AVS 46th International Symposium
    Magnetic Interfaces and Nanostructures Technical Group Friday Sessions
       Session MI-FrM

Paper MI-FrM8
Dimensional Crossover in Ultrathin Ni Films on Cu

Friday, October 29, 1999, 10:40 am, Room 618/619

Session: Magnetic Thin Films
Presenter: R. Zhang, The Pennsylvania State University
Authors: R. Zhang, The Pennsylvania State University
M. Hochstrasser, The Pennsylvania State University
N. Gilman, The Pennsylvania State University
R.F. Willis, The Pennsylvania State University
Correspondent: Click to Email
Theory predicts that in a magnetic system the long-range order parameter, the magnetization, as a function of the temperature disappears at the Curie temperature according to M=M@sub 0@(1-T/T@sub C@)^@beta@. For 3D Heisenberg and Ising systems @beta@ are 0.365 and 0.325 respectively. For 2D Ising system @beta@ is 0.125. In our experiments, we have studied the finite-size-effect shift of the T@sub C@(n) of a thin film of n layers, as phenomenologically described by the shift exponent @lambda@. There are two ways of defining this exponent. Traditionally, one measures the shift of T@sub C@(n) with respect to the bulk critical temperature T@sub C@(bulk). Alternatively, one may also define: @Delta@T:=[T@sub C@(bulk)-T@sub C@(n)]/T@sub C@(n) ~ n^(-@lambda@'), which defines @lambda@'. We studied with the surface magneto-optical Kerr effect (SMOKE) the behavior of @beta@ and @lambda@ of Ni films on Cu(100), Cu(110) and Cu(111) in a wide temperature range and with changing thickness. We observe a different behavior for films on Cu(100) and Cu(110) compared to films on Cu(111). Ni films on Cu(100) and Cu(110) show a sharp transition from a 3D Heisenberg @beta@ value to a 2D exponent of ~0.21, whereas for Ni films on Cu(111) no such sharp transition can be observed. This behavior is a strong indication of the role of quantum size effects on the behavior of electronic states, i.e., the sharp transition is a manifestation of quantum-well states existing in a gap in the bulk continuum of sp states, and the absence of such a gap along the <111> direction (E.D. Hansen et al. J.Phys, 9, L435 (1997)). The transition is indicative of a cross-over from 3D to 2D. The finite-size scaling exponents reflect the magnetic behavior of the bulk phase with corrections, as recently argued theoretically by Henkel et al.(PRL, 80, 4783 (1998)). What this work shows is that field theoretic corrections are sensitive to the symmetries of the epitaxial lattices.