Abstract:
We have used molecular-beam epitaxy to grow high-quality pseudomorphic Ni and Co₁Ni₉ films on Cu(001). From temperature-dependent surface magneto-optic Kerr effect measurements of these films, we have determined the finite-size scaling behavior of the Curie temperature of ultrathin films for a thickness range of n=2.5-16 monolayers (ML). The film thickness dependent Curie temperature for each of these ferromagnetic thin-film systems, T_C (n), is described by a finite-size scaling formula: [T_C (∞) − T_C (n)]/T_C (n) = [(n − n’)/n0]^(−1/ν), where T_C (∞) is the bulk Curie temperature, n_0=2.5±0.5 ML for Co films and 3.5±0.4 ML for Ni and Co₁Ni₉ films is the microscopic length scale, and ν=0.76±0.08 is the bulk correlation length exponent. An interesting result is that T_C (n) extrapolates to zero in the single mononolayer limit, n’=1.
