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 st ate. The exchange field HE and coercivity He of the coupled bilayer show co mpletely different temperature dependence from conventional FM/AF bilayers with T-C >T-N. With increasing temperature, He vanishes at Te, whereas HE p ersists to TN. The results show that the exchange coupling can be establish ed in FM/AF bilayers regardless of the relative values of T-C and T-N. [S01 63-1829(99)08525-2].