Universal thermal stabilization of the magnetization in ultrathin ferromagnetic films

Very thin FeNi films are coupled over nonmagnetic interfacees of varied thickness to bulk FeNi generating exchange couplings ${\mathrm{J}}_{\mathrm{\perp }}$/J of varied strength on a path perpendicular to the surface. The relative magnetization M(T)/M(0) decreases faster at low T for ${\mathrm{J}}_{\mathrm{\perp }}$/J≠0 than for ${\mathrm{J}}_{\mathrm{\perp }}$/J=0. This implies a scarcity of spin waves in uncoupled films which we show to be very likely a universal property of ultrathin 2D ferromagnets on a nonmagnetic substrate.