Temperature-induced sign change of the exchange bias in Fe[sub 0.82]Zn[sub 0.18]F[sub 2]/Co bilayers.

A single crystal, (110)-oriented dilute antiferromagnet (AF) Fe[SUB0.82]Zn[SUB0.18]F[SUB2] film was grown via molecular beam epitaxy on a (110)-MgF[SUB2] substrate by codepositing FeF[SUB2] and ZnF[SUB2], followed by 1.0 nm pure FeF[SUB2] and 18 nm Co layers. The exchange bias (H[SUB E]) and coercivity (H[SUBC]) of the Co film strongly depend on the cooling field (H[SUBCF]) and temperature. For 0≤H[SUBCF]<2 kOe, H[SUBE]<0 in the whole temperature range before reaching zero at the blocking temperature (T[SUBB]). For(H[SUBCF])&ges;15 kOe, H[SUBE]>0 for T<T[SUBB]. In both cases,H[SUBC] peaks when T∼T[SUBB] For 2 kOe&les;H[SUBCF]<15 kOe, H[SUBE]<0 at low temperatures, and then suddenly becomes positive at a characteristic switching temperature T[SUBS] (<T[SUBB]). T[SUB S] decreases as H[SUBCF] is increased and H[SUBC] peaks at both T∼T[SUBS] and T∼T[SUBB]. These results indicate that for intermediate H[SUBCF] unstable domains are created in the AF during the cooling procedure. The domains suddenly disappear as enough thermal energy is available to switch them when perturbed by the rotation of the ferromagnetic magnetization. [ABSTRACT FROM AUTHOR]