Film thickness dependence of the enhanced EuS interface ordering temperature in EuS/Co thin films

The temperature dependent magnetism of EuS(t nm)/Co(t nm) films, where t=3.5, 5.0, 7.8, and 20 nm, reveals two EuS ordering temperatures T_C: one magnetic phase order below T_C∼16 K that corresponds to pure EuS and the other phase order at a T_C≫200 K that has a EuS thickness dependence. This enhanced T_C is the result of EuS interface moments exchanged coupled to Co moments in an antiparallel configuration. The interface T_C varies with inverse EuS film thickness, a behavior that is consistent with a magnetic proximity effect, and the amount of EuS that orders at the enhanced T_C decreases with film thickness, t≪10 nm.