Exchange coupling in the paramagnetic state

Exchange coupling has been observed in a ferromagnet (FM)/antiferromagnet (AF) bilayer with Curie temperature (Tc) much less than Neel temperature (T-N) in the regime of T<T-N, even when the FM layer is in the paramagnetic state. The exchange field HE and coercivity He of the coupled bilayer show completely different temperature dependence from conventional FM/AF bilayers with T-C >T-N. With increasing temperature, He vanishes at Te, whereas HE persists to TN. The results show that the exchange coupling can be established in FM/AF bilayers regardless of the relative values of T-C and T-N. [S0163-1829(99)08525-2].