PARAMAGNETIC FERROMAGNETIC PHASE-TRANSITION DURING GROWTH OF ULTRATHIN CO/CU(001) FILMS

We have investigated the magnetic response of ultrathin paramagnetic Co/Cu(001) films in an applied field using the magneto-optic Kerr effect. We find that the paramagnetic susceptibility χ increases sharply upon Co deposition within a narrow thickness range close to the critical thickness at which the onset of ferromagnetism occurs. We attribute the observed behavior to a geometrical, or percolation phase transition, since the corresponding critical exponent γ=43/18=2.39 agrees well with the experimentally determined value of 2.40±0.07. © 1994 The American Physical Society.