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Positive exchange bias and upward magnetic relaxation in a Fe-film/CoO-nanoparticle hybrid system
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Image of FIG. 1.
FIG. 1.

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.

Image of FIG. 2.
FIG. 2.

(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.

Image of FIG. 3.
FIG. 3.

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.

Image of FIG. 4.
FIG. 4.

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.


Generic image for table
Table I.

Summary of fitting parameters of the relaxation curve, using Eq. (1).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Positive exchange bias and upward magnetic relaxation in a Fe-film/CoO-nanoparticle hybrid system