Magnetic susceptibility measurements near the multicritical point of the spin-reorientation transition in ultrathin fcc Fe(111)/2 ML Ni/W(110) films

Iron films grown on a two-monolayer Ni/W(110) substrate undergo a temperature-driven spin reorientation which can be followed experimentally from a low-temperature, perpendicularly magnetized monodomain state all the way to the high-temperature paramagnetic state without a significant change of the atomic structure. Measurements of the magnetic susceptibility, using the magneto-optic Kerr effect, give the entire temperature vs thickness phase diagram for the spin reorientation, including measurements close to the multicritical point where the reorientation and Curie temperatures are equal. The technique is particularly sensitive to the formation of the perpendicularly magnetized domains associated with the spin reorientation and reveals that films with a thickness in the neighborhood of the multicritical behavior also display a maximum in the temperature at which domain formation begins. Thinner films undergo the transition from ferromagnetic-to-paramagnetic behavior directly from the domain state, but no signature of the critical temperature itself is seen in the magnetic susceptibility.