K. Sample was cooled selectively under different fields, i.e., 0.5, 1, 2, 3, 5, 10 kOe. The curves are fitted by stretched exponential function (Eq. (1)) with fitting parameters listed in Table I.
Relaxation behavior, M TRM(t), of Fe/Co-oxide measured at various temperatures from 10 to 300 K. Upward relaxation is only observed for T > 200 K, where the antiparallel coupling (J 2 < 0) dominates.
Schematic illustration of (a) the antiparallel coupled M FM and M SG due to interface superexchange coupling and (b) antiferromagnetic superexchange interaction between Fe2+-O-Co3+ couple.
Summary of fitting parameters of the relaxation curve, using Eq. (1).
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