Thickness-dependent Curie temperatures of ultrathin magnetic films: Effectof the range of spin-spin interactions

We present a simple model of spin-spin coupling which provides insight into the nature of the rapid decrease in the Curie temperature with decreasing thin film thickness n (number of monolayers). The shift of Curie temperatur e t(n) = 1 - T-c(n)/T-c(infinity) follows the usual power law t(n) similar to n(-lambda) in thin films crossing over to linear behavior t(n) similar t o n in the ultrathin film thickness limit. Experimental results for ferroma gnetic thin films are compared, and shown to follow curves of t(n) with lam bda values dependent on the nature of the spin-spin interactions.