Finite-size scaling behavior of ferromagnetic thin films

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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, TC(n), is described by a finite‐size scaling formula: [TC(∞) − TC(n)]/TC(n) = [(n − n’)/n0]−1/ν, where TC(∞) is the bulk Curie temperature, n0=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 TC(n) extrapolates to zero in the single mononolayer limit, n’=1.