Evidence for domain condensation near the ferromagnetic to paramagnetic transition in perpendicularly magnetized, ultrathin Fe/2 ML Ni/W[110] films

Ultrathin, fcc Fe/2 ML Ni(111) films were grown on a W(ll0) substrate in UHV by electron beam evaporation. Fe films less than 2.2 ML thick posses a perpendicular moment that does not reorient to an in-plane easy axis below T_c, the temperature of the ferromagnetic to paramagnetic transition. The magnetic susceptibility of the fllms was measured as a function of temperature using the polar Kerr effect. The real part of the susceptibility is large, peaking at well above 100 SI units, and exhibits a simple exponentJal decay over a range of several tens of Kelvin above the temperature T_REM where the remanent magnetization disappears. This behavior of the susceptibility is in agreement with that expected from the perpendicularly magnetiaed domnin structure usually identified as a precursor to a spin reorientation transition. No signature of T_c is found in the susceptibility.